Sky at a Glance | August 21st, 2009

Some daily events in the changing sky for August 21 – 29.

Mars on Sept. 2, 2009
It's starting to be Mars season again — barely. The planet is high in the morning sky but only 6 arcseconds wide. Nevertheless, S&T's Sean Walker managed to record some surface detail on the morning of September 2nd. The dark area at top includes Mare Sirenum and Mare Cimmerium. The small dark spot just upper left of center is Phoenicis Lacus. Note the north polar haze. South is up. Walker used a 12.5-inch reflector and IRGB color filters for this stacked-video image.
S&T: Sean Walker

Friday, August 21

  • Bright Vega crosses the zenith soon after dark this week, as seen from mid-northern latitudes. (It goes exactly through the zenith at latitude 39°.) Whenever Vega is highest overhead, you know that the Teapot of Sagittarius, rich with telescopic wonders, is at its highest in the south.

    Saturday, August 22

  • With summer growing late, bright golden Arcturus shines ever lower in the west after dark. And the Big Dipper is swinging lower in parallel with it in the northwest.

    Sunday, August 23

  • 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 11:30 p.m. Eastern Daylight Time. The "red" spot is actually pale orange-tan. It should be visible for about an hour before and after in a good 4-inch telescope if the atmospheric seeing is sharp and steady. A light blue or green filter helps. The Red Spot transits about every 10 hours 56 minutes; for all of the Red Spot's transit times, good worldwide, use our Red Spot calculator or print out our list for 2009.

    Monday, August 24

  • The season is changing; around 9 or 10 p.m. (depending on where you live in your time zone), Cassiopeia has risen as high in the northeast as the Big Dipper has sunk in the northwest.

    Tuesday, August 25

  • It was 20 years ago today that Voyager 2 flew by Neptune, which was then near Saturn and Uranus in Sagittarius. Remember? A lot of folks found Neptune in their telescopes for the first time that night.

    Wednesday, August 26

  • The tiny black shadows of both Ganymede and Europa are on Jupiter's face tonight from 10:20 p.m. EDT to 1:12 a.m. EDT. Moreover, Jupiter appears to have only one moon (Callisto) from 9:58 p.m. EDT to 12:35 a.m. EDT.

    Thursday, August 27

  • First-quarter Moon (exact at 7:42 a.m. EDT).

  • In late afternoon daylight, the dark limb of the Moon occults Antares for much of North and Central America. See local timetables. The Moon is still very close to Antares by the time evening arrives.

    Update: David Dunham of the International Occultation Timing Association (IOTA) writes that this will be "our last occultation of Antares until 2023." At locations where the Moon is reasonably high "this occultation should be visible with any small telescope, weather permitting." Accuweather predicts "only scattered clouds in the narrow graze zone that crosses northern New York and Massachusetts, including part of the Boston area. Let me know if you might be interested in joining an expedition to observe the graze." Dunham's email is dunham AT starpower DOT net.

    Friday, August 28

  • Before the beginning of dawn Saturday morning, use binoculars to spot the open cluster M35 in Gemini just 1° left of bright Mars high in the east.

    Saturday, August 29

  • The Moon this evening shines near the top star of the Sagittarius Teapot, 3rd-magnitude Lambda Sagittarii.


    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 map in the middle of each Sky & Telescope diagram" target="new_window">Sky & Telescope, the essential magazine of astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

    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
    Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts; the standards are
    Sky Atlas 2000.0 or the smaller Pocket Sky Atlas) and good deep-sky guidebooks (such as Sky Atlas 2000.0 Companion by Strong and Sinnott, the more detailed and descriptive Night Sky Observer's Guide by Kepple and Sanner, or the classic Burnham's Celestial Handbook). Read how to use them effectively.

    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 and a curious mind." Without these, "the sky never becomes a friendly place."

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


    This Week's Planet Roundup

    Mars on Sept. 2, 2009
    It's starting to be Mars season again — barely. The planet is high in the morning sky but only 6 arcseconds wide. Nevertheless, S&T's Sean Walker managed to record some surface detail on the morning of September 2nd. The dark area at top includes Mare Sirenum and Mare Cimmerium. The small dark spot just upper left of center is Phoenicis Lacus. Note the north polar haze. South is up. Walker used a 12.5-inch reflector and IRGB color filters for this stacked-video image.
    S&T: Sean Walker
    Mercury and Saturn (magnitudes 0.2 and 1.1, respectively) are deep in bright twilight just above the horizon due west. Try scanning for them with binoculars, preferably tripod-mounted, 20 or 30 minutes after sunset. Saturn is off to the right of brighter Mercury. Good luck.

    Venus (magnitude –4.0, moving from Gemini into Cancer) blazes in the east before and during dawn.

    Mars (magnitude +1.0, between Orion and Auriga) is high to the upper right of Venus before dawn. To its own upper right is similar-looking Aldebaran. To its lower right is similarly colored Betelgeuse.

    Jupiter (magnitude –2.9, in Capricornus) is just past opposition. It comes into view low in the southeast in twilight — the first "star" to appear after sunset. It's higher in better telescopic view by 11 p.m.

    Polar projection animation
    Watch the impact mark spread and grow over the course of four weeks! It's the dark mark near the pole at the 2 o'clock position. Theo Ramakers writes, "Here is an updated animation containing the images of a large number of dedicated Jupiter imagers, members of the ALPO Jupiter listserve. Hans Joerg Mettig from Jupos.com in Germany converted the submitted images to a polar projection, and I put them together in an animation."


    Notice the rather that just spreading out, the original impact site seems to keep pouring out black stuff that then drifts away.

    Theo Ramakers
    Jupiter impact mark fading. A black dust marking, like those made by the Comet Shoemaker-Levy 9 impacts in 1994, appeared suddenly in Jupiter's south polar region around July 18th. Backyard observers tracked it as it spread and elongated. By August 17th it had broken up and faded nearly to invisibility.

    Uranus (magnitude 5.8, just below the Circlet of Pisces) is well up in the southeast by 10 or 11 p.m.

    Neptune (magnitude 7.8, in Capricornus) appears 4° from Jupiter but 20,000 times fainter. See our finder charts for Uranus and Neptune.

    Pluto (14th magnitude, in northwestern Sagittarius) is highest in the south-southwest just after dark. See the finder chart in the June Sky & Telescope, page 53.

    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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