Concepts in Astronomy #4. Right Ascension
Right Ascension
The Right Ascension (RA) is the angular distance (in hours, minutes and seconds of arc)measured eastward along the celestial equator, from the position of the Sun at the March equinox (0h0min0sec) to the position we want to map in the celestial sphere. It increases due East. It is the equivalent of the longitude in an Earth's map.
When the plane of the ecliptic is projected in the celestial sphere (pathway of the sun), it will cross the celestial equator in 2 points (the equinoxes). The point of the March equinox marks 0h RA. Just as in the terrestrial coordinates the line of 0h RA goes from the north celestial pole to the south celestial pole.
Previous Posts
Concepts in Astronomy #1. Introduction
Concepts in Astronomy #2. The Ecliptic
Concepts in Astronomy #3. The Celestial Equator