The equator is a line around the earth that is exactly half way between the north and south poles at every point. Position north or south of the equator is measured in degrees. If you were to draw a line from your location to the center of the earth and then a line back out to the equator, these two lines would form an angle. This angle is your latitude. The reference for this is an arbitrarily drawn line that runs from the North Pole to the South Pole and passes through the Royal Greenwich Observatory outside of London, England.
Longitude is measured halfway around the world in each direction.
The equivalent of latitude is called declination , and the equivalent of longitude is called right ascension. The reference for declination is the celestial equator . This is a line in the sky directly over the earth's equator. Right ascension is a little more complicated than longitude. The reference for this measurement is a line from the north celestial pole to the south celestial pole, passing through the vernal equinox .