I am still very new to many physics theories, however while sat in class today, a thought came to mind that I have not been able to answer from simple googling.

What is so specific about our sun that we orbit it? It is by no means the largest star and it's mass is apparently around average for a star. So why, out of all the stars, do we orbit the sun? Is it due to position, pure coincidence or is it something I do not know about with my limited knowledge. Thanks for your help.

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    $\begingroup$ It's because of position: the sun is closer to us than the other stars in the sky, and gravity strength is strongly dependent on distance. $\endgroup$ – DumpsterDoofus Apr 22 '14 at 19:31
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    $\begingroup$ How do you know an alien student sitting in a classroom orbiting another star isn't asking itself exactly the same question? $\endgroup$ – John Rennie Apr 22 '14 at 19:33
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    $\begingroup$ Think a bit. Any star we would be orbiting we would call the Sun anyway. In the news we hear of planets found around other stars, and speculations of life there. $\endgroup$ – anna v Apr 22 '14 at 19:33

Philosophical answer

We orbit Sun because we called the star that is so important to our life "Sun".

That's actually not as silly as it may look.

Let's imagine we would orbit one of the other stars.
We would see a bright star at the sky during day.
We would call that star Sun.

Maybe the day would be a little longer, and the star a little more redish. But we would devide the day into 24 hours, so the day would be 24 hours long. I even expect that we would call the color of the Sun yellow, because the Sun is something important to living organisms that develop languages.

So, still orbiting that other star, we would discuss on the internet why we are orbiting the Sun instead of one of the other stars...

(See also Anthropic principle)

Physical answer

The Earth formed from matter near to the Sun, so it ended up near the Sun, and is orbiting it, because gravity depends heavily on distance to the influencing masses, such that oher stars have negligible effects to Earth's orbit. (see comment of @DumpsterDoofus and your reference to position)

To be exact, Earth and Sun are actually orbiting their total center of mass. But because of the mass difference, that is just above the surface of the Sun. The center of mass is called barycenter in this context and is useful as origin of a coordinate system to describe the orbiting movements in.

Logical answer

"We orbit around the Sun instead of one of the other stars."

is true because

"Sun is defined as the star which we orbit around."

  • $\begingroup$ Thank you for the physical explanation. I suppose I didn't think that the others star's were too far, I thought the mass would compensate for it. $\endgroup$ – Harvey Apr 22 '14 at 20:19
  • $\begingroup$ This "too far" is actually because gravity depends very much on distance - so even though there are indeed much heavier start than sun, it does not matter. $\endgroup$ – Volker Siegel Apr 22 '14 at 20:29
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    $\begingroup$ And furthermore: the Sun is way way more massive than the Earth, but we are still glued to it by gravity, not falling to the Sun. Again, the Earth is much closer. $\endgroup$ – Davidmh Apr 22 '14 at 21:24
  • $\begingroup$ By now, I'm very curious - is every vote on the physical part, or are there votes meant for the first section? Should I split it into two, creating a new answer (with no votes) from the first section? One can see the first part as "intro" or decoration - but I find it more interesting, somehow. But not sure I got the point across there, so nobody is interested in that part? $\endgroup$ – Volker Siegel Apr 23 '14 at 6:28
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    $\begingroup$ The Earth-Sun barycenter is inside the sun, not "just above the surface". $\endgroup$ – Justin Aug 23 '16 at 13:19

We orbit the sun, our sun, because the planets and the sun (and all suns and their planets) were formed by a cloud of interstellar gas and dust that collapsed under its own gravity, thus gaining angular momentum, and forming an accretion disk that became our solar system. In other words the earth and the sun are linked by their common birth, just as children are linked to their parents, if a simple analogy will explain it more clearly!


protected by Qmechanic Jul 29 '14 at 13:47

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