Twilight view

The waxing crescent Moon is passing the Mars-Antares pairup. The visibility of faint objects in bright twilight is exaggerated here. (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.)

Sky & Telescope diagram

Friday, Oct. 12

  • Telescope users: Jupiter's Great Red Spot (currently pale orange-tan) should cross the planet's central meridian tonight around 12:47 a.m. Saturday morning EDT. Jupiter will be high up by then for eastern and central North America.

    Saturday, Oct. 13

  • Now that it's mid-October, Deneb has replaced Vega as the zenith star after dark (for skywatchers at mid-northern latitudes) — and accordingly, Capricornus is replacing Sagittarius as the most notable constellation low in the south.

    Sunday, October 14

  • Jupiter's moon Io disappears into eclipse by Jupiter's shadow, barely west of the planet, around 1:51 a.m. Monday morning EDT; 10:51 p.m. Sunday evening PDT. By then Jupiter's Great Red Spot will be nearing the planet's central meridian — which it crosses about 19 minutes later.

    Monday, October 15

  • This week the time of year when the W shape of Cassiopeia is tipping nearly vertically in the northeast after dusk. It stands exactly vertically around 9 or 10 p.m., depending on your location. The W's brightest side is on top.
  • New Moon (exact at 8:03 a.m. EDT).

    Tuesday, October 16

  • A twilight challenge: Use binoculars to look for Mercury and the hairline crescent Moon very low in the west-southwest shortly after sunset.

    Wednesday, October 17

  • Jupiter, Aldebaran, Beta Tauri, and the Hyades and Pleiades adorn the eastern sky this season, but that's not all. Below naked-eye visibility in the same area are the leading asteroids Vesta and Ceres, currently magnitudes 7.5 and 8.3, respectively. Find them with a small telescope or good binoculars using the finder chart on page 51 of the October Sky & Telescope. They're on their way to opposition in December.

    Totally invisible between them is NASA's Dawn spacecraft, which left Vesta earlier this year and will arrive at Ceres in February 2015.

    Thursday, October 18

  • The waxing crescent Moon poses over Mars and Antares low in the southwest in twilight, as shown above.

    Friday, October 19

  • The annual Orionid meteor shower should be getting under way in the hours before dawn Saturday morning. You might see 10 or 20 Orionids per hour during that time of night for the next several days. There will be no moonlight. The shower's radiant point is at the top of Orion's Club, which doesn't rise high until the early-morning hours.

    Saturday, October 20

  • As twilight fades this evening, Mars and Antares, similar in color and brightness, are at their minimum separation of 3½°. Look for them quite low in the southwest. Mars is the one on the upper right.

    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 guide to 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'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope effectively.

    You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the classic if dated Burnham's Celestial Handbook.

    Can a computerized telescope replace charts? Not for beginners, I don't think, and certainly not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability). As Terence Dickinson and Alan Dyer say in their invaluable 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

    Jupiter on Oct. 7, 2012

    Jupiter's Great Red Spot had just crossed the planet's central meridian when Jim Phillips in South Carolina took this image on October 7th. South is up. Red Spot Junior (Oval BA), with a small very dark spot just behind it, has finished passing south of the Great Red Spot with no apparent effect on any of them. Intense turbulence continues on the following side of the Great Red Spot. Below center, the North Tropical Zone has rebrightened to once again separate the tan North Equatorial Belt from the North Temperate Belt. The bright point is Io.

    Jim Phillips

    Mercury (magnitude –0.2) is deep in the sunset. Using binoculars, try scanning for it about 30 minutes after sundown very low in the west-southwest. This will be a poor apparition of Mercury. It stays lying low there for a month, then drops back into the Sun's glare.

    Venus (magnitude –4.0, in Leo) rises in darkness around 4 or 5 a.m. daylight saving time (depending on where you live), coming above the eastern horizon more than an hour before the first glimmer of dawn. By dawn it's shining brightly in the east. Look increasingly far above it for Regulus this week, as shown at the top of this page.

    Mars (magnitude +1.2, in Scorpius) remains low in the southwest in evening twilight, close to twinklier orange Antares ("Anti-Mars") to its left or lower left. The gap between them shrinks from 7° to 3½° this week. They're nearly the same brightness.

    Jupiter (magnitude –2.6, in Taurus) rises in the east-northeast around 9 p.m. daylight saving time. Once it's clear of the horizon, look for fainter orange Aldebaran twinkling 7½° to its right and Beta Tauri (Elnath) a little farther to Jupiter's left. By dawn this lineup-of-three stands high and vertical in the southwest.

    Saturn is lost in the sunset.

    Uranus (magnitude 5.7, at the Pisces-Cetus border) and Neptune (magnitude 7.8, in Aquarius) are in the southeast to south during evening. Finder charts for Uranus and Neptune.

    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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