February 29
The Extra Day
Sun Position
The Sun is in Pisces near +12° declination. On this rare day, northern hemisphere daylight is just under 12 hours at mid-latitudes, two days before the astronomical spring.
Sky Highlight
No annual event unique to February 29. The day itself is the sky's own correction (a calendar accounting for the 365.25-day orbital year) as astronomical as anything that happens in it.
Deep Sky Object
NGC 2359, an emission nebula (Thor's Helmet) roughly 12,000 light-years away. A bubble nebula in Canis Major blown by a massive Wolf-Rayet star at its center, the stellar wind has swept surrounding gas into a helmet-like shape visible in H-alpha imaging. Best from southern hemisphere and low northern latitudes in late winter.
Featured Star
Aludra (η CMa) is a blue supergiant roughly 3,200 light-years away, spectral class B5Ia, one of the most luminous stars in Canis Major, shining with the combined output of about 100,000 suns. A star that appears once every four years on this date, paired with a day that exists only to keep the calendar honest, both are corrections against drift.
Around This Date
- February 29, 1504Christopher Columbus, stranded in Jamaica, used his knowledge of a predicted lunar eclipse to convince the local population he could darken the Moon, a celebrated example of astronomical knowledge deployed as leverage.
- 46 BCJulius Caesar, acting on the advice of Alexandrian astronomer Sosigenes, introduced the leap day into the Julian calendar, the direct ancestor of February 29, a correction for the fact that Earth's year is approximately 365.25 days long.
The extra day exists because the Earth takes slightly longer than 365 days to circle the Sun, even the calendar is, finally, an astronomy problem.