During the first half of June, Mercury will be easily visible low in the western post-sunset sky. Peak visibility will occur on June 3-4 when the swift planet will reach its greatest eastern elongation at an angular separation of 24° from the Sun. On those dates, Mercury will reside among the stars of Gemini and will set shortly before 11 p.m. local time. The optimal viewing times at mid-northern latitudes fall between 9:15 and 10 p.m. local time. Mercury’s position above (i.e., north of) a moderately dipping evening Ecliptic will make June’s appearance a good one for Northern Hemisphere observers, but a poor one for observers in the Southern Hemisphere. For most of June, Mercury will be moving towards Earth as it prepares for inferior conjunction at month-end. Telescope views of the planet will reveal a waning phase that drops from 43% illuminated on June 1 to a slim crescent by mid-month, while its apparent disk size will grow daily and its visual magnitude will decrease from magnitude 0.2 to 3.0.
Venus will encounter the Sun at inferior conjunction on June 3, and then enter the eastern pre-dawn sky among the stars of Taurus — but its position below the shallow morning ecliptic will make the planet a challenge to see against the bright morning sky until mid-month. On June 24, Venus will complete a retrograde loop and begin to travel east on a trajectory that will carry it through the Hyades cluster in early July. The planet will brighten to magnitude -4.66 at the end of June. Viewed in a telescope, Venus will exhibit a waxing crescent phase and an apparent disk diameter that shrinks from 58 to 43.5 arc-seconds. An hour before sunrise on June 19, the very slim crescent Moon will rise with Venus, making a spectacular wide-field photograph opportunity. The duo will be close enough to appear together in the field of view of binoculars and backyard telescopes. Observers in the Azores; the Canary Islands; northern and eastern Canada; Greenland; and the northern parts of Europe, Russia, and Mongolia can see the Moon occult Venus between 07:20 and 08:07 GMT.
Mars will begin June shining at magnitude -0.02 and moving rapidly prograde through the stars of eastern Aquarius. All month long, the planet will rise between about 1-2 a.m. local time and it will be easily visible in the lower third of the southeastern pre-dawn sky until almost sunrise. On June 24, the Red Planet will cross into southern Pisces. As the distance between Earth and Mars decreases, Mars will continuously increase in brightness, reaching magnitude -0.49 at month-end. Viewed in a telescope during June, Mars will exhibit an 85 per cent illuminated disk that will grow from 9.3 to 11.4 arc-seconds. On June 12-13, Mars will pass 1.75 degrees to the south of Neptune, but the waning last quarter Moon located nearby will make seeing that distant planet more difficult.
During June, Jupiter will shine very brightly from midnight to dawn while moving retrograde west through the stars of eastern Sagittarius, less than a handful of degrees northwest of the globular cluster Messier 75. Jupiter’s slowly increasing visual magnitude, from -2.57 to -2.72 during June, will allow it to remain easily visible until sunrise. Dimmer Saturn, positioned only 5-6 degrees to the east of Jupiter all year, will chase Jupiter across the sky. The two planets will be rather low in the sky for mid-latitude observers, but southerly observers will have a higher, better view of them. Throughout June, telescope views of Jupiter’s disk will show it growing from 44.71 to 47.25 arc-seconds as Earth’s distance from the giant planet decreases. Several Jovian moon shadow transit events will be visible from different parts of the world during June. The shadows of Europa and Ganymede will cross simultaneously with the Great Red Spot on June 4 and on June 11, and Io and Ganymede’s shadows will cross together on June 18. The waning gibbous Moon will hop past Jupiter on June 8-9, making a lovely binoculars sight and a photo opportunity with nearby Saturn.
During June, Saturn will be travelling retrograde westward through the stars of western Capricornus, approximately 5 to 6 degrees to the east of much brighter Jupiter and just 2 to 3 degrees north of the globular cluster Messier 75. The Ringed Planet will be observable from the wee hours until almost dawn. The low morning ecliptic in the Northern Hemisphere will keep Saturn in the lower part in the sky, but southerly observers will have a better view of it. Throughout June, Saturn’s disk and rings will grow slightly larger in telescopes. They’ll reach maximum apparent size at opposition in July. The waning gibbous Moon will pass to the south of Saturn and Jupiter on June 8-9, making a lovely binoculars sight and photo opportunity.
Uranus will spend June in the eastern predawn sky among the stars of southern Aries. The blue-green, magnitude 5.85 planet will be difficult to observe until later in the month, when its larger angular separation from the sun will surround the planet with a darker sky. Even then, the shallow morning ecliptic will keep Uranus too low in the sky for decent views from mid-northern latitudes. A 14-per-cent illuminated old crescent Moon will pass less than 5 degrees below Uranus on June 17.
During June, Neptune will be observable for several hours before dawn in the southeastern sky among the stars of eastern Aquarius. On June 24, the magnitude 7.9 planet will cease its eastward motion and commence a retrograde loop that will last until late November. The shallow morning ecliptic will keep the dim, distant planet in the lower third of the sky during June. On the mornings surrounding June 13, Mars will pass within 1.5 degrees to the south of Neptune, allowing the red and blue planets to appear together in the field of view of a telescope with a wide-field eyepiece. The waning last quarter moon will join the two planets on June 13.
Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the universe together.