Sky at a Glance | July 9th, 2010

Venus passes closely by Regulus on July 9th.

Friday, July 9

  • Venus continues to shine in the west at dusk, lower every week. This evening look for little Regulus, 150 times fainter, just a pencil-width at arm's length to Venus's lower left, as shown here. Binoculars help. Dim Mars looks on from the upper left.

    Saturday, July 10

  • This evening, look for Regulus 1.2° straight below Venus (as seen from mid-northern latitudes).

    Sunday, July 11

  • New Moon (exact at 3:40 p.m. EDT). A total eclipse of the Sun crosses the South Pacific, Easter Island, and (at sunset) part of southern Chile and Argentina. Details.

    Monday, July 12

  • At this time of year, bright Scorpius is highest in the south shortly after nightfall. Now is the narrow time-and-date window to explore the rich area around the Scorpion's tail, quite far south. See Sue French's Deep-Sky Wonders column in the July Sky & Telescope, page 67.

    Tuesday, July 13

  • Soon after sunset, use binoculars to sweep up Mercury and the thin crescent Moon far to the lower right of Venus, as shown below. Mercury and the Moon are about 10° apart (at the times of dusk for North America).

    Westward view in bright twilight
    The waxing crescent Moon marches along south of the ecliptic day by day. Mercury, Venus, Mars, and Saturn lie much closer to the ecliptic (the plane of the solar system projected onto Earth's sky).

    Wednesday, July 14

  • As the glow of sunset fades, look for the thin crescent Moon about 7° lower left of Venus.

    Thursday, July 15

  • Now the Moon is farther left of Venus. They appear the same altitude above your horizon if you're near latitude 40° north (the latitude for which our sky scenes are always drawn).

  • Saturn's large satellite Titan is at eastern elongation from the planet this evening. A small telescope will show it.

    Friday, July 16

  • Look for Saturn and Mars to the right of the Moon at nightfall, as shown above.

    Saturday, July 17

  • Vega is the brightest star shining high in the east. Deneb is the brightest to its lower left, by 2 or 3 fist-widths at arm's length. Farther to Vega's lower right is Altair (with little Tarazed just above it). Vega, Deneb, and Altair form the big Summer Triangle.


    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.

    Sky Atlas 2000.0 (the color Deluxe Edition is shown here) plots 81,312 stars to magnitude 8.5. That includes most of the stars that you can see in a good finderscope, and typically one or two stars that will fall within a 50× telescope's field of view wherever you point. About 2,700 deep-sky objects to hunt are plotted among the stars.
    Alan MacRobert

    For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of 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 must have a detailed, large-scale sky atlas (set of charts). The standards are the Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger and deeper Uranometria 2000.0 (stars to magnitude 9.75). And read how to use your charts effectively.

    You'll also want a good deep-sky guidebook, such as Sky Atlas 2000.0 Companion by Strong and Sinnott, or the more detailed and descriptive Night Sky Observer's Guide by Kepple and Sanner, or the classic if dated Burnham's Celestial Handbook.

    Can a computerized telescope take their place? I don't think so — not for beginners, anyway, and especially not on mounts that are less than top-quality mechanically. As Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."


    This Week's Planet Roundup

    Mercury (about magnitude –0.6) is deep in the glow of sunset. Scan for it with binoculars shortly after sundown just above the west-northwest horizon, far to the lower right of Venus. By late in the week Mercury climbs higher and is easier to see.

    Venus (magnitude –4.1, in Leo) is the bright Evening Star sinking in the west as twilight fades. The much fainter star Regulus (magnitude +1.4, less than 1% as bright) is nearby — hardly more than 1° below or lower left or Venus on July 9th and 10th, and farther to Venus's lower right after that.

    In a telescope Venus is still a small (17-arcsecond) gibbous disk. You'll have the cleanest telescopic views of it when it's higher in the blue sky of afternoon — if you can find it then. (Don't accidentally sweep up the Sun!) Not until late summer will Venus assume its larger and more dramatic crescent phase.

    Mars (magnitude +1.4, by the hind foot of Leo) is upper left of Venus. Watch Mars closing in on Saturn, glowing to its upper left, day by day. In a telescope Mars is just a tiny blob 5 arcseconds in diameter.

    Jupiter on June 25, 2010
    Jupiter's Great Red Spot is still floating free in the absence of the South Equatorial Belt. Christopher Go took the bottom image at 20:32 UT June 25th, and the top image 24 later earlier. South is up.

    Jupiter (magnitude –2.6, in Pisces) rises around 11 or midnight daylight saving time and shines high in the southeast before dawn. It's the brightest starlike point in the morning sky. See our article on Jupiter's disappearing South Equatorial Belt.

    Jupiter's Great Red Spot is near System II longitude 150°. Assuming it stays there, here's a list of all the Great Red Spot's predicted transit times for the rest of 2010.

    Saturn (magnitude +1.1, in the head of Virgo) is in the west during evening, upper left of Mars. The diagonal line of Saturn, Mars, Venus, and Mercury is shrinking. The first three of these planets will bunch up low in the sunset in early August.

    Uranus (magnitude 5.8, in Pisces) is just under 3° west of Jupiter. In a telescope Uranus is only 3.6 arcseconds wide, compared to Jupiter's 43″.

    Neptune (magnitude 7.9, at the Aquarius-Capricornus border) is up in good view after midnight, well to Jupiter's west. See our finder charts for Uranus and Neptune in 2010.

    Pluto (magnitude 14, in northwestern Sagittarius) is high in the south-southeast by 11 p.m. See our big Pluto finder charts for 2010.


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


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