Some daily events in the changing sky for July 13 – 21.

Getting up early? Mercury lies about a fist-width above the north-northeast horizon as the morning sky grows bright. The planet hangs in nearly the same spot for the remainder of July, but every morning the stars move a little farther up and to the right.

S&T Illustration

Friday, July 13

  • Jupiter's Great Red Spot should cross Jupiter's central meridian (the imaginary line down the center of the planet's disk from pole to pole) around 11:41 p.m. Eastern Daylight Time. It should be visible for at least 60 minutes before and after in a good 4-inch telescope if the atmospheric seeing is sharp and steady. A light blue or green filter helps. (For the times of all Red Spot transits this month, visible worldwide, see the July Sky & Telescope, page 52.) See the photo under "This Week's Planet Roundup" below.

    Saturday, July 14

  • New Moon (exact at 8:04 a.m. EDT).

  • Jupiter's largest satellite, Ganymede, casts its tiny black shadow onto Jupiter's face tonight from 11:42 p.m. to 2:01 a.m. Eastern Daylight Time; 8:42 to 11:01 p.m. Pacific Daylight Time.

    Sunday, July 15

  • Soon after sunset, use binoculars to look for the thin crescent Moon far lower right of Venus, as shown above.

  • Also with your binoculars, take a look at Regulus passing just 2° north (upper right) of Venus. And look much closer to Venus for the much fainter star 31 Leonis, magnitude 4.5. As seen from the West Coast around 9 p.m. PDT, 31 Leonis is just 0.2° from Venus in almost the same direction Regulus is.

  • Have you ever monitored an eclipsing binary star all the way through eclipse? Tonight, if you're in North America, you can track SZ Herculis high overhead dipping from magnitude 10.5 to 12 and back. Make a timing! See the article, chart, and timetable in the July Sky & Telescope, page 58.

    Monday, July 16

  • The crescent Moon shines amid Venus, Saturn, and Regulus in twilight for North America, as shown above.

  • The waxing crescent Moon occults (covers) Saturn for observers in Hawaii (around midday) and western South America (after sunset).

    Tuesday, July 17

  • This evening the Moon shines upper left of Venus, Saturn, and Regulus for North America, as shown above.

  • The Moon occults Regulus for Europe (after sunrise), western and southern Asia (midday), and Indonesia and northwestern Australia (in evening twilight).

    Wednesday, July 18

  • Jupiter's Great Red Spot should transit around 10:49 p.m. EDT.

  • If you've got a telescope, you probably know the constellation Hercules overhead and its showpiece globular star cluster M13. But what else have you explored here? Check out Sue French's Deep-Sky Wonders column for a tour of the many sights near the head of Hercules in the July Sky & Telescope, page 62.

    Thursday, July 19

  • Jupiter's satellite Io casts its tiny black shadow onto Jupiter's face tonight from 10:16 p.m. to 12:28 a.m. Eastern Daylight Time. For a listing of all events among Jupiter's moons this month, visible worldwide, see the July Sky & Telescope, page 52.

    Friday, July 20

  • Mercury is at greatest elongation, 20° west of the Sun in the dawn.

  • Jupiter's moon Io reappears out of eclipse from Jupiter's shadow around 9:36 p.m. EDT. A small telescope will show it gradually swelling into view just off the planet's eastern limb.

  • Jupiter's Great Red Spot should transit around 12:27 a.m. Saturday morning Eastern Daylight Time; 9:27 p.m. Friday evening Pacific Daylight Time.

  • You've got another shot at an eclipse of SZ Herculis tonight; see July 15th above.

    Saturday, July 21

  • It's the height of summer (for us in the Northern Hemisphere), so the big Summer Triangle shines very high in the east at nightfall. Its brightest star is Vega, nearly overhead. Its others are Deneb, the brightest star two or three fist-widths at arm's length to Vega's lower left when you face east — and Altair, farther to Vega's lower right. See the photo below.

    Face east after dusk, look up, and there's the big Summer Triangle, looking just like this only a lot bigger. Its bright white stars are Vega (top), Deneb (lower left), and Altair (lower right). Herve Dole shot this picture between saguaro cactuses in the southwest desert.

    Alan MacRobert

    Want to become a better amateur astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly foldout map in each issue of Sky & Telescope, the essential magazine of astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

    Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of maps; the standard is Sky Atlas 2000.0) and good deep-sky guidebooks (such as Sky Atlas 2000.0 Companion or the enchanting though somewhat dated Burnham's Celestial Handbook). Read here how to use them most effectively.

    More beginners' tips: "How to Start Right in Astronomy".

    This Week's Planet Roundup

    Mercury is low in the glow of dawn, brightening rapidly from magnitude +1.6 to +0.3 this week. Look for it above the east-northeast horizon about 60 minutes before sunrise. It's far lower right of Capella, and far lower left of Aldebaran. See article.

    To find your local sunrise and sunset times, and much else, make sure you've put your location into our online almanac. If you're on daylight saving time, like most of North America, make sure the Daylight Saving Time box is checked.

    Venus is bright at magnitude –4.7, but it's getting quite low in the west after sunset. Saturn and Regulus, much dimmer, are also in the vicinity. A telescope — or even steadily mounted binoculars — shows Venus to be a thin crescent!

    Mars (magnitude +0.6, in Aries) rises after about 1 a.m. daylight saving time is and high in the east by dawn. Look for the Pleiades to its lower left, and Mars-like Aldebaran below the Pleiades. In a telescope, Mars is still just under 7 arcseconds wide. It's on its way to a Christmas-season opposition, when it will reach 16 arcseconds wide.

    Jupiter on July 2, 2007

    The Great Red Spot had crossed Jupiter's central meridian about 12 minutes earlier when Christopher Go took this image at 13:56 UT on July 2, 2007. The longitude (System II) on the central meridian was 128°.

    Christopher Go

    Jupiter (magnitude –2.5, in southern Ophiuchus) glares in the south during evening — you can't miss it. Antares, less bright, sparkles redly 5° below it; the two remain evening companions all summer. Other stars of Scorpius shine below them and to their right. In a telescope, Jupiter is a satisfying 43 arcseonds wide.

    Saturn (magnitude +0.6) is sinking out of sight into the sunset glow, to the right of Venus. Binoculars will help. Don't confuse Saturn with twinkly Regulus closer to Venus.

    Uranus (magnitude 5.8, in Aquarius) and Neptune (magnitude 7.8, in Capricornus) are well up in the southeast and south during early morning hours.

    Pluto (magnitude 13.9, in the northwestern corner of Sagittarius) is highest in early evening, about 17° east of Jupiter. Finder charts for Uranus, Neptune, and Pluto are in the July Sky & Telescope, page 60.

    All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's midnorthern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America. Eastern Daylight Time (EDT) equals Universal Time (UT, UTC, or GMT) minus 4 hours.

    To always get the up-to-date Sky at a Glance, bookmark this URL:
    http://SkyTonight.com/observing/ataglance .

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