May 16
The Bear's Guardian
Sun Position
The Sun is in Taurus at roughly +19.5ยฐ declination. Northern spring evenings are some of the longest and warmest of the year; daylight exceeds 14.5 hours near 45ยฐN. 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 45ยฐ 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 (ฮฑ Boรถtis) 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.