Sky Diary

The Sky at Night

It is said that if you have been waiting some time for a bus, two are sure to turn up together. This spring it seems to be the same for comets. Unpredictable beasts at the best of times, the last really bright comet seen was Hale-Bopp in 1997. Through history, comets have been associated with disasters and of deaths of leaders and kings. In Julius Caesar, Shakespeare has Calpurnia say to Caesar ‘When beggars die, there are no comets seen; the heavens themselves blaze forth the death of princes’, a warning to him that danger had been foretold.

In the last few days of 2019 a comet was discovered by Mauna Loa Observatory, Hawaii. It is known as Comet Atlas and is coming towards the Sun from the outer reaches of the solar system. Early calculations showed that it was in a similar orbit to the Great Comet of 1844 and that its orbit would take about 5,000 years to complete. Comets are fragile lumps of ice and dust and it may be that Comet Atlas is a broken fragment of the Great Comet. From the orbit deduced it was found that Comet Atlas would be closest to Earth on 23rd May and it was hoped that it would be visible to the unaided eye, or at least using binoculars, during May, and best during the last two weeks of the month. However, images taken on 11th April showed that it had broken into three parts. Because of this it is unlikely that when it is closest to Earth on the 23rd May it will reach a reasonable brightness. In case the comet fragments survive it will be worth looking northwards at around midnight as it moves from Camelopardalis into Perseus from around mid-May.

On March 25th this year the SWAN camera on board the SOHO spacecraft picked up a comet in the southern constellation of Sculptor. This comet, now known as Comet SWAN, will be seen from the southern hemisphere until May when it will rise from the constellation Cetus into Pisces, then Aries on the 14th May and will pass close to the galaxy Messier 33 on the 16th. It will be closest to Earth on May 12th but it’s brightness at that time is as yet unknown. It will reach the same area of sky in which what remains of Comet Atlas will reach around the 23rd May and if both survive the approach to the Sun, they may be seen together, low in the sky to the north-east before dawn. It is always very much of a lottery as to the brightness of comets and whether they will stand the great heat of their close approach to the Sun and all we can do is hope for a spectacular display.

High altitude ice clouds, known as noctilucent clouds, usually make an appearance towards the end of May. Because these clouds are as high as 85km they are above the Earth’s shadow and are lit by the Sun which is below the observer’s horizon. These clouds have increased in frequency over a number of years and their appearance in the southern polar sky during our past winter was one of the most active seasons recorded. This may mean that we will have an active season in the northern hemisphere from the end of May until early August so keep a lookout towards the north after about 11pm and you may well see these pearly white clouds shining as the sky darkens.

The Planets

Mercury

Mercury

During the last two weeks of May, Mercury will be seen low in the north-west after sunset. Mercury will be close to Venus on the 21/22 May and this may help to locate it as it will be less bright than Venus.

Venus

Venus

Venus remains very bright during the month and can be seen in the west north-west by late evening, setting two hours after the Sun.

Mars

Mars

Mars is very low in the south-east before sunrise at around 4.30am. It is gradually brightening and gaining elevation as it becomes closer to Earth.

Jupiter

Jupiter

Jupiter is low in the south south-east before sunrise at about the same time as Mars can be seen. However, Jupiter is considerably brighter than Mars and shines with a yellow light while Mars has an orange hue.

Saturn

Saturn

Saturn sits between Mars and Jupiter but is closer to Jupiter, less bright and about 5º to the east of Jupiter.

The Moon

The Moon

The Moon will full on the 7th, at last quarter on the 14th, new on the 22nd and at first quarter on the 30th May.

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