April 3
The Double Revealed
Sun Position
The Sun is in Aries near +6° declination. Northern spring is firmly underway; in the southern hemisphere, evenings are noticeably shorter than a month ago.
Sky Highlight
The Virgo Cluster continues its spring transit at high elevation after dark from northern mid-latitudes. Wide-field binoculars sweeping the region between Vindemiatrix and Denebola can pick out multiple fuzzy patches, a rare chance to see genuine large-scale cosmic structure with minimal equipment.
Deep Sky Object
M87 (NGC 4486), giant elliptical galaxy, Virgo Cluster, about 53 million light-years. M87 is one of the most massive galaxies known and hosts a central black hole whose shadow was directly imaged by the Event Horizon Telescope in 2019, marking a milestone in observational astronomy. Visible in small telescopes from both hemispheres.
Featured Star
Mizar (ζ UMa) is a white main-sequence pair 83 light-years away (two A1V stars orbiting a common center) and it was the first double star resolved through a telescope, by Giovanni Battista Riccioli in 1650. Look for its naked-eye companion Alcor just 0.2° away; the two are a true gravitationally associated system.
Around This Date
- April 3, 1966Luna 10 entered lunar orbit, becoming the first spacecraft to orbit the Moon, and began transmitting data on the Moon's magnetic and radiation environment.
- April 7, 1964IBM announced the System/360 family of computers, which later became foundational tools for the data processing needs of space mission planning.
Two stars locked in orbit, 83 light-years out, and we have known about them since 1650. That is a reasonable head start on knowing a neighbor.