Astronomy | Astrophysics Answers

Estimate the radius of a star in thermal equilibrium of mass 10^30 kg and average internal temperature 10^7 K. It is given that
kB =1.38 x 10^-23 JK^-1, mH - 1.67 x 10^-27 kg and G=6.7 x 10^-11 m³ kg^-1s^-2.

Explain the horizon coordinate system used in astronomy. Show the horizon coordinates of a star on a celestial sphere for an observer at latitude 30°N.

The apparent magnitude of the sun is - 26.8. Determine its absolute magnitude. It is given that the distance between the sun and the earth is 1.5 x 10^11m.

A galaxy of absolute magnitude M= - 20 is at a distance of 700 kpc. Would it be visible to the unaided eye.

The estimated life time of the sun on mainsequence is ~10^10 yrs. Determine the mainsequence life time of a star of 0.5 Mo.

Explain the origin of 21 cm radiation.

Explain why sunspots appear dark ?

In the H-R diagram, three stars are found to be having luminosities L1, L2 and L3 such that
L1 > L2 > L3. Determine the ordering relation of their radii if the effective temperatures of these stars are the same.

Compute the magnitude of the faintest object observed with a 1 m optical telescope.

The apparent magnitudes of two stars are 0.06 and 1.06 respectively. Calculate the ratio of their brightness.