June 21st marks the official start of summer in the northern hemisphere, but observers in far-northern latitudes are to a large extent deprived of views of the summer night sky by persistent twilight that washes out all but the brightest stars. However, the Summer Triangle will return to prominence as summer wears on, so look out for this beautiful celestial asterism that is bisected by the Milky Way, and is made up of the stars Altair in Aquila, Vega in Lyra, and Deneb in Cygnus.
Far northern observers will also have several opportunities to view noctilucent clouds towards the north-west after sunset, and again towards the north-east just before dawn. These “night-shining” clouds are typically located about 80 km or so high in the Earth’s upper atmosphere, and are thus lit by the Sun from beneath as it passes low behind the horizon.
This month, some observers in the US can observe two first-quarter moons. The first occurs at 8:42 AM Eastern Daylight Time on the June 1st for observers on the East Coast, while the second occurs on June 30th at 8:51 PM Eastern Daylight Time. The phases of the Moon will be as follows in June:
First Quarter: 1st
Full Moon: 9th
Last Quarter: 17th
New Moon: 24th
– Mercury is not visible this month, due to it being too close to the Sun.
– Venus dominates the pre-dawn sky in the east, and reaches its maximum elongation west of the Sun on the 3rd of the month. The planet dims only marginally from magnitude -4.3 to magnitude -4.1 as the month wears on, and while it remains fairly close to the horizon during June, its elevation increases from 8 degrees to an almost respectable 18 degrees by months’ end, at which time Venus will rise about two hours before the Sun. Look for Venus to the left of the waning Moon on the 20th, when its 20-arcsecond-wide disc will be 58% illuminated.
– Mars currently found in the constellation of Taurus is now nearing an almost year-long apparition in the evening sky. As June starts, Mars sets about 90 minutes or so after the Sun, which will make it very difficult to spot low on the north-western horizon. Mars will remain difficult to spot as the month wears on, and by the beginning of July, the planet will become lost in the glare of the Sun as it reaches apposition of conjunction with the Sun on the July 26th.
– Jupiter now dominates the early evening sky in the south-southwest, but it will sink to towards the west-south-western horizon somewhat as the month wears on. The King of the planets is now moving westwards through the constellation Virgo, but by the 10th will appear to come to a standstill, and reverse its motion from a point about 3 degrees or so from the south-eastward of the double star Porrima. Jupiter will dim somewhat as the month wears on, reducing from magnitude -2.2 to magnitude -2.0, while its angular diameter will shrink from 41 to 37 seconds of arc. Look for Jupiter close to the Moon on the 3rd, and 30th of the month.
– Saturn reaches a point of opposition with the Sun on the 15th, when it will be 1,353 million km away. At this time it will shine at magnitude 0.0 in the constellation Ophiuchus, and although its angular diameter at this time will be a full 18 seconds of arc, it will only be between 10 and 15 degrees above the southern horizon. Without an atmospheric dispersion corrector, Saturn’s low elevation might make it very difficult to observe the ring system that stretches across a full 41 seconds of arc, being tipped towards our line of sight by more than 26 degrees.
Deep Sky Objects
– Whirlpool Galaxy (M51a)
– Messier 5
Look for this magnificent globular cluster in the constellation Serpens Caput (Serpent’s Head). Located about 24,000 light years away in the halo surrounding the Milky Way, this cluster is estimated to be about 13 billion years old, making it more than twice as old as the solar system. It is estimated to contain at least 100,000 stars, although some estimates go as high as 500,000 stars.
– Black Eye Galaxy (M64)