Planet Four Talk

Mars and The Solar System - For Beginners.

  • Kitharode by Kitharode moderator

    When you first arrive on Planet Four, there's no denying that it's all a bit 'in your face' and it can be rather overwhelming.

    We know from the discussions that a number of people feel uneasy about joining in because "I'm new to astronomy and don't know very much". You shouldn't let this hold you back.

    There are some good people here and they're all willing to share their knowledge with you. Your questions will often generate very informative discussions and you will learn a lot this way. However, we want to give you the best start possible so we hope that this discussion will be useful. Think of it as an 'astronomy workshop for beginners' Q&A session.

    We'll only deal with Mars and the Solar System here and it's aimed specifically at newcomers to astronomy. If you want to discuss quarks, quasars, dark energy, black holes, Jimi Hendrix, and other spaced-out stuff, please take these to the Just Chatting board and hopefully someone will help. They might not of course, because we're all into martian astronomy here and besides, why would anybody want a quark when they can have a yardang?!

    But that still leaves us with the Sun, nine (or eight?) planets, an asteroid belt, the solar wind, meteors, Mars,.... You get the idea.

    One last thing; The 'daft' question. The 'daft' question is the one you don't want to ask because you think everybody, except you, will know the answer and think you were 'daft' for having to ask. Not true. Most of the time if you ask that question, somebody will say "Glad you asked about that because I wondered how that worked". So, beginners; how might we help you today?

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  • Kitharode by Kitharode moderator

    Buying Your First Telescope? This is my advice. http://talk.planetfour.org/#/boards/BPF0000006/discussions/DPF0000ca2

    Feel free to add your own advice there. Maybe you have a telescope already that you would recommend to beginners.

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  • Kitharode by Kitharode moderator

    Distances. Now here's something we can get a handle on.

    For best effect you'll need a football and a tennis ball, or any two spheres of unequal size. You'll need a looooong piece of string and a friend to hold one end of it. We'll get to them in a minute. You might find pencil and paper useful to begin.

    Let's think about the question 'how far away is Mars from the Earth'? Seems simple enough, until we remember that everything in the solar system is on the move, so everything keeps changing distance-wise. Let's just consider the Sun, Earth, Mars relationship to show what this means. Sun in the middle, Earth and Mars going round it in their orbits. Mars is further away from the Sun than the Earth, so its orbit is bigger, therefore Mars moves more slowly.

    Let's imagine the Earth and Mars on the same side of the Sun as each other. Your drawing would have the Sun, Earth, and Mars all in a line in that order. The Earth goes round the Sun in a year and ends up in the same place it started. But Mars has only made it half way round. So now your drawing has Mars on one side of the Sun, with Earth on the other side. You can see for yourself that when they are both on the same side of the Sun they are much closer to each other than when they are on opposite sides of the Sun.

    So no single answer there, but we could settle for a max/min number for the distances to get a feel for the situation. Now, you could just google the answers but all you'll get is two large numbers. For a real understanding of the distances involved we need to consider the Earth-Moon distance, and for that you'll need your spheres and string. Oh, and your friend.

    I'll need a minute to gather my thoughts, so why not draw some orbits and see if what I've said so far makes sense.....

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  • angi60 by angi60

    Thanks for the lesson so far, Kitharode. I have some (all be it limited) knowledge, but get lost with the deep discussions. I don't know where you find the time! You obviously don't sleep!! Wish I could get away with that! Any info is good though.

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  • Kitharode by Kitharode moderator

    Hey, thanks for dropping in angi60. I'm just going to keep talking until any questions arrive, then when we find a level I'll try to move up into it. Do jump in when you want. Let's see what I should be talking about.

    Now, where's that ball and string.......5mins max...

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  • Kitharode by Kitharode moderator

    OK. We're looking first at the Earth-Moon distance. This is the furthest that human's have travelled so far.

    Your two globes will represent the Earth and the Moon, so a football or beachball is ideal for the Earth. Because we're not concerned with the scale of the bodies (only the distance between them) any ball smaller than the earth-globe will do for the Moon.

    Working in very round figures, the distance around the equator of Earth is 25,000 miles. In equally rounded figures, the distance from Earth to the Moon is 250,000 miles. Therefore, travelling ten times round the Earth is the same, distance-wise, as travelling to the Moon.

    Take your Earth globe and the ball of string. Take the end of the string and hold it tight throughout the exercise. Wind the string all the way around the globe ten times. Now the second person can take the 'other end' of the string and hold it against the Moon globe. The Earth and Moon can now be drawn apart until the length of string is taut.

    OK, I'm sure you'll be impressed if you've not seen this before - it's got a great 'wow-factor' - but the punchline really drives it home. The model shows the distance from Earth to the next nearest body in space; the Moon. After that, the most useful body that comes close to Earth is the planet Mars. The distance to Mars is 200 times the distance from Earth to Moon. And that's when Earth and Mars are on the same side of the Sun. What's the number when they're on opposite sides of the Sun. Like I said earlier, two big numbers. Ball and string is much more fun. Try it. I guantee the WOW.

    So if you want to place a third football in your model, you're gonna need a lot of string! Enjoy.

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  • Kitharode by Kitharode moderator

    Here's some big numbers for Mars - and some big words too. If you get too far down the list and you've got a question, then you might not get it from me. Don't let that you stop you from asking though, I can always lay my hands on an astronomer. Got a couple of them just down the road from here. Useful opening table in the link:

    http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html

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  • angi60 by angi60

    Wow, very impressive way to demonstrate it. Thanks. It certainly brings it home how vast the distances are. And I 've managed not to tie myself in knots!!

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  • Kitharode by Kitharode moderator

    Double wow!! Have you done the sketch or the string thing? Either one makes the point, eh?

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  • angi60 by angi60

    The string. Thanks for the NASA link too. I admit I've always neglected the Solar System, in favour of the Universe at large (not that I know much!). However this project has sparked more of an interest in Mars.

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  • Kitharode by Kitharode moderator in response to angi60's comment.

    Then that alone makes it all worthwhile. Thanks angie60, really. Might as well ramble on a bit whilst I'm here....

    Just to wrap up (for now) this string thing, you'll find it really good fun in the park/on the beach with a few interested youngsters. More room in a park than a front room. For me that is - you might live in a castle!

    Thing is, the 'look how far' excercise is really good, but it's a bit static. Try making the Moon go round the Earth (with string tight) and see how much space this involves - another wow! And of course, if you stride out the length of your string, and multiply by 200, you get one of the young folk to carry the third globe that distance. Wow three - how much space do you need now? Can the mars carrier get round their orbit as quickly as Earth does? Hours of fun.

    So what's next? I'll think of something else but with a bit of luck there'll be a question or two to deal with and I can use it later...

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  • Kitharode by Kitharode moderator

    The Up's and Downs of Binoculars. No wonder you can't see Mars and the belts of Jupiter.....

    Using binoculars is a great way to start your observing experience, but they are difficult to hold steady. Any little shake is magnified and the image 'jiggles' around, making it difficult to observe clearly whatever you are looking at. A cheap tripod can wobble, good tripods are expensive. Here's what to do.

    Equipment List:

Binoculars (of course)

Roll of sticky tape

Plastic football (about 12" across)

Small saucepan (about 8" across)

    Stay with me - all will become clear. Take the sticky tape and fix the binoculars to the football. Make sure you don't tape up the focussing wheel. Place the bino's and ball onto the saucepan. Let go.

    The binoculars stay perfectly still, giving a clear steady image. You have constructed what is essentially a 'universal joint'. By placing the 'Set-up' on a table, wall, car roof, or whatever, you can turn your wobbly observing sessions into useful and informative experiences.

    Still think I'm fooling? Give it a go and share your results. Enjoy.

    NEVER LOOK DIRECTLY AT THE SUN - IT CAN BE DANGEROUS.

