The description of the word you requested from the astronomical dictionary is given below.
The right ascension is the coordinate from the equatorial coordinate system in the sky that has the same role as the longitude in other coordinate systems. The right ascension is measured from the vernal equinox. The right ascension is usually measured not in degrees as the other longitudes are, but rather in units of time, such that 360 degrees correspond to 24 hours of right ascension, and 15 degrees to 1 hour of right ascension. Just like for real time, an hour (symbol: h) of right ascension is divided into 60 minutes (symbol: m), and one minute into 60 seconds (symbol: s). Here is an example of a right ascension: 5h23m12s, or 5 hours, 23 minutes, and 12 seconds.