March 30
The Brightest Bear
Sun Position
The Sun is in Aries at roughly +6.5° declination; the Northern Hemisphere is solidly in spring, with sunset arriving nearly an hour later than at the solstice midpoint.
Sky Highlight
Ursa Major is near the zenith from mid-northern latitudes at midnight in late March. The Dipper's handle arcs to the southeast, following it leads to Arcturus (Arc to Arcturus), one of the brightest stars of the spring sky. Alioth, at the handle's base, is the jumping-off point for this seasonal navigation exercise known to every beginning stargazer.
Deep Sky Object
M81 (Bode's Galaxy), a grand spiral galaxy in Ursa Major about 11.7 million light-years away, one of the brightest galaxies in the sky and visible in binoculars as a distinct elongated glow; it is gravitationally interacting with the nearby irregular galaxy M82 (Cigar Galaxy), which shows signs of a starburst driven by that interaction. Northern Hemisphere object.
Featured Star
Alioth (ε UMa) returns, the brightest of the Dipper's seven stars, 81 light-years away, spectral class A0pCr. Its slow rotation (about 5 days) is fast enough to bring its chromium-rich magnetic patch in and out of the line of sight, producing the subtle Alpha-2 CVn variability. It is one of the most closely studied chemically peculiar stars in the sky because of its proximity and brightness.
Around This Date
- March 30, 1842Carl Friedrich Gauss, who had made fundamental contributions to orbit calculation and least-squares fitting of planetary positions, wrote his last scientific paper on geomagnetism, his methods remained standard in positional astronomy for over a century.
- March 31, 1966Luna 10 launched, becoming the first spacecraft to achieve orbit around the Moon the following month, the first lunar orbiter in history.
The arc from Alioth to Arcturus is one of the most reliable navigation lines in the spring sky, one chemically peculiar star pointing the way to a brilliant orange giant.