December 16
The Rear Foot Pulses
Sun Position
The Sun is in Sagittarius, near 23.4 degrees south declination. Northern Hemisphere daylight holds near its annual minimum; southern observers are near midsummer.
Sky Highlight
Gemini is well-placed for evening observing this week, with Castor and Pollux riding high in the northeast by 9 PM for northern observers. The Geminid radiant is now past peak but the constellation rewards attention: M35 and NGC 2392 are both accessible in modest telescopes.
Deep Sky Object
M35 in Gemini, about 2,800 light-years away, contains around 500 stars spread across about 24 arcminutes (larger than the full Moon in apparent diameter) making it one of the most satisfying open clusters for low-power eyepieces or wide-field binoculars.
Featured Star
Tejat (μ Gem) is an M3III red giant about 230 light-years away, another variable star in Gemini that brightens and dims over a period near 72 days. It marks the rear foot of the twins, and its variability is more rapid than Propus's, making it a good target for observers tracking naked-eye brightness changes.
Around This Date
- December 15, 1965Gemini 6A and 7 completed the first-ever orbital rendezvous, with Schirra and Stafford bringing their capsule to station-keeping proximity with Frank Borman and Jim Lovell, demonstrating control techniques needed for Apollo.
- December 19, 1972Apollo 17 splashed down in the Pacific Ocean after a 12-day mission, ending the Apollo program's crewed lunar exploration; no humans have returned to the Moon's surface since.
Tejat pulses every 72 days (shorter than a human season) a giant variable working on a schedule the eye can almost keep up with.