May 31
The Bear's Thigh
Sun Position
The Sun is in Gemini at roughly +21.9° declination, very close to its solstice maximum, which it will reach in late June. Northern days are at their longest stretch of the year; southern days are at their shortest.
Sky Highlight
May ends with the Big Dipper nearly overhead from northern mid-latitudes and the spring galaxy season drawing to a close. Virgo and Leo begin to descend toward the western horizon after sunset, and by June the summer Milky Way will start to claim the eastern sky. It is a transitional sky: the last of the galaxies and the first hint of the coming star fields.
Deep Sky Object
M51 (NGC 5194), the Whirlpool Galaxy in Canes Venatici, about 23 million light-years away. On a final late-May night, M51 is still well-placed overhead for northern observers. The spiral arms of M51 extend to touch the smaller companion NGC 5195, and on a night of good seeing, that interaction is directly visible through a modest telescope. Best from northern latitudes.
Featured Star
Phecda (γ Ursae Majoris) is a main-sequence A-type star 83.2 light-years away, spectral class A0Ve, forming part of the bowl of the Big Dipper. The 'e' in its spectral code indicates emission lines in its spectrum, marking it as a Be star: it spins rapidly and has ejected a circumstellar disk of gas from its equator, which generates that characteristic emission. Its name means 'the thigh of the bear.'
Around This Date
- May 31, 2008Space Shuttle Discovery launched on STS-124, delivering the second and largest section of the Japanese Kibo laboratory module to the International Space Station.
- May 29, 1919The Eddington eclipse expedition confirmed general relativity through stellar deflection measurements, a result that reshaped the whole of 20th-century astrophysics.
May closes with the Dipper overhead and the summer star clouds just beginning to rise.