do the stars moving? if so why?
Answers
Stars does not move it appears to move or twinkle due to refraction of light (as the temperature differs in the atmosphere the light changes its speed) and therefore appears to be twinkling
The stars appear "fixed" to the sky. However, the earth's rotation from west to east make the star appear to move in the sky from east to west during the night. In reality, the stars are in constant motion. In fact, everything in the universe is in motion. Because of the great distances to the stars - the nearest star being 4 light years away - their apparent motions across the sky are very small during a human lifetime and not perceived by us.
The Sun - also a star - is moving, orbiting the Milky Way galaxy at a speed of about 220 km/s and takes about 230 million years to make one revolution around the center of the Galaxy. Of course, stars also have some random motions - they don't always orbit the galaxy in exact circles.
Take for instance the easy to see Northern constellation of Great Bear (Saptharishi Mandala in India) due to the proper motions of the stars that make up this familiar constellation, its shape has changed slowly over time. It takes many thousands of years, however, for the effects to be visible to the naked eye.
In almost all cases, the stars belonging to a constellation have nothing to do with each other , they are all at different distances from us, and tend to move in different directions. We get to see this motion of the stars as what's called 'proper motion' - this is the apparent angular motion of a star across the sky with respect to nearby / more distant stars.
Typical proper motion of stars is ~0.1 per year. The 'radial motion', which is the motion of a star away from or towards the earth along its line of sight, is expressed kilometers per second and determined by the shift in the wavelength of light emitted by the star. if it is moving away from us; if towards us. Astronomers can detect radial motion by looking at the wavelength shift it creates in the spectrum of the star.
Proper motion is detected 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 arc seconds (0.003 degrees) per year.
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