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This might be a weird question, but I'll ask it anyway.

If one year on earth is the time it takes for the earth to orbit around the sun, then (if it were possible for humans to survive on the sun), how long would be a year on the sun?

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  • $\begingroup$ It's not exactly clear what you're looking for (the whole "what if humans could live on the sun" part makes this seem like speculation about human standards instead of an astronomical question), but perhaps you're looking for this: Galactic year - Wikipedia? $\endgroup$ – called2voyage Jun 17 '14 at 19:35
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There are (at least) two possible answers.

  1. The concept of a "year" has no meaning for the Sun. For Earth, a year is the time it takes to complete one orbit around the Sun. Since the Sun doesn't orbit around the Sun, it doesn't have a year.

  2. But the Sun does orbit around the core of the Milky Way Galaxy. One orbit takes from 225 million to 250 million years. (Current estimates are uncertain, and the chaotic nature of star motions is likely to cause it to vary a bit.) This is called a "galactic year" or "cosmic year". Reference: http://en.wikipedia.org/wiki/Galactic_year

(I suppose there could be a third answer. If humans were able to put a colony on the surface of the Sun, using some advanced technology that obviously doesn't exist yet, it's likely they'd still use an Earth-based calendar to measure time.)

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  • $\begingroup$ Another possible answer: the Sun orbits the center of mass of the solar system and has 99.8% of the mass. Jupiter has most of the rest of the solar system mass, about 2.5 times more mass than the other planets and stuff combined. Therefore you can consider Sun-Jupiter as a binary system, so one "year" of this system is the period of Jupiter, about 12 earth-years long. The center of mass of the Sun-Jupiter system is about 740,000 km from the center of the Sun, and the Sun has a radius of 350,000 km, so the center of mass of the solar system is about one Sun radius outside of the Sun. $\endgroup$ – Prof Huster Sep 26 '18 at 14:05
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I hope you mean if a sun was 'rotating around' another sun, how long it would take to complete a revolution.

There is this thought process. Since they both have equal mass, they would definitely rotate around their center of mass. So now, many factors come into the picture.

  • Distance: How far they are from each other.
  • Mass: Mass of sun, i.e. their individual masses (same in this case of course)

Using the mass and distance we can make some basic calculations using $F = G*\frac{M^2}{d^2}$, where $M$ is the mass of sun and $d$ is the distance of separation between the two 'suns'. Keeping in mind of the fact they must obviously be rotating about their center of mass which is half-way in this case, we can use $a = \frac{v^2}{r}$ accordingly and get to the solution you are seeking.

So, depending on the above factors (there may be few more), we may find the linear or angular velocity with which they are rotating around their center of mass, and accordingly we can calculate the period of rotation.

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