Some daily events in the changing sky for October 16 – 24.

Say hello this week to the Moon coming up from its monthly conjunction with the Sun, and goodbye to Antares disappearing down toward its own conjunction.

Sky & Telescope diagram


Friday, October 16

  • The Great World Wide Star Count continues through this week. Go outside, follow the directions to estimate how dark your sky is, and enter it into a worldwide database — it's fun!
  • Look very high to Jupiter's upper right during evening this week for bright Altair. Look from Jupiter in the opposite direction for Fomalhaut on the rise. Both are near stellar neighbors, as stars go; Altair is 17 light-years from Earth, and Fomalhaut is 25. Jupiter, by comparison, is currently 37 light-minutes from Earth.
  • The Orionid meteor shower continues! Will it still be going tonight during the good Orionid-watching hours, from midnight or 1 a.m. until dawn Saturday morning? Check the International Meteor Organization's activity profile of the shower, compiled from early reports of amateurs' observations.

    Saturday, October 17

  • New Moon (exact at 1:33 a.m. Sunday morning EDT).
  • During or just after dusk for eastern North America, Jupiter's moon Io occults Europa partially — from 7:01 to 7:07 p.m. EDT.

    (For a complete list of such mutual events among Jupiter's satellites visible from North America through the end of the year, see the October Sky & Telescope, page 56.)

  • 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) at midnight tonight EDT; 9:00 p.m. 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.

    (The Red Spot transits about every 9 hours 56 minutes; 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 2009.)

    Sunday, October 18

  • The Orionid meteor shower is active in the early mornings this week, probably peaking on the morning of Wednesday the 21st. The Moon is out of the sky. This could be a good year for the shower; the Orionids show signs of a 12-year periodicity (unrelated to their longer orbital period), and 2009 is at the top of this cycle assuming it continues. Under a dark sky you might see up to 30 meteors per hour in the hours before dawn — but no guarantees.
  • The bright eclipsing variable star Algol should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 2:49 a.m. Monday morning EDT; 11:49 p.m. Sunday evening PDT. Algol takes several additional hours to fade and to rebrighten. Use our comparison-star chart.

    Monday, October 19

  • Watch Jupiter's moon Ganymede gradually reappear out of eclipse from Jupiter's shadow, just east of the planet, around 8:23 p.m. EDT. (For a list of all such events among Jupiter's moons this month, good worldwide, see the October Sky & Telescope, page 58.)
  • By mid-evening in mid-October, the eastern sky displays harbingers of the winter constellations to come. By 9 p.m. Capella and the stars of Auriga sparkle in the northeast — including Epsilon Aurigae, which is now dimming slightly into eclipse for first time in 27 years. See the illustration below.

    Eastward late-evening view

    The Pleiades and Aldebaran shine in the east these evenings, and Capella sparkles in the east-northeast. To Capella's right are the three moderately dim stars called "the Kids" (as in baby goats; Capella is the Goat Star). One of them, Epsilon Aurigae, has begun to fade into its much-awaited, two-year-long partial eclipse. See our article with a comparison-star chart, and our big feature on this mysterious star in the May Sky & Telescope, page 58.

    Sky & Telescope diagram


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    Tuesday, October 20

  • Jupiter's Great Red Spot should transit around 9:30 p.m. EDT.

    Wednesday, October 21

  • After sunset, look very low in the southwest for the waxing crescent Moon. Can you still see the summer star Antares sparkling redly to its lower right? The farther south you are, the higher they will appear. Binoculars will help. See the illustration at the top of this page. (Like all these scenes, it's drawn for latitude 40° north).
  • Algol should be at minimum light for a couple hours centered on 11:37 p.m. EDT.

    Thursday, October 22

  • During early evening for the East Coast of North America, and late at night for westernmost Europe, Jupiter's moon Ganymede occults Io partially, from 7:12 to 7:17 p.m. EDT (23:12 to 23:17 UT).
  • Jupiter's Great Red Spot should transit around 11:09 p.m. EDT.

    Friday, October 23

  • During early evening for eastern North America, Jupiter's moon Ganymede occults Europa partially, from 8:31 to 8:40 p.m. EDT.

    Saturday, October 24

  • The Ghost of Summer Suns. Halloween is approaching, and this means that Arcturus, the star sparkling low in the west-northwest in twilight, is taking on its role as "the Ghost of Summer Suns." What does this mean? For several days every year around October 29th, Arcturus occupies a special place in the sky above your local landscape. It closely marks the spot where the Sun stood at the same time (by the clock) during warm June and July — in broad daylight, of course. So at this season every year, you can think of Arcturus as the chilly Halloween ghost of the departed summer Sun.
  • Algol should be at minimum light for a couple hours centered on 8:26 p.m. EDT.
  • Jupiter's moon Io occults Europa partially from 9:19 to 9:24 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'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

    Venus, Mercury, and Saturn are low in the east during dawn, changing configuration daily. Venus is by far the brightest. Mercury is barely above the horizon below Venus and may be gone from sight by week's end. Saturn just had a close conjunction with Venus (on October 13th) and now climbs higher to the bright planet's upper right. Look carefully; Saturn (magnitude +1.1) is only a hundredth as bright as Venus (magnitude –3.9). Binoculars help as dawn grows bright.

    Mars (magnitude +0.6, in Cancer) rises around midnight and is very high in the southeast before dawn. It's below Gemini's head stars, Pollux and Castor. In a telescope Mars is still only 7.2 arcseconds wide: a tiny, fuzzy blob, though noticeably gibbous. Mars is on its way to an unremarkable opposition late next January, when it will be 14.1 arcseconds wide.

    On this side of Jupiter away from the Great Red Spot, the South Equatorial Belt (dark band above center) is straight, double, and fading. The North Equatorial Belt is darker and busier. The black dot is the shadow of Io. Note the small red oval in the north edge of the NEB just past (left of) the central meridian. It used to be white but picked up dark material from the belt. South is up.

    Christopher Go took this image on October 25th at 11:12 UT, when the System II longitude on the central meridian was 10°. The Great Red Spot follows behind by 3½ hours, at about longitude 138° (in the south edge of the SEB).

    Stacked-video images like this show more detail than you're ever likely to see visually on Jupiter. For all of the Great Red Spot's central-meridian crossing times, good worldwide, use our Red Spot calculator, or print out our list for the rest of 2009.

    Christopher Go

    Jupiter (magnitude –2.6, in Capricornus) shines brightly in the south in early evening and lower in the southwest as night grows late. It sets around 1 or 2 a.m.

    Uranus (magnitude 5.7, below the Circlet of Pisces) is well up in the southeast to south during evening.

    Neptune (magnitude 7.9, in Capricornus) is about 7° east of Jupiter.

    See our finder charts for Uranus and Neptune. For a guide to spotting the challenging satellites of Uranus and Neptune at any date and time (you'll need a big scope), see the October Sky & Telescope, page 59.

    Pluto (14th magnitude, in Sagittarius) is sinking low in the southwest after dark.

    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.

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

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    • 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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