Russell Eberst's Sky View

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August 2018

The short nights of summer are lengthening as the month of August progresses. The stars of the Summer triangle - Vega, Deneb and Altair are well placed throughout the month, with the star clouds of the Milky Way extending from Cygnus down to Sagittarius being visible for U.K. observers. Already the constellations associated with autumn are rising in the East during the night including Pegasus, Andromeda and Lacerta. This means that the Andromeda galaxy (M31), located about one degree from nu Andromedae, is well displayed and should be easily found in binoculars or a telescope. If skies are exceptionally clear and free from light pollution, it is worthwhile trying to spot it with the unaided eye. In the neighbouring constellation of Perseus we can find the star Algol, also known as beta Persei. It consists of two stars in close orbit around each other, with regular dimming of its brightness as one star eclipses the light of the other. This unending cycle of light variation was noted by ancient civilisations, and led to its nickname of "demon star". The other regular event of Perseus is an annual meteor shower whose members appear to radiate from a point in northern Perseus, giving it the designation as the Perseid meteor shower. The meteors originate from cometary debris, in this case the comet in question is Comet Kegler first observed in 1737 and again in 1862 when it was designated Swift-Tuttle. The observations from 1862 showed that the meteors had virtually the same orbit as the comet and established the connection between these two types of object. The meteors are visible throughout the first half of August, but reach a maximum number on August 12-13.

On this date about 60-80 meteors may be seen each hour, and with the Moon virtually absent there will be little interference from bright moonlight. The meteors can appear in any part of the sky but will appear to radiate from a point in northern Perseus, providing the shower with its associated name. It is not necessary to direct your attention to that particular constellation, since the meteors can appear in any part of the sky and it may be more productive to watch some of the nearby constellations such as Pegasus, Cassiopeia or Ursa Major. Whilst watching for meteors, it is very likely that several bright satellites will be spotted moving steadily across the heavens. The evening sky contains four bright planets. By far the brightest of these four is Venus, shining at magnitude -4.4 but is not the nearest of the four. It reaches its greatest eastern elongation on August 17, when it has its widest separation from the Sun in the sky (46°). However, for observers in high northern latitudes, the low angle that the ecliptic makes to the western horizon at this time of year means that Venus will be rather badly situated. In the southern hemisphere, or near the equator (such as the Seychelles) the position is more advantageous, with Venus being seen against a dark sky and setting more than three hours after the Sun. Also on August 17, the planet Jupiter passes close to the star Zubenelgenubi in the constellation of Libra and is just 4°.7 from the first quarter Moon. Saturn and Mars follow Jupiter low across our southern sky. Saturn displays its ring system to advantage, and Mars glows brightly in Capricornus. A partial solar eclipse occurs on August 11. It is best seen from Arctic regions, such as Greenland, Iceland, Scandinavia (except Denmark) and Siberia. From Scotland, observers would have to be to the north of Inverness, and even then only a tiny percentage of the Sun's disc will be covered at around 08.35 U.T.

As with any solar observing great care must be taken, especially as most of the solar disc will remain uncovered. In space exploration, Asteroids and atmospheres will receive media attention. A Japanese spacecraft called Hayabusa 2 is orbiting an asteroid, Ryugu at very low altitudes. Images taken at close-quarters show an irregular shape with rocks and boulders strewn across its surface. The mission's aim is to collect samples of asteroidal material, with a view to mining asteroids well into the future. Estimates of the value of an asteroid's raw materials range into many billions of dollars. The U.S.A. is also in the race for exploiting these very valuable minor planets. Another spacecraft named Osiris-Rex, which was launched in 2016, has been chasing another asteroid, Bennu. During August it will reach its target and fire its jets, in order to match the speed of the asteroid, and thereby go into orbit around it. So a new 'space race' begins. Meanwhile, investigation of atmospheres takes a step up. An E.S.A. mission called Aeolus is due for launch in August. First planned over a decade ago, it will provide accurate measures of the wind speed and direction worldwide. Wind movement is an important factor in accurate forecasting, and Aeolus will contribute valuable data to aid improvement in our knowledge of Earth's atmosphere. The Sun's atmosphere will be receiving something similar when a NASA probe named 'Parker' is launched early in August. Its aim is to fly closer to the Sun than any previous spacecraft. Using a number of close approaches to Venus, Parker will reduce its solar orbit until by 2024-5, it will 'touch the Sun' at less than 4 million miles distant.

Moon phases:

  • Last Quarter August 4
  • New Moon: August 11
  • First Quarter: August 18
  • Full Moon: August 26

Sky View Image

The maps show the sky at midnight BST on the 1st, 23:00 on the 16th and 22:00 on the 31st. An arrow depicts the motion of Mars.