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  • angi60 by angi60

    Castle? Me?! I wish! Yes, I've done similar things with pupils- it's the best way to learn. Off to sleep now zzzzz. Not that it's your teaching, or anything...

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  • Kitharode by Kitharode moderator

    OK - So it's dangerous. But how can we study the Sun if it's so dangerous to look at? This is a great question because the answer will keep you safe. Not only that, it will allow you to do some serious astronomy. This is the binocular 'setup'. The description might make it sound complicated, but I promise you it isn't.

    To observe the Sun safely, we need to project the image of the Sun onto a piece of card, rather than into your eye (dangerous bit!). This can be done with telescope or, as described here, with the binocular 'set-up'. The procedure is basically the same for both. In addition to your optics you need two pieces of stiff card, paper and pencil, and a modicum of invention.

    Binoculars give two images - one to each eyepiece. Take the binoculars and cover one lens with it's lens cap. If you have no lens caps you can make one with thick card and black tape. This stops the second image from burning your hand , or ear, whilst you study the first image on the card.

    The first piece of card needs a hole in it so it will fit over the front end of the binoculars. This card, and the binoculars, will cast a shadow onto the second card which should be held a few inches behind the eyepiece. (Use white card or paper).

    Keep your eye on the card at the back and move the set-up, slowly, until you have it lined up with the Sun. You'll know when this happens when a bright circle appears on the card at the back. This is an image of the Sun. It'll probably jump around a bit until you get your bearings, but you'll soon get the hang of it.

    Move the card nearer or further from the eyepiece until you have an image, say, 4" - 8" across (this can vary widely). At a good size, get the image in focus. Look for a clean, sharp edge to the image. You'll have to keep adjusting things as the image drifts off to one side. That's the problem with living on a rotating planet I suppose 😃

    You'll soon see where the modicum of invention comes in. Once you've got a safe image, of a good size and brightness on the card, you'll be able to cook up some ideas on how to make things steady and stable. With just a little practice and planning you will be plotting sunspots in no time - if there's any about that is. That's what the pencil is for. You can draw round the image. Fill in anything you see. It's a safe and easy way to take photos too.

    Point to remember: The image in a telescope is inverted (upside-down). In binoculars the image is the 'right way up'.

    BE SAFE and Enjoy. Cheers.

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  • Kitharode by Kitharode moderator

    In case I'm away for a while I'll leave some questions for you that I need answers to. It'll also leave a gap in case someone else want to pose questions/ideas. But first.....

    I've got a simple equation for triangles that works well for this problem. Apparently it's distance that does it - huge distance, skinny triangle. I can see that. It was a mathematician that gave it to me and she explained how the equation came about and why it was valid. Didn't understand a word of it but I'll take her word for it. It was for a little study I wanted to do on shadows. Planetary shadows. Obviously they would be big and long, but how long? I knew the shadow of the Moon could easily reach the Earth (eclipses and all that) but I wondered what else might cast a shadow that would fall onto another body.

    For example, Mars has two moons; Phobos and Deimos. Do they ever cast a shadow on Mars? If not, how close did they get to doing so? Can one cast a shadow onto the other? What about the four Galilean moons of Jupiter, some of which are pretty big objects? I've done these 'moons of gas giants' in the past, but for some reason never did the moons of Mars. Perhaps you can help?

    Here's the equation I've got. Insert 'Phobos' or 'Diemos' for 'body' as required.

    Length of shadow, L = d / (S/p-1) where;

    d = distance of body from Sun

    S = diameter of Sun

    p = diameter of body.

    The diameter of the Sun is easily found, as are those of the two moons. The distance (from the Sun) for each moon you might want to think about for a moment (in a way, everything goes round everything else) and I'd be delighted if after all these years I learnt something about Mars that didn't have a spider in it. Cheers.

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  • Kitharode by Kitharode moderator

    Lots of people have asked me over the years whether I'd like to travel through space at awesome speeds. My usual reply was "I've been doing that since the day I was born" (with appropriate smile attached)!. Not strictly true I know, but fortunately we're not being too strict here.

    Let's spend a minute back on Earth before we do some martian astronomy. We're outside looking south at noon, so the Sun is at its highest point in the sky that day. We are stood on the surface of a rotating planet, therefore we are being rotated with it at rotation speed. We could probably work that out. We could use our rough Earth circumference from earlier (250,000 miles) and make that equal to 360 degrees, then with 24hrs (rotation time) ..... well, like I said, maths isn't my thing. But I think that'll do it. (?)

    Let's say we work out that speed of rotation and then let the Earth move in its orbit round the Sun. The Earth - Sun distance is roughly 93 million miles, the orbit takes 365 days(ish). You'll probably get a number. But the numbers I'd be most interested in would be those where we are rotating on the surface in the same direction as the Earth moves in its orbit (two speeds combined) compared to the senario where we are rotating in the opposite direction to the direction of the Earths orbital motion (one speed taken away from the other).

    Feels to me that just rotating gives us one speed, but when in orbit at the same time we'll end up with two values. And my guess is (I haven't done this yet) is that whatever round numbers we get will prove me right. We're all moving through space at great speed.

    But we're not really on the Earth - We're on Mars. Things are a little different here. To keep things simple we can forget for now the odd forty minutes difference between the rotation periods of Earth and Mars. Let's have a 24hr clock, giving a 24hr Sol (day), and let's pretend now that we are outside, looking south, at noon, so the Sun is at it's highest in the sky on that day (sound familiar) and let's see if anybody can tell us how fast we'd be going then. And with such a thin atmosphere on Mars, and whatever the speeds are, we have been travelling through space since the day we were born - at awesome speeds too, probably.

    I'd love to know without looking it up. Anybody?

    If you get into orbits, check out Phobos and Diemos orbiting Mars. I'd love to see that live - really cool. Cheers.

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  • JellyMonster by JellyMonster

    Really well written Kith (and there's a lot of it) 😃. Try not travelling through time... now there's a challenge!

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  • Kitharode by Kitharode moderator

    Thanks Muchly JM. That most certainly is a challenge - And I'll accept it too. (It's just something else I've done most of my life). Not here though; it's an 'off-the-wall' topic and a bit deep, certainly for me anyway, but yeah, I'll take the challenge - sounds like fun!!

    Next up on here I hope will be some info/questions from the Talk community, but you've probably guessed that if they don't get in quick I'll be filling up some more pages. Had some astrofriends round and I got them talking about 'planets falling over' and I'd like to tell the story later, if I can put it into words. We've got an answer to a question I raised and it was pure, simplistic, citizen science. Got to check if the answers right, but it hardly matters really because sometimes the journey is more important than the destination. Our own lives might be a good example. 😉

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  • Kitharode by Kitharode moderator in response to JellyMonster's comment.

    PS to JM. What I've written isn't a lot. When I'm in the mood that's just my opening paragraph 😉 Mostly already written hence quick.

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  • Kitharode by Kitharode moderator

    For those of you on facebook, here's a page that you'll probably find useful. I'm admin there, so please 'Like' it if you do (get me up to 200?). I'm not in the business anymore so I'm not trying to sell anything (there's nothing in it for me).

    http://www.facebook.com/pages/Planet-Earth-Education-Mobile-Stars-Planetarium/316550651998

    First thing to do if you go there is to capture and store the free monthly star charts over the next 12 months (on website). These can be used every year. You can also use them to see (over the year) which stars are circumpolar, that is they always remain above the horizon at that latitude, and non-cicumpolar stars which dip below the horizon. You could make copies and build a flick-book so that you can see the 'rotation of the heavens'. The planetary data changes each year. If you're not sure why this is, please ask.

    In the 'Notes' on facebook, you'll see where I got my first entries for this thread. Not as prolific as you first thought am I? But I did write the stuff there too! Few images in there from the old days you might like. Cheers All.

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  • angi60 by angi60

    You HAVE been busy! I loved the tip about keeping binocs steady, especially useful as I have very unsteady hands. I'll give it a try when I get chance.

