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# Physics/Sun's motion

Question
Hi,

I read that Sun moves towards the galactic center. How long would the Sun take to reach the galactic center. Also if space in universe is expanding, why the space in between the sun and planets not expanding? Please clarify.

It actually revolves, with us, around the galactic center.  It will never reach there.

Space in the universe is expanding, but you have to understand two things.  1)  We don't know if the nature of the expansion is due to some long-range cosmic repulsion or whether the space itself is expanding for sure (beyond the capabilities of human measurement for the time being).  2)  The scale of the expansion is RIDICULOUS (I cannot stress that enough) compared to the space between the Sun and planets, so we would never notice it on such a tiny and local scale.  It's funny to call billions of miles tiny and local, but it really is when you compare to billions of light years.  Light travels an awfully long way in a year.  Calculate it, light travels 300,000 km per second, and there are close to 31,000,000 seconds in a year.  Both those numbers are hard to comprehend by human scales, now you have to multiply...don't try it in your head, it would stress anyone's brain to try and keep something that big inside...

Physics

Volunteer

#### Dr. Stephen O. Nelson

##### Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

##### Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.