December 19
The Herald of Sirius
Sun Position
The Sun is in Sagittarius, near 23.4 degrees south declination. The solstice is within two to three days; the Northern Hemisphere is at its tilt maximum away from the Sun.
Sky Highlight
Canis Major is rising in the east-southeast by late evening, with Mirzam clearing the horizon before Sirius. The sequence of Mirzam then Sirius rising has been noted for millennia as a reliable herald pattern, the same rising order plays out each clear December night.
Deep Sky Object
NGC 2244, the open cluster at the heart of the Rosette Nebula in Monoceros, lies about 5,200 light-years away; the cluster is visible in binoculars while the surrounding circular nebula requires a wide-field telescope or camera, the cluster's young hot stars have blown a cavity in the surrounding cloud.
Featured Star
Mirzam (β CMa) is a B1II-III blue-white giant about 500 light-years away, a Beta Cephei variable with oscillations too small to detect without instruments but real enough to classify it. It rises slightly before Sirius, earning its ancient name 'the herald' or 'the announcer', a star known more for its position in the sequence than for its own light.
Around This Date
- December 19, 1972Apollo 17 returned safely, ending 50 months of human lunar surface operations that began with Apollo 11 in July 1969.
- December 25, 2021JWST launched successfully after over two decades of development; its first year of science operations would return images of galaxy clusters, exoplanet atmospheres, and star-forming regions at resolutions and wavelengths no prior observatory could reach.
Mirzam announces Sirius the way opening acts announce the main event, it knows its role, and the role is worth playing.