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  • Kitharode by Kitharode moderator

    Hi. Good of you to call in again. This is true; I got the binocs idea from a cub scout. Like many things, you just wonder why you never thought of that. I use it a lot because I'm lucky, got two pair of bino's so can leave one set up all the time. Do give it a go on the Moon, but beware, you might never get back to Mars.

    If you play with any of the other stuff I'd love to know how you got on. It'll help me gauge whether or not this will be a useful area for a wide range of tourists here. Please don't feel obliged. Any thoughts on the level so far? Anything specific you want to hear about?

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  • angi60 by angi60

    Yes, it's often the simple ideas that are the best. Well, as far as I'm concerned any info can only be good. I'll let you know if I find something specific that's puzzling me. Think I might give the calculations a miss though!

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  • Kitharode by Kitharode moderator

    I'm trying to gather together a few links to discussions on these boards, so that I can drop them in here on occasion in case they spark an area of interest for anybody who visits here. I'll try to pick shortish discussions, with something of a focus on a particular question, and if possible lots of good information.

    I hope they'll also show you what we're up to here on Talk and maybe some of them will be in your 'area of expertise'. If a good number of people pass through here there's a good chance a chemist, physicist, maths teacher, etc will be able to visit and move the investigations forward.

    So here's one of Wassock's 'daft' questions that just needs a spark; http://talk.planetfour.org/#/boards/BPF0000006/discussions/DPF0000cas PS: It's a little over one page long that's all .. so far.

    PPS: The 'orbit' of the asteroid belt is further from the Sun than that of Mars. That's why (in wassock's thread) I say that to reach the Earth any 'asteroid dust' would have to cross the orbit of Mars. (Draw a picture?)

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  • angi60 by angi60

    HAHA- area of expertise! I don't really have one, but I'll try to obtain one. Seriously though, I always read through all the Talk posts with interest before I start my classifying stints. I saw that Horizon programme, and I had no idea we have so material from meteors reaching us.

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  • Kitharode by Kitharode moderator

    I'll take your word for that, but I've a sneaking suspician you know something we don't. 😉 I'm managing to squeeze some musical references in, one of favourite 'expertise' areas, and I'm hoping to introduce Mars, Music, and Johannes Kepler as an example of the way music and astronomy (used to) go hand in hand. Maybe you could do the same. How to wallpaper the inside of a black hole, cookery on Mars. Actually that last one sounds interesting ... couldn't do it outside I wouldn't have thought. But if you could, what would be needed? Oh no, more work.

    I'm doing 'planets falling over' next. No maths, but might need your knitting. I can knit, not very well, but not since I met this lot on Mars!!

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  • angi60 by angi60

    From a very young age I've always loved listening to Gustav Holst's Planet Suite, whilst floating across the solar system, then out to interstellar space in my imagination! Afraid I can't knit, but I can sew - perhaps I could run up some spacesuits. I'm intrigued to find out what 'planets falling over' are, though I might not be here on Planet Four over the weekend. Then again I might not be able to resist a peek!

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  • Kitharode by Kitharode moderator

    Planets Falling Over (1)

    I’m working with an image from the blog. It’s about seasons and timekeeping on Mars. If you haven’t seen the blog you’ll probably find it interesting so do please call back when you’ve finished. http://blog.planetfour.org/

    If you have seen the blog here’s the article with image and, because I’m not doing what it talks about in the article, give it a read if you want and call back later. http://blog.planetfour.org/2013/02/11/martian-timekeeping/

    So what does knitting have to do with astronomy? Well, there’s bound to be balls of wool and there’s sure to be needles about. So you take a ball and shove a needle straight through the centre and, what a surprise, it’s turned into a planet with an axis of rotation. You can spin it, wobble it, and walk round a light bulb with it, until it turns into a comet with hazy coma round its nucleus and a long tail that gets wrapped around your legs. But you get the idea.

    A white ball is obviously better. A rolled up, sticky taped, sheet of paper, cut in two and snipped at one end of each, will give you a north and south pole to stick on the ball. Now we can do some serious astronomy. (Did he just say serious?). With this white planet the ‘walk round a light bulb in the middle’ scenario starts to make sense. The bulb, especially if it’s bright yellow in a dark room, makes a great sun and you can be your own chosen planet doing its thing in its orbit. (in Part 2)

    We’ll use just the image instead. http://planetfourzoo.files.wordpress.com/2013/02/orbit.png?w=623&h=468

    I’d like you to pay particular attention to the tilt of the planet in the image. To a large extent we can imagine the planet to be either Mars or Earth. The planet does not sit up straight in its orbit but instead its axis of rotation tilts to one side. Now for Mars this axial tilt is 25.19 deg. For the Earth the axial tilt is 23.44 deg. The diagram in the link above gives you an idea of what 23-25 degrees looks like(ish).

    The most important thing to grasp for now is the fact that the axis of rotation always points in the same direction. (I’m ignoring the 26,000yr cycle of precession). A planet doesn’t keep one pole pointing at the Sun all the time as it goes round its orbit and again this is made clear in the diagram. Now I know that the pole star, Polaris, is just about directly over the north pole of Earth, which is why it’s called the pole star. And because it’s always ‘at the pole’ the axis of Earth must always be pointing at it.

    Then I thought of a ‘daft’ question and put it to my astrofriends mentioned earlier. It being a daft question, nobody in the group could give me an answer. I’ve not had chance to look it up, but it’s bound to be on the web. If anybody bumps into the answer , please post it here.

    Oh yeah, the question. Well you’ve probably guessed what it is but here goes anyway:

    Mars and Earth both have the ‘same’ axial tilt, so do they both point to Polaris, or is the tilt of Mars in a different direction so that Mars has a different pole star? If so, what is that star? I don’t know.

    Part 2 is a lot of fun and behind the tomfoolery is some great astronomy. So a bit of rotational knitting will get you in the mood and you’ll need something like a planet with axis to get your head around what’s coming up.

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  • Kitharode by Kitharode moderator

    Planets Falling Over (2)

    As long as you have something like a football (even a round balloon) you’ll be fine with this. Stick a finger on each pole and keep them as straight as you can and you’ll get the idea. If you get it together to make a planet with axis of rotation so much the better.

    When we’re discussing the solar system as a whole, we generally accept that we’re looking down at the north of the system. This means that when we look down on it (a drawing would be useful) all the orbits of the planetary bodies go round the Sun anti-clockwise. So give yourself a few orbits to play with, then arrow the orbits anti-clockwise. Put a circle on each orbit for your planets and mark their rotation, which is also anti-clockwise.

    We now have an overall starting point for our investigation. This will change dramatically very quickly, so don’t read the drawing as overall fact. Nevertheless, this probably was the situation in the early life of the solar system but it’s not the situation now. And this raises all sorts of interesting questions.

    All the planets rotate in an anti-clockwise direction. So why does Venus rotate in the opposite direction to the other planets? Something must have occurred which caused Venus to ‘fall over’ and that would make it appear to rotate differently. What might have caused this; I don’t know. Or what about Mercury who’s day is longer than its year? Being nearest to the Sun it flies round its orbit fastest but rotates so slowly that it takes more than a year to get once round. None of the others do this, if my memory serves. (Might be worthwhile to check that out).

    Ok, so Mars and Earth are a bit boring because they’ve only tilted, but this solar system has loads more to offer. Especially if you begin to muse about doing astronomy on another planet!!

    So this is where the fun comes in. You’ve got a feel for astronomy on Earth and we know that astronomy on Mars, in some respects, will be the same due to their very similar rotation times and axial tilts. Things like sunrise/sunset and seasonal change can be easily compared. But what’s it going to be like doing astronomy on the ‘gas giant’ planet Uranus?

