Brought to you by Dr. Roy Gretton, Journal Editor of The Nottingham Astronomical Society.
Contact details are on the Nottingham Astronomy website: https://nottinghamastro.org.uk/
Please note, the NAS new permanent venue for our main meetings on first Thursday of the month is ยญNottingham Emmanuel School, Gresham Road, West Bridgford, Nottingham. NG2 7YF
The Stars of Winter
The Southern Hemisphere is blessed with some of the most spectacular celestial vistas available on Earth, as the richest section of the Milky Way is best seen from downยญunder, while it just scrapes along the horizon here in the north. By way of compensation, though, we have a very special portion of sky visible in our winter. Special in that it contains a large concentration of bright stars โbright enough to be seen through the light pollution of towns. Iโm thinking of our view of the constellations of Auriga, Taurus, Gemini and Orion, together with the Great Dog and the Lesser Dog, which are seen in all their glory on January and February evenings. So letโs look at some of these bright stars, which this winter happen to be joined by the planet Jupiter.
Almost overhead is the yellow star Capella, similar in colour to our Sun, but much larger and brighter. Directly below Capella is the orange star Aldebaran, which marks the eye of Taurus the Bull and is classed as a red giant, over 40 times the diameter of the Sun. To the lower left of Aldebaran is the even bigger giant, Betelgeuse, which is over 700 times the diameter of the Sun! If we were to replace the Sun with Betelgeuse, our Earth would be swallowed up inside its ๏ฌery mantle. Further down below Betelgeuse but in the same constellation (Orion) is Rigel, classed as a blue supergiant. Rigelโs colour is due to its temperature: blue stars are much hotter than orange ones. Rigel is about twenty times more massive than our Sun, and perhaps 100,000 times more luminous. You wouldnโt want to go anywhere near it! Looking across to the left of Rigel we come to the star that looks brightest to us on Earth: Sirius, the Dog Star. Sirius is 25 times as luminous as the Sun, and about twice as massive โ therefore much smaller and dimmer than Rigel โ but it looks brighter to us because itโs relatively close to our Solar System. Over tens of thousands of years it is expected that Sirius will migrate southward and eventually disappear from British skies, within 70,000 years becoming the southern โPole Starโ. Moving our gaze upward from Sirius, and a little to the left, we come to Procyon, the brightest star in the tiny constellation of the Little Dog. Procyon is a white star about 50 percent more massive than the Sun. Above Procyon and to the left of Capella is Pollux, one of the Heavenly Twins. Pollux is a giant orange star โ in fact the nearest giant to the Sun โ and it is single, without any companions, unlike the other stars we have been considering. Procyon, for example, is a double star, as is Sirius, while Rigel has at least two companions and Capella has three. Our Sun is probably in a minority in that it is a single star, although some scientists have suggested that it may indeed have a very faint companion (called Nemesis), a dwarf star far out beyond the normal edge of the Solar System. But although searches have been made, no proof of the existence of Nemesis has yet been found.
The Planets
As we have already noted, Jupiter continues to be visible in the evening sky in the constellation of Aries, brighter than any of the surrounding stars, but it will become less prominent as the winter wears on, settng at 11 pm by the end of February. Saturn is fast disappearing from view as it heads toward conjunction with the Sun on February 28th. Mars is creeping slowly away from the Sun as dawn breaks, but will remain little more than an insigni๏ฌcant dot in the bright sky. Mercury is visible in the morning sky shortly before sunrise in early January but then moves rapidly in toward the Sun, reaching solar conjunction along with Saturn on February 28th. Venus also disappears from the morning sky by the end of February. In short โ this is not the most favourable season to be observing planets!
Phases of the Moon
| JAN | FEB | |
| Last Quarter | 4th | 2nd |
| New Moon | 11th | 9th |
| First Quarter | 18th | 16th |
| Full Moon | 25th | 24th |
