Comet Hartley 2 on September 6th

Rolando Ligustri photographed 103P/Comet Hartley 2 on September 6th. Since then the round coma has grown larger, but the central condensation remains weak.

Rolando Ligustri


Periodic Comet Hartley 2 remains about 6th magnitude, appearing big, round, and dim in binoculars. This week it's crossing Auriga and passing its closest to Earth (on October 20th). But moonlight is returning; the waxing Moon sets later each night. You can have a Moon-free view through about the morning of the 19th if you observe in the pre-dawn hours; find your local moonset time using our online almanac. What you'll see of the comet, if anything, depends strongly on the quality of your sky. See our article Comet Hartley 2 At Its Closest, with finder charts.

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 barely resolve with the unaided eye. Binoculars resolve it easily into a golden-yellow pair — and also show that Beta too is a wide double.

    Cetus rising

    Now at naked-eye visibility, Mira in Cetus climbs the eastern sky in late evening — in this case, over hills in Iran.

    Babak A. Tafreshi

  • Mira, the brightest long-period red variable star, is having an unusually bright maximum! As of October 19th observers were still reporting it at about magnitude 3.0, very plainly visible to the naked eye. It's up in good view in the east-southeast by about 10 p.m. daylight saving time. Use the comparison-star chart in the September Sky & Telescope, page 58.

    Saturday, October 16

  • 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 8:19 p.m. Eastern Daylight Time. A light blue or green filter helps. (For all of the Red Spot's transit times, good worldwide, use our Red Spot calculator or print out our list of all Red Spot transit times for the rest of this observing season.)

    Sunday, October 17

  • This week the big Summer Triangle is still nearly overhead after dark. Look for Deneb close to the zenith (if you're in the north temperate latitudes). Brighter Vega shines to Deneb's west. And Altair is less high toward the south-southwest (with little Gamma Aquilae, or Tarazed, just to its upper right).
  • Jupiter's Red Spot should transit around 9:57 p.m. EDT.

    Monday, October 18

  • Jupiter shines lower left of the waxing gibbous Moon early this evening, and directly left of it later in the night.

    Tuesday, October 19

  • Jupiter's Red Spot should transit around 11:35 p.m. EDT.
  • Jupiter shines straight under the Moon this evening, as shown below.

    Looking east as the stars come out

    As the Moon waxes toward full night by night, it draws away from Jupiter a month past its own opposition.

    Sky & Telescope diagram

    Wednesday, October 20

  • The Moon is now to Jupiter's left, as shown above.

    Thursday, October 21

  • The Great Square of Pegasus is straight above the bright Moon this evening after dark (not shown above). It's tipped on one corner and somewhat larger than your fist held at arm's length.

    Friday, October 22

  • Full Moon (exact at 9:37 p.m. Eastern Daylight Time).
  • This week the Big Dipper lies level in the north-northwest after dusk, quite low, far below the bowl of the much dimmer Little Dipper.
  • Jupiter's Red Spot should transit around 9:05 p.m. EDT.

    Saturday, October 23

  • The tiny black shadows of both Ganymede and Europa fall on Jupiter from 9:40 to 11:04 p.m. EDT.
  • Algol is at its minimum light around 12:10 a.m. Sunday morning Eastern Daylight Time.

    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

    Mercury is hidden behind the glare of the Sun.

    Venus is finally disappearing deep into the sunset.

    Mars, dim at magnitude +1.5, continues to linger very low in the southwest after sunset. Look for it early in twilight with binoculars. Don't confuse it with twinklier Antares, well off to its left and a trace brighter.

    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.

    Christopher Go


    Jupiter (magnitude –2.8, at the Pisces-Aquarius border) shines 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 p.m. daylight saving time. Jupiter is having an unusually close apparition; in a telescope it continues to appear 48 or 49 arcseconds wide.

    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 (magnitude +0.9, in Virgo) is emerging from the glow of sunrise. Look for it very low in the east about an hour before your local sunrise time. It's within 1° of fainter Gamma Virginis.

    Uranus (magnitude 5.7) is 2½° to 3° east of Jupiter this week.

    Neptune (magnitude 7.8, in Capricornus) is 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 Sagittarius) is sinking in the southwest 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.

    To be sure to get the current Sky at a Glance, bookmark this URL:
    http://SkyandTelescope.com/observing/ataglance?1=1

    If pictures fail to load, refresh the page. If they still fail to load, change the 1 at the end of the URL to any other character and try again.

    • About Alan MacRobert

    Alan M. MacRobert became an avid Sky & Telescope subscriber in 1966 at age 14, joined the editorial staff in 1982, and is now a senior contributing editor, semi-retired. He played a role in practically every part of the magazine and the company's other products for more than a generation, both on the amateur-observing side and the science-reporting side. In 1994 a book collection of his observing how-tos and telescopic sky tours was published as Star Hopping for Backyard Astronomers. He has produced This Week's Sky at a Glance online every week since 1989.

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