May 17
The Blue Pointer
Sun Position
The Sun is in Taurus at about +19.7° declination. Northern evenings are long and nights short; the window of true astronomical darkness is at its narrowest before the summer solstice. Southern observers enjoy clear autumn nights with good darkness.
Sky Highlight
For Southern Hemisphere observers, May is prime season for the Southern Cross (Crux), which rides at or near the meridian at nightfall at southern mid-latitudes. The two Pointer stars (Alpha and Beta Centauri) appear close together and are easily recognizable. This is one of the southern sky's most celebrated seasonal sights.
Deep Sky Object
NGC 5128 (Centaurus A), peculiar galaxy in Centaurus, about 13 million light-years away. It is the nearest radio galaxy and one of the most studied objects in the southern sky, with a prominent dark dust lane cutting across an elliptical body, the result of an ancient galactic merger. Visible to the naked eye from a dark southern site; from northern latitudes it remains below the horizon.
Featured Star
Hadar (β Centauri) is a blue giant 390 light-years away, spectral class B1III, and one of the two Pointer Stars that guide southern observers to the Southern Cross. It is actually a triple system: two close companions orbit each other in about 357 days, and a third orbits the pair at a wider distance. What the eye sees as a single blue point is quietly three.
Around This Date
- May 17, 1902Antoine Becquerel, Pierre Curie, and Marie Curie were jointly named as recipients of the Royal Medal from the Royal Society, recognizing their foundational work on radioactivity, research that later enabled radiometric dating of meteorites and the Earth.
- May 19, 1910Earth passed through the ion tail of Halley's Comet, producing no observable effects despite earlier fears of atmospheric poisoning from cyanogen compounds.
Three stars in a handshake, pointing south.