Where is the meridian on the personal celestial sphere?
“The meridian” is a feature of the local sky, not the celestial sphere. If you are at some spot on Earth looking up, the meridian is the line from north to south through the zenith. On the celestial sphere, any line from north to south is a line of right ascension (analogous to a meridian of longitude). The line of RA that goes through the spring equinox is defined to be the zero line, where .
