Posted by on May 29, 2017 in Main |

Noctilucent clouds

June brings our summer solstice on the 21st and sees  Jupiter remain as the stand-out object in a night sky that is blighted by persistent twilight at our latitudes. The latter is so severe over northern Britain that it swamps all but the brighter stars and planets. Those bright stars include Vega in Lyra, which is high in the eastern sky, as is the Summer Triangle it forms with Altair in Aquila and Deneb in Cygnus returns to prominence.


The Sun follows a shallow arc below our N horizon overnight, the geometry allowing views of noctilucent clouds, whose silvery-blue tracery may gleam low down between the northwest after nightfall and the northeast before dawn. Noctilucent clouds are formed by ice crystals coalescing around dust particles. They float near 82km in altitude where they reflect sunlight after our normal clouds are in darkness.


Jupiter is now unmistakable in the south west at nightfall but shifts rather lower as the night progresses and sets in the west two hours later. As it dims a shade between magnitude -2.2 and -2.0, its slow westerly progress against the stars of Virgo reverses at a stationary point on the 10th when it lies three degrees south east of the double star Porrima. Shrinking in width from 41 to 37 arcseconds, it stands near the Moon on the 3rd and 30th.



Saturn lies below the full Moon on the 9th/10th and comes to opposition on the 15th when it is directly opposite the Sun at a distance of 1,353m km. Prominent at magnitude 0.0 in the constellation of Ophiuchus, it stands 16 degrees left of Antares in Scorpius. Its disc spans 18 arcseconds, with bands of cloud that are a pale imitation of those of Jupiter. The unrivalled rings, though, stretch for 41 arcseconds and are wide open with their north face tipped 27 degrees towards us.


The night ends with Venus blazing in our morning twilight as it reaches its furthest westerly point from the Sun on the 3rd and dims only slightly from magnitude -4.3 to -4.1 during June. Its altitude almost due east at sunrise improves from 8 degrees to 18 degrees this month and by the end of the period it rises more than two hours before the Sun. Look for it to the left of the waning Moon on the 20th when a telescope shows it to be 20 arcseconds wide and 58% illuminated. Both Mercury and Mars stay hidden in the Sun’s glare.


Phases of the Moon for June

First Quarter 1st

Full Moon 9th

Last Quarter 17th

New Moon 24th