Sky at a Glance | October 8th, 2010

Periodic Comet Hartley 2 is at its best early this week — before moonlight becomes a problem late in the week. At 6th magnitude the comet is visible in binoculars in a moderately dark sky, well placed in the evening high in Perseus. It has a small central condensation and a large, dim coma. As a result of this, what you'll see of it depends strongly on the quality of your sky; in the last few days different observers have reported the comet as anywhere from magnitude 5.3 to 7.2 overall. Use the finder chart below, and see our article.

Path of Comet Hartley 2
This week Comet Hartley 2 speeds across Perseus toward bright Capella. Click image for larger chart. The comet symbols (visibility much exaggerated) are placed at 0:00 UT on the October dates indicated. Remember, 0:00 UT falls on the evening of the previous date in the times zones of the Americas.
Sky & Telescope

Cetus rising
Now at naked-eye visibility, Mira in Cetus climbs the eastern sky in late evening — in this case, over hills in Iran. Click image for larger view.
Babak A. Tafreshi

Friday, October 8

  • Mira, the brightest long-period red variable star, is having an unusually bright maximum! As of October 7th many observers were reporting it at magnitude 3.1, very plainly visible to the naked eye. Will it grow any brighter? It's up in good view in the east-southeast by 10 or 11 p.m. daylight saving time. See the comparison-star chart in the September Sky & Telescope, page 58.

  • It's certainly fall now; look for Arcturus, the brightest star of Bootes, low in the west-northwest as twilight fades. To its right in the north-northwest, the Big Dipper is lying almost sideways now and holding water.

  • Comet Hartley 2 is still only about 1° from the Perseus Double Cluster this evening. Think photo opportunity!

    Bright sky 15 minutes after sunset
    Use binoculars to look for these objects hiding in bright twilight shortly after sunset.

    Saturday, October 9

  • Soon after sunset, use binoculars to look for the thin Moon and Venus very low in the southwest, as shown here. Can you also find Mars and Antares?

  • Late tonight (for North America) Comet Hartley 2 grazes Eta Persei, magnitude 3.8, the tip of Perseus's hat. Eta Per is a pale-yellow-orange K3 giant, which, in a telescope, should make a nice color contrast with the comet's pale green.

  • 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 1:20 a.m. Sunday morning EDT; 10:20 p.m. Saturday evening PDT. 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. 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 print out our list for the rest of this observing season.

    Still in bright twilight
    The waxing Moon, on its way back into the evening sky, passes Antares on its way out. (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.)

    Sunday, October 10

  • In twilight, look for twinkly little Antares upper left of the crescent Moon low in the southwest, as shown here. Binoculars help.

  • Jupiter's Red Spot should transit around 9:12 p.m. EDT.

    Monday, October 11

  • Look for Antares lower right of the Moon after sunset this evening, as shown here.

  • Jupiter's Red Spot should transit around 2:58 a.m. Tuesday morning EDT; 11:58 p.m. Monday evening PDT.

    Tuesday, October 12

  • Do you know little Sagitta's lone Messier object? Find the loose globular cluster M71 right in the Arrow's shaft using Gary Seronik's Binocular Highlight article and chart in the October Sky & Telescope, page 45. Sagitta is also your jumping-off point for brighter M27 right nearby.

  • Jupiter's Red Spot should transit around 10:50 p.m. EDT.

    Wednesday, October 13

  • Right after dark, look for the Sagittarius Teapot tipping directly below the Moon.

    Thursday, October 14

  • First-quarter Moon (exact at 5:27 p.m. EDT). As the stars come out, look high above the Moon for Altair.

  • The center of the Comet Hartley 2 passes very close to the 4.6-magnitude star forming Perseus's eastern wrist (HIP 20070) early Friday morning for North America: around 10:30 October 15th Universal Time. Don't mistake the star for the comet's nucleus. In fact the true nucleus of the comet is predicted, as of two days in advance, to occult the star along a track from British Columbia through Calgary, Alberta (at about 10:28:40 UT) and on through Montana, South Dakota, Nebraska, Kansas, Missouri, Arkansas, Mississippi, Alabama, and the western end of the Florida panhandle (at about 10:33 UT). An occultation could last for up to 0.9 second.

