April 19
The Uncertain Herdsman
Sun Position
The Sun crosses into Taurus around April 19–20. Its declination is near +20°, and northern days are now about two and a half hours longer than nights; southern hemisphere observers are in the approach to their longest nights.
Sky Highlight
Boötes is rising well in the northeast by mid-evening in April, bringing with it the Boötes Void, one of the largest known voids in the large-scale structure of the universe, roughly 250 million light-years across and containing almost no galaxies. It is not visible directly, but lies in the direction of Boötes, giving the constellation an uncanny context.
Deep Sky Object
M3 (NGC 5272), globular cluster in Canes Venatici, about 34,000 light-years. Resolving M3's outer stars in a medium-aperture telescope is one of the pleasures of April skies; the cluster contains approximately 500,000 stars and more cataloged variable stars than any other Milky Way globular. Visible from both hemispheres.
Featured Star
Seginus (γ Boo) is a white A7III giant 85 light-years away, one of the brighter stars in Boötes. Its name may derive from an Arabic transliteration of a Greek original, but the chain of transmission is broken and the etymology remains uncertain. It is a mild Delta Scuti variable, oscillating in brightness at low amplitude with periods of a few hours.
Around This Date
- April 19, 1971The Soviet Union launched Salyut 1, the world's first space station, beginning the era of sustained human presence in Earth orbit.
- April 21, 1997A Pegasus rocket carried the cremated remains of 24 people into Earth orbit on the first Celestis memorial spaceflight, including those of Gene Roddenberry, creator of Star Trek, and Timothy Leary.
Seginus keeps its name without knowing where it came from; so does almost every other star we can see.