March 23
The Cross at Its Sharpest
Sun Position
The Sun is in Aries, declination near +2°; the Northern Hemisphere is building its surplus of daylight, and Southern Hemisphere observers are heading deeper into autumn.
Sky Highlight
From southern latitudes, Crux is now high enough after dark to observe its interior clearly, including the Coalsack Nebula, a dark absorption nebula silhouetted against the Milky Way immediately adjacent to the cross. The Coalsack requires no telescope; it is the conspicuous dark patch that makes the cross's star field look suddenly empty.
Deep Sky Object
The Coalsack Nebula, a dark molecular cloud about 600 light-years away in Crux, spanning roughly 7° × 5° and visible to the naked eye as an absence of stars against the bright Milky Way background; it is one of the most prominent dark nebulae in the sky and was noted by early Portuguese navigators. Visible only from latitudes below about +25°.
Featured Star
Acrux (α Cru) (again the foot of the Southern Cross) shines 321 light-years away as a close blue double, spectral class B0.5IV + B1V. Seen again tonight because the Cross is gaining altitude in the southern evening sky, Acrux's blue light is an O/B stellar emission set against one of the densest Milky Way backdrops available to naked-eye observation.
Around This Date
- March 23, 1840John William Draper took the first successful photograph of the Moon, a daguerreotype from New York City, one of the founding moments of astrophotography.
- March 23, 2001The Russian space station Mir was deliberately deorbited, breaking up over the Pacific Ocean after 15 years in orbit and more than 86 crew members served.
The Cross rises a little higher each night now, and the Coalsack beside it (a dark nebula you see by what's missing) is one of the sky's most striking absences.