December 27
The Belt's West Pearl
Sun Position
The Sun is in Capricorn, at roughly 23.2 degrees south declination. Northern Hemisphere days are lengthening, though by only seconds per day at this point; the shift becomes perceptible toward late January.
Sky Highlight
Orion's Belt rises with the celestial equator and is accessible from every populated place on Earth; tonight Mintaka's unique equatorial position makes this a worthwhile night to note how precisely the belt aligns along the east-west axis of the sky. For an observer exactly on the equator, all three belt stars transit at the zenith.
Deep Sky Object
M79 in Lepus is accessible in small telescopes in December evenings, reaching a reasonable elevation from mid-northern latitudes; it is a compact globular cluster about 41,000 light-years away, a distinct ball of old stars that may have originated outside the Milky Way proper.
Featured Star
Mintaka (δ Ori) is a multiple system about 900 light-years away, pairing an O9.5II blue giant with a B1V companion, returning as the western anchor of Orion's Belt. Its position within about a tenth of a degree of the celestial equator is one of the most precise coincidences in naked-eye astronomy. It rises due east and sets due west to within the precision of casual observation from any latitude.
Around This Date
- December 27, 1571Johannes Kepler was born in Weil der Stadt; his Astronomia Nova of 1609 established that Mars moves in an ellipse with the Sun at one focus, ending the two-thousand-year assumption of circular planetary orbits.
- December 28, 1882Arthur Eddington was born in Kendal, England; he would later lead the 1919 solar eclipse expedition that confirmed Einstein's prediction of light deflection by gravity, making the confirmation of general relativity as much Eddington's work as Einstein's.
Kepler and Mintaka share something: they both eliminated assumptions that had no business surviving as long as they did.