What's in the sky over your head? Wayyy... over your head. I'm not talking about pigeons, or even airliners. Out beyond where the air runs out. (Which isn't actually very far, from some points of view.)
What's the first, most obvious, thing, in the heavens? Think... don't be satisfied with the first answer that occurs to you. (Answer in a moment.) And the second "obvious" thing?
Who cares? Lots of people spend their lives on the question. Maybe you would find it rewarding... if you knew a little more than you do now, if you are asking "Who cares?"
Source: NASA, ESA: Ming Sun (UAH), and Serge Meunier (https://www.spacetelescope.org/images/heic1404a/),via Wikimedia Commons. (Cropped)
But of course, we can't all know everything. Flat Earth Academy only attempts to introduce. Call it "speed dating with knowledge", if you like.
Throughout this page, except where I hope it is obvious, whenever I say "see", I mean "see with your naked eye, absent clouds, etc". After all, mankind has only had telescopes for 500 years or so. When the shepherds were abiding, they only had their eyes to watch the heavens, and the same was true.. sort of (what does THAT mean?) for thousands of years before the shepherds.
What's overhead? Any six year old can tell you: "Stars"
And what's a better answer?...
Before we go on... remember the "what are the two most obvious things in the sky?" question? Answers: The sun... a star, quite like most of the things we call "stars"... but it looks different due to being so close to us.... and earth's moon. If you think the sun "doesn't count", do you think that the stars are no longer up there during the day? What would you see, if the sun "went out"? How could you tell?
You could spend a lifetime on the sun or our moon, but we'll put them aside for now, and keep skimming the surface...
"The stars" (by our six year old's reckoning) are mostly actually "stars" in the narrow sense. We'll come back to them.
A few of the things that look like a point of light (unless you look at them very closely, and not always then) aren't stars, but are planets. We'll come back to them.
Some of the things that look like a point of light are actually millions of stars in a group, but the group is so far away that all we see is the single point. These are galaxies (WP). We're in a galaxy, too. The Milky Way is the other stars in our galaxy, as they appear from the earth. (Image to left from jpl.nasa.gov.)
And you'll see a comet once in a while, although by the time we can see it, it often has a tail, an no longer looks like "a star".
From time to time, very briefly, you will see a "shooting star". This isn't a star. It is a meteor (WP), atiny bit of rock falling out of the sky though our atmosphere. If a star were even as close as our star, the sun, it wouldn't look like a shooting "star". And it would cause disruption which would end life on earth. So maybe "meteor" is a better name, so that the next generation won't ever wonder if there's anything star-like about a "shooting star".
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That's the overview of some of what's overhead.
If you're a quitter, now's the time. Quite a bit of work lies ahead. However, if you complete it, I hope that what I've written will help you find what is overhead "interesting". But it will take some work.
Still reading? Well done. We will now return to two categories of object...
We're going to talk about them for quite a long time, to "build" in your head a "model" of the universe. That model will make it possible for you to understand why you see what you see in the sky at night.
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Think about The Sun for a moment. It is a star. (Quite an "ordinary" star, as it turns out. It has relatives which are extraordinary, though.)
Why does it look so different from the other stars? Because it is much, much, MUCH closer to us than the rest of them are.
Forget the sun for a moment.
Imagine looking at a clear night sky. Some stars are brighter than others... but not so very much brighter. Nothing like as much brighter as they "should" be. But the brightness of a star isn't all that matters. Some quite small stars are close, and some almost uncomprehendably big stars are, luckily, very distant. If the distances happen to be right, the distance factor and the brightness factor balance. A faint close star can look (from earth) brighter than a bright distant star.
Things to ponder, though I won't be going into them here: How do you tell how far away a star is? How do you measure how big, or how bright it is? Does its size or brightness change?
Something else to ponder: A star is essentially a whole bunch of atomic bombs going off one after the other... for thousands of years. If an atomic bomb was just dynamite, it is almost as if the star were a candle made of dynamite. A star has enough fuel to burn, and burn and burn... but this "burning" is the same physics as what goes on when a hydrogen bomb goes off. Kind of hard to get your head around, no? That's typical of astronomical knowledge. That's why hard-to-imagine numbers are called "astronomical". And why, for some, even if not you, astronomy is "interesting". Stick with us... maybe you'll start being interested, too. Hope so.
Planets, by comparison, are really rather boring. But, like relatives, they are our bits of "stuff in the sky", and thus get our attention.
They are much, MUCH smaller than stars, and much, MUCH closer. And they aren't "going bang".
And there aren't very many of them.
The Earth is a planet... a big ball of rock around a core molten iron, hotter than the surface of the sun, flying through space, in an orbit around the sun. (No planet is "going bang", but there are many "designs", not all are rock and iron.)
