CDAA

Written by David Pugh

In the night sky this month the planets Saturn and Venus emerge into the pre-dawn sky and there is the chance to see noctilucent clouds.

Mercury, the inner-most planet, becomes visible as an early evening object low in the west in the second half of June. Dazzling Venus (mag -4.2) lies very low in the pre-dawn eastern sky but improves slowly in altitude through the month. Mars, the red planet, (mag +1.4), is best seen soon after sunset during the first half of June in Leo low in the western sky.

Jupiter, king of the planets, is not on view this month. The wonderful ringed planet Saturn (mag +1.1) is making progress in the pre-dawn eastern twilight to become a viable telescopic target by late June. The outer gas giants Uranus and Neptune will be difficult pre-dawn objects to observe in the increasing twilight conditions.

June and July provide the best chance of seeing noctilucent clouds. These are beautiful high level clouds, often bright, iridescent blue, silver and white. At altitudes of 75-85 kilometres, they are visible only in twilight after sunset. Look to the northern sky between the NW and NE horizons.

Still nothing happening concerning the possible outburst of the recurrent nova T Coronae Borealis currently at mag 10 as I have been keeping an eye on this area with binoculars.. If it does outburst in the next few weeks, it lies below the handle of the Plough in Corona Borealis. It last outburst in 1946 reaching mag 3.0 and mag 2.0 in 1866 when it was discovered. It is nicknamed the "Blaze Star"

For all of June and the first three weeks of July the night sky does not get truly dark, just astronomical twilight. This means it is not worth trying for faint "fuzzies" like galaxies or faint nebulae. Rather, apart from planets and the Moon, try for bright concentrated objects. Fortunately the early summer night sky includes a number of globular star clusters that are both fairly bright and concentrated into tight balls of millions of old stars. As such, with their high surface brightness, they are a good choice to view with a telescope and take magnification well if seeing conditions are favourable. Many are also easy binocular targets.

Starting our tour of globular clusters over in the western sky, to the west of the bright star Arcturus, we find M3 at mag +6.2 in Canes Venatici. At 18' diameter it is one of the best globular clusters visible from the UK. Incidently not all globular clusters look the same. They are divided into 12 classes according to how concentrated they appear with class 1 the most concentrated and class XII the most loose in appearance. M3 for example is class VI.

Moving further south into Coma Berenices we find mag +7.6 M53 13' in diameter and, at 58,000 lys distant, almost twice as far as M3 (33,000lys). Both contain some half a million stars! If you would like a real imaging challenge the fainter globular cluster NGC 5053 (mag +9.5) lies only a degree to the SE of M53 such that it is possible to image both together in a small to medium scope. I say that because visually you would struggle to see NGC 5053 as its stars average mag 16.6 and there are only 3,500 of them.

Moving east into Hercules we have the Great Globular Cluster in Hercules M13, arguably the best globular cluster for northern observers. It is easy to find on the western side of the "Keystone" asterism marking the centre of Hercules. M13 shines at mag +5.7 and 21' in diameter. It is a truly lovely sight with chains of stars extending outwards from its core. To the NE in Hercules there is M92, another impressive globular cluster of mag +6.4 and 14' diameter, often overlooked in favour of M13 which is unfortunate. Finally moving south into Serpens we have M5 at mag +5.7 and 20' diameter. It is virtually as good as M13 but its more southerly location from the UK and a nearby mag +5 star hampers observation to some degree.

Lastly, if you would like something else apart from globular clusters why not try for the famous Ring Nebula in Lyra M57. It is a mag + 8.8 planetary nebula appearing like a 1' diameter smoke ring in the sky. Well worth a look.

Good Hunting and I hope to see you next Thursday evening at the society's monthly meeting.

Best Regards

David