December 11
The Shoulder Awaiting Catastrophe
Sun Position
The Sun is in Sagittarius, at roughly 23.4 degrees south declination, very close to its annual minimum. Northern Hemisphere solar energy per unit area is at its yearly low; southern midsummer approaches.
Sky Highlight
The Geminid meteor shower is building toward its December 13-14 peak this week, with increasing activity already apparent on the nights of December 11 and 12. The radiant in Gemini rises by evening, making the late hours productive for watching.
Deep Sky Object
M42, the Orion Nebula, transits the meridian around midnight local time, making it an ideal late-evening target; the four Trapezium stars at its core are young enough (a few hundred thousand years old) to have not yet existed when Betelgeuse, tonight's featured star, was already aging.
Featured Star
Betelgeuse (α Ori) is an M1-M2Ia-ab red supergiant about 700 light-years away, one of the largest stars observable with the naked eye, if placed at the Sun's position, it would engulf Mercury, Venus, Earth, and Mars. Its spectral type marks it as nearing the end of a massive star's life cycle; it will eventually explode as a Type II supernova.
Around This Date
- December 11, 1972Apollo 17's lunar module Challenger landed in the Taurus-Littrow valley, and astronauts Cernan and Schmitt began the last human surface operations on the Moon, conducting geological surveys of unprecedented scientific depth.
- December 13, 1920Albert Michelson used the newly installed interferometer on the 100-inch Hooker Telescope at Mount Wilson to measure the angular diameter of Betelgeuse, the first direct measurement of a star's apparent size other than the Sun.
Betelgeuse is already in the slow fall; we watch it without knowing whether the collapse is a thousand years away or a million.