IT is the beginning of a new year, a great time to begin exploring the night sky. The nights, although cold, are long and clear and there are some spectacular stars and constellations to be seen. What is perhaps less well known is that in early January the Earth is at its closest point to the Sun in its yearly orbit.
This year the Earth was at perihelion, or closest point to the Sun, on January 4. The word perihelion comes from the Ancient Greek words peri, meaning near, and helios, meaning the Sun. In July when we have summer in Britain the Earth is at aphelion which comes from the preposition apo, meaning away, off, or apart. At first glance this seems very strange because in January the Earth will be 91 million miles from the Sun compared to 94 million miles in July. So why is winter in Britain in January? In fact, the seasons do not depend on how close or far away the Earth is from the Sun, but are determined by which hemisphere is tilted towards the Sun. If you look at a globe of the Earth you will notice that it is tilted over. The tilt is actually 23.5 degrees, and it is this tilt that affects the seasons. The hemisphere that is tilted towards the Sun will have more light and heat and will experience summer, while the hemisphere that is tilted away will have less light and will be colder and this of course is winter. In January the northern hemisphere is tilted away from the Sun so here in Britain we have winter while in Australia it is now summer. When neither hemisphere is titled towards the Sun we have spring and autumn where the periods of daylight are equal and these are known as the equinoxes. January is such a good time to start exploring the night sky. We have our two main signposts, the Plough and Orion in the sky to help us find our way around. If you look north east you will notice the Plough or Great Bear, its pointers pointing to the North Star, called Polaris, which cannot be anywhere else but in its customary position, due north. The ‘W’ of Cassiopeia will be high in the northwest.
At this time of year the overhead point is marked by Capella, the brightest star in the constellation of Auriga the Charioteer. Capella is a bright yellow star whose name means ‘the she goat’. Next to Capella you will notice a small triangle of comparatively faint stars. This is officially called the Haedi but it is nearly always referred to as ‘the kids’. This is because wherever the female goat goes, the kids will always follow. The southern part of the sky is dominated by Orion the Hunter which cannot possibly be overlooked. The stars of Orion act as pointers to help us locate the bright stars of winter. There are three stars that form the belt of Orion. There are four stars that form a giant rectangle around Orion’s Belt. The top left hand star is the bright red star called Betelgeux, or as some people like to call it, Beetlejuice. The bottom right star of the rectangle is the bright blue star Rigel.
Betelgeux and Rigel give us a good example of the different star colours. These colours tell astronomers which stars are the hottest and which are cooler. In everyday language we refer to things being red hot meaning that they are very hot. In actual fact blue stars are much hotter than red stars. While Betelgeux has a surface temperature of around 3,300 degrees centigrade, Rigel is much hotter, with a surface temperature of around 12,000 degrees centigrade. In comparison the Sun is around 5,800 degrees centigrade.If you use the three stars of Orion’s Belt and point down and to the left you will see Sirius, the brightest star in constellation of Canis Major ‘the Great Dog’. Sirius is also the brightest star in the sky and is often called ‘the Dog Star’. Then, use the belt stars and draw a line to the right and upwards and you will reach the red star Aldebaran, the brightest star in the constellation of Taurus the Bull. If this line is then continued you will come across a small glowing patch, which is the Pleiades or Seven Sisters. In drawing a line from Betelgeux to the left, you will come across the star Procyon, the brightest star in the constellation of Canis Minor ‘the Small Dog’. A line drawn from Betelgeux upwards and slightly to the left will come across Castor and Pollux, the two bright stars in the constellation of Gemini ‘the Twins’.Just below Orion’s belt you will notice a misty patch, the Orion Nebula, a stellar nursery where astronomers can study and watch stars form out of clouds of dust and gas. The Orion Nebula is also known as M42, after the eighteenth century French astronomer Charles Messier, who was searching for comets but often got confused with the many fuzzy and misty patches in the sky. He drew up a list of over 100 such objects to help him determine what he was seeing. Today astronomers do not worry too much about the comets he found, as most were quite unremarkable; however Messier’s list is used extensively by astronomers all around the world today!
The Planets in January
This month is all about the two brightest planets, Jupiter and Venus. Jupiter can be seen in the morning sky before the Sun rises in the east. However, it will be Venus that attracts most attention because it can be seen as a very bright ‘star like’ object in the west up to an hour after the Sun has set. The other planets; Mars, Mercury and Saturn, are all too close to the Sun to be seen.
This month we have the last of the major meteor showers of the winter. Many people refer to meteors as ‘shooting stars’. This one is the Quadrantids meteor shower. The Quadrantids reached their peak of activity on the evening of January 3, when as many as 80 meteors per hour could be seen. Meteor showers are named after the constellation where the meteors appear to come from, however, the Quadrantids is the only one named after a constellation that no longer exists. In 1930 the International Astronomical Union which governs world astronomy defined the constellations we use today. Although we still use many of the constellations created by the ancient Greeks, over the last few hundred years many new constellations have been created by astronomers, some of which have survived and some have not. Quadrans Muralis, ‘the Mural Quadrant’, named after a device for measuring angles in the sky, is one that did not survive, so you will not find it on any modern star map. Unlike other constellations that have been consigned to history however, we still recognise the Mural Quadrant because of the meteor shower that bears its name. This constellation occupied the area of sky at the end of the handle of the Plough.
Phases of the Moon for January
First Quarter 5, Full Moon 12, Last Quarter 19, New Moon 28
This month’s full moon is called the ‘The Wolf Moon’. In January long ago when the snow was deep in the forests the howling of wolves could be heard echoing in the cold still air.
The next meeting of the Earby Astronomical society will be on Friday January 27 at All Saints’ Church, Earby from 7.30pm to 9pm. The speaker will be Martin Lunn MBE FRAS, and the title of the talk will be ‘The Winter Sky’.The Earby Astronomical Society, together with astronomers from the Bradford and Keighley Astronomical Societies, will be staging a Star Party at the village hall, Cracoe, on Wednesday, January 18 from 6pm until 9pm. There will be the chance to look through telescopes, hear some short astronomy talks and talk to the astronomers. The event is free, all are welcome.