April 25
The Herdsman's Star
Sun Position
The Sun is in Taurus near +22° declination. Northern hemisphere long evenings continue; southern hemisphere autumn nights are at their best, dark by 7:30 PM from mid-southern latitudes.
Sky Highlight
Boötes is now well up in the east by 9 PM from northern mid-latitudes, and the entire Virgo-Boötes galaxy corridor is accessible throughout the evening. This is the last reliable week before northern twilight begins to compress observing time; southern observers have the advantage from here through August.
Deep Sky Object
NGC 5466, globular cluster in Boötes, about 52,000 light-years. NGC 5466 is a very loosely concentrated globular cluster, almost lacking a central concentration; it has been shown to have a stellar stream, a trail of stripped stars along its orbit around the galaxy, detectable in deep sky surveys. Visible in medium telescopes from both hemispheres.
Featured Star
Seginus (γ Boo) again tonight, 85 light-years, a white A7III giant. Its low-amplitude Delta Scuti variability operates on a period of about 6.9 hours, too slow to notice visually but measurable with a photometer over a single night. Boötes, the herdsman, is rising to his best evening position of the year.
Around This Date
- April 25, 1990Hubble Space Telescope was deployed from Space Shuttle Discovery, successfully unfolded its solar panels, and began initial checkout in Earth orbit.
- April 28, 2001Dennis Tito, an American businessman, launched to the International Space Station aboard a Soyuz rocket, becoming the first self-funded space tourist.
Seginus is variable by a fraction of a percent every few hours; nothing a human eye would catch, but the photometer keeps a faithful record.