13h

13h is a time notation used in some locales to denote 13 hours after midnight, i.e., 1:00 PM on a 24-hour clock. The 'h' stands for hours and is used as a delimiter, with minutes written as 13h00 or 13h05. In many contexts, particularly in French-speaking regions, times are written with 'h' instead of a colon.

In everyday use, 13h equals 13:00; 13h30 equals 13:30; 13h05 equals 13:05. This notation aligns with the 24-hour clock, avoiding ambiguity between morning and afternoon times.

In astronomy, 13h is also a unit of right ascension, a celestial coordinate used to locate objects in the sky. Right ascension progresses from 0h to 24h, and each hour corresponds to 15 degrees of arc. Therefore, 13h RA equals 195 degrees, a direction on the celestial sphere that helps observers align telescopes and catalog stars.

ISO 8601, the international standard for date and time representations, uses durations like PT13H to denote a period of 13 hours. For times of day, the standard prefers representations such as 13:00 or 13:00:00 rather than the compact 13h form.

Overall, 13h serves as a locale-specific shorthand for a time of day—specifically 13:00—while in other contexts, especially astronomy or formal standards, more explicit formats or alternate conventions are used.