GPS in Outer Space?

A GPS app can tell you your numerical “address” or location on the globe with a set of latitude and longitude coordinates. Calculating a position and expressing it, latitude first then longitude, is pretty simple when you know where to start. Zero degrees latitude is at the equator, while zero degrees longitude is the prime meridian that passes through the Royal Observatory in Greenwich, England.

Lines of latitude drawn parallel to the equator will place you in the northern or southern hemisphere, while vertical lines of longitude indicates a position east or west

A set of coordinates are first expressed in degrees because a position on the surface of the globe is fixed in relation to the center of the earth. Picture a line drawn from the north or south pole down to the earth’s core and then outward to the equator, forming a 90 degree angle.

Then, since the earth spins approximately 360 degrees in 24 hours (15 degrees per hour or four degrees each minute) a theoretical grid can be drawn around the globe that equates degrees with units of time. Minutes and seconds can then be used to even more precisely identify a location. Each parallel line drawn either horizontally (latitude) or vertically (longitude) represents one degree, and each degree is divided up into 60 minutes, and each minute into 60 seconds.

Celestial Coordinates

When this same theoretical grid is extended into space, a two dimensional “map” is created and you can just as easily determine coordinates for the visible stars, planets, and constellations.

In place of latitude and longitude, equatorial coordinates are measured with right ascension and declination

Declination is the equivalent of latitude. The 0° starting point is the celestial equator, a horizontal line drawn across the sky that represents the earth’s equator projected out into space. Following lines of declination locates a point in the north or south, expressed as either “+ or -” degrees and then minutes and seconds.

Right ascension is comparable to longitude. Because the earth spins counter clockwise, the sun, stars, and constellations seem to rise in the east and set in the west. Right ascension is measured in hours rather than degrees, with each 15 degrees of “celestial longitude” being equal to 1 hour.

The measure of right ascension is at 0° where the equator and orbital plane intersect at the vernal equinox in the constellation Pisces. Following the celestial equator eastward from that point and then either north or south results in a set of equatorial coordinates that can be verified from anyplace in the world.