Sky Notes for January 2013, with James Abbott #stargazing
The Earth reaches its closest point to the Sun along its elliptical orbit on January 2nd when it is about 3 million miles closer than at its furthest point on July 5th. The difference is relatively small compared to the mean distance of 93 million miles, but it is important. It means that currently, our northern hemisphere winters are that bit warmer. Due to cycles in the Earth’s tilt, thousands of years from now, our winters will coincide with the furthest point from the Sun. These cycles, along with other long-term variations in the eccentricity of Earth’s orbit combine to create the mechanism believed to drive ice ages and interglacial periods. The next ice age is predicted for around 50,000 AD.
Following the Winter Solstice, daylight hours begin to slowly lengthen during January. By the end of the month the Sun rises about half an hour earlier than on the shortest morning and sunset is almost an hour later than the darkest evenings in December.
New Moon is on January 11th so the best evenings for observing without the Moon will be between about the 2nd and the 15th. Full Moon is on the night of the 26th/27th. On the night of the 21st/22nd, the Moon will again pass close to Jupiter.
Jupiter remains dominant in the winter night sky, and is due South around 9pm mid-month in Taurus. The North Equatorial Belt and North Temperate Belt are currently prominent in telescopic views.
At 11pm mid-month the brightest star in the sky, Sirius, is due South. Sirius is a moderately luminous star, but nowhere near as luminous as stellar powerhouses such as Rigel in Orion. But being just under 9 light years from our Solar System, Sirius is relatively very close to us and it is this factor that trumps all else to make it the brightest star in the sky. When looking at Sirius, the light we see now left the star as recently as the year 2004. Looking at Rigel, the light we see now left that star about 800 years ago.
Looking ahead through 2013, there are the prospects for 2 bright comets, both with the potential to be easily visible without optical aid. No doubt the appearance of these comets will lead to wild predictions of impending doom from certain quarters, much as they did in the middle ages and before. In reality there are telescopes dedicated to surveying the sky and the information they provide is used by astronomers to keep a close watch on the myriad of comets and asteriods orbiting the Sun. So we know that both of the expected bright comets in 2013 will be comfortably far from the Earth, but we can still enjoy the view.
Cometary behaviour is notoriously difficult to predict. So whilst circumstances for both comets look promising, they could still disappoint. As leading comet observer David H. Levy put it so well: “Comets are like cats; they have tails, and they do precisely what they want.”
James Abbott is an astronomer, NEAS member and CfDS Regional Information Officer.
Posted on 2 January, 2013, in Observing News, Popular Science, Stargazing and tagged comet, ison, january, jupiter, moon, panstarrs, rigel, sirius, solstice, taurus, winter. Bookmark the permalink. Comments Off on Sky Notes for January 2013, with James Abbott #stargazing.