May 11
The Test of Keen Sight
Sun Position
The Sun is in Taurus at about +18.2° declination. Daylight continues to gain a couple of minutes each day in the Northern Hemisphere; southern days are approaching their solstice minimum.
Sky Highlight
Mid-May evenings are among the year's best for observing the Coma-Virgo supercluster, the extended structure of which the Virgo Cluster is the dense core. More than just a cluster, this supercluster is home to thousands of galaxies spread across tens of millions of light-years, all of which lie within a roughly 10° patch of sky.
Deep Sky Object
M53 (NGC 5024), globular cluster in Coma Berenices, about 58,000 light-years away. One of the more distant Messier globulars, and notably distant from the galactic center, yet still densely packed enough to appear as a well-resolved, round glow in moderate apertures. Visible from both hemispheres.
Featured Star
Alcor (80 Ursae Majoris) is a main-sequence A-type star 81.7 light-years away, spectral class A5V, and the faint companion to Mizar in the handle of the Big Dipper. For centuries it served as an informal test of visual acuity (if you can split the pair with the naked eye, your eyesight is good) though modern measurements have confirmed that Alcor and Mizar form a genuine gravitationally bound sextuple system.
Around This Date
- May 11, 1916Albert Einstein's final presentation of general relativity to the Prussian Academy formalized the theory that correctly predicts gravitational lensing, black holes, and the expansion of the universe.
- May 14, 1973NASA launched Skylab into orbit atop a Saturn V rocket, establishing the United States' first crewed space station.
Some separations that look small turn out to be real distances.