During evening twilight in June, three planets form a diagonal line in the western sky: Saturn at upper left, Mars in the middle, and bright Venus fairly low on the right. Jupiter and dim Uranus are partway up the southeastern sky at dawn. And early in June, Mercury hovers low in the east before sunrise.
A partial eclipse of the Moon on June 26th is visible in its entirety over most of the Pacific Ocean. It's interrupted by moonset and daybreak across the western two-thirds of North America (see page 60 for details).
DUSK
Venus won't reach greatest elongation from the Sun until August. But for viewers at mid-northern latitudes, June is the month when Venus appears highest right after sunset. This is true because the planet is moving rapidly south relative to the Sun.
Venus, shining at magnitude -4.0, forms a straight line, just over 10° long, with fainter Pollux and Castor on June 11th. On June 19th and 20th Venus is in central Cancer, less than 1° from the center of big Messier 44, the Beehive Star Cluster - a lovely sight for binoculars and for telescopes at low magnification.
Mars spends the first dozen evenings of June near 1.4-magnitude Regulus. The planet is only a little brighter than the star, but their proximity intensifies the orange- yellow of Mars and blue-white of Regulus.
On June 3rd, Mars is less than 2° right of Regulus in North America's evening sky. The pair is closest on June 6th, with Mars just 50' upper-right of the star. Mars is 1° above Regulus on the 7th, and after that Mars moves roughly Vi° per day to the star's upper left.
Mars sets around the middle of the night. In telescopes it's a nearly featureless dot less than 6" wide.
Saturn reaches quadrature (90° east of the Sun) on June 19 th. Saturn dims a trace in June, from magnitude +1.0 to +1.1, because Earth is moving away from it now, as shown on the facing page. But the bigger reason that Saturn is dim is the narrowness of its rings. In late May the rings were tilted 1.7° from edgewise, and now they're just beginning to open, reaching 2.1° at the end of June. Not until 2024 will the rings appear this thin, and the faint inner moons of Saturn this easy to observe (see last month's issue, page 61).
By month's end Saturn sets not long after midnight (daylight-saving time). Note that Mars and Venus are closing in on Saturn from the lower right. They will catch the ringed planet, just nine days apart, in early August.
LATE NIGHT
Pluto, in Sagittarius, is at opposition to the Sun on June 25th and highest in the south in the middle of the night. Even now, when Pluto is closest to Earth for the year, you will probably need at least an 8- inch telescope and quite dark skies to see the 14th-magnitude Kuiper Belt object. For a finder chart, see next month's issue or SkyandTelescope.com/pluto.
AFTER MIDNIGHT
Neptune, at the border of Capricornus and Aquarius, rises before the middle of the night and is highest at the beginning of morning twilight. Finder charts for the two outermost major planets are available at SkyandTelescope.com/uranusneptune.
Jupiter and Uranus, in Pisces, are within 2° of each other throughout June. They rise after midnight (daylight-saving time) and are still fairly low in the east or southeast as the sky starts to grow light. But by mid-June they should be high enough for you to get reasonably crisp telescopic views just as dawn begins to brighten. Even if you can't resolve Uranus's 3.5"-wide disk every morning, a telescope may reveal its blue-green hue.
Jupiter and Uranus are less than 1° from each other from June 1st through 16th, and less than Vi° apart from the 6th through 10th. They reach conjunction - their first of three in a six-month span - on June 8th, when Jupiter shines at magnitude -2.3 with 5.9-magnitude Uranus 26' to its northwest. Uranus is at quadrature (90° west of the Sun) on June 22nd, Jupiter on June 23rd.
DAWN
Mercury rises in the dawn a respectable one hour before sunrise during the first half of June for observers at mid-northern latitudes, and it brightens from magnitude 0 to -1. But these statistics are misleading. June dawns are long, just like June evening twilight, and the sky is quite bright by the time Mercury rises a few degrees above the eastern horizon. This makes Mercury a fairly tough target unless you use binoculars.
MOON AND SUN
On June 6th in North America, the waning crescent Moon is 6° or 7° upper left of Jupiter before dawn. On June 10th, Mercury should be visible in binoculars 8° or 9° below and slightly left of a thin Moon a half hour before sunrise. At the same time on the 11th, a very thin crescent Moon may be visible about 6° to Mercury's left.
The Moon is waxing again at dusk on June 14th, when it's 4° or 5° below Venus. After that, the Moon passes below Regulus, Mars, and Saturn on June 16th, 17th, and 18th. The Moon is full on June 26th, when it will be partially eclipsed by Earth's shadow at dawn for western North America.
The Sun arrives at the solstice at 7:28 a.m. EDT on June 21st, beginning summer in the Northern Hemisphere and winter in the Southern Hemisphere.
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