Question

How would astronomers use spectra A, B and C to precisely calculate how fast the star was moving? How would the speed the star is moving allow astronomers to be able to deduce information about the orbiting planet? What type of information could the astronomers calculate?

Answer 1

Ans: A star with a planet will move in its own small orbit in response to the planet's gravity. This leads to variations in the speed with which the star moves toward or away from Earth, i.e. the variations are in the radial velocity of the star with respect to Earth.

The planet and star are both orbiting a shared center of mass. If the orbit is edge-on, the star will move towards us and then away from us in its tiny orbit. When an object is moving towards us, the light we detect is blue-shifted (we see the light at shorter wavelengths than normal) and when an object is moving away from us. the light we detect is red-shifted (we see the light at longer wavelengths than normal).

The Doppler shift for light is very similar to the Doppler shift for sound which you have probably witnessed if you've ever stood on the side of the road when an ambulance passed by. The ambulance’s sirens sound different when they are approaching than when they are receding because the sound waves are compressed and then stretched.

These changes in the star's spectrum (a plot of brightness coming from the star versus wavelength) due to the Doppler shift can be detected. This method has detected a good portion of all discovered extrasolar planets.

In order to locate position in space we need at least there different reference points that is here three spectra will help to locate it's position precisely.