The Night Sky This Month: June 2018

Summer Triangle

The summer solstice occurs on June 21st, which is the longest day of the year and officially marks the start of summer in the northern hemisphere. Although visible throughout a good part of the year, the Summer Triangle also rises to prominence in the night sky and can be seen overhead around midnight. This beautiful asterism consists of the three brightest stars in constellations Lyra, Cygnus, and Aquila, and contains rich pickings for stargazers, including double stars, star clusters, and nebulae.

This month further offers an opportunity to view noctilucent clouds towards the north from mid-northern latitudes, and especially between twilight and nightfall during the send half of the month. The exact nature of these clouds that typically form at altitudes of about 120 km or so is not clearly understood, but their incidence, brightness, and extent are all steadily increasing, which has prompted some investigators to conclude that they may be the result of climate change, although no direct link between the clouds and climatic changes has been found or identified.

Moon Phases

Last Quarter: 6th
New Moon: 13th
First Quarter: 20th
Full Moon: 28th

Planets

Mercury reaches a position of superior conjunction with the Sun during the first week of June, but the little planet will again become visible at around magnitude -0.7 low over the western horizon by the middle of the month. Note that Mercury’s magnitude will reduce to about -0.2 and an angular diameter of 6.5 seconds of arc by month’s end, when it will set about 90 minutes or so after sundown. Also, note that Mercury will be furthest position west of the Sun on July 12th.

Venus still dominates the western evening sky after sunset, shining with a magnitude of -3.9, which will increase to about -4.1 due to slight increase in its angular diameter from 13 seconds of arc to 15 seconds of arc as the month wears on. Note that although Venus gains a little altitude during the month, it will remain at or below 20 degrees above the horizon, so look for it slightly below and to the left of the star Pollux in Gemini at the beginning of the month. During June, Venus will pass into the constellation Cancer, and by the about the 20th will be close to the Beehive Cluster (M44).

Mars is now in the constellation Capricorn, and will start its retrograde (westward) motion on the 28th. The Red planet is now moving towards its point of closest approach to Earth since 2003, which it will reach in about 60 days’ time. Note that although Mars rises at about astronomical midnight at the beginning of the month, and will rise progressively earlier as the month wears on, it will remain below 15 degrees above the horizon before sunrise, which means that views of the planet before dawn won’t be spectacular. However, since Mars’ magnitude will increase from -1.2 to -2.1, as its angular diameter increases from 15.3 seconds of arc to 20.7 seconds of arc, it might just be possible to view surface details such as Syrtis Major with small telescopes.

Jupiter was in a position of opposition during the first week of May, so it will be visible for much of the early to late evening for most of the month. However, even though Jupiter will shine at magnitude -2.3 by month’s end, and have an angular diameter of about 41.5 seconds of arc, the King of the planets will only reach an elevation of about 20 degrees above the southern horizon when it transits the meridian. This means that obtaining views of the planet through the atmospheric murk might be difficult, unless an atmospheric dispersion corrector is used during times of good seeing.

Saturn will be at a position of opposition on the 27th, and will therefore be visible for most of the night during the month. Even though its ring system is still tilted towards our line of sight by slightly more than 27 degrees, Saturn will remain below about 15 degrees above the southern horizon when it transits the meridian. As with Jupiter, the use of an atmospheric dispersion corrector is recommend to obtain even reasonable vies of the ringed planet, despite the fact that at magnitude +0.0, the planet will be brighter at this time than at any other time during 2018.

Deep-Sky Objects

To compensate for the poor views of planets in June, several bright, conspicuous deep-sky object (DSOs) are now visible, some of which are easy targets for binoculars and small telescopes. Below are some details of three such objects-

Messier13Messier13, located in the constellation Hercules, is the brightest globular cluster that can be observed from the northern hemisphere. Under dark skies, the cluster is visible to the naked eye, but with binoculars, it appears as a fuzzy ball of light that stretches across about 30% of the diameter of the full Moon. With small to medium telescopes, more detail becomes apparent, such as the fact that the cluster brightens considerably towards its central regions, which is to be expected when more than 300,000 stars are packed into a ball that is only 100 light years in diameter.

The Double-Double star; although the star Vega dominates the constellation Lyra, a pair of binoculars will reveal a beautiful double star slightly above, and to the leftward of Vega. While this pair of stars is visible without optical aid to some people, a pair of binoculars will reveal the fact that each component of the binary system is in fact itself a binary star hence the name, Double-Double star.

Albireo, found in the constellation Cygnus, is a spectacular double star marking out the Swan’s head. The color difference between the two stars in the system is among the most pronounced of all double stars, and for many observers, this pair of stars is the most beautiful binary system in the entire night sky. We tend to agree.

Related Articles