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

Question

Harper Clark · Accepted Answer

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

In contrast, the Doppler method requires us to measure only 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 challenging because it is difficult to measure the motion of distant stars because they move so little when viewed from Earth. In contrast, astronomy requires us to measure only the frequency shift of the light we receive from distant stars, and this is independent of our distance from them.

Joseph Allen · Answer

undefined While the Doppler method measures the slight changes in a star's spectrum caused by its motion toward or away from Earth, which can be detected with greater ease and accuracy, the astrometry method requires longer observation times and is more sensitive to observational errors and systematic effects. Overall, the astrometry method is more challenging than the Doppler method because it relies on measuring the tiny shifts in a star's position relative to background stars over a period of time, which requires high precision and stability in observations.