May 18
Foot of the Cross
Sun Position
The Sun is in Taurus at roughly +19.9° declination. Northern days are approaching their solstice maximum length, while southern days are near their shortest of the year.
Sky Highlight
The Southern Cross is at its highest in the evening sky for observers between latitudes 25°S and 50°S, transiting the meridian at a convenient hour after dark in mid-May. From northern latitudes south of 25°N (including Hawaii, southern Florida, and much of Mexico) Crux just clears the southern horizon, and the Pointers are visible nearby.
Deep Sky Object
The Jewel Box Cluster (NGC 4755), open cluster in Crux, about 6,400 light-years away. One of the finest young clusters in the southern sky, its blue supergiant stars are punctuated by a contrasting red supergiant at the center. John Herschel named it the Jewel Box. Visible from southern and equatorial locations; too far south for most northern observers.
Featured Star
Acrux (α Crucis) is a blue subgiant and blue main-sequence pair 321 light-years away, spectral class B0.5IV + B1V, and the brightest star in the Southern Cross. The two main components are resolved with a small telescope. Acrux lies very close to the plane of the Milky Way, placing it against a rich background of nebulosity and star clouds visible in photographs.
Around This Date
- May 18, 1910Earth passed through the outer reaches of Halley's Comet's tail, with no detectable effects on the atmosphere, ending a period of widespread public anxiety about the encounter.
- May 20, 1990The Hubble Space Telescope returned its first images, which revealed a spherical aberration in the primary mirror; corrective optics were subsequently designed and installed in 1993.
The Cross is a short figure (four stars) but it does a lot of navigational work.