    We’ll pretend that Uranus is a place where you can stand on the surface. (Always difficult on a gas planet). Like Earth, and Mars, Uranus rotates anti-clockwise and has an axis of rotation which always points in the same direction (are you spinning?). Its rotation period is 17hr 14min which for a ‘giant’ is pretty fast. The interesting bit is the axial tilt of Uranus which is just about 98 degrees. Tilt your globe a quarter of a circle and put yourself on the planet. Mark a spot or something like that.

    So you’re on a planet that has a diameter of 51,000km (Mars 7,000km) that is rotating anti-clockwise once every 17 hours. The axis of rotation is tilted 98 degrees. The weather is set fair for a complete orbit round the Sun (which takes 84yrs) with clear skies guaranteed throughout.

    What would you see if you did your astronomy from the equator on Uranus? You will be able to work this out if you play with your homemade planet – and if you can stop laughing long enough. A real brain teaser, but it does eventually give you an “Ahhh, I get it now” moment. Cheers, and don't get too dizzy. ** 😦 **

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  • Kitharode by Kitharode moderator

    Telescope for sale: If any of you are into parallel universes I have a telescope that might be of interest to you. Any reasonable offer.

    http://www.facebook.com/photo.php?fbid=455575746998&set=pb.316550651998.-2207520000.1364013903&type=3&src=http%3A%2F%2Fsphotos-g.ak.fbcdn.net%2Fhphotos-ak-prn1%2F35959_455575746998_6922755_n.jpg&size=720%2C628

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  • Kitharode by Kitharode moderator

    Opposition and Conjunction. These are two terms that pop up regularly in astronomy and sometimes its easy to forget where you are, so they become mixed up. Generally, we use these terms to explain a situation from our point of view. Usually this is from Earth so that's good place to start. Always a good idea to make quick sketches but you can do this in your head probably.

    The Sun is in the middle. The Earth (where we are) is on the right, with Mars on the right further out. Both planets are on the same side of the Sun. However, the Sun and Mars are on opposite sides of us so they are in opposition. But as you saw earlier in your drawings, sometimes the Earth and Mars end up on opposite sides of the Sun but we say that, from our point of view the Sun and Mars are in conjunction. They're in the same place(ish) in the sky from where we are.

    Now let's look at it from the martian perspective. On Mars in a larger orbit. If the Earth and Mars are on the same side of the Sun then from a martian point of view it is the Sun and Earth that appear to be in the same place, so they are in conjunction. For an opposition to occur it requires the Sun and Earth to be on opposite sides of Mars. There's no chance of that happening is there? (Because neither the sun nor earth can get outside of mars' orbit to 'make it so').

    In this scenario, with only conjunction able to occur, astronomy on Mars is actually easier than astronomy on Earth - I hadn't spotted that detail before so I've learnt something here. We must not forget however that there are other planets that do have larger orbits so that scenario is a one-off. Anyway, that was my reminder to take care with oppositions and conjunctions. Make sure you know where you are and what you're looking at. I think I've just tempted myself to go visit all the planets in the solar system and see what's what with this opposition/conjunction thingy. What was it again?

    I take it from my point of view; that is, from whichever planet I'm on.

    When objects are on opposite sides of me, it's opposition.

    When objects appear to be in the same place in the sky they become conjoined, so it's conjunction.

    Yeah, this'll be fun ... back in a bit.

    Posted

  • Kitharode by Kitharode moderator

    Good exercise that, I enjoyed it. Can't put answers up because its from the DIY selection. You can though, if you want to!

    Percentage Distribution of Mass in the Solar System - A Beginners View

    The Suns got 99%, Jupiter and Saturn have 1% between them. Two gas blobs, throw a few rocks in, Job Done.

    Here's the picture: http://en.wikipedia.org/wiki/File:Sun_vs_planets.png

    Cheers. Kitharode.

    Posted

  • JellyMonster by JellyMonster

    Wasn't there a conjunction of Sun and Moon a while back?

    Posted

  • Kitharode by Kitharode moderator

    Yes indeed JM, well spotted. I'm also thinking you might already know that there'll be another one coming along shortly. I'm really glad you've pointed this out because it gives me a chance to 'muddy the waters' about something we 'know' and it'll help introduce a couple of new terms that beginners might find useful; Eclipse and Occultation. So thanks for asking.

    If anybody is playing with the stuff here you'll know by now that paper and pencils and models really help. So rather than keep banging on about it I'll assume you'll have them to hand when you visit, then I don't need to mention it again.

    To make things clear. When I say two objects are in the 'same place in the sky', this is what I mean. From your point of view (frame of reference) your mate is up the ladder and the sky is in the background. You can imagine your mate being 'at that place in the sky'. However, there is also a large aircraft in your view just behind your mate and for a moment they 'appear to be in the same place' in the sky. Obviously they are not so it's purely a visual conjunction.

    Conjunctions might be perfect, as in an eclipse when one body passes directly in front of another. There are close conjunctions when they just pass each other. Just being a bit close in the same area can be enough, eg., if Jupiter and a crescent Moon both fit in your camera viewfinder they may be approaching/leaving conjunction. For my discussions I'll bundle all of them together into 'the same place in the sky'. If an eclipse is involved I'll try to make sure I say so.

    Until I get my notes together you can play with an apple (or whatever) and a lampshade in the opposite corner of your room. It'll give you a chance to do some eclipses and conjunctions effects. Back in a while.

    Posted

  • Kitharode by Kitharode moderator

    First things first: We often talk about the ‘plane’ of the solar system, or a galaxy, and this is very much what we’re going to do now. National Geographic has a nice description:

    “An orbital plane is the flat, disk-shaped space that connects the centre of the object being orbited with the centre of the orbiting objects”. And I say; If you look down on your dinner plate you see a circle, when you look across the plate from the edge you see a line. (It’s also easier to get hold of a plate than it is a galaxy)!

    So when you were looking at the lampshade in one corner, with you in the other corner, you were sitting in the ‘plane’ of the solar system so orbits of moons and planets become much more of a straight line from your point of view. These two views are very useful for getting to grips with the shape of our own Milky Way galaxy and other spirals like it, as well as giving us an intimate feel for our home system.

    Look down on a spiral galaxy and you get a ‘Catherine Wheel’ (circle) effect, but along the plane we get the two fried eggs back to back effect (bumpy line). Between the line effect and the circle you will find every ellipse possible. You’ll probably enjoy this link so call back when you’ve done. You can substitute the solar system for these galaxies and the effect would be the same.

    http://cas.sdss.org/dr5/en/proj/basic/galaxies/spirals.asp

    Let’s begin on Earth and have a look at the Sun/Earth/Moon relationship with regard to conjunctions, eclipses, and occultations. We’re in the plane of the system looking at the Sun as we go round our orbit. The Moon is going round the Earth and (for now) it too is in the plane of the system.

    So if you set up a Sun (lampshade) and have the Moon (apple) orbiting around you (hold apple at arm’s length as you rotate) you will see the straight line effect as the Moon passes between you and the Sun. You should rotate yourself anti-clockwise to keep everything in order. This is also a good time to practice your oppositions. Can there be an opposition of the Sun and Moon?

    Now you probably know already that we get a solar eclipse when the Moon passes directly between you and the Sun. You also know that it takes a month(ish) for the Moon to circle the Earth. So it’s not unusual to be asked the question; “Why don’t we get an eclipse every month?” The reason is that although the Moon goes round us in the plane of the system, its orbit is tilted a bit away from that plane. Therefore it sometimes gets a little above the plane, other times it sits a little below the plane.

    Most planets and moons don’t orbit precisely in the plane and some of them deviate significantly. This introduces all sorts of interesting stuff to play with and it explains why some things don’t occur when we might have expected them to. So what you need to do now is to rotate yourself and your moon in a circular orbit with one side of the orbit lower than the other.

    Begin with your moon below your sun and make the high point of the orbit when the moon is ‘behind you’. As you rotate you will not see an eclipse because the moon is dipping below the sun. Dipping below makes it sound close, and so it is. This is JellyMonsters conjunction when the Sun and Moon get to the ‘same place in the sky’. This situation will occur each month as the Moon completes each orbit.

