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Why is right ascension usually measured in hours instead of degrees?

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Astronomical map Star trails over banksia trees, in Gippsland, Vic., Austl. The south celestial pole, located in the constellation Octans, is at the centre of the trails.

Right ascension is typically measured in hours, minutes, and seconds rather than degrees to emphasize the clocklike rotation of the celestial sphere. Because the Earth rotates on its axis, the celestial sphere appears to complete a full rotation relative to an observer every 24 hours. By dividing the 360° of the celestial equator into 24 hours, astronomers can easily relate a celestial object's position to the time elapsed since its transit across an observer's meridian.12

This system is directly analogous to terrestrial longitude, but it is expressed in units of sidereal time to reflect the Earth's motion. While right ascension can be converted to degrees—with 15° of arc being equal to one hour—using time units simplifies calculations involving the hour angle and the timing of celestial observations.1342