Sky at a Glance | September 10th, 2010

Thursday, Sept. 9

  • Mira, the prototype red long-period variable star in Cetus, is on its way to a maximum predicted for early October. It's probably not quite visible to the unaided eye yet but should be easy in binoculars. You'll need to look for it after about midnight, however. See the chart in the September Sky & Telescope, page 58.

    Early twilight as the Moon returns
    Soon after sunset on September 10th and 11th, Venus and the crescent Moon guide the way to some much more difficult sights. The visibility of faint objects in bright twilight is exaggerated here; bring 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. In the Far East, move it halfway.)

    Friday, Sept. 10

  • Can you spot the thin Moon lower right of Venus after sunset, as shown above? In the illustration, the visibility of objects in bright twilight is exaggerated; binoculars will help.

  • Algol in Perseus is well up in the northeast by about 10 p.m. daylight saving time. Tonight it should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 11:58 p.m. EDT (8:58 p.m. PDT). It takes several additional hours to fade and to rebrighten. Use our comparison-star chart. For all the times of Algol's minima in September and October, good worldwide, see the October Sky & Telescope, page 59.

    Saturday, Sept. 11

  • Venus shines 6° or 7° to the right of the waxing crescent Moon low in the west-southwest during twilight, as shown above.

  • 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 10:20 p.m. Eastern Daylight Time. 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. For all of the Red Spot's central-meridian crossing times, good worldwide, use our Red Spot calculator or our complete list for the rest of this observing season.

    Sunday, Sept. 12

  • Jupiter's moon Europa slips into eclipse by Jupiter's shadow, barely off the planet's western limb, around 12:24 a.m. Monday morning EDT.

    As the waxing Moon moves upper leftward from evening to evening, it passes Scorpius sinking for the season toward the lower right. (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.)

    Monday, Sept. 13

  • At dusk, look for Antares sparkling 3° or 4° left of the Moon, as shown here.

  • Jupiter's Great Red Spot should transit around 11:58 p.m. EDT.

    Tuesday, Sept. 14

  • First-quarter Moon tonight (exact at 1:50 a.m. Wednesday morning EDT).

    Wednesday, Sept. 15

  • Jupiter's Great Red Spot should transit around 1:36 a.m. Thursday morning EDT (10:36 p.m. Wednesday evening PDT).

    Thursday, Sept. 16

  • The Moon shines above the handle of the Sagittarius Teapot this evening.

  • Jupiter's Great Red Spot should transit around 9:27 p.m. EDT.

    Friday, Sept. 17

  • Uranus is passing 0.8° north of Jupiter tonight and tomorrow night. Although Uranus is easily visible in binoculars at magnitude 5.7, Jupiter outshines it by nearly 3,000 times at magnitude –2.9. In fact, Uranus appears roughly as bright as one of Jupiter's four Galilean moons.

    Saturday, Sept. 18

  • You know summer is near its end: as the stars come out, Cassiopeia in the northeast is already as high as Big Dipper in the northwest!

  • Jupiter's Great Red Spot should transit around 11:05 p.m. EDT.


    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 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).

    Pocket Sky Atlas
    The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but that's less than one star in an entire telescopic field of view, on average. By comparison, Sky Atlas 2000.0 plots 81,312 stars to magnitude 8.5, typically one or two stars per telescopic field. Both atlases include many hundreds of deep-sky targets — galaxies, star clusters, and nebulae — to hunt among the stars.
    Sky & Telescope

    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

    On what date can you first see Mercury emerging in the dawn?

    Mercury is emerging from deep in the glow of sunrise and brightening rapidly. It should be clearly visible after about the 15th; look for it low due east about 45 to 30 minutes before your time of sunrise. Don't confuse Mercury with little Regulus twinkling above it!

    Venus, though bright at magnitude –4.7, is quite low in the southwest during bright evening twilight. It sets before dark.

    Mars, vastly dimmer at magnitude +1.5, is 6° to Venus's upper right all week. Use binoculars. Look too for Spica (magnitude +1.0) to the lower right of Mars, as shown at the top of this page. Good luck.

    Jupiter (magnitude –2.9, in Pisces) is nearing its opposition on the night of the 20th. As twilight fades, Jupiter becomes visible low in the east. It's well up in the east-southeast by mid- to late evening — by far the brightest starlike point in the sky. It's highest in the south around 1 or 2 a.m. daylight saving time.

    Jupiter is having an unusually close apparition; from now through mid-October it appears 49 arcseconds wide. In fact, at opposition on the night of September 20th Jupiter will be closer than at any other time from 1963 to 2022. However, that's only 1% or 2% closer than in any year when opposition occurs from mid-August through October, including last year and next.

    Jupiter with two red spots, Aug. 30, 2010
    This is an amateur image? Taken from Earth? Star planetary imager Anthony Wesley in Australia took this stacked-video image on August 30th at 17:38 UT, using the 14.5-inch Newtonian reflector he's pictured with at the bottom of this page. North is toward lower left.


    Jupter's Oval BA, also known as Red Spot Junior, has just passed the Great Red Spot without any visible effect on either. Here, Junior is just south of (above) the Great Red Spot.

    Jupiter's Great Red Spot is near System II longitude 157°. Assuming it stays there, here's a list to print out of all the Great Red Spot's predicted transit times for the rest of this observing season.

    Saturn is lost in the sunset.

    Uranus (magnitude 5.7) is only about 1° from Jupiter this week. They're closest (0.8°) on the 17th and 18th, with Uranus passing north of Jupiter.

    Neptune (magnitude 7.8, at the Aquarius-Capricornus border) is well placed during evening. See our finder charts for Uranus and Neptune online or in the September Sky & Telescope, page 56. Can you see any color in Uranus and/or Neptune?

    Pluto (magnitude 14, in northwestern Sagittarius) is in the south-southwest after dusk, but with the moonlight this week, forget it.

    P.S. regarding Pluto: We list its whereabouts because people want us to, not because "Sky & Telescope officially says Pluto is a planet!" as internet gossip would have it.


    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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