Sky Diary

June brings us the summer solstice on the 21st at 3am. At this point the Sun momentarily stands still at its highest point before beginning its southward journey. The longest day occurs on this date when the Sun rises at 4.21am and sets at 10.05pm BST giving a day of length 17 hours 44.5 minutes. It can be seen, therefore, that we have very little night time darkness on this day and indeed during the entire month.

Observing anything in the night sky will have to be done between around 11pm and 3am, and even then, the sky will not be completely dark so only the brightest stars and planets will be seen. The bright stars which will stand out during late June evenings will be Arcturus, quite high in a southerly direction, Regulus, brightest star of Leo towards the west, and the Summer Triangle of Vega, Deneb and Altair towards the east. The constellations Hercules and Corona Borealis which I mentioned last month will be even more difficult to locate in June. The anticipated recurrent nova in Corona Borealis has, at the time of writing, not yet appeared, but the constellation is well placed high in the south and, should it appear in June, will be an easy target using binoculars.

June brings us the summer solstice on the 21st at 3am. At this point the Sun momentarily stands still at its highest point before beginning its southward journey. The longest day occurs on this date when the Sun rises at 4.21am and sets at 10.05pm BST giving a day of length 17 hours 44.5 minutes. It can be seen, therefore, that we have very little night time darkness on this day and indeed during the entire month.

Observing anything in the night sky will have to be done between around 11pm and 3am, and even then, the sky will not be completely dark so only the brightest stars and planets will be seen. The bright stars which will stand out during late June evenings will be Arcturus, quite high in a southerly direction, Regulus, brightest star of Leo towards the west, and the Summer Triangle of Vega, Deneb and Altair towards the east. The constellations Hercules and Corona Borealis which I mentioned last month will be even more difficult to locate in June. The anticipated recurrent nova in Corona Borealis has, at the time of writing, not yet appeared, but the constellation is well placed high in the south and, should it appear in June, will be an easy target using binoculars.

Recent fine weather conditions have given us increasing hours of sunshine, and the Sun has been of interest for at least two years with numerous sunspots appearing on its surface. However, these have diminished since the start of 2025 and there have only been a few large sunspots since the start of the year. In contrast with solar activity last year, the recent large sunspots have not been very active in producing solar flares. There have been times recently when the Sun has only shown a few small spots which makes me wonder if solar cycle 25 is in rapid decline. Remember that if you would like to look at the Sun, do so using a proper solar filter which can be purchased from any on-line astronomical equipment supplier.

I await the first signs of noctilucent clouds, which should appear by early June. These high altitude ice clouds, seen towards the north from about an hour after sunset, are only seen at relatively high latitudes and appear as bands or ripples of delicate pearly clouds. They form at about 85 km height, well above any normal clouds seen in the sky, and there is good evidence that their appearance and frequency is related to global climate change. For this reason they have been extensively studied by ground based observers, and by a few specialised NASA satellites for a number of years. A good display is well worth seeing, and as no telescope is required, keep a lookout for them if you are out and about late at night.

_{Sky Notes courtesy of Ken Kennedy of Dundee Astronomical Association}