Lecture 2: the night sky and its motions. The night sky that we see depends on where we are (and our latitude) on the earth. In the observable universe, there are 88 constellations. However, only 44 of which were known in ancient times. This is because the greeks never travelled to the southern hemisphere, effectively rendering them not able to see half of the constellations. We see the constellations as flat, however the stars are hella far apart. We see them on the same plane (ish) because the further stars are much brighter, therefore appearing as close as the other stars in the group. Because the earth is revolving around the sun and rotating around its poles, there are two types of star/sun motions. Daily (diurnal) motions are seen due to earth rotating on its n/s axis. Annual (yearly) motions are seen due to travelling around the sun.