Lyra – easy to find

Ken Kennedy, of Dundee Astronomical Society, tells us what we can expect to see in the July night sky.

“The Summer Triangle formed by the stars Vega, Deneb and Altair hold the south-western sky and are the first stars to be seen in the gradually darkening July skies,” he says. “The brightest of these, Vega, is the primary star of the constellation Lyra, which represents the lyre of Orpheus which he played so beautifully that it was placed in the heavens by the muses.

“Vega, the second brightest star in the northern hemisphere makes Lyra easy to find. The star is bright because it is only 25 light years from our sun but it is also twice as massive and has a much hotter surface at around 10,000°C.

“Because the earth’s axis is inclined and with the gravitational attraction of the sun and moon, the earth wobbles gradually and the point towards which the North Pole points in the sky changes.

“At present that point is marked by Polaris, the Pole Star, but Vega was the Pole Star around 12,000 BC and will be again around 13,700. A short distance to the north-east of Vega is a fainter star which when viewed with binoculars can be seen to be a double star with components of almost equal brightness.

“These stars are actually binary stars which means that they are gravitationally linked and orbit each other but each orbit takes around 400,000 years.

“To the south of Vega are two stars, Beta and Gamma Lyrae, and on a line joining these stars can be found the splendid planetary nebula Messier 57, known as the Ring Nebula. It requires a telescope to see this gem but it is worth searching for as it appears as a tiny, but quite sharply defined, ring.

“The ring is the expanding remains of a sun-like star which, within the last 2,000 years, exhausted its supply of hydrogen and ejected its outer layers before shrinking to become a compact, hot white dwarf star.

“Last month I mentioned the globular cluster Messier 13, in Hercules. Towards the eastern part of Lyra there is another of these distant clusters, this one, discovered by Charles Messier in 1779 is numbered 56 in his catalogue. Messier 56 is 32,900 light years away from earth and is more than 13 billion years old.

“Mercury moves eastwards from the sun throughout July but only sets an hour after the sun so will not be visible. Venus will be bright in the east rising two hours before the sun during July. It will be seen best between 3 and 4am.

“Mars will be too close to the sun to be seen during July. The best of Jupiter is now past but it can still be seen low in the sky towards the west, setting at midnight, two hours after the sun. Saturn is low towards the south at 11pm mid-month and sets at about 2.30am.

“The moon is at first quarter on the 1st, full on the 9th, at last quarter on the 16th, new on the 23rd and at first quarter again on July 30.”