Compared to one another, the planets of the sun (other stars have planets, too) are of quite different sizes. Compared to "stuff" in the sky overhead, they are all about the same size- "very small".
Fine theory. But one of the objectives of the Flat Earth Academy is to get you to think: "Is that right? Could I check it for myself? How would I prove that is true? Myself."
Proving all of it is a big task. Proving that just a few of the "stars" in the sky are different is quite easy. See the Planets page. (To qbe written yet.)
The night sky really doesn't change very much. The "changes" are mostly due to which way we are looking. If you stand on a beach in California looking west, you will see mountains. If you look east, you will see the Pacific Ocean. Both are "really" there all the time, regardless of which way you are facing.
Think of our sun as being at the center of everything.
Imagine... because it is true!... that you are on a big ball, and it is going 'round and 'round the sun. (And spinning on it's own axis at the same time.) How long to go around the sun? How long to complete one revolution. (You know basic answers to both already. But those answers aren't the whole story though, if you think about the issues. I'll qtry to get back to both. But as a "teaser", think about this: A second can be defined as a 60th of a 60th of a 24 hour "day". But for precise scientific work, that's really not "good" enough. The motion isn't a simple enough, when you look at it closely, as a physicist likes a Basic Unit to be. Hmmm. Problem. So, in a sense, there are now two "seconds".... the everyday "second" we all use in our lives, and the "scientist's second", used in some high precision work.
Hover your mouse over this for answer to the "go around/revolution" question... which is repeated further down the page if hovering doesn't work for you. (Did that "hover for answer" thing work? Work well? Do you like it as a way to give you a chance to look for your own answer, before being "given" answer? Comments very welcome, as I haven't used this before, am wondering whether to use it more.)
Now... so far, so reasonable, and reasonably close to "reality". Now I want you to imagine something that isn't at all like it is in the real world, but which works just fine for many of our needs. (I've done a page about the true scale of things.)
Let's say the sun is a ball 400cm in diameter. And let's imagine the earth a ball 1cm in diameter, orbiting 5m from the sun. (Those numbers are "all wrong", by the way. The differences are much greater... but those numbers are fine for what I want.
Now add to your imaginary picture of the universe a huge hollow brass ball 200m in diameter. With lots of glowing LEDs stuck onto the inside surface. And our "sun" and "earth" floating and moving inside the huge ball, at its center.
That will do very nicely for a "model" of the universe. Even if it would be a bit hard to build.
Diversion: In Victorian times, in Leicester Square, London, there was (WP) a hollow globe, 18m in diameter. You could buy a ticket, go inside, climb staircases, and look at different parts of the world, done in plaster of Paris on the inside of the globe. Too cool! (Leicester Square was owned by an individual. I wish I could own it today!) Today, in Boston, USA, there is something along the same lines, the Mapparium (WP).(end of diversion.)
Just before we get back to work... Answers to questions posed further up the page: I know you knew the answers. But could you "see" what I was asking? I don't think the question was unfair... but were you thinking hard enough about what was being asked? The answers: It takes a year for the earth to go around sun once, and 24 hours to rotate once about its own axis. (But what do we mean by "a year", "an hour"? And if a second is a 60th of a 60th of an hour, if you don't know what an hour is, you don't know what a second is, do you. It's no good saying that a year is the time for the earth to go around the sun AND saying that going around the sun takes a year. That's "circular logic", and you come away not knowing what either is. In a similar vein: How do you know when the earth has spun 360 degrees? Is that from when the sun is exactly overhead on day one until it is directly overhead again on the next day? No. The earth is in a new place on the next day. Suppose a year took 4 days. From "sun overhead" to "sun overhead" would only need 270 degrees, do you see? Or would it be 450 degrees? What would decide which is right? (If four spins=one orbit.) Yikes! This astronomy stuff isn't as simple as they said at school!)
So. We have the sun. (400cm ball), the earth (1cm ball, orbiting sun at 5m), and, around them, the huge hollow brass sphere, 20m in diameter, with glowing LEDs all over the inside.
Imagine you were the size of an ant, and on the earth. The LEDs (if they were arranged correctly!) would look like the (true) stars in the sky. (Our model isn't going to do the planets for a while yet.)
Sadly, the model doesn't quite "work", but you only have to use a little imagination to fix the problem. What's a little more imagination matter? You have to imagine that when you are on the side of the earth facing the sun then you can't see the stars. But you do see them when you are on the side of the earth away from the sun.
That's it. That's a good picture of an astronomer's place in the universe. It is a good picture, because it lets us wonder "what if" things, and get correct answers.
