Suppose you are observing the Milky Way from another galaxy at a distance of 10 Mpc. We assume that we have a face-on view of the Milky Way and that the Sun is in a circular orbit of radius Ro = 8 kpc and moving at Vo = 220 km s '. (a) Calculate the angular distance the Sun will appear to move in a single year, in arcseconds. (This is the angle in the sky as measured by you, not the angle covered by the Sun in its orbit.) Do you think it is feasible to "watch" the Milky Way rotate by observing it over a few years? (b) Calculate the V-band surface brightness of the disk at the location of the Sun, in mag arcsee ?, assuming the total luminosity of the disk is 1010 Lvo and that the exponential scale length is hp = 4 kpc.

Suppose you are observing the Milky Way from another galaxy at a distance of 10 Mpc. We assume that we have a face-on view of the Milky Way and that the Sun is in a circular orbit of radius Ro = 8 kpc and moving at Vo = 220 km s '. (a) Calculate the angular distance the Sun will appear to move in a single year, in arcseconds. (This is the angle in the sky as measured by you, not the angle covered by the Sun in its orbit.) Do you think it is feasible to "watch" the Milky Way rotate by observing it over a few years? (b) Calculate the V-band surface brightness of the disk at the location of the Sun, in mag arcsee ?, assuming the total luminosity of the disk is 1010 Lvo and that the exponential scale length is hp = 4 kpc.