March 4
The Belt's Eastern Anchor
Sun Position
The Sun is in Pisces, declination near +9°; Northern Hemisphere days are perceptibly longer now, and Southern Hemisphere evenings are shortening toward the autumn equinox.
Sky Highlight
Orion is still well-placed in the western evening sky in early March, but it is setting noticeably earlier each week, a reminder that the winter constellations are departing. The Belt, with Alnitak as its easternmost star, clears the horizon in the southwest after dusk.
Deep Sky Object
IC 434 and the Horsehead Nebula, a dark nebula about 1,500 light-years away in Orion, silhouetted against the emission nebula IC 434 just south of Alnitak; it requires a moderately large telescope and dark skies, but is one of the most recognizable shapes in deep-sky imaging. Best seen from latitudes between +60° and -60°.
Featured Star
Alnitak (ζ Ori) blazes 1,260 light-years away as a blue supergiant of spectral class O9.5Iab, the hottest and most luminous of Orion's Belt trio. The Horsehead Nebula owes its famous silhouette to the intense ultraviolet radiation this star pours into the gas cloud immediately surrounding it.
Around This Date
- March 4, 1835William Henry Smyth completed observations used in his Cycle of Celestial Objects, an influential catalog of double stars and nebulae that informed Victorian amateur astronomy.
- March 6, 1787William Herschel discovered Titania and Oberon, two moons of Uranus, on this date, the first moons found orbiting that planet.
Alnitak blazes at the Belt's eastern edge, its light old enough to have left the star before the last glacial maximum.