May 23
The Pointer Who Drifts
Sun Position
The Sun is in Gemini at roughly +20.7° declination. Northern afternoons are long and warm; the summer solstice is now less than four weeks away. Southern observers are in the middle of autumn, with the last clear cold nights before winter.
Sky Highlight
The Big Dipper rides high overhead for northern mid-latitude observers in May evenings, making this an ideal month to practice star-hopping. The two stars at the outer edge of the Dipper's bowl (Dubhe and Merak) point directly to Polaris, and they have done so reliably for centuries, though Dubhe is slowly drifting away from the rest of the Dipper's moving group.
Deep Sky Object
M101 (NGC 5457), the Pinwheel Galaxy in Ursa Major, about 21 million light-years away. A nearly face-on spiral with loosely wound, asymmetric arms, M101 has a low surface brightness that rewards dark skies and wide fields. Several of its outlying HII regions are bright enough to have received their own NGC numbers. Best from northern latitudes.
Featured Star
Dubhe (α Ursae Majoris) is an orange giant 123 light-years away, spectral class K0III, and one of the two Pointer Stars used to locate Polaris. While five of the Big Dipper's stars share a common space motion as members of the Ursa Major Moving Group, Dubhe is moving in a different direction, which means the familiar ladle shape is slowly distorting and will look noticeably different in 50,000 years.
Around This Date
- May 23, 1949Gerard Kuiper announced the discovery of Nereid, Neptune's irregular moon, based on photographic plates taken at McDonald Observatory.
- May 25, 1961President John F. Kennedy delivered his 'We choose to go to the Moon' speech before a joint session of Congress, formally committing the United States to the Apollo program.
Even the Pointers are moving, the directions they point will change.