That said, the celestial coordinates system has some differences. Instead of latitude, for example, it uses something called declination to describe the distance north or south of the celestial equator, and instead of longitude, right ascension describes the east-west orientation.
"Like any coordinate system, it needs a zero point/calibration," Palma explains. "For celestial coordinates, we project the Earth's equator onto the sky, and so just like latitude measures degrees north or south of Earth's equator, declination measures an angle north or south of the celestial equator. So, for example, the star Spica, which is very prominent in the southern sky tonight from most locations in the U.S., has a declination of -11 degrees 10 minutes, so it is actually south of the celestial equator.
"For longitude on the Earth, we arbitrarily assigned Greenwich, England as the Prime Meridian," Palma says. "The Prime Meridian for the right ascension system is called 'The First Point of Aries,' and it is defined as the position of the Sun on the sky as it moves from south to north along the Ecliptic" — an imaginary line that denotes the path of the Sun — "and passes through the celestial equator. When the Sun is at that location, it is the vernal (or March) equinox on Earth. Right ascension increases to the East from there. So, a star on the sky that is exactly halfway around the sky from the Sun on the vernal equinox would have a right ascension of 180 degrees."
"Because the sky rotates, though, we don't often use degrees to measure it," Palma continues. "Instead, we express angles in hours. So, 180 degrees equals 12 hours of right ascension. The same star I mentioned above, Spica, has an RA of 13 hours, 25 minutes. Which can be interpreted as the point on the sky that is [13h25m* (180 degrees/12 hours)] = 201.25 degrees on the sky eastward from the location of the Sun on the vernal equinox."