    If you keep the orbit of the moon ‘stiff’ and turn yourself through 180 degrees, then the high point of your moon’s orbit will carry it above your sun and again we have conjunction but no eclipse. However, if you now turn 90 degrees the tilted orbit of your moon will be side-on to the sun. Now the high and low points of the moon orbit are to your left and right as it orbits, but your moon will cross the plane of your solar system. This is when an eclipse can occur because this is the time when your moon can pass directly between you and your sun.

    That’s probably enough to make you dizzy for now, but these rotating, tilted planes are very important. They’re also a good laugh when you get stuck into the drawings and models. Before I leave you, I mentioned the muddying of ‘what we know’. This involves our other new term; occultation.

    Occultation comes from ‘occult’ (hidden, invisible) and if, for example, the Moon passes in front of Jupiter then Jupiter is occulted by the Moon. Similarly, if Jupiter passes in front of Saturn then Saturn becomes ‘hidden’ from our view so Saturn has been occulted by Jupiter. Hopefully that’s clear. You will often hear the term ‘transit’, as in transit of Venus, where a small body passes in front of a much larger body. A small moon will be occulted when it goes behind a large planet, but it will transit as it passes between you and the large planet.

    Jupiter’s moons will often transit and they often create shadow transits (which partly answers an earlier question). Often, before they become occulted by Jupiter they will be eclipsed as they pass into the huge shadow of Jupiter. We have eclipses of the Moon when the Moon passes into the shadow of the Earth. There are many eclipses like this for you to discover yourself, if you want to.

    The muddy water? An eclipse takes place when one body passes through the shadow of another. An occultation occurs when one body obscures another. So if the Sun is hidden by the Moon, but does not pass through any shadows, why do we call a solar eclipse an eclipse? Enjoy your swim.

    Posted

  • Kitharode by Kitharode moderator

    Prepare Your Toolkit for a Trip to The Galaxies.

    This would probably be a good place to take a break for a day or three, so that I can gather a few more items together for later and you’ll have time to post a question or two if you have them. You might want to post a ‘lesson’ of your own or share something similar.

    What I’d like to do here is gather a few things together so that you can go and take a fresh look at things like galaxies, exoplanets, and other things of that nature, before we get back to Mars. We’ve all spent time with these exotic objects and we probably know a lot about them from what we’ve read.

    But now is the time to get up close and personal with them and get a real ‘feel’ for what’s going on. If you spend just a little time getting to grips with what has gone before, you’ll see that you’re not just learning and understanding the solar system, you really do begin to ‘feel’ how it works. Leave aside the equation that popped up and any mass, distance, orbital, or other numbers and only bring along the drawings, knitting, and arm-waving stuff.

    Build a mental picture of the solar system that you can look down on. Be able to slide yourself into the plane of it and understand how this changes the view. Gather together all the obvious stuff you know and consider it carefully as if it were a piece of forensic evidence. You’ll see later how real science questions pop up when you are familiar with these obvious items. For example, rotating systems (solar, galactic) concentrate their mass in the centre. The further an object is from the centre the slower it moves. Orbits can tilt. The obvious stuff.

    Now let’s look at some of the new exoplanets that are being discovered. Many stars in our galaxy have now been found with more than one orbiting body. You’ll probably find a list on Wikipedia or similar. Grab a few details about how many, how big, how far, or whatever and then get out your knitting, start your juggling, run round your light bulb a few times and then tell me whether you think you’re getting a ‘feel’ for this astronomy lark. Any eclipses going on, transits perhaps? That’ll depend on how many planets you’ve got and which one you want to be on. If that doesn’t make you an astronomer I’m giving up!

    Or perhaps you’d like to look at a nice sparkly galaxy? Why not I say? Big mass of stars in the middle and stars going around it. Many have spirals. Perhaps that’s a density wave thing, maybe gravity ripples interfering with the rotating disc, I don’t know. But we can assume, I think, that stuff on the edge of the rotating system is going to move more slowly than stuff nearer the middle. In some respects it’s not much more than a complex solar system.

    So we might expect the spiral arms to ‘drag’ at the ends and, with a little wave action thrown in I can see how that might work. Maybe the spiral will ‘wind up’ over time and the whole galaxy will be a tight disc. But I’ve learnt that many spiral galaxies rotate ‘into’ the spirals and that makes you wonder whether or not they might unwind and become more widespread. Much of that is my speculation but I hope you see where the questions lie.

    A final tip to help you with your astronomy on Mars, or Earth, when you get back here. After looking around your galaxies make sure you get an edge on view of a spiral galaxy and allow yourself to move in from the edge and become embedded in the plane of the galaxy so that you are surrounded by stars. You see stars all around you and stars above and below you. Looking around you the stars appear dense because you are looking through so many of them, but above and below you in this thin flattened system there are far fewer stars to look through into the depths of deep space.

    When you feel that view, and you feel your place in that galaxy, then back home if you ever see the Milky Way in the sky you can tell your mate; “We’re inside a galaxy, going round a star on a rotating planet – and I can ‘feel’ the whole thing moving”!!

    At least I hope you will.

    Safe trip and I’ll be waiting for any questions and observations you have.

    Posted

  • lonelystar by lonelystar

    Hi Kitharode,
    I cheated!
    Mars has a faint South Pole star called Kappa Velorum (in the constellation of Vela) that is about 3 degrees from the true pole. The North Pole points somewhere between Deneb, the brightest star in the constellation Cygnus, and Alderamin, the brightest star in the constellation Cepheus (in some places Deneb is listed as the pole star of Mars). Interestingly enough Deneb will be our own pole star some time in the future, although it does not get that close to the pole (about 5 degrees away). I guess our wobbles are out of sync.

    Balls and string are good if you have a lot of space. I use paper clips and blue tac (due to cutbacks in educational spending, I cant afford a football and that much string!) A paper clip bent so that there are two upright prongs 3 cm apart makes a good Earth- Moon distance. Add a 1 mm diameter blob of blue tac makes a good Earth. A smaller blob makes a good Moon (but it easily falls off so take care). The whole thing is now roughly to scale- size and distance. A second paper clip and small red blob produces a suitable Mars. Now ask your audience to locate the position of Mars. Lots of discussion and arm waving follows until you get someone to take six big steps away from you (about 6m). This is Mars- at its furthest (opposition). Values vary as the orbit of Mars is quite elliptical (I just recalculated it at over 7m but I could be wrong). It its closest (conjunction) it is about 2.5m away. Either way it makes the kids go WOW!

    I'll get back to you on eclipses- I think I have an answer!

    Lonelystar

    Posted

  • Kitharode by Kitharode moderator in response to lonelystar's comment.

    Hi Lonelystar. Nice to see you here and thanks a lot for your post. It's taught me a thing or two. 😉

    Great idea for the distance model and it gives everybody a chance to grab something similar that's lying around and make their own models. That's three of us now that have mentioned "WOW", so hopefully tourists of the future will be tempted to have a go.

    You say " Interestingly enough Deneb will be our own pole star some time in the future" (which is true) and for anybody wondering how this comes about it's to do with the '26,000yr precessional cycle' that I mentioned earlier. Precession is not particularly difficult to understand, but it's a tricky thing to explain in words. Better off googling for it and finding a few diagrams I think.

    It could be that I'm reading it wrong, but at the end of your post you say 'its closest (conjunction) 2.5m'. Could you clarify that for me please - so I know where I'm looking from. Can't wait for the eclipse answer to pop up!!

    Many Thanks. Hope you'll call in again....

    Posted

  • Kitharode by Kitharode moderator in response to lonelystar's comment.

    Ten second animation from NASA showing the 26,000yr cycle of precession. Replay a few times and get a 'feel' for what's happening. Keep the timescale in mind. Same thing is happening to Mars, but there are differences in size of precessional circle and timescale.

    http://www.youtube.com/watch?v=J9Chu4-VlT0 (Check out the direction of the 'wobble').

