How do stars move in the Galaxy?
How do stars move? I do not mean the daily rising and setting of the stars in the sky, but the movement of stars in the galaxy...if there is any. I would really like to know more about this as I am very curious about it. I am a 19 year old student who is very interested in the study of astronomy. Thank you very much.
Our Galaxy, like all other spiral galaxies is rotating. The stars move on orbits around the centre of the Galaxy. It was the motions of stars in external galaxies that lead to the idea of dark matter in the universe - their motions indicated that there was more mass within their orbit than could be accounted for by visible matter alone. This is also true in our Galaxy.
At the distance of the Sun from the centre of the galaxy (about 8 kpc or 24 thousand light years) we move at an orbital speed of about 220 km/s and take about 230 million years to make one revolution around the centre of the Galaxy.
Stars also have some random motions - they don't orbit the galaxy in exact circles. This random motion usually amount to a few tens of km/s in some direction.
As observers we see this motion of the stars as what's called 'proper motion' - the projection of their velocity onto the plane of the sky, and 'radial motion', which is the projection of their velocity along our line of sight. We can dectect radial motion by looking at the wavelength shifts it creates in the spectrum of the star. Proper motion we detect by plotting the position of the star over time and seeing how it moves relative to more distant "fixed" objects. The star with the largest proper motion is Barnard's star which moves about 10 arcseconds (0.003 degrees) per year. A more typical proper motion is about 0.1 arcseconds a year.
Get More 'Curious?' with Our New PODCAST:
- Podcast? Subscribe? Tell me about the Ask an Astronomer Podcast
- Subscribe to our Podcast | Listen to our current Episode
- Cool! But I can't now. Send me a quick reminder now for later.
- How often does the Sun pass through a spiral arm in the Milky Way?
- Does the Sun move around the Milky Way?
- How can we distinguish a star's "real" color from the change in color that we observe due to the star's motion?
- Why do constellations look the same after several years even though all the stars are moving?
- Do stars move in the sky?
- Do stars' orbits in galaxies obey Kepler's Laws?
- Are the planes of solar systems aligned with the plane of the Galaxy?
- Does the Milky Way spin counter-clockwise? If so, do all spiral galaxies spin in this direction and why?
How to ask a question:
If you have a follow-up question concerning the above subject, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.Table 'curious.Referrers' doesn't existTable 'curious.Referrers' doesn't exist
This page has been accessed 112691 times since November 7, 2002.
Last modified: October 18, 2005 6:56:17 PM
Ask an Astronomer is hosted by the Astronomy Department at Cornell University and is produced with PHP and MySQL.
Warning: Your browser is misbehaving! This page might look ugly. (Details)