The Equator is at 0° latitude. The Prime Meridian separates the Eastern and Western Hemispheres. The Prime Meridian runs through Greenwich, England and is at 0° longitude.

This is the preferred coordinate system to pinpoint objects on the celestial sphere. An object’s position is given by its RA (measured east from the vernal equinox) and Dec (measured north or south of the celestial equator). …

Zenith, point on the celestial sphere directly above an observer on the Earth. The point 180° opposite the zenith, directly underfoot, is the nadir. Astronomical zenith is defined by gravity; i.e., by sighting up a plumb line.

NASA uses a spherical Coordinate system called the Topodetic coordinate system. Consider the position of the space shuttle. The first variable used for position is called the azimuth. Azimuth is the horizontal angle of the location on the Earth, measured clockwise from a line pointing due north.

The Earth is on the galactic plane, so we are at 0o latitude. Instead of going from 0o to 180o east and 180o west, galactic coordinates simply go from 0o to 360o. There is no east/west or plus/minus in galactic longitude coordinates. 360o is the same as 2 x 180o, or 180o is half of 360o.

Right ascension is analogous to longitude, is usually measured in units of time: hours, minutes, seconds. The zero-point for right ascension is the Vernal Equinox (also called the Aries Point in the text), location on the celestial equator of sunrise on the first day of spring.

The geographic coordinate system consists of latitude and longitude lines. Each line of longitude runs north–south and measures the number of degrees east or west of the prime meridian. Values range from -180 to +180°. Lines of latitude run east–west and measure the number of degrees north or south of the equator.

Latitude and longitude are broken into degrees, minutes, seconds and directions, starting with latitude. For instance, an area with coordinates marked 41° 56′ 54.3732” N, 87° 39′ 19