    Update Thursday morning: David Dunham writes: "The star is b Persei (small "b", NOT beta; after Greek letters ran out, Bayer used small Roman letters) or SAO 24531, spectral type A2, a tight spectroscopic binary with a period of only 1.527 days; it is an elliptical variable, and radio flaring has been observed, indicating that there is probably active mass exchange between the components....

    "In spite of the visible coma, the area around comets is an almost perfect vacuum; you have little chance to detect any dimming of the star's light, with the odds being not much better than finding a satellite of an asteroid, unless you are within perhaps 40 km of having an occultation by the nucleus. One of the few occultations by a comet ever observed was seen by Richard Nolthenius when IRAS-Araki-Alcock occulted an 8th-mag. star.... He saw the star fade, then brighten again over a period of less than a second, as I remember. Many have tried to look for dimmings during predicted close appulses by comets with almost no success...."

  • Jupiter's Red Spot should transit around 12:28 a.m. Friday morning EDT; 9:28 p.m. Thursday evening PDT.

    Friday, October 15

  • Look just upper right of the Moon this evening (as seen from most of North America) for the 3rd-magnitude stars Beta and Alpha Capricorni, in that order counting up. Alpha is a double star that, with good or well-corrected vision, you can just resolve with the unaided eye. Binoculars resolve it easily into a golden-yellow pair.

    Saturday, October 16

  • Jupiter's Red Spot should transit around 8:19 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 hidden in the glare of the Sun.

    Venus, though bright at magnitude –4.6, is approaching inferior conjunction with the Sun. Even early in the week, it's barely above the west-southwest horizon just 10 or 15 minutes after sunset. Sweep for it with binoculars.

    In a telescope, however, Venus is taking on its most interesting form: a lengthening, thinning crescent. The time to view it in a telescope is in daylight long before sunset — but don't accidentally sweep up the Sun! In mid-afternoon, place your scope in the shadow of a building or other obstacle where you have a clear view of the sky 28° to 21° to the Sun's left, while the Sun will remain hidden.

    Mars, way dimmer at magnitude +1.5, continues to linger low in the southwest after sunset (7° to 10° above Venus). You'll need those binoculars.

    Jupiter on October 13, 2010
    Jupiter on October 13th at 12:55 UT. South is up. To the upper left of the Great Red Spot is Oval BA (Red Spot Junior) with a distinct dark halo around it. The two spots continue slowly drawing apart. Note the strange, thin, wide-dipping dark plume forming what's normally the Great Red Spot Hollow, just below the spot. Also, huge disturbances are taking place in the broad, dark North Equatorial Belt and the adjacent part of the Equatorial Zone at about the same longitude as the Great Red Spot.


    Don't expect an eyeball view like this in any telescope, no matter how big! Planetary imager Christopher Go continues to demonstrate the extraordinary power of stacked-video imaging done with years of experience.


    Jupiter (still a brilliant magnitude –2.9, at the Pisces-Aquarius border) shines low in the east-southeast in twilight and high in the southeast by mid-evening — by far the brightest starlike point in the sky. It's highest in the south around 11 or midnight daylight saving time.

    Jupiter is having an unusually close apparition; it continues to appear 49 arcseconds wide. (In fact its opposition three weeks ago was closer than any other of Jupiter from 1963 to 2022, though only 1% or 2% closer than in any year when opposition occurs from mid-August through October, including last year and next. See 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 (times and dates in UT) for the rest of this observing season.

    Saturn is deep in the glow of sunrise.

    Uranus (magnitude 5.7) is 2° to 2½° east of Jupiter this week.

    Neptune (magnitude 7.8, at the Aquarius-Capricornus border) highest in the south after dinnertime. 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 14.0, in northwestern Sagittarius) remains in the south-southwest right after dark.


    All descriptions that relate to your horizon — 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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