Via the rotation curve method, we can estimate the mass of galaxies like M31 from
a. Doppler shifts of material at the edge of its disk and computing P = 2r/v.
b. the distances of the Doppler shift points from its center.
c. Doppler shifts of material at the edge of its disk and computing P = 2r/v and the distances of the Doppler shift points from its center.
d. It is impossible to estimate the mass of M31.
Question 2
A planetary nebula
a. produces an absorption spectrum.
b. produces an emission spectrum.
c. is contracting to form planets.
d. is contracting to form a star.
e. is the result of carbon detonation in a 1- star.