December 25
The Once and Future Brightest
Sun Position
The Sun is in Capricorn, at about 23.3 degrees south declination. Northern Hemisphere days are still near their minimum and barely lengthening; southern midsummer continues.
Sky Highlight
Canis Major is in prime position in the southeast this evening for northern observers and high in the north for southern observers. The Winter Triangle (Sirius, Betelgeuse, and Procyon) is rising in full by 9 PM, framing a large portion of the winter sky.
Deep Sky Object
M41 is well-placed south of Sirius for December 25 evening viewing; in binoculars the cluster shows its extent clearly, and observers near latitude 30°S see it nearly overhead, one of the more pleasantly situated southern-hemisphere Messier objects in December.
Featured Star
Adhara (ε CMa) is a B2II blue-white bright giant about 430 light-years away, the second-brightest star in Canis Major and the 22nd-brightest in the current sky. Calculations suggest that roughly four million years ago Adhara was nearer to the Sun's position and would have been the brightest star in the sky, an ancient distinction that left no record except the orbital mechanics to reconstruct it.
Around This Date
- December 25, 2021The James Webb Space Telescope launched on Christmas Day, following years of delays; it represented the most complex and expensive space observatory ever built, carrying instruments sensitive to infrared light from the earliest galaxies.
- December 27, 1571Johannes Kepler was born in Weil der Stadt in the Duchy of Württemberg; he would go on to derive the three laws of planetary motion that transformed astronomy and laid groundwork for Newton's gravitational theory.
Adhara held the sky's top honor four million years ago, stellar brightest-star records are not permanent, just very long-term leases.