December 15
The Supergiant's Long Reach
Sun Position
The Sun is in Sagittarius, at roughly 23.4 degrees south declination, within a week of the solstice. Northern nights are long and cold; southern skies carry their longest, warmest days.
Sky Highlight
Orion is well past the meridian by midnight, placing the Belt and the Orion Nebula in prime position for late-evening observing. The combination of M42, M43, M78, and the Running Man Nebula in a single region of sky makes December one of the best months for nebula observing with any aperture.
Deep Sky Object
M42, the Orion Nebula (about 1,344 light-years away) shows the Trapezium cluster clearly in any telescope in steady air; the four brightest Trapezium stars are all within the past million years of their formation, cosmically newborn in a nebula still dense with the material they are ionizing.
Featured Star
Alnilam (ε Ori) is a B0Ia blue supergiant about 1,340 light-years away, one of the most luminous stars in its neighborhood of the galaxy. Even at this great distance, its intrinsic brilliance keeps it in the middle of the Belt's trio, a reminder that what the naked eye calls 'equally bright' often hides enormous differences in actual power.
Around This Date
- December 15, 1970The Soviet Venera 7 became the first spacecraft to successfully land on another planet and return data, measuring Venus's surface temperature at around 465°C, confirming what had been suspected about the runaway greenhouse effect.
- December 15, 1965Gemini 6A and Gemini 7 flew in formation for over five hours, the two capsules maneuvering close enough for crew members to read each other's mission patches, proving that orbital rendezvous was operationally feasible.
The middle pearl of the Belt is 275,000 times the Sun's luminosity, its modesty on the sky is entirely a matter of geography.