Our night sky in the summer

The skies in June stay light until the very wee hours making it more difficult to observe our starry wonders. Our night sky expert Geoffrey Lindop takes this opportunity to explain about constellations and the summer triangle you will see more easily later in the summer. And he gives us the low down on when and how we can observe a spectacular meteor shower starting at the end of July and a rare lunar event in August.

Constellations

Over the centuries people have looked at the random pattern of stars in the sky, and imagined they formed recognizable shapes. Storytellers, gathered round a camp-fire at night, have made up wonderful stories based on the pattern they see.

They have seen a lion, a hunter, a bear, a dog, the list seems endless. These patterns of stars, known as constellations, vary from culture to culture. What western astronomers know as Orion, the Hunter, Australian aboriginals know as the Seven Brothers. Their story goes that they are attracted to the Seven Sisters, what westerners know as the Pleiades.

Spotting your birth constellation

As the Earth orbits the Sun, different constellations can be seen, in the same way as someone on a merry-go-round sees a different view of the fairground during each revolution. Astrologers think that our destiny is defined by what constellation the Sun was shining in when we were born. This means that we can not observe our birth sign on our birthday because, by definition, that constellation is above the horizon during daylight hours. In order to see our birth constellation at its best, we have to wait six months before, or after, our birthday, when that constellation will be due south at midnight.

In the 1920’s the International Astronomical Union decided to rationalise the constellations. They defined their shape by drawing the borders of each constellation on a star map.

There are far more easily recognisable star patterns than the eighty-eight official constellations. The Plough, for example, is perhaps the most familiar grouping of seven bright stars in the whole sky. However, the Plough is not an official constellation, but forms part of Ursa Major, (The Great Bear). Astronomers call the Plough an asterism to distinguish it from a constellation.

Similarly the asterism of the ‘W’ is just part of the much larger constellation of Cassiopeia. However, asterisms are not restricted to constellation boundaries.

Summer Triangle

The three brightest stars during the summer months form an asterism known as the Summer Triangle, which consists of Deneb, the brightest star in the constellation of Cygnus, (the Swan), Vega, in the constellation of Lyra, (the Harp), and Altair in Aquila, (the Eagle).

In 8,000 years from now, Deneb will be known as the Pole Star, as it will be seven degrees from the North Pole. The wobble of the Earth’s rotation will move today’s Pole Star, Polaris, further from the pole. A further 3,700 years will shift the pole star again and this time it will be Vega.

Lunar Occultation

A fairly rare event can be seen in the early hours of August 21 when the Moon will pass directly in front of Saturn. The planet should disappear at about 4:27am. The Moon will be nearly full and very bright, but Saturn is also bright so the event, known as a lunar occultation, should be well seen.

How to watch

With the unaided eye, observers will see how fast the Moon moves across the sky, compared to the stars. As the time of disappearance approaches, binoculars will help spot Saturn. If you have a telescope it would make a good picture to capture the Moon and Saturn in the same field of view. Saturn will reappear at about 5:13am. Just before that time, the Starlink 1852 satellite will pass in front of the Moon as seen from Moffat, although the line of sight will be different for locations away from Moffat. Nevertheless, whilst observing the lunar occultation of Saturn, three other Starlink satellites will pass close to the Moon, and in locations away from Moffat may well pass across the Moon’s face. Mobile Planetarium Apps, like Stellarium, will give the exact timings from your location.

Perseids meteor shower

While watching an event such as the lunar occultation is time critical, meteor showers can be seen over a period of days. August brings the Perseids, one of the most spectacular showers. Shooting stars can be seen in many parts of the sky, but if you have time to plot their path, they will seem to originate in the constellation of Perseus, hence the name. If you don’t know where that is, look into the northern sky for the ‘W’ of Cassiopeia, which is close enough.

Remains of Comet Swiftle-Tuttle

The meteors, which are the remnants of Comet Swift-Tuttle can be seen between July 23 and August 20, with the maximum being seen on August 12. Comet Swift-Tuttle returns to the Sun about every 133 years, the last time being in 1992. When it does so, it loses material from its 16 miles (26km) diameter core, which at the time gives it the appearance of having a long tail. Debris is spread over a large area of space because it has returned to our skies so often. It is for this reason that the meteors can be seen over several weeks.The first reported observation was in 69BC and some astronomers think it was also visible in 322 BC.

You can learn more with our Top Tips for stargazing and be sure to visit our Dark Skies section for all the information for inspiration and to plan your next visit.

Geoffrey has written a guide to the night sky to assist visitors in the South of Scotland, available to purchase at various locations or directly from the publisher.

We are grateful to Geoffrey for also producing a monthly night-by-night guide to the skies above us, so you can check out what there is to see throughout the upcoming summer months. Geoffrey’s final installment to complete the night sky’s year will be out later in the summer so you can be ready for autumn sky viewing!