EYES ON THE NIGHT SKY: MAY 2021
Welcome to our monthly astronomy article for May. We have selected the best objects in the night sky to make the most of the darkness that remains in May, as in Wales from 18th May, we move into astronomical twilight instead of true night, as the sun sets no lower than 18 degrees below the horizon.
A Feast of Dazzling Star Clusters
Take some time in the first two weeks of May to search out some stunning Globular clusters. These are astonishingly beautiful and dense balls of stars which lie in our galaxy. Gravitically bound to each other, these balls of hazy glitter can sometimes comprise up to several hundred thousand stars!
They also orbit around the Milky Way core. Not much is known about how they are formed but they are thought to be the oldest objects in the galaxy, with no star-forming regions.
This month, there are six to look out for in the south-east, spanning across the constellations of Hercules, Boötes, Serpens and Ophiuchus. Some, in very dark skies with no light pollution, can be seen with the unaided eye, but they can be mainly seen with binoculars or telescopes. You can start searching for the brighter ones from 11pm onwards but true darkness commences from midnight and lasts for a few hours.
Number of stars: 330,000
Distance: 26,700 light-years
Position: RA: 17h 17m 07.39s | Dec+43° 08′ 09.4″
Situated in the constellation of Hercules, Messier 92 is thought to be one of the galaxy’s oldest clusters and one of the brightest but is often overshadowed by its neighbour, Messier 13. Apparently, it can be spotted with the unaided eye in very dark, clear skies. Use your binoculars away from urban light pollution and you may be able to see it easily. Use a small to medium size telescope to try and spot the stars encrusting the outer circumference of this object.
Number of stars: Around 300,000
Distance: 25,100 light-years
Position: RA 16h 41m 41s | Dec +36° 27′ 35″
Known as the Great Globular Cluster in Hercules, this is also the jewel of the summer sky. It can be easily found in the constellation of Hercules – look for the keystone asterism to the left of the semicircle-shaped constellation of Corona Borealis. The cluster is on the right hand side of the keystone asterism. If you have a telescope, you will not be disappointed with this spectacular object, with stars resolved to the core. Try upping the magnification and using averted vision to tease out more detail. It’s a more ‘straggly’ looking globular cluster when compared to Messier 3, but a real showpiece object.
Number of stars: 500,000
Distance: 33,920 light-years
Position: RA 13h 42m 11.62s | Dec+28° 22′ 38.2″
In the constellation of Boötes, look for one of the brightest and largest globular clusters in the northern hemisphere. It can be found with binoculars – just slowly scan the sky in the two o’ clock position from the star Arcturus and you will spot a fuzzy ball of light. Using a small to medium telescope will reveal the densely packed, tight ball of stars.
Number of stars: Between 100,000 and 500,000
Distance: 24,460 light-years
Position: RA 15h 18m 33.22s| Dec+02° 04′ 51.7″
Situated in the not-so-bright constellation of Serpens, Messier 5 might be a bit of a challenge to find for star-hoppers. It is thought to be visible to the unaided eye in excellent, dark skies but we would rate this as a binocular or telescope object. Small telescopes will reveal a bright core with a fuzzy halo of nebulosity and larger ones will reveal more stars around the circumference of the object. Try to see if you can find it this month, but late July might be a better time to see this globular cluster at its best.
Number of stars: 100,000
Distance: 14,350 light-years
Position: RA 16h 57m 8.92s | Dec−04° 05′ 58.07″
Situated in the constellation of Ophiuchus, this is a telescope object as it is too dim to be seen with binoculars. Use a 3 inch telescope to resolve this object as a fuzzy ball - larger telescopes will show a bright core and a fuzzy outer halo.
Number of stars: 200,000
Distance: 15,660 light-years
Position: RA 16h 47m 14.18s| Dec –01° 56′ 54.7″
Also known as the Gumball Globular, Messier 12 is situated in the constellation of Ophiuchus. Like its neighbour Messier 10, it’s not a very bright object and will have a similar appearance to its neighbour through a 3 inch telescope. However, stars may be seen through larger telescopes.
Moon, Planets and More
The new Moon falls on 11th May and the full Moon on 26th May.
You may be able to spot a tiny sliver of a two day old Moon passing close to Mercury, with Venus making a very brief appearance in the west-north-western sky on 13th May.
On 28th May, Mercury will pass close to Venus, as the planet will appear higher in the sky over the month. Using Venus, find the planet in your binoculars and you should see a small pinprick of light to the left. You have found Mercury!
As the length of astronomical twilight lengthens, there are still wonders to be discovered in the night sky. Noctilucent Cloud (or night shining clouds) season commences from the middle of May – these are very high altitude clouds that comprises ice crystals and appear blue, silvery, orange or even red in colour and is lit by the Sun. This photograph shows how dark the lower cloud formations are compared to the bright noctilucent clouds which are high in the mesosphere. It is thought that they are made of water, possibly meteor particles and mad-made pollutants. The best time to spot these is about 90 minutes to 2 hours after sunset and before sunrise.