Question

Why is the astrometry method more difficult than the doppler method?

Answer 1

Astrometry is more difficult because distant stars move an extremely small amount as viewed from Earth, so it is difficult to measure that motion.

Explanation:

For the Doppler Method, on the other hand, we need only measure the Doppler Shift of the light we receive from distant stars and this is independent of our distance from them.
b. The Doppler method is more difficult because distant stars move an extremely small amount as viewed from Earth, so it is difficult to measure that motion. For Astrometry, on the other hand, we need only measure the frequency shift of the light we receive from distant stars and this is independent of our distance from them.