October 27
The Circumpolar Constant
Sun Position
The Sun is in Scorpius near -16.5ยฐ 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 (ฮฑ 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.