The sun orbits the galaxy and takes around 230 million years to do. At nearly 900,000 km per hour. Why then do the stars appear in the same exact position in our sky year after year?
Wouldn't you expect that stars like the North Star would stop appearing directly above earth's rotational axis? Yet, for centuries, the North Star (Polaris) is reliably in the same spot, which is why sailors have always been able to use it as a guide.
But if the sun is orbiting the galaxy, shouldn't that movement cause Polaris' position relative earth to change? Shouldn't some constellations start to appear either further or closer over time due to the sun's orbit?
Is it that the distances are so vast that even the sun's orbit around the galaxy doesn't affect the apparent positions of stars? Or do all the stars orbit together at the same rate in a way that keeps their proximities to earth constant?
Thank you to anyone who can clear this up for me.
@vivify said"Wouldn't you expect that stars like the North Star would stop appearing directly above earth's rotational axis?"
The sun orbits the galaxy and takes around 230 million years to do. At nearly 900,000 km per hour. Why then do the stars appear in the same exact position in our sky year after year?
Wouldn't you expect that stars like the North Star would stop appearing directly above earth's rotational axis? Yet, for centuries, the North Star (Polaris) is reliably in the same spot, w ...[text shortened]... at keeps their proximities to earth constant?
Thank you to anyone who can clear this up for me.
It does because of Axial precession in a cycle of approximately 26,000 years, but you will not notice a difference in your lifetime. The same is true for the stars rotating around the galaxy. Too slow to notice constellation differences.
https://en.wikipedia.org/wiki/Axial_precession
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Everything, and I mean everything, is moving at incredible rates. However, due to the distance (light years) between us and the objects we observe, then like Metal Brain says, you wouldn't notice in your lifetime.
For a better and sensible example, note how fast an airplane flies overhead at a close distance to earth. Then, notice a jet high in the sky. It seems to be going much slower.
@vivify saidCheck this out.
The sun orbits the galaxy and takes around 230 million years to do. At nearly 900,000 km per hour. Why then do the stars appear in the same exact position in our sky year after year?
Wouldn't you expect that stars like the North Star would stop appearing directly above earth's rotational axis? Yet, for centuries, the North Star (Polaris) is reliably in the same spot, w ...[text shortened]... at keeps their proximities to earth constant?
Thank you to anyone who can clear this up for me.
@vivify saidRemember, space is 3D. What you're speaking of is tangential motion, or the motion of stars on the 2D sphere around us. Not all stars are moving tangentially, some are getting closer at the same time, others are moving further away. This means their apparent tangential motion to us is even smaller. Most of the issue is, indeed, the vast distances involved. Also remember, the age of the universe is estimated at 13.7 billion years. The motion involved in 230 million years is far, far less, but at the same time, far, far longer than a human lifespan. One year's motion is practically nothing compared to millions of years..
The sun orbits the galaxy and takes around 230 million years to do. At nearly 900,000 km per hour. Why then do the stars appear in the same exact position in our sky year after year?
Wouldn't you expect that stars like the North Star would stop appearing directly above earth's rotational axis? Yet, for centuries, the North Star (Polaris) is reliably in the same spot, w ...[text shortened]... at keeps their proximities to earth constant?
Thank you to anyone who can clear this up for me.
You can search Google for stuff like "Ursa Major in 250 million years" or even longer, and get what that constellation will look like then. I bet there are videos that show real motion of stars as seen from earth (not photography, of course, but artist's renderings), and the constellations ARE changing, but astronomical times are far longer than the blip of a human lifetime.
Edit: Here's one with a time frame of only 200,000 years.
https://www.popularmechanics.com/space/deep-space/a20347/how-the-big-dipper-has-changedand-will-changeover-200000-years/
It seems I was way off, and tens of thousands of years is enough to see changes.
@Suzianne
Nice post! It is kind of like cars traveling on a road, some of them are standing still relative to a car nearby so you could think there is no movement but it is relative to the greater world around you.
So in our galaxy, they are all spinning around roughly the same rate, which is something in itself, one would think the outer stars would be going slower but that is not the case, galaxies are more like on a giant plate where they all spin at the same rate more or less the same which means somehow the stars in the periphery
are going faster than the ones closer to the center.
Vera Rubin figured that one out and a few more discoveries too:
https://en.wikipedia.org/wiki/Vera_Rubin
@sonhouse saidI keep wondering how they measured the speed of stars in the galaxy they studied. Since Vera's observations are said to be confirmed since then it seems to be settled, but if they are using a method that might be affected by the movement of our solar system though our own galaxy I want to know how they measured the speed.
@Suzianne
Nice post! It is kind of like cars traveling on a road, some of them are standing still relative to a car nearby so you could think there is no movement but it is relative to the greater world around you.
