Spot the ‘smiley face’

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

“As the days lengthen,” he says, “the times during which observations can be made are reduced. Astronomical twilight is the term used to define the sun’s position as being between 12 and 18 degrees below the horizon. After May 3 astronomical twilight persists for the night and, as a consequence, the sky never becomes completely dark.

“The brighter stars of the major constellations will show how the sky changes month by month with Regulus, marking Leo, now in the south-west and Arcturus, brightest star of Böotes, approaching due south by late evening.

“The brightest stars of Ursa Major which form the Plough are still almost overhead and the tail of the Bear points in a curving arc to Arcturus, the fourth brightest star in the entire sky, including the southern hemisphere. Following Böotes in the south-east is the fainter constellation of Corona Borealis or Northern Crown, once likened by a youngster at Mills Observatory to a ‘smiley face’.

“Below Arcturus and more easterly, a brighter object will draw the eye. This is the planet Jupiter which will be due south by midnight. Not as high in the sky this year as planetary observers would wish but it will still be possible to see the four Galilean satellites in binoculars and the main atmospheric belts using a small telescope.

“The Summer Triangle, which consists of three bright stars, emerges from its winter residence low in the northern sky. If you look to the northeast you will be able to see the star Vega with Deneb, less bright and further south, and with Altair pulling clear of the eastern horizon at about 10pm. Now you can be sure that summer has arrived!

“The young moon is well placed for observation from May 17 when it will appear low in the west at about 10pm as a slim crescent. Have a look at it then and for another two days with binoculars and see if you can detect the faintly shining part which is in shadow. This is earthshine, light reflected by earth and gently lighting up the part of the moon onto which the sun is not shining. As my Auntie Mary told me when I was very young: ‘that’s the old moon in the new moon’s arms’.

“The end of May is the time when first sightings of the delicate noctilucent clouds are usually reported. These extremely high clouds are formed by ice crystals and reflect the light of the sun after it has set. Look northwards after 11pm and you may catch a display.

“Mercury rises just before the sun for much of May so will not be visible. Venus remains low but bright in the west setting about two hours after the sun. Mars rises in the south-east around 2.30am but remains low in the sky until it fades into twilight by 4am.

“Jupiter rises at 8.30pm mid-month in the constellation of Libra and will be due south just after midnight. Saturn rises at 1am and is due south at 4am when it will fade in the brightening sky. However, Saturn will only be about 11 degrees above the southern horizon as seen from central Scotland.

“The moon is at last quarter on the 8th, new on the 15th, first quarter on the 22nd and full on May 29.”