April 6
The Spinning Bowl
Sun Position
The Sun is in Aries near +9° declination. Northern daylight continues to lengthen; southern evenings are growing noticeably shorter as the hemisphere tilts away.
Sky Highlight
April is the best time of year for the Ursa Major Moving Group, a loose association of stars, including most of the Big Dipper, that share a common motion through the galaxy. While not a visual event, this is a fine week to contemplate that the Dipper's shape is temporary: its stars are drifting, and 100,000 years from now the familiar outline will be gone.
Deep Sky Object
M101, the Pinwheel Galaxy (NGC 5457), face-on spiral in Ursa Major, about 21 million light-years. M101 is a large, loosely wound spiral best seen in dark skies, where it reveals asymmetric arms and bright H II regions; it hosted a bright supernova, SN 2023ixf, one of the nearest supernovae in recent decades. Best from northern mid-latitudes; low or below horizon from deep southern locations.
Featured Star
Phecda (γ UMa) lies 83.2 light-years away and is an A0Ve main-sequence star, the 'e' designation meaning it is a Be star, spinning fast enough to fling a disk of gas off its equator. It marks the base corner of the Big Dipper's bowl, one of five Dipper stars that belong to the Ursa Major Moving Group.
Around This Date
- April 6, 1965Early Bird (Intelsat I), the first commercial communications satellite, was launched into geostationary orbit, inaugurating the era of live transatlantic television and demonstrating the practical utility of the Clarke belt.
- April 6, 1984Space Shuttle Challenger launched on mission STS-41-C, which included the first on-orbit repair of a satellite (the Solar Maximum Mission spacecraft) demonstrating that humans could service instruments in space.
Phecda is quietly spinning fast enough to wear a disk of its own gas, a detail invisible to the naked eye but written in every spectrum taken of it.