    I strongly advise you NOT to visit the other links on the sidebar. Lots of bad ideas mixed in with the good and too many people trying to tell you something 'interesting' but have, sadly, told you wrong. Up to you of course.

    Posted

  • lonelystar by lonelystar

    Sorry, I think that is me rushing and not rereading my message before I post! I got opposition and conjunction the wrong way around. School girl error? (Blushes)

    Posted

  • Kitharode by Kitharode moderator

    No worries lonelystar. In fact , you've done me a favour - proves my point that it's easy to get them mixed up. 😉

    There's every chance that I'll do the same thing ocassionally (regularly?) so when I do I'm really hoping that someone will spot it and tell me I'm wrong. Thanks again. Kitharode.

    Posted

  • lonelystar by lonelystar

    Okay, this is an answer- it may not be the correct one mind you.

    Eclipse- the phenomenon of one body passing in front of another, cutting off its light.
    Occultation- the eclipse of a star or planet by the moon or another planet.
    (from introductory astronomy and astrophysics by Zeilik and Gregory)

    So, does that make a solar eclipse a special type of occultation or a solar occultation a special type of eclipse?

    Posted

  • lonelystar by lonelystar

    .....
    Having done some reading around in massive, dusty tomes (thanks for the books Kith) it would appear that eclipses are 'the full or partial obscuring of one celestial body by another', or 'when one body passes into the shadow of another'. So, are transits and occultations just types of eclipses? Would we be having this conversation if we lived on Mars? Would we say that Phobos and Diemos transit the face of the Sun or would we be able to say that they partially eclipse it as viewed from the surface of Mars?

    Another question- Occultation- the eclipse of a star or planet by the moon or another planet. The Moon (as in Luna) or the moon of the planet you are standing on? Is it relative to location?

    Kith- not sure about eclipses being just to do with shadows- what about eclipsing binaries??? Or is this a case of misnaming the phenomena?

    Glad I managed to do you a favour by getting muddled up with conjunction and opposition- however I should know better as I was taught by the best 😃

    Posted

  • Kitharode by Kitharode moderator

    What an excellent question. So there you have it Citizen Scientists. Nice little item to work on.

    Eclipse cuts off light, so in a solar eclipse it's the Moon cutting off the light from the Sun - or does it?

    Occultation is eclipse, so light is cut off if one planet blocks another. Planets don't burn though, so they don't have light of their own.

    There may be special types of occultation and eclipse.

    Water muddy enough for you yet? Thanks lonelystar. And to everybody else, I'm just messing with you for fun :-X

    Posted

  • Kitharode by Kitharode moderator

    I've said earlier that I'd occasionally drop a link to any discussions that might be useful to you. Here's another one that might interest you. I'm plugging my own 'Spiders by Latitude' thread, but I'm sure you won't hold that against me.

    There are a couple of graphs included that you can ignore, but they're well worth revisiting if you get interested in the southern icelayer as I am now. There's a few of my blunders in there but fortunately they were all corrected(ish) later in the thread.

    I'm offering it here because I think you'll get most of it, so you'll start to get a feel for Mars, but I also wanted you to see what I mean by Citizen Science here on Talk. This wasn't one of my 'daft' questions that got the thread moving, it was one of my 'seems logical enough to me' ideas that I wanted to answer. To be honest, I expected either "yes, well spotted" or "no, because...". It was neither of those.

    So this sparked the digging session where we dig out bits of information, ask questions, toss ideas about, change direction, apologise for blunders, and finally end up with a whole new picture of what's going on here on Mars. Worth a look I think and just go as far as you want to. There's a 'nice detail' from Anya (scientist) that arose from our questioning and it's a tiny indication of what we can 'discover' here.

    I hope you'll try it. There may be a few new terms you haven't met before that we can chat about, so bring them along here if you find any. Enjoy.

    Spiders by Latitude: http://talk.planetfour.org/#/boards/BPF0000008/discussions/DPF0000c2e

    Posted

  • DrTechnical by DrTechnical

    Hi there

    Although I'm a 'Newbie', my 'better' half has encouraged me to get stuck into the discussion on eclipses and occultations.

    Like Lonelystar said, I could be wrong, but I have been led to believe that Occultation just means one body passing in front of another, but is usually taken as referring to an apparently small object such as a star, being hidden from view by a much larger one such as The Moon or a planet (when viewed from here on Earth). If the body passing in front is appreciably smaller than the one behind, then it is a Transit. If the object passing in front has a very similar or identical angular size, then it is Eclipse. These terms can be used in any location but are usually taken to mean the observer is at that location and that the body doing the occulting or eclipsing falls between the observer and the object being affected. The exception to this is the Lunar eclipse, where the moon is in the Earth's shadow.

    As far as Eclipsing Binaries go, I think it refers to the observations being from Earth and due to the large distances involved, the two stars would have similar angular sizes.

    Hope this question doesn't come up when I take my GCSE Astronomy (eventually)...

    Posted

  • Kitharode by Kitharode moderator

    Well hello DrTechnical. How nice of you to visit. If it carries on like this I'll have to get some more chairs!!

    So there you go. I introduced the subject and muddied the water. Lonelystar spotted the missing details and exposed my wicked plot, and I think we can take what DrT has offered as a good explanation of what's going on. If you stick with that you'll not go far wrong. Well done Everybody.

    Good luck with your workshop. If it doesn't work out as an astronomy education centre you could always do classes on building and DIY methinks. The GCSE exam won't have any 'muddy' questions in it, but I can't always say the same thing about the pictures they use. I once saw a question which asked whether the object displayed was a star, planet, or comet. The image displayed was just a completely black square!! Nobody got that one right. 😃

    Anybody got a table of shadow lengths yet? Cheers, Kitharode.

    Posted

  • Kitharode by Kitharode moderator

    One that Angie60 might like to look at, as well as other sol-sys investigators. I've linked to Mars.

    On the 'Mars and Satellites Data' page you'll meet the AU, the Astronomical Unit.

    One AU = Sun-Earth distance = 93 million miles (150 million km) approx. You can easily use this to put a bit of 'scale' into your drawings. I'll try and bring a list of AU values for planets later.

    http://airandspace.si.edu/research/ceps/etp/mars/

    Posted

  • Kitharode by Kitharode moderator

    Planetary Data: Distance Table.

    Nice find on AU's http://idahoptv.org/ntti/nttilessons/lessons2000/lau1.html Enjoy.

    Posted

  • angi60 by angi60 in response to Kitharode's comment.

    Hi Kitharode
    You HAVE been busy again. It'll take me a bit to catch up, whilst still trying not to let the classifying drop. That'll teach me to have a weekend off! I didn't know about precession, so that video was very useful, thanks. The AU table makes you realise the vast distances involved, and that's just our tiny solar system! Thanks too for the link with the Mars info. I'm still trying to get my head round the eclipse/occultation thing. I'm glad to see we have company now, the more the merrier as they say.

    Posted

  • Kitharode by Kitharode moderator

    (And just between you and me, they're both good friends of mine. They've just posted in 'Introduce Yourself')

    Hi Angi60. Yes, lots for you to play with there and I'm so pleased you're finding stuff useful. Nice thing about being able to pull some of this 'easy astro' material together in one place is that 'catch up' can be taken at your own pace. Your feedback is invaluable and I hope you'll keep it coming - along with any questions or suggestions for topics.

    If you find us getting a bit heavy between us then you should tell us off; "Oi, title says Beginners. Can't you read!"

    Or some such gentle reminder .. 😉

    Posted

  • angi60 by angi60

    Friends - you have friends?!! HA HA, only joking! Yes, I'm finding it all very useful, thanks. Basically, I used to read about Astronomy in my youth, and had a (very) small telescope. Then marriage, children and career took over! So Planet Four has re-ignited my interest. Don't worry, I'll tell you all off if you loose me!