So in our galaxy, they are all spinning around roughly the same rate, which is something in itself, one would think the outer stars would be going slower but th ...[text shortened]... bin figured that one out and a few more discoveries too:
https://en.wikipedia.org/wiki/Vera_Rubin
https://www.scientificamerican.com/article/how-einstein-revealed-the-universe-s-strange-nonlocality/
If a star is moving away from you there might be a redshift observed. If it is moving away from you at the same speed you are moving toward it, you would see no redshift. If it is moving away from you at twice the speed you are moving toward it, you would see half as much redshift. Am I right?
Perhaps they already took that into account. Then again, how do you know they did until you ask?
Astronomers have discovered that all galaxies rotate once every billion years, no matter how big they are. Given how long that is I am forced to question the methods of measuring star speeds and taking into account all the varying speed factors. A complete orbit of the Earth around the Sun gives us a year. Did they measure 6 months apart to observe the difference if any? Stars orbit a galaxy. Did they measure both sides of the outer part of the galaxy on both sides to observe the difference? There should be a noticeable difference because galaxies move too.
https://phys.org/news/2018-03-astronomers-galaxies-clockwork.html
@Metal-Brain
"Astronomers have discovered that all galaxies rotate once every billion years, no matter how big they are. Given how long that is I am forced to question the methods of measuring star speeds and taking into account all the varying speed factors. A complete orbit of the Earth around the Sun gives us a year. Did they measure 6 months apart to observe the difference if any? Stars orbit a galaxy. Did they measure both sides of the outer part of the galaxy on both sides to observe the difference? There should be a noticeable difference because galaxies move too."
Beyond the factual errors, five minutes of thinking about this as written should provide all the insight you need as to why this is stupid.
You're talking about parallax, and the reason you can't use an entire galaxy's parallax should be more than obvious to a smart high schooler.
@suzianne saidAnd once again you fail to provide a source of information.
@Metal-Brain
"Astronomers have discovered that all galaxies rotate once every billion years, no matter how big they are. Given how long that is I am forced to question the methods of measuring star speeds and taking into account all the varying speed factors. A complete orbit of the Earth around the Sun gives us a year. Did they measure 6 months apart to observe the differe ...[text shortened]... rallax should be more than obvious to a smart high schooler.
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You don't know what you are talking about.
@metal-brain saidCommon knowledge doesn't need a source.
And once again you fail to provide a source of information.
You don't know what you are talking about.
Do I need a source to say 2 + 2 = 4?
You're simply an idiot.
Here, educate yourself.
https://en.wikipedia.org/wiki/Parallax
@suzianne saidStop trolling BS that makes no sense.
Common knowledge doesn't need a source.
Do I need a source to say 2 + 2 = 4?
You're simply an idiot.
Here, educate yourself.
https://en.wikipedia.org/wiki/Parallax
You have to be one of the most science illiterate people on the face of the planet.
You continue to prove absolutely nothing with absurd irrelevancies.
@metal-brain saidNo kidding science doesn't make sense to you, it requires a functioning brain.
Stop trolling BS that makes no sense.
You have to be one of the most science illiterate people on the face of the planet.
You continue to prove absolutely nothing with absurd irrelevancies.
@Metal-Brain
It would REALLY help if you ever had a decent education, for instance your talk about stars not having redshift when they move away is right but you have not heard the opposite effect, BLUE SHIFT, if a star comes towards us the light and every other form of radiation changes frequency UP so that can make a yellow star look green if it is moving fast enough and using that data they don't have to have an extreme closeup look to a star, just look at the spectrogram and see if that kind of star which should have X temperature and therefore Y color if it is not moving relative to the sun but a green star moving toward us could shift the green to blue if it is fast enough and the same for very distant objects except THERE there is no blue shift due to the expansion of the universe, the RED shift shows stars more red and in fact the most distant objects have colors that if could be seen from a few million miles away and not moving relative to that star, there would be a color that can be calculated based on the mass and such, they would know what the star SHOULD be if still compared to us and then the amount of redshift can be used to calculate the distance and velocity it is from Earth but not so much the tangential velocity, that has to be figured out by other means, watching them for years which they have done thanks to Suzi's post.
The amount of parallax is roughly the same as the size of Earth's as Earth's orbit around Sol, which is a base of about 186 million miles, the diameter of our orbit or 300 million Km, take your pick.
What I am dying to see is a real telescope go into deep space like Voyagers, now out some 10 BILLION miles away from Sol, two scopes that far apart would make for direct parallax measurement some 50 times further than they can do now, which is about 600 light years so with two scopes 10 billion miles apart or 16 billion Km, we could measure the parallax all the way in to the center of our galaxy, some 30,000 light years.
And if this new quantum superposition technology can link those hypothetical scopes optically, the resolution would be so great you could see the hairs on the head of a person standing on a planet a thousand light years away if it was in direct line of sight,