Sky at a Glance | September 17th, 2010

Eastward view in late twilight
Watch the Moon at opposition pass Jupiter close to opposition.

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 cross Jupiter's central meridian (the imaginary line down the center of the planet's disk from pole to pole) around 11:05 p.m. Eastern Daylight Time. The "red" spot appears very 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.

    Sunday, Sept. 19

  • Mira, the prototype red long-period variable star in Cetus, has been visible to the unaided eye for a couple weeks now; it's on its way up to a maximum predicted for mid-October. Cetus is in good view in the east-southeast by about 11 or midnight daylight saving time. See the comparison-star chart in the September Sky & Telescope, page 58.

    Monday, Sept. 20

  • Jupiter's Great Red Spot should transit tonight around 12:43 a.m. EDT; 9:43 p.m. PDT.

    Tuesday, Sept. 21

  • The dim little constellation Scutum, high in the south after dark in September, lies in one of the richest parts of the Milky Way. It sports not only the famous open star cluster M11, but the nice globular cluster NGC 6712, the big, dim planetary nebula IC 1295 — and the tiny planetary nebula Kohoutek 4-8 in the same high-power view. Get out your OIII filter, and see Ken Hewitt-White's "Going Deep" article and chart in the September Sky & Telescope, page 64.

    Wednesday, Sept. 22

  • This evening Jupiter (and Uranus) are below the full Harvest Moon, as shown above. The Moon is exactly full at 5:17 a.m. Thursday morning EDT.

  • Autumn begins in the Northern Hemisphere, and spring in the Southern Hemisphere, at 11:09 p.m. EDT. This equinox marks when the Sun crosses the equator heading south for the year. Day and night (if you include twilight as night) are about equally long.

    Thursday, Sept. 23

  • Jupiter and Uranus are now to the right of the Moon during evening, as shown above.

  • Jupiter's Great Red Spot should transit around 10:12 p.m. EDT.

    Friday, Sept. 24

  • This is the time of year when, after nightfall, the dim Little Dipper (you'll need a dark sky) is dumping water into the bowl of the Big Dipper far below it. Bailing out for fall?

    Saturday, Sept. 25

  • Jupiter's Great Red Spot should transit around 11:50 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).

    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 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 is coming into a fine morning apparition this week, brightening from magnitude 0.0 to –0.8. Look for it low in the east about 45 minutes before your time of sunrise. Look too for little Regulus twinkling above or upper right of it, higher every morning.

    Venus, though brightest now at magnitude –4.8, is sinking quite low in the southwest during bright twilight. It sets before dark.

    Mars, vastly dimmer at magnitude +1.5, is 6° or 7° to Venus's upper right all week. Use binoculars; good luck.

    Jupiter on Sept. 16, 2010
    Right on schedule, Jupiter's Great Red Spot (GRS) was crossing the planet's central meridian when Christopher Go in the Philippines took this image at 15:29 UT Sept. 16, 2010. Just to its upper left is pale Red Spot Junior (Oval BA), which has finally passed the GRS with no apparent effect on either. Notice too the pale hints of the South Equatorial Belt coming back into view, including the dent in it below the GRS known as the Red Spot Hollow. On the other side of the equator, the North Equatorial Belt is full of busy activity. South is up.
    Christopher Go

    Jupiter (magnitude –2.9, in Pisces) is at opposition this week. As twilight fades, Jupiter becomes visible low in the east. It's well up in the east-southeast by mid-evening — by far the brightest starlike point in the sky. It's highest in the south around 1 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 Monday the 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. See our article.

    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 (in UT) for the rest of this observing season.

    Saturn is hidden behind the glare of the Sun.

    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. Photo on SpaceWeather.com.

    Neptune (magnitude 7.8, at the Aquarius-Capricornus border) is well placed earlier in the 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 bright moonlight this week, forget 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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