Stand out star

Ken Kennedy of the Dundee Astronomcal Society tells us what we can expect to see in the May sky. “It’s amazing how the days lengthen so quickly after the spring equinox,” he says, “and by May there are only a few hours during the night when the sky can be seen in reasonable darkness.

“The brightness of the sky following sunset is defined by three levels of twilight, civil, nautical and astronomical. By May 3, astronomical twilight lasts the entire night so the sky will never become totally dark at the latitude of Scotland as the sun sinks no further than 18 degrees below the northern horizon.

“Fewer hours of darkness are, to some extent, compensated for by relatively mild conditions in which to study the sky.

“Jupiter will still dominate the southern sky during May and will be easily seen despite the brighter sky conditions. The brightest star of Virgo, Spica, will also be visible below and to the east of Jupiter but looking eastwards from Virgo there are not many bright stars in the constellations of Libra and Ophiuchus.

“One star which does stand out is Arcturus at the southern end of the constellation Boötes, the herdsman. The star Arcturus means guardian of the bear in Greek and if you look upwards from Boötes you will see that the tail of Ursa Major, the Great Bear, points directly at Boötes. One myth is that Boötes was an ox-driver, driving along the Plough which was seen by some as a cart pulled by oxen.

“Summer evenings bring new interest to the northern sky in the form of noctilucent clouds. These usually make their first appearance in the last 10 days of May but are best seen in June and July.

“These exceptionally high ice clouds are now observed by a large number of observers in UK and Northern Europe and also by the Aeronomy of Ice in the Mesosphere (AIM) satellite of NASA. Look northwards about an hour after sunset and you may see these clouds shining with a pearly, slightly blue glow and forming bands or waves.

“Mercury is not visible during May. Venus rises at about 4am (BST), an hour before the sun, but is quite low in the east, although bright, so may be seen with a low horizon. Mars is very low in the north-west setting at 11pm, an hour and a half after the sun.

“Jupiter still dominates the night sky and is well placed for observation for most of the night. It can be found almost due south at 10.30pm during May.

“Saturn rises at midnight and is due south by 3.30am but is very low in the sky making it a poor object for observation despite the rings being favourably open. The moon is at first quarter on the 3rd, full on the 10th, at last quarter on the 19th and new on May 25.”