May 16
The Bear's Guardian
Sun Position
The Sun is in Taurus at roughly +19.5° declination. Northern spring evenings are some of the longest and warmest of the year; daylight exceeds 14.5 hours near 45°N. Southern sunsets arrive well before 6 PM.
Sky Highlight
Arcturus, featured tonight, blazes in the southwest after sunset and can guide the eye to the Spring Triangle: Arcturus, Spica, and Regulus. The triangle is one of the largest informal asterisms in the sky, spanning nearly 45° of arc, and it covers the spring rich patch of extragalactic sky from Virgo to Leo.
Deep Sky Object
M3 (NGC 5272), globular cluster in Canes Venatici, about 34,000 light-years away. At magnitude 6.2, M3 is just visible to the naked eye from a dark site, and in any binoculars it resolves into a glittering ball. It contains an exceptional number of RR Lyrae variable stars, which have made it a key calibration target for distance measurements. Visible from both hemispheres.
Featured Star
Arcturus (α Boötis) is a red giant 36.7 light-years away, spectral class K1.5IIIFe-0.5, the brightest star in the northern celestial hemisphere and fourth-brightest in the sky overall. It is moving through the galaxy on a different trajectory than the Sun, drifting south at a rate that will eventually carry it below southern horizons and out of reach of northern stargazers within a few hundred thousand years.
Around This Date
- May 16, 1960Theodore Maiman operated the first working laser using a synthetic ruby crystal, launching a technology central to modern astronomy including gravitational wave detection and astrometry.
- May 18, 1910Earth passed through the tail of Halley's Comet without incident, despite widespread public alarm; observers noted no effects whatsoever.
Arcturus is heading somewhere, it just hasn't told us where.