April 4
The Rider's Test
Sun Position
The Sun is in Aries near +7° declination. Northern spring days are distinctly longer; in southern mid-latitudes, sunset is arriving earlier and evenings are cooler.
Sky Highlight
The spring Virgo Cluster window remains open. This is also a fine time to hunt the Coma-Virgo supercluster region, where on a truly dark night binoculars will reveal a field of galaxies denser than almost anywhere else in the sky accessible to amateur instruments.
Deep Sky Object
M64, the Black Eye Galaxy (NGC 4826), spiral galaxy in Coma Berenices, about 17 million light-years. M64 has a dramatic dark dust lane across its nucleus, visible in amateur telescopes, and an unusual outer disk that rotates in the opposite direction from its inner disk, evidence of an ancient merger. Best seen from northern mid-latitudes; visible but low from southern hemisphere.
Featured Star
Alcor (80 UMa) sits 81.7 light-years away, an A5V main-sequence star that has spent millennia serving as an informal vision test: cultures from Arabia to South Asia used the ability to split Alcor from Mizar with the naked eye as a measure of sharp sight. Modern measurements confirm Alcor is gravitationally bound to the Mizar system.
Around This Date
- April 4, 1967Surveyor 3 launched toward the Moon, later becoming the first spacecraft to have pieces returned to Earth when Apollo 12 astronauts retrieved its camera in 1969.
- April 6, 1965Early Bird (Intelsat I), the first commercial communications satellite, was launched into geostationary orbit, demonstrating the practical utility of the Clarke belt.
Alcor has been the naked-eye benchmark for keen vision across dozens of cultures; it has no idea it is famous.