    Posted

  • Kitharode by Kitharode moderator

    Excellent. I'm just gathering thoughts on a couple more things to do with orbits to complete something of a 'working model' of the solar system. Haven't explained 'obliquity' yet, but if I say that that's the posh word for a 'fallen over' planet like Venus or Uranus (axial tilt), well that'll probably do it. I'll find a list or diagram for planetary tilts then you'll have the full set of rotation, revolution (orbit), and obliquity (tilt). All you need then is to consider the 'ellipticity' of an orbit, because orbits are not quite perfect circles but are slightly flattened into an ellipse, hence elliptical.

    If you have the Sun in the centre of a drawing, with a straight line running through its centre across the page, then this will be the plane of the solar system. The equatorial plane of the Sun sets the stage. This is our datum point if you will. When I find the 'tilt' list, you'll be able to draw other lines through the centre of the Sun at the correct angle to see what that means.

    My next rant and rave will be about magnitudes - because Mars has got one at least !! 😉

    Posted

  • angi60 by angi60

    Brilliant. Obliquity is another term new to me! Thanks.

    Posted

  • Kitharode by Kitharode moderator

    Obliquity (axial tilt, degrees) and Rotation (hours)

    Mercury 0.1 deg and 1407.5 hrs

    Venus 177.4 deg and 5832.5 hrs

    Earth 23.5 deg and 23.9 hrs

    Mars 25.2 deg and 24.6 hrs

    Jupiter 3.1 deg and 9.9 hrs

    Saturn 26.7 deg and 10.6 hrs

    Uranus 97.9 deg and 17.2 hrs

    Neptune 29.5 deg and 16.1 hrs

    Pluto 119.6 deg and 153.3 hrs

    I've edited my earlier post because I made a 'blunder'! Please read new version in case we crossed over.

    Posted

  • Kitharode by Kitharode moderator

    And if you want to draw your tilted lines to scale, then here are the AU's for each planet. The AU is the astronomical unit used for the Sun-Earth distance, so the Earth is 1AU from the Sun.

    Mercury 0.4, Venus 0.7, Earth 1.0, Mars 1.5, Jupiter 5.2, Saturn 9.5, Uranus 19.2, Neptune 30.0, Pluto 39.5.

    Numbers are rounded. Very roughly, Pluto's 40 AU's ~4,000,000,000 miles (4 billion miles). Very roughly indeed.

    That should draw, build, juggle, and knit a nice model of the general 'mechanics' of the solar system and give you a good feel for the old home place. It'll also be useful in deep space, remember!

    I'm going to get a little more colourful and chatty in my next blathering session and try to make some sense of magnitudes. There's more than one for each object and I'll try to get it right. * 😛 *

    Posted

  • JellyMonster by JellyMonster

    I didn't realise there was such a gap between Saturn and Uranus.

    Posted

  • DrTechnical by DrTechnical

    I found a nice interactive model of the solar system which you can scroll through if you want a more visual representation of the solar system.
    Visual Solar System.

    Just one hint, when you scroll, scroll very slowly or you'll miss bits out. The page is approximately half a mile wide...

    Posted

  • Kitharode by Kitharode moderator

    Blimey. Who needs deep space when there's this much empty space to play with. Big gap indeed JM.

    Nice one DrTechnical. I thought the 1/2 mile wide page was a joke, but it's true. Your 'take it v slowly' advice is good advice indeed. Good find.

    Posted

  • Kitharode by Kitharode moderator

    Beginners only allowed to answer this one. (Lonelystar will have to knit a planet or something for now. 😉 )

    Is the 'Darkside of the Moon' the same as the 'Farside of the Moon'?

    Have a think about it first, then try this (Blilliant!): (Again, I advise ignoring side panel of links)

    Posted

  • angi60 by angi60

    I didn't realise Venus has such a big axial tilt. Thanks for the info. I'll have to get glueing or knitting now, as you say! I don't think the darkside of the moon is the same as the farside. But then again.... Was there meant to be a link with your last post?
    Dr Technical - well that did take some scrolling. but it illustrated the point well.

    Posted

  • Kitharode by Kitharode moderator

    Oops ... Yes, there should have been a link and it's here now. Sorry. Thanks Angie60.

    http://www.youtube.com/watch?v=OZIB_leg75Q

    Venus - Yes, Fallen Over! How weird is that.

    The story so far makes a nice 'package' and we can add details as and when. But yes, models is the way. If you can mock up a globe with a circular disc round it (one small, one large is better) than you can see how Saturn's rings work (and Jupiters and the others) or with bigger ring round a sun you can put your planet on the edge and play with inclinations of orbits. Putting tilted rings (always tilted the same way, axial tilt) with the orbits inclination shows you why Saturns rings are sometimes very thin and other times 'wide open' - from our point of view. If you have a go and it makes sense, fine; if you try it and don't get it, please bring it up here.

    Having fun?

    Posted

  • Kitharode by Kitharode moderator

    PS. You're right about darkside/farside, they're not the same - most of the time!

    I believe there will be one instance when they are the same, though. Or have I got that wrong .. ?

    Posted

  • angi60 by angi60

    At full moon? Or am I on the wrong track?

    Posted

  • Kitharode by Kitharode moderator

    And you told me you didn't know much astronomy - pulling my leg you are!! 😛

    Absolutely Correct. Oh, the joys of knitting, eh?

    PS. Put yourself on the darkside of the Moon during a total solar eclipse as seen from Earth. One day somebody will probably see this for real, but you can get in first - mindwise.

    Posted

  • angi60 by angi60 in response to Kitharode's comment.

    Yippee! Do I get a gold star (or any star? Betelgeuse?) I need some consolation for tying myself in knots! Haha! You've probably noticed by now that I suffer from a chronic lack of confidence.

    Posted

  • Kitharode by Kitharode moderator

    Not Betelgeuse. It's really big but it's only red. You deserve Alberio - and you can see it in your binoculars...

    http://www.nightskyinfo.com/archive/albireo/ Well done. You've really got the hang of this knitting lark. 😉

    Posted

  • angi60 by angi60

    Oh that'll do - it's beautiful! Thanks for the link. I'll try looking for it with binocs when I get chance 😃

    Posted

  • Kitharode by Kitharode moderator

    I'm thinking that there's still so much to talk about here in and around the solar system (asteroids, comets and meteors, temperatures, etc.) that perhaps I'll start a MkII version of this 'beginners' session.

    Something to bring us to Mars in isolation. Have a look round at what we know, land on the surface and take in the landscapes, that sort of thing. Maybe I could put up a few things I've learnt here about the martian surface. Gentle introduction to the citizen science that's going on here. Good idea?

    Posted

  • angi60 by angi60

    Yes I'd LOVE to know more about the martian surface. I've often been lost with some of discussions! Any other topics are welcome too.

    Posted

  • Kitharode by Kitharode moderator

    Me and my big mouth 😮 -- Right then, I'll get on it straight away. Might be a day or two, but you'll see it when it pops up. Anything you'd like to discuss/ask before I have (another) late night?

    Posted

  • angi60 by angi60

    Heehee that'll teach you! Nothing at the moment thanks. I'll leave you to toil away! No rush though 😉

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  • Kitharode by Kitharode moderator

    For any visitors here who have not drawn ellipses before, spend a couple of minutes with this video and then join in later. http://www.youtube.com/watch?v=PQjeTmY0cdQ

    We're dealing with the orbits of planets and moons not being perfect circles. They are slightly elliptical in shape and they are eccentric from the circle, hence the term eccentricity.

    Eccentricity is a measure of how elliptical an orbit is.

    What needs to be added to what you see in the video is that when you have drawn an ellipse (or paused the video) you should remove one of the pins (cover it up) leaving the other alone and surrounded by the ellipse. The isolated pin is now the Sun and the ellipse is the orbit of a body around it. The Sun does not sit in the 'middle' of a flattened circle, it occupies one of the two foci (pins) of an ellipse. The other focus is empty.

