I begin this month with a closer look at the Plough. Ursa Major or the Great Bear is a large constellation, writes Martin Lunn.

The Plough, which is made up of seven stars, is only part of it. The Plough is extremely easy to find, not because its stars are strikingly brilliant, but because the pattern is so well known.

During spring the Plough is practically overhead. The group is often known under its American name of the Big Dipper, while a very old English name for it is ‘King Charles’ Wain’, meaning a cart. Most of the star names in the sky are Arabic including those in the Plough, which I have labelled on the sky map.

Starting at the end of the handle of the plough is Alkaid; next in line is Mizar, with a faint companion star Alcor nearby. There is a minor mystery here because the Arab astronomers a thousand years ago described finding Alcor as a test of naked eye vision, hinting that it could only be seen if the sky was very clear. Today it is quite easy to see Alcor, so it is possible that the star has brightened. The third star in the handle is Alioth.

The four stars that make the blade of the plough form a rectangular shape connected to the handle. Staring with top left we have Mizar; bottom left is Phad; the top right hand star is Dubhe while the bottom right hand star is Merak. Dubhe and Merak are called the pointers because they point to the North Star. Megrez is obviously fainter than the other six members of the Plough and there is another minor mystery here. Astronomers living a thousand years ago said that Megrez was as bright as the other stars in the Plough. It is believed that Megrez might be a type of star that changes brightness over a period of hundreds of years.

If you use the pointers and draw a line across the sky from Merak through Dubhe you will come across a star all on its own and this is the North Star, or to give its proper name, Polaris. The North Star is the end star of the tail of Ursa Minor the Small Bear. Again there is a plough shape to the main stars in this constellation. The Americans refer to this group as the Little Dipper. Compared to Ursa Major the stars that make up Ursa Minor (with the exception of the North Star) are quite faint and not so easy to see.

According to legend, Ursa Major was a princess named Callisto who was so beautiful that the queen of the gods Juno became jealous of her and turned her into a bear. Later Callisto’s son Arcas came across the bear while he was out hunting and drew his bow to shoot her. Clearly he did not recognise his mother! Seeing what Juno had done and what was about to happen, Jupiter turned Arcas into a bear. He then grabbed both bears by their tails and threw them in to the sky. This is why both bears have longer tails than usual.

The Spring Sky

The seasonal changeover in the sky is more or less complete and can be observed on April evenings. The symbol of winter, Orion, has to all intents and purposes disappeared, although it is true that the northern part of the constellation does not set until midnight. Of the other winter stars, Aldebaran in Taurus and Sirius in Canis Major have now set, while only Capella in Auriga, Procyon in Canis Minor and Castor and Pollux in Gemini are easy to see.

The Plough is now directly overhead which means that the ‘W’ of Cassiopeia is at its lowest in the sky in the north, although it is not difficult to find. Two of the stars of the summer triangle; Vega in Lyra and Deneb in Cygnus, are now above the horizon and will be very easy to spot in the summer months.

The winter night sky is often described as being the best, with many bright stars to be seen, making it a difficult act for the spring sky to follow. This is rather unfair because there are some spectacular sights to be seen.

Beginning our tour around the spring sky with the Plough, follow the curve of the handle down and around and you will come across a bright orange star called Arcturus, the brightest star in the constellation of Bootes the Herdsman. There are no definite legends connected with this constellation, although one story says that Arcturus was the person who invented the two-oxen plough. Arcturus is an orange giant star around 36 light years away. Its orange colour indicates that it is cooler than the Sun, its temperature being only around 4,000 degrees centigrade compared to the 5,800 degrees centigrade of the Sun. If you imagine Arcturus as the bottom of a large letter ‘Y’ in the sky, move upwards to the star Epsilon and then the two arms of the ‘Y’ lead to the star Gamma on the right and to a star called Alphekka on the left, which is actually the brightest star in the constellation of Corona Borealis, the Northern Crown.

Corona Borealis does resemble a crown in the sky with its stars forming a little semi-circle. There are two remarkable variable stars, one of which is called ‘R Corona Borealis’, a star normally just at the limit of naked eye visibility but which occasionally fades away so it can only be viewed through a telescope. The other is ‘T Corona Borealis’, a star which has brightened twice, in 1866 and 1946, starting from below naked eye visibility and becoming a bright star. We never know when the star might brighten again, so it is always worth watching this constellation. T Corona Borealis is referred to as ‘The Blaze Star’.

If the line drawn from the handle of the plough towards Arcturus is continued down and around, it will reach the bright white star Spica in the constellation of Virgo the Virgin. Apart from Spica the stars in this constellation are not very bright.

The southern sky is dominated by Leo, the celestial Lion, who in mythology was one of the victims of Hercules. He had been ordered to perform a series of twelve labours, one of which was to kill a huge black lion. Despite losing the battle, Leo is much easier to see in the sky than Hercules!

Leo is the most splendid of the spring constellations. Its brightest star, Regulus, is not as bright as Arcturus but it does have a very distinctive shape. To find Regulus, return to the Plough and go to the two pointers; these are the two stars furthest from the handle. We normally use the pointers to find the North Star by drawing a line from the right hand pointer through the left pointer and up. However, to find Regulus we go the other way; a line drawn from the left hand pointer star through the right one and then continued downwards will take you to Regulus which is a less bright star located at the bottom of a quite distinctive backwards question mark in the sky.

The last star to mention in the spring sky is Alphard in the constellation of Hydra the Water Snake. Although it is the largest constellation in the sky, Hydra contains very few bright stars except the red star Alphard, which can be found by continuing the line from the pointers of the Plough past Regulus and continuing down towards the horizon. As Alphard is in such a featureless part of the sky it is often referred to as ‘The Solitary One’

The Planets in April

The western sky is still dominated by Venus which is at its brightest this month and can be seen until around midnight. Jupiter, Mars and Saturn can still be seen in the morning sky, in the east before the Sun rises. Mercury is still too close to the Sun to be seen this month.

Meteor Showers

This month sees the first of the major meteor showers since January. This is the April Lyrids, which will be at maximum on the night of 21st / 22nd when around twenty meteors per hour might be seen. The Lyrid shower is connected with comet Thatcher which was discovered in 1861. It is the oldest recorded meteor shower we can still see today it was first recorded in 687 BCE.

Phases of the Moon for April

First Quarter 1st and 30th Full Moon 8th Last Quarter 14th New Moon 23rd

The Full Moon in April is called the Egg Moon. This has nothing at all to do with Easter eggs but is due to the increasing amount of daylight which results in hens, ducks and geese laying more eggs.

The next meeting of the Earby Astronomical Society on Friday April 24 at All Saints’ Church, Earby, has been cancelled.