October 27
The Circumpolar Constant
Sun Position
The Sun is in Scorpius near -16.5° declination. The asymmetry between day and night lengths is now substantial in both hemispheres, six weeks to each solstice, and the tilt is telling.
Sky Highlight
Late October evenings are a good time to demonstrate Polaris's fixed position by photographing a 10-minute exposure of the northern sky, the resulting star trails will circle a nearly stationary point. For Southern Hemisphere observers, there is no equivalent bright southern pole star: Sigma Octantis (magnitude 5.4) marks the south celestial pole but is barely visible to the naked eye.
Deep Sky Object
NGC 7789 (Caroline's Rose), an open cluster about 7,600 light-years away. Caroline Herschel discovered NGC 7789 in Cassiopeia in 1783 while systematically sweeping the sky, a reminder that many of the sky's rewarding objects were found by someone working methodically through a region, not looking for anything in particular. Best for Northern Hemisphere observers; inaccessible from far southern latitudes.
Featured Star
Polaris (α UMi) is a yellow-white supergiant (F7Ib) about 433 light-years away, and also a Cepheid variable, pulsating with a very small amplitude (less than 0.1 magnitude) over a period of about four days. Its role as the current North Star is temporary: in about 14,000 years, the precession of Earth's axis will have moved the pole toward Vega. Polaris, the still point, while all other stars wheel around it.
Around This Date
- October 28, 1971The UK launched its Prospero satellite on a Black Arrow rocket from Woomera, Australia, becoming the sixth nation to independently achieve orbital launch capability.
- October 29, 1998John Glenn, at age 77, launched aboard Space Shuttle Discovery as a payload specialist, becoming the oldest person to fly in space, 36 years after his Mercury flight.
Polaris will not always be the North Star, but for now it is doing a good enough job.