1.1 - Terminology

This project is astronomy-based, so let's find/define what some of the usual terms mean, to give us a better insight as to what exactly we are dealing with. It's not a comprehensive list, but it's a good start.

Right Ascension (RA) is the celestial equivalent of longitude on Earth. It is the angular distance measured eastward along the celestial equator from the Sun's position at the vernal equinox (the First Point of Aries) to the hour circle passing through the celestial object in question. RA is measured in hours (h), minutes (m), and seconds (s), with 24 hours being a full circle or 360 degrees.

Declination (Dec) is the celestial equivalent of latitude on Earth. It is the angular distance of a celestial object north or south of the celestial equator, measured in degrees (°), minutes ('), and seconds ("). Declination ranges from +90° at the north celestial pole to -90° at the south celestial pole, with 0° being the celestial equator.

Together, Right Ascension and Declination form the equatorial coordinate system used to specify the precise location of stars, planets, and other celestial objects on the celestial sphere.

A prime meridian is an arbitrarily-chosen meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian (the 180th meridian in a 360°-system) form a great circle. This great circle divides a spheroid, like Earth, into two hemispheres: the Eastern Hemisphere and the Western Hemisphere (for an east-west notational system). For Earth's prime meridian, various conventions have been used or advocated in different regions throughout history. Earth's current international standard prime meridian is the IERS Reference Meridian. It is derived, but differs slightly, from the Greenwich Meridian, the previous standard.

Decimal degrees (DD) is a notation for expressing latitude and longitude geographic coordinates as decimal fractions of a degree. DD are used in many geographic information systems (GIS), web mapping applications such as OpenStreetMap, and GPS devices. Decimal degrees are an alternative to using sexagesimal degrees (degrees, minutes, and seconds - DMS notation). As with latitude and longitude, the values are bounded by ±90° and ±180° respectively.