Right ascension (RA) and declination (Dec) are the two main components of the celestial coordinate system, which is used to locate objects in the sky, much like how latitude and longitude are used on Earth.
- Right Ascension (RA):
- RA is the celestial equivalent of longitude but instead of being measured east or west of the Prime Meridian (which is 0° on Earth), it is measured eastward along the celestial equator, starting from the vernal equinox.
- It is usually measured in hours, minutes, and seconds, with 1 hour of RA corresponding to 15° of angle (since 24 hours make a full 360° circle).
- RA gives the object’s position along the celestial equator, helping to specify its “horizontal” location in the sky.
- Declination (Dec):
- Declination is the celestial equivalent of latitude, and it measures the angle of an object north or south of the celestial equator.
- It is measured in degrees, with the celestial equator being at 0° declination, the North Pole at +90° and the South Pole at -90°.
- Dec indicates how far above or below the celestial equator the object is.
Together, RA and Dec allow astronomers to pinpoint the exact location of stars, planets, and other celestial objects in the sky.