Russell Eberst's Sky View

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May 2018

The month of May is a good time for observing meteor showers. These showers are seen when a cloud of cometary debris enters the Earth's atmosphere over a period of a few hours or days. The individual members of the shower move on parallel paths, but from the observer's point of view they will appear to diverge from a particular point in the heavens as a result of perspective. The constellation from which each shower radiates gives rise to the name given to the shower. For example, the shower in mid-November comes from the constellation of Leo, and is therefore called the Leonids. Similarly the Perseids radiate from Perseus in August. Early in May, around May 5-6, a shower is seen coming from Aquarius and is called the eta Aquarids. The 'eta' part of its name helps to distinguish it from other minor showers that come from Aquarius later in the year. During May Aquarius is rising during the pre-dawn hours and does not reach great elevations before the dawn twilight begins to interfere. Therefore it is not an ideal shower for observers at our high northern latitudes. The icy particles that are ejected from Halley's Comet will continue to orbit the Sun for thousands of years. However, whenever they encounter the Earth, they will make their presence known (very briefly) as meteors, vapourising in the Earth's upper atmosphere. We can see showers of these meteoric particles on two specific dates each year. The Earth has two close passages to the orbit of Halley's comet which occur in May and in October. Any observers under excellent dark skies may expect to see up to 20 meteors per hour, but U.K. is not likely to be among these privileged places. This year we have some compensation, with a number of bright planets becoming better placed.

The brilliant planet Venus graces the western sky after dusk, with its prominent location causing many members of the public to enquire as to its identity. Its Greek equivalent was Aphrodite, and it was also known by two further names - Lucifer, when a morning star and Hesperus as an evening star. Its magnitude remains around -4, which is bright enough for it to be spotted in broad daylight, if atmospheric conditions allow. It leaves Taurus, and chases through the neighbouring constellation of Gemini. The thin crescent Moon can be seen on May 17 below and to the left of Venus. The next planet to be seen is Jupiter which is at opposition on May 7. This mighty Gas Giant will be directly opposite the Sun in our skies. This means that it will rise as the Sun sets, then will be due south at midnight and set as the Sun rises. Opposition also indicates that it will be at its closest and brightest for this year. Although it is visible for many hours of the night, it is not ideally placed for northern observers, since it is located in the southern constellation of Libra. Its declination of 16 degrees south of the celestial equator means that it will not exceed more than 18 degrees elevation for most of Scotland. Views of Jupiter will be affected by the long path that its light will traverse in our atmosphere, causing a 'boiling' appearance. The situation is even worse for our next planet, Saturn. At present it is located in Sagittarius, at the extreme southern portion of the zodiac, with the maximum elevation from Edinburgh being around 12°. Nevertheless, the sight of its wide open ring system may encourage those seeing it for the first time to pursue astronomy as a hobby.

The third bright planet in the south is Mars. During the month, it races eastwards from Sagittarius into neighbouring Capricorn. Never getting far above our horizons, there is some compensation in that it doubles in brightness, in a rather barren area of the zodiac. Its disc size also rapidly increases allowing some detail to be seen in large amateur telescopes. The Earth-Mars distance drops from 78.5million miles at the beginning of May, to 57m miles at the end. For a much closer view of this planet, there is a launch of a Mars probe called InSight. It is designed to land on Mars next November 26, and will drill below its surface to examine the 'soil' The launch takes place from Vandenberg Base on the west coast of the U.S.A. and the landing site is Elysium Planitia. Its task is to carry out many geophysical (or should that be Areophysical) studies. It carries a seismometer, a drill, and many 'weather' instruments. After its two-year mission is completed we will know a great deal more about Mars and its environment. Another project, already in orbit aboard the I.S.S. is the British "RemoveDebris" which will be performing various methods attempting to solve the problem of the ever increasing amounts of junk in Earth orbit. There are nearly 10,000 tonnes of varied material in near Earth space, with only a small percent being useful, working satellites. The rest are debris that threaten high speed collisions and impacts, and are likely to make low Earth orbit unusable for many future missions.

Moon phases:

  • Last Quarter May 8
  • New Moon: May 15
  • First Quarter: May 22
  • Full Moon: May 29

Sky View Image

The maps show the sky at 01:00 BST on the 1st, midnight on the 16th and 23:00 on the 31st. Arrows depict the motions of Jupiter during May and of Venus from the 20th.