    The eccentricity of a perfect circle is zero. Both pins are in the same place. Theoretically, if you separate your pins wide enough you'd get a straight line. The eccentricity of the line is one (1). Eccentricities of the planets are small, so their eccentricity, e, might be something like e = 0.04 or perhaps e = 0.12. These differences are indeed small, but the effect of this eccentric behaviour on the planets is significant.

    I'll see if there's a table of data somewhere...

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  • Kitharode by Kitharode moderator

    I've deliberately chosen to post this particular table of data because I'm hoping that it'll not only give you the numbers, but it should make you feel something like an astronomer. I'm hoping that this sort of table is exactly the sort of thing you've met in the past and said; "No chance, I'll never understand all that". Well now you can!!

    Don't be scared - just start with the top line of the table. 😃

    http://nineplanets.org/data.html

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  • Kitharode by Kitharode moderator

    I will get round to magnitudes I promise (about page 30!) but I keep finding fun stuff and can't resist putting it up here. You'll love this one, because you can use it anywhere in the solar system. Angular Measure.

    The Sun is large, but it is a great distance away from us so it appears small. The Moon is much smaller than the Sun, but it is much closer to us and, fortunately for eclipse watchers, looks to be the same size. Their diameters therefore have the same angular measure on the sky. The angular size of the Sun and Moon is just about 0.5 degrees, as seen from Earth.

    The Moon is slowly drifting away from the Earth so its distance is increasing, therefore its angular size is becoming smaller. Given enough time, the 'perfect' eclipses that we see will be a thing of the past, as less and less of the Sun is covered. So if you get a chance to see an eclipse - don't miss it.

    Now let's look at this from here on Mars. We're farther away from the Sun, so it will appear to have a smaller angular measure. We have two moons, Phobos and Diemos, which are quite small but are fairly close to Mars. What sort of angular sizes will the Sun and our two moons have? What is the angular size of Jupiter if you're on Mars and how different is it to what you see from Earth? This is how you find out...

    Find the diameter of your target and its distance from you. Divide the diameter by the distance. This gives you a number of radians. Take this number and type it in the radians box in the link provided below. You will see the equivalent number of degrees below the box and this is the angular measure of your target.

    Why not begin with the Sun and Moon and check out how close they are in angular measure?

    Diagram: http://www.astro.virginia.edu/~jh8h/glossary/angularsize.htm

    Sun diameter, d, 1 million miles(ish). Distance from Earth, D, 93 million miles. So d/D = 0.01 radians.

    Radians to Degrees: http://www.unitconversion.org/angle/radians-to-degrees-conversion.html is your answer.

    It'd be nice to know how big the Earth looked from here on Planet Four, don't you think? 😉

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  • Kitharode by Kitharode moderator

    Venus shows phases just like the Moon, but there's something odd going on. The Moon is brightest when it is full, less bright at crescent phase. Venus on the other hand gets brighter as she moves into crescent phase.

    Try not to go straight to the links, but instead have a think about where you, Venus, and the Sun are, and what's going on orbit wise. If you get tangled in your knitting then;

    here's what's happening: http://upload.wikimedia.org/wikipedia/commons/2/29/Phases-of-Venus2.jpg

    and what it looks like: http://www.eso.org/public/outreach/eduoff/vt-2004/Background/Infol2/vt2004-if9-fig5.jpg

    Strange how less can sometimes be more !! Enjoy.

    Posted

  • angi60 by angi60 in response to Kitharode's comment.

    Excellent info yet again, thanks. I think it's amazing that the angular sizes of the Moon and Sun (as seen from Earth) are the same! I didn't know about eccentricity (except the normal sort, which I probably am!). I'm not quick on the uptake, but going back a bit, doesn't Venus' axial tilt mean it's virtually upside down? Due to time constraints, I may only be able to keep up with one of your 'classes', so if I disappear I've moved to the Mars one!

    Posted

  • Kitharode by Kitharode moderator

    No problem Angie60. You come and go as you please. It'll slow down soon so you can digest what you want over time and call in whenever you can - you'll always be welcome.

    Yes, Venus is just about upside down. Sooooo, if a planet is rotating anticlockwise as you look down on it, when it falls right over it will appear to rotate clockwise as you look down on it. In the plane of the system it would appear to be rotating in the opposite direction (which it is) but for a very good reason. This is Venus.

    I'm hoping you don't ask me how we know its fallen over and hasn't always been like that because I don't rightly know the answer. Astronomers do know, so the answer is 'out there' somewhere.

    Posted

  • angi60 by angi60

    Well, thanks so much for teaching me that. I had no idea!

    Posted

  • Kitharode by Kitharode moderator

    Beautiful Earth - Venus video here. The straight red line is the distance between the planets, with the centre point of the line tracing out the spiral shapes.

    Use the pause button to stop/start the video and see why Venus shows phases from our point of view on Earth. When Venus is at its 'widest point' from the Sun, from our perspective, we say Venus is at its 'greatest elongation' from the Sun. From this you will understand that Mercury can also show phases and will also have a 'greatest elongation'.

    http://www.youtube.com/watch?v=4cgQNUhtmHM (No sidebar please).

    Posted

  • angi60 by angi60

    Wow, that's an amazing video- it certainly is a beautiful 'dance of the heavens'. It just shows how maths is at the heart of everything in the Universe. Isn't nature wonderful? I behaved and didn't look at the sidebar! It must be quite difficult to sort the 'chaff from the wheat' online sometimes.

    Posted

  • Kitharode by Kitharode moderator

    Its beautiful alright. Also explains, if you think about it, why Venus is known as the evening AND morning star.

    When Venus (or Mercury) are at greatest elongation, say on the left of us in the video, then as the Sun sets (from here) and the sky begins to get dark, that's when we see Venus; in the west, left of the setting Sun. Later on when we've danced round the light bulb for a bit, Venus will be on the right of the Sun (from us) at the other greatest elongation, so Venus rises before the Sun in the east and fades as the Sun rises.

    Exactly the same for Mercury, but its harder to see because its closer to the Sun so the sky is never totally dark, and it's smaller and farther away. Please don't search for it until the Sun has set. Too easy to catch the Sun by mistake as your binoculars jiggle around. Cheers.

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  • Neha_pk by Neha_pk

    I had started a new discussion....then bumped into this ...must say....feel a little better and more comfortable as a beginner...

    Posted

  • Kitharode by Kitharode moderator

    Hey Neha_pk. Great to see you here. We're having some good fun here and everybody is learning something new. Please join in whenever you're ready. I promise we don't bite, but I can't say the same thing about the spiders and yardangs. ** 😮 **

    PS. Just seen your 'team work' post. Wassock and JM have it right so you can safely follow their advice. Cheers.

    Posted

  • Kitharode by Kitharode moderator

    When you're trying to find a faint comet or similar object that you've been told is "about 5 degrees to the left of 'that' star", then sometimes all you need is a rough guide to get you in the area. This works very well....

    http://www.reocities.com/angolano/Astronomy/Images/Dippers.jpg

    If you try it on Orion or Cygnus, for example, then look up their true angular sizes you can 'calibrate' your hand and fingers accordingly. Surprisingly effective and effectively surprising. * 😃 *

    Posted

  • angi60 by angi60 in response to Kitharode's comment.

    Oh that's a useful tip! Brilliant. I see you have a new pupil 😃 You're making progress with encouraging people!

    Welcome Neha_pk! I'm very new to all this too, so don't be too shy to contribute!

    Posted

  • Kitharode by Kitharode moderator

    And just to prove my point (phew!!)...

    http://migall.fastmail.fm/astronomy/stars_and_nebulae/orion/size/size.htm

    Glad you like it Angie60.

    Posted

  • angi60 by angi60

    You certainly can't miss Orion in the night sky! The Orion Nebula is a fascinating area.

    Posted