Mars, the best placed of our three bright evening planets, stands low in Britain’s S sky in the early evening while Venus is brilliant but sets in the SW less than one hour after sunset. Saturn lies between them at present and is due to be passed by Venus on the 30th. Meantime, Jupiter and Mercury are in close conjunction low in the E just before dawn the 11th as Mercury sinks sunwards and Jupiter climbs to prominence in the mornings.
The Summer Triangle stands above Mars at nightfall but by 23:00 BST, as the Earth’s rotation carries it westwards, its place in the S is taken by the Square of Pegasus, relatively empty of stars. Our chart depicts the S sky at that time up to an altitude of 70° and shows not only Pegasus, but at least parts of the quintet of watery constellations that lie to its S.
The first, its rear just nudging into view from the SW, is Capricornus the Sea Goat which plays host to the gibbous Moon on the 10th and 11th.
Then comes Aquarius the Water Carrier which is currently being crossed, albeit slowly, by the Sun’s most distant planet, Neptune. This reached opposition on 2 September and lies 2.2° SW of the star Lambda on the 10th, shining at mag 7.8 from a distance of 4,363 million km. A web search should yield a more detailed chart and allow Neptune to be identified through binoculars once the current moonlight subsides. Its greenish disk, though, is only 2.3 arcsec wide and may be too small to show detail in anything but a large telescope under ideal conditions.
A steering-wheel-like asterism to the NW of Lambda represents Aquarius’ water-jar while a cascade of stars to the S of Phi is taken as spillage from the jar.
Pisces the Fish is the next constellation of the zodiac through which the Sun, Moon and planets appear to move. It is here we find Uranus which reaches opposition on the 15th at a range of 2,835 million km and a more manageable mag 5.7 and 3.7 arcsec in diameter.
The Circlet of stars to the S of the Square represents one of the two fish of Pisces, while a V-shaped cord connects it to the second below Mirach in Andromeda. The famous Andromeda Galaxy, M31, is visible as a hazy oval almost 8° and 2.5 million light years away on the opposite side of Mirach and just above the upper edge of our chart.
South of Pisces is Cetus the Sea Monster or Whale, while Fomalhaut in Piscis Austrinus, the Southern Fish, hovers low above our S horizon, in line with the W edge of the Square. At mag 1.2 and the brightest star on our chart, this lies 25 light years away and is almost twice as massive and more than 15 times more luminous than our Sun.
Fomalhaut is also the proud parent of the first exoplanet to be imaged from the Earth. Some 50° to its N, and just to the right of the Square, is 51 Pegasi, which in 1995 became the first normal star (after the Sun) known to possess a planet. At 51 light years, the star shines at mag 5.5 and is easy to spot through binoculars.
