December 22
The Outstretched Paw
Sun Position
The Sun has moved into Capricorn, now sitting just past its southernmost point at about 23.4 degrees south declination. Northern Hemisphere days begin their slow return to length; southern days have begun their equally slow retreat.
Sky Highlight
Canis Major is well-placed in the southeast by 10 PM for northern observers and high in the north-northeast for southern observers; Sirius rises in the east-southeast and the whole large-dog figure is visible in a single sweeping view. The Ursid shower still produces occasional meteors near its peak.
Deep Sky Object
NGC 2362, a tight open cluster in Canis Major about 4,800 light-years away, clusters around the brilliant Tau CMa; it is a very young cluster with an estimated age of just a few million years, making its stars among the youngest accessible in a small telescope this month.
Featured Star
Mebsuta (ε Gem) is a G8Iab yellow supergiant about 840 light-years away, the outstretched paw of one of the twins in traditional depictions. It is a luminous giant roughly 8,500 times the Sun's power, but at almost a kiloparsec of distance, that power is reduced to a modest third-magnitude point, the 'hiding' the assigned caption refers to is purely geometric.
Around This Date
- December 23, 1672Giovanni Domenico Cassini discovered Rhea, the second-largest moon of Saturn, from the Paris Observatory, the fourth major Saturnian moon to be identified and a discovery that contributed to the growing recognition of the solar system's scale.
- December 25, 2021JWST launched, beginning a journey and an unfolding of instruments that would, over the following months, return the deepest infrared images of the universe ever made.
Mebsuta holds 8,500 suns of power at a distance that makes it look ordinary, distance is the great equalizer in the night sky.