A Digital Supplement to Astronomy Insights Astronomy Magazine © 2018 Kalmbach Media Saturn Looms Large June 2019 • Astronomy.com Visible to the naked eye Visible with binoculars SKY THIS MONTH Visible with a telescope THE SOLAR SYSTEM’S CHANGING LANDSCAPE AS IT APPEARS IN EARTH’S SKY. BY MARTIN RATCLIFFE AND ALISTER LING SATURN LOOMS LARGE when it reaches opposition this month. With the rings tipped wide open, observers should look for the dark Cassini Division and other fine details. NASA/ ESA/A. SIMON (GSFC) AND THE OPAL TEAM/ J. DEPASQUALE (STSCI) JULY 2019 The ringed planet at its peak These warm summer In between the brilliant Mercury and Mars are in planets continue to drop lower nights bring magnifi- flashes and explosions of your conjunction with each other with each passing day and will cent views of Saturn. The ringed local July 4 fireworks, look to July 7. That evening, magnitude disappear within a week. planet remains visible all night, the west for a noticeably fatter 2.0 Mercury lies 4° south (lower You won’t have to search a feat nearly matched by its crescent Moon, now some 15° left) of magnitude 1.8 Mars, as hard to find Jupiter. The equally stunning sister world, high a half-hour after sunset. though both prove difficult to giant planet stands clear of the Jupiter. Alas, the solar system’s The two planets lie about 10° see in the bright twilight even southeastern horizon after sun- smaller planets don’t fare as to our satellite’s lower right. through binoculars. The two set and climbs nearly 30° high well. Mercury and Mars hang in the south well before mid- low in evening twilight, while night. It shines at magnitude Saturn takes center stage Venus appears just before dawn. –2.5 against the faint backdrop Let’s start our celestial tour of southern Ophiuchus the with Mercury and Mars, which OPHIUCHUS Serpent-bearer. we can see only in early July. Any telescope shows Altair The two planets glow faintly in Jupiter’s disk. In mid-July, the the west-northwest shortly after AQUILA world spans 44.4" across its sundown. Your best opportu- equator and 41.6" through its nity to find them comes July 3, Jupiter poles. The 6 percent discrep- when a waxing crescent Moon Antares ancy, caused by a combination points the way. Saturn SCORPIUS of Jupiter’s gaseous nature and The one-day-old Moon then its less than 10-hour rotation stands 5° above the horizon period, becomes obvious once 30 minutes after sunset. Once SAGITTARIUS you know to look for it. you locate it, use binoculars to 10° Even more striking are the July 9, 11 P.M. spy magnitude 1.8 Mars 3° to Looking south-southeast details you can see in the jovian the upper left. Mercury glows a atmosphere. Look for two dark bit brighter, at magnitude 1.4, The gas giant shines at magnitude 0.1 at opposition July 9, when it remains cloud belts straddling a brighter some 4° to the Red Planet’s left. visible all night amongDiagram the stars ASY-SM0719_10: of Sagittarius. ALL ILLUSTRATIONS: ASTRONOMY: ROEN KELLY zone that coincides with the 2 ASTRONOMY INSIGHTS • JUNE 2019 SKY THIS MONTH RISING MOON I A crater worthy of an eminent astronomer TERRACED WALLS, complex central peaks, Copernicus a rough ejecta blanket, and an expansive ray system at Full Moon — it’s no surprise that lunar observers visit the crater Copernicus again and OBSERVING again. The Sun first rises over this crater’s tall, Copernicus modestly sharp rim July 11, two nights after HIGHLIGHT First Quarter phase. SATURN peaks July 9, when The low Sun angle on the 11th casts long it shines at magnitude 0.1 and spans 18.4" with rings shadows, accentuating the visibility of peaks extending 41.8" when seen and bumps as well as holes and mild depres- through a telescope. sions. Notice the jagged black teeth the eastern rim projects onto Copernicus’ floor. A textured apron surrounds the entire crater. It origi- N nated when surface material got splat- tered outward in all directions in the E equator. The southern belt car- immediate aftermath of the impact that created Copernicus. Lunar geologists This spectacular crater first appears ries the Great Red Spot, which July 11, but it remains a fine sight until appears obvious whenever the call it an ejecta blanket. after Full Moon on July 16. CONSOLIDATED LUNAR planet’s spin brings it onto the The terraced walls are a delight to see ATLAS/UA/LPL; INSET: NASA/GSFC/ASU Earth-facing hemisphere. at high power. To imagine how they formed, Jupiter’s four bright moons dig a hole in a wet sandy beach. Within seconds, on the 60-mile-wide