They use a tool called a SPECTROSCOPE.
The star's chemical composition; the star's rotation; pulsations of the star; planets or other invisible objects moving around the star; how quickly the star is moving towards us or away from us.
How close and far something is from you.
The spectral lines move towards one direction, or towards the other direction, depending on the relative speed.
Yes. If the star is moving away from the Earth, its spectral lines will shift towards the red end of the spectrum. If it is moving towards the Earth, its spectral lines will shift towards the violet end of the spectrum. This is due to Doppler effect.
You can infer that the universe is getting larger.
Astronomers determine whether a star is moving toward or away from the Earth via the Doppler effect. Imagine a motorcycle moving past you. As it drives towards you, it has a higher frequency, and a lower frequency when it drives away. The same thing happens with light. As an object moves towards us, its light has a higher frequency and lower wavelength - this is called blueshift. As an object moves away from us, its light has a lower frequency and higher wavelength - this is called redshift.
Astronomers determine whether a star is moving toward or away from the Earth via the Doppler effect. Imagine a motorcycle moving past you. As it drives towards you, it has a higher frequency, and a lower frequency when it drives away. The same thing happens with light. As an object moves towards us, its light has a higher frequency and lower wavelength - this is called blueshift. As an object moves away from us, its light has a lower frequency and higher wavelength - this is called redshift.
By examining its spectrum, and identifying absorption lines in it. Lines are shifted toward shorter wavelength if the object is moving towards us. They're shifted toward longer wavelength if the object is moving away from us.
The star's chemical composition; the star's rotation; pulsations of the star; planets or other invisible objects moving around the star; how quickly the star is moving towards us or away from us.
How close and far something is from you.
The object is moving away from the observer.
They can determine how fast the star is moving toward or away from us. The chemical spectral signature is used to determine the Doppler shift of the visible light reaching us. This is then used to calculate how fast we and the star in question are moving toward or away from each other.
The spectral lines move towards one direction, or towards the other direction, depending on the relative speed.
Speed an object is moving away from the observer.
Yes. If the star is moving away from the Earth, its spectral lines will shift towards the red end of the spectrum. If it is moving towards the Earth, its spectral lines will shift towards the violet end of the spectrum. This is due to Doppler effect.
The star attracts the planet; the planet attracts the star. As a result of the latter, the star changes position. If this change is such that the star moves away from us during one part of the planet's orbit, and towards us at another (or more generally, the star's speed towards us, or away from us, changes slightly), then this can be detected as a Doppler shift.
A freaking telescope