Because the LEDs are stuck to the inside of the huge hollow ball, they don't move. When you (the ant) look up into "the sky", the patterns of the stars don't change. This is how things are in the real universe.
When I say, "they don't change", I mean that if there is a neat pattern of bright stars like the one on the left, it will be there again, and again... and again, pretty well "forever". (Well... in 100 human lifetimes, anyway.) (Of course, "there" might be a part of the sphere of stars that is on the "sun" side of the earth at the time you are trying to see them... but they are still "there".)
The human brain is very good at spotting patterns. We are hard wired to notice them, and "worry" about them. So, despite the fact that the positions of the stars don't really "mean" much, we, as humans, find patterns that "jump out" at use, and pretend that they look like things we know here on earth. If you've never looked at clouds with a friend and said "that looks like...", then you've missed something. But clouds change. Stars stay in the same patterns. Long, long ago, certain groups of stars were said to "look like" this or that, and the names have stuck. You can see a bunch of them in the image along the edge of the page... and a rather more splendid representation, thanks to the excellent (and free) software from Stellarium.org below.
We call these things "constellations". I have a page for you "all about" constellations, as you may have guessed, but there are other links to that. Finish this page first?
Here, I are trying to create an overview of basic things you should know about astronomy, so that you can go further on your own, based on the framework, or "skeleton" of knowledge to be built on by studying at my Flat Earth Academy.
Going back to you, as an ant, on the 1cm ball orbiting our model "sun".
Now... this next bit may be a bit tricky to worry about, especially during the overview. If what follows is too hard, think "Look "up" at midnight." That will be close.
In a perfect world, imagine yourself looking up into the heavens at midnight, looking along the line which passes through the center of the earth, and the point on the equator due south of your position....
{{ILLUSTRATION TO COME}}On any two nights which are not many days apart, what you are looking at won't change much. If you do it each year on your birthday, what you see when you are ten will be about the same as what you will see when you are sixty.
But if you were to do it on the first of each month, what you would see would change....
What used to be on the center-of-earth/ you-on-equator (at midnight) line a month ago is now 30 degrees from where that line points now.
But after 12 months, you'd be back to the view you had 12 months earlier.
The illustration on the right is, if you like, a "panorama" of what you see over the course of a year, looking "out" towards the stars in the plane of the earth's equator. (The earth doesn't "wobble", as you might think from the illustration (q-to be done, above). It is like a spinning top, always tipped the same amount (23.5°) as it goes around the sun. So once a year, the north pole leans towards the sun, once a year away from the sun, and twice a year, the north and south poles are equally distant from the sun.
In the diagram along the right, where you see a month's name, it shows you what would be more or less on the line from center of the earth out into space, though someone standing on the equator at midnight. Don't worry if the lines and the tipping aren't clear. The month labels show what is (approximately) overhead (for most people on the earth, not polar explorers and Innuit). We'll try to "do" the lines stuff again in a page about cooridinates for the heavens.{{page to be created}}
What if you look "up" or "left"? Well... "up" and "left" are complicated ideas to use, in this context. Forget about them for now? Forget about the other parts of the sky?
You already know that the moon "works differently". You might not know "the rules", but you just know. That's why, for now, we've left the moon out!
Besides the moon, the planets "work differently", too. And so they've been left out.
The moon and the planets are "local" events. They can be thought about quite separately from the stars. You only need to put the topics together when you begin to wonder "What stars will the moon (or this or that planet) be "near", when I look at the night sky on this or that date and time?" When you've covered some other topics I {{q-am going to}} provide, then you'll find getting answers to that question easy.
CREDIT: Stellarium.org provides (free) excellent software, with which many of the diagrams in these pages were created. Give it a try... and learn some things about how the heavens work! You can (as I have been doing, while writing these pages) use the simulator to test whether what you think is true about how "it works" actually is true. I wrote a first "expalanation" of certain things. Found it was wrong. Re-wrote it. Found that was wrong. And re-wrote it again (more or less going back to original!!). I think it is finally right.
Just whining... The bit I stuggled with was how the equitorial grid is defined, and how to help you grasp how the fact that the axis of the earth's rotation is not perpendicular to the plane of the earth's orbit affects what we see "overhead". The very concept of "overhead" becomes tiresome when you are writing for a global audience. What is overhead in New York at midnight, on a given date is almost the same as what is overhead Madrid (at midnight, same date... although what you mean by midnight can be a small issue, too!) But what is overhead in Madras, India, on that date, at midnight will be quite different!
Right! At the time I was writing the whining above, one of the other pages in this website needed the re-re-write, so, having got my whine out of the way, I went off to do that. If you appreciate these pages, the odd bit of feedback would be welcome once in a while! (Note: I said "odd BIT" of feedback, not ODD feedback...)
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