23h

23h is a shorthand notation that can refer to several different concepts depending on the context. Its most common meanings are a time duration of twenty-three hours, a unit used in astronomy for right ascension, and a hexadecimal literal in some programming and assembly languages.

In timekeeping, 23h indicates a duration of 23 hours. It equals 82,800 seconds and represents almost a full day (one day is 24 hours). This notation is often used in schedules, deadlines, or durations where hours are the primary unit, and it can be combined with minutes and seconds (for example, 23h 15m 42s) to express precise intervals.

In astronomy, hours are used to measure right ascension, the celestial equivalent of longitude. Right ascension is expressed in hours, minutes, and seconds, ranging from 0h to 24h, with 24h corresponding to a full circle (360 degrees). An object located near 23h right ascension lies near 345 degrees of the celestial equator. This system aligns with the rotation of the Earth, so the RA value determines when an object rises and transits in the sky.

In computing and programming, some languages and assemblers designate hexadecimal numbers with a trailing h suffix. In this usage, 23h represents the hexadecimal value 0x23, which equals decimal 35. The exact rules for using the h suffix vary by language and may require a leading zero or a different prefix (for example, 0x23 or 023h in other contexts) to avoid confusion with identifiers.

Because 23h can mean different things in different domains, the exact interpretation depends on the surrounding notation and field of application.