December 13
The Geminid Peak
Sun Position
The Sun is in Sagittarius, at about 23.4 degrees south declination, within days of the solstice minimum. The long northern night provides ideal dark hours for meteor watching; southern observers also benefit from the peak, though the radiant is lower.
Sky Highlight
The Geminid meteor shower peaks on December 13-14, with rates up to 120 meteors per hour under ideal dark-sky conditions. The shower's parent body is 3200 Phaethon, a rocky asteroid rather than a comet, making the Geminids unusual among major showers. The radiant lies near Castor in Gemini and is visible all night for northern observers; southern observers see diminished but real rates when the radiant clears the horizon.
Deep Sky Object
NGC 2392, the Eskimo Nebula (a planetary nebula in Gemini about 2,870 light-years away) is well placed in December and shows a double-shell structure: a bright inner disk surrounded by an outer halo of radial filaments, reminiscent from Earth-based telescopes of a face surrounded by a fur-trimmed hood.
Featured Star
Elnath (β Tau) is a B7III blue-white giant about 131 light-years away, returning as the bull's northern horn-tip. It marks the nearest edge of Taurus as you trace the constellation eastward toward the rich winter Milky Way, and on Geminid nights it stands as a useful naked-eye reference point for tracing meteors back to their radiant.
Around This Date
- December 13, 1920Albert Michelson measured Betelgeuse's angular diameter as approximately 0.047 arcseconds, confirming for the first time that stars other than the Sun have measurable physical sizes.
- December 14, 1972Gene Cernan became the last human to stand on the Moon, writing his daughter's initials in the lunar dust before ascending the ladder of Challenger's ascent stage, a moment that has not been followed by any crewed lunar landing since.
The Geminids are the one major shower born of a rock, not a comet, even the exceptions in astronomy have their own consistency.