An eastward angle along the equator
Traditional right ascension runs eastward from a specified equinox along the celestial equator to the target’s hour circle, commonly over a 0-to-24-hour range. The hour circle passes through the poles.
Many declinations can share one right ascension, so RA alone is not a complete direction. Modern catalogues can use ICRS axes, which should not be confused with the changing equinox of the observing date.
Time-style units express angle
One hour of RA equals 15 degrees; one minute equals 15 arcminutes and one second 15 arcseconds. An RA second is therefore not numerically interchangeable with a declination arcsecond.
The coordinate wraps at zero: 23 h 59 m and 0 h 1 m differ by two RA minutes, not almost a full circle. Circular coordinates require that wrap when comparing directions.
References: [2]
RA and hour angle serve different roles
RA describes longitudinal position in a celestial frame; hour angle describes position relative to a local meridian. Earth’s rotation changes a nearly fixed target’s hour angle without making its RA advance with the local clock.
Predicting a meridian crossing combines RA with local sidereal time under consistent conventions. Horizons reports local apparent sidereal time and hour angle separately to preserve that distinction.