crater. Thread in a filter to — Io, Europa, Ganymede, and the steep walls collapse inward to form giant reduce the glare, pump up the power, and take Callisto, in order of increasing staircases down to the floor. Sharp-eyed observ- in the scenery. The rough terrain and differences distance — circle the gas giant ers may notice that Copernicus’ terraces tilt in elevation and texture have completely disap- peared, replaced by a land of light rays and in periods ranging from a cou- down to the outside because the higher inner edge casts a shadow toward the rim. The eastern darker mare material showing through from ple of days to a couple of weeks. terraces show up best on the 11th. In case you underneath. These brightness variations help The three inner satellites cross get clouded out, the sequence almost repeats astronomers piece together the history of the in front of and pass behind the the evening of August 9, but with an even lower lunar surface. The impacting asteroid may have planet once each orbit. Many Sun angle than the image shown here. landed in a dark lava field, but the blast exca- observers consider these events For a few days on either side of the July 16 vated down to lighter-hued rocks and hurled the highlight of a Jupiter view- Full Moon, the nearly overhead Sun beats down them outward to create the superb ray system. ing session. Let’s take a look at a few of July’s best. Io transits Jupiter’s disk during the evening hours METEOR WATCH I The year’s longest-running show July 4, 11, 18, and 27. On the 4th, the transit begins at 10:02 p.m. EDT while the Southern Delta Aquariid meteors THE SOUTHERN STRAND of moon’s shadow follows 34 min- the Delta Aquariid meteor stream utes later. Both appear against encounters Earth during much of Enif July and August, but reaches a broad the planet’s North Equatorial PISCES peak from July 28–30. And with New Belt. The July 11 transit starts at DELPHINUS Moon arriving on the 31st, viewing 11:48 p.m. EDT with the shadow AQUARIUS conditions this year should be close trailing 42 minutes behind. The to perfect. Under a dark sky with the longer gap arises from a shift in CETUS radiant — the point in Aquarius from the relative positions of Jupiter, Radiant which the meteors appear to ema- the Sun, and Earth. nate — overhead, observers could Io circles Jupiter quickly, Fomalhaut CAPRICORNUS see up to 25 meteors per hour. and the following evening you Unfortunately for Northern can see the moon as it comes Hemisphere skygazers, the radiant around the planet’s far never passes overhead. From mid- side. At 11:51 p.m. EDT on SOUTHERN DELTA GRUS northern latitudes, the radiant peaks 10° the 12th, Io emerges from AQUARIID METEORS at an altitude of 35° between 3 and July 30, 4 A.M. Jupiter’s shadow some 14" Active dates: July 12–August 23 4 A.M. local daylight time. This cuts Looking south off the eastern limb and Peak: July 30 the observed number of meteors Moon at peak: New Moon adjacent to the South roughly in half, with observers in the Maximum rate at peak: ASY-SM0719_11With New Moon arriving just one day after Equatorial Belt. 25 meteors/hour this shower peaks, viewing conditions southern United States seeing a few should be ideal. more and those in Canada a few less. WWW.ASTRONOMY.COM 3 WHEN TO SKY THIS MONTH— Continued from page 49 VIEW THE PLANETS See Saturn’s top six satellites remains within a few hun- dredths of this magnitude EVENING SKY S all month. Mercury (west) For viewers at mid-northern Mars (northwest) Saturn Jupiter (south) W Titan Enceladus latitudes, Saturn reaches a Tethys Saturn (southeast) Iapetus Dione peak altitude of nearly 30° at Rhea 1:30 a.m. local daylight time MIDNIGHT July 9, 11:30 P.M. EDT 1' July 1 and about 30 minutes Jupiter (southwest) earlier each week thereafter. Saturn (south) With outer Iapetus in line with Titan and inner Enceladus near greatest Neptune (east) elongation, the Diagramringed world’s ASY-SM0719_12: moons show up well at opposition July 9. Skywatchers farther north will find Saturn lower in the sky, MORNING SKY Europa transits Jupiter’s southeast of magnitude 3.8 and those farther south will see Venus (northeast) disk starting at 9:54 p.m. EDT Omicron (ο) Sgr. it climb higher. Saturn (southwest) on July 23. The satellite tra- The ringed planet reaches Observers should take every Uranus (east) verses three-quarters of the opposition and peak visibility opportunity to view the ringed Neptune (south) disk before its shadow drops July 9, when it lies opposite the world through a telescope.