Sky at a Glance | July 6th, 2007

Some daily events in the changing sky for July 6 – 14.

Looking east-northeast as dawn brightens
A preview of some "winter" stars awaits early risers in July. For a few mornings, the waning crescent Moon directs you to faint Mercury coming into view very low down. For Mercury, you'll need binoculars. (These scenes are drawn for the middle of North America. European observers: move each Moon symbol a quarter of the way toward the one for the previous date. For clarity, the Moon is shown three times actual size.)
Sky & Telescope diagram

Friday, July 6

  • Earth is at aphelion, its farthest from the Sun for the year — 3.4% farther than we are from the Sun at perihelion in January.

  • 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 10:55 p.m. Eastern Daylight Time. It should be visible for at least 50 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.)

    Saturday, July 7

  • Bright Venus, low in the west in twilight, is now roughly midway between Saturn (to its right) and Regulus (to its upper left).

  • Last-quarter Moon (exact at 12:54 p.m. EDT).

  • Happy 100th birthday to the late science-fiction great Robert A. Heinlein, who started so many of us on our way.

    Sunday, July 8

  • Jupiter's Great Red Spot should transit around 12:33 a.m. Monday morning EDT; 9:33 p.m. Sunday evening PDT.

  • Before and during dawn Monday morning, Mars shines roughly 5° below the waning Moon (for North Americans).

    Monday, July 9

  • Jupiter's Great Red Spot should transit around 8:24 p.m. EDT.

    Tuesday, July 10

  • After nightfall is complete, Vega is the brightest star nearly overhead when you face east. Arcturus is the bright star almost as high toward the west-southwest. Look a third of the way from Vega to Arcturus for the dim Keystone of Hercules. Look two-thirds of the way for the mostly dim little semicircle of Corona Borealis, the Northern Crown.

    Wednesday, July 11

  • 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. See the article, chart, and timetable in the July Sky & Telescope, page 58.

  • Jupiter's Great Red Spot should transit around 10:03 p.m. EDT.

    Thursday, July 12

  • This evening and tomorrow evening, Venus is passing only about 1.7° below Regulus. Look low in the west at dusk. Saturn is now 6° off to their right.

  • Venus is at greatest brilliancy.

    Friday, July 13

  • Jupiter's Great Red Spot should transit around 11:41 p.m. EDT.

    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.

    Looking west in early twilight
    Watch the Moon passing through the Venus-Saturn-Regulus activity on the 16th and 17th. The blue 10° scale is about the size of your fist held at arm's length.
    Sky & Telescope diagram

    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 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 dim and very low in the glow of sunrise, but getting higher and brighter daily.

    Venus is at its greatest brilliancy this week (magnitude –4.7), but it's getting low in the west during twilight. Saturn, much dimmer, continues moving farther off to its right. Meanwhile Regulus closes in on Venus from the upper left — and crosses above it late in the week.

    Despite Mars's still-tiny apparent size, Larry Owens of Alpharetta, Georgia, recorded the developing Martian dust storm (bright area from left edge to lower right) on the morning of June 27th. The dark feature protruding toward the top is Syrtis Major. Owens used a 14-inch Celestron Schmidt-Cassegrain telescope and an Imaging Source DMK 21AF04 webcam. North is up.
    Larry Owens

    Mars (magnitude +0.6, in Aries) is gradually getting higher in the east before dawn. In a telescope it's still only 6 or 7 arcseconds wide. Nevertheless, amateurs who can do top-quality planetary imaging have been tracking the dust storm that is now reducing solar power to the Mars Exploration Rovers on the surface. The drop in available power has delayed the descent of Opportunity into Victoria Crater.

    Jupiter (magnitude –2.5, in southern Ophiuchus) is a month past opposition. It glares in the southeast to south during evening — you can't miss it. Antares, less bright, sparkles redly 5° to Jupiter's lower right. The two remain evening companions all summer.

    Saturn (magnitude +0.6, in Leo) continues to move farther to the right of Venus in twilight, as both sink lower toward the horizon day by day.

    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 not far from 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.

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    http://SkyTonight.com/observing/ataglance .