Sky and Telescope - July 2018 - 46
JULY 2018 OBSERVING Sun, Moon & Planets by Fred Schaaf To find out what's visible in the sky from your location, go to skypub.com/ almanac. Mars and Its Supporting Cast July is all about Mars, but the other planets put on a pretty good show, too. T his is the month that Mars comes dramatically nearer to Earth than at any time in the past 15 years. It comes about 12 million kilometers closer than in 2005 and a whopping 18 million kilometers closer than in 2016. By late July, Mars shines almost twice as bright as it did at 2016's fine opposition - in fact, almost twice as bright as Jupiter! - and its disk grows to 25% wider than it ever got in 2016. There's no doubt that this is the bestin-a-generation month - and summer - for Mars. But Venus shines bright in the west until the end of July's long twilights, with Mercury still visible well to the lower right of Venus in the first half of July. Jupiter is near its highest in the south at nightfall, while Saturn is low in the southeast. And Saturn is followed, earlier and earlier in the evening as July progresses, by fiery Mars, the final attraction in what ends up being an all-night parade of bright planets across the sky. DUSK Venus glows fairly low in the west at nightfall, lower with each passing week even though its greatest elongation (46° east) from the Sun doesn't occur until August 17th. Telescopes show Venus's phase thinning from about 70% to 57% lit, while the overall diameter of its disk grows from 16″ to around 20″, less than that of Mars. Still, the much greater surface brightness of Venus makes it shine magnitude -4.1 to -4.3 this month, a lot brighter than Mars. Venus has two exciting conjunctions this month. On July 9th, Regulus is about 1° to the lower left of fantasti- Dusk, July 9 Dawn, July 9-11 45 minutes after sunset 1 hour before sunrise cally brighter Venus. On July 15th, the waxing lunar crescent stands less than 2° lower right of Venus. Mercury is a roughly zero-magnitude object about 15° lower right of Venus for the first half of July. Mercury reaches a greatest elongation of 26° east of the Sun during the evening and night of July 11-12 in the Americas. By July 17th Mercury has dimmed to magnitude 1.0 and is rapidly fading from view. DUSK TO MIDNIGHT Jupiter is near the meridian in the south soon after sunset in early July. The kingly planet this month fades from magnitude -2.3 to -2.1 and in telescopes shrinks from 41″ to 38″ wide. Jupiter shines 2° upper right of the wide double star Alpha (α) Librae Dusk, July 14 -16 Denebola 45 minutes after sunset Pleiades 10° Moon July 9 Moon July 16 LEO γ Leo 1° apart Hyades Venus TAURUS Venus Moon July 10 Regulus Moon July 15 γ Aldebaran Regulus Moon July 14 (Occultation for parts of Canada) Mercury Moon July 11 Looking West 46 J U LY 2 0 1 8 * S K Y & T E L E S C O P E Mercury Looking East Looking West