Some daily events in the changing sky for September 11 – 19.

Mars and the waning Moon shine in the early-morning hours. (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, Sept. 11

  • Last-quarter Moon (exact at 10:16 p.m. Eastern Daylight Time). After the Moon rises around the middle of the night tonight, you'll see it shining between Beta and Zeta Tauri, the Bull's horn-tips, as shown at right.
  • Jupiter's Great Red Spot should transit tonight around 12:15 a.m. Eastern Daylight Time; 9:15 p.m. Pacific Daylight Time.
  • Jupiter's moon Io reappears out of eclipse just off the planet's eastern limb at 10:53 p.m. EDT. Later Europa reappears out of eclipse, at 1:12 a.m. EDT.

    Saturday, Sept. 12

  • Jupiter's Great Red Spot should transit around 8:06 p.m. EDT.
  • The Moon shines over Mars in the early-morning hours of Sunday, as shown at right.
  • Just before the first light of dawn Sunday morning, the asteroid 4 Vesta (magnitude 8.4) is passing 1/3° south of the star 35 Cancri (magnitude 6.5) next to the Beehive Cluster. Meanwhile, Venus shines to the lower left of this scene, low in the east.

    You can always find your local sunrise and start-of-dawn times, and much else, once you put your location into our online almanac. (If you're on daylight saving time like most of North America, make sure the Daylight Saving Time box is checked.)

    Sunday, Sept. 13

  • Jupiter's big moon Ganymede emerges out of eclipse from Jupiter's shadow around 12:18 a.m. Monday morning EDT (9:18 p.m. Sunday evening PDT). A small telescope will show it swelling into view just east of the planet.

    For a timetable of Jupiter's satellite phenomena throughout September, good worldwide, see the September Sky & Telescope, page 56.

    Monday, Sept. 14

  • As the stars come out this week, you'll now find Cassiopeia as high in the northeast as the Big Dipper is in the northwest.
  • Jupiter's Great Red Spot should transit around 9:45 p.m. EDT.

    Looking east in early dawn

    Watch the waning Moon pass Venus at dawn, while Regulus approaches Venus from below. (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.)

    Sky & Telescope diagram

    Tuesday, Sept. 15

  • Two mutual events occur tonight between Jupiter's moons Io and Europa. From 8:41 to 8:51 p.m. EDT, Io occults Europa partially. Then from 10:12 to 10:19 p.m. EDT, Io's shadow eclipses Europa partially, dimming it by 86%.

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

  • Before and during dawn Wednesday morning, look low in the east for Venus near the thin waning crescent Moon, as shown at right.
  • Also before dawn Wednesday, Vesta (magnitude 8.4) is skimming the southern edge of the Beehive Cluster.
  • And if you're out before dawn, don't forget to look for the zodiacal light (the "false dawn") towering up at an angle in the east.

    Wednesday, Sept. 16

  • Bright Vega shines just west of the zenith after dark. Arcturus, equally bright, shines moderately low in the west. A third of the way from Vega down to Arcturus is the dim Keystone of Hercules. Two-thirds of the way down, look for the mostly-dim semicircle of Corona Borealis.
  • Jupiter's Great Red Spot should transit around 11:23 p.m. EDT.

    Bright Venus and much fainter Regulus pair up closely on the morning of Sunday the 20th. Bring binoculars.

    Sky & Telescope diagram

    Thursday, Sept. 17

  • Uranus is at opposition, opposite the Sun in the sky.

    Friday, Sept. 18

  • New Moon (exact at 2:44 p.m. Eastern Daylight Time).
  • Jupiter's Great Red Spot should transit around 1:01 a.m. Saturday morning Eastern Daylight Time; 10:01 p.m. Friday evening Pacific Daylight Time.

    Saturday, Sept. 19

  • Jupiter's Great Red Spot should transit around 8:52 p.m. EDT.
  • As dawn begins to break on Sunday morning, use binoculars to examine Venus low in the east. Sparkling just ½° from it is 1st-magnitude Regulus, less than 1% as bright, as shown here.

    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 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

    Mars on Sept. 2, 2009

    It's starting to be Mars season again — barely. The planet is high in the morning sky but only 6 arcseconds wide. Nevertheless, S&T's Sean Walker managed to record some surface detail on the morning of September 2nd. The dark area at top includes Mare Sirenum and Mare Cimmerium. The small spot just upper left of center is Phoenicis Lacus. Note the north polar haze. South is up. Walker used a 12.5-inch reflector and IRGB color filters for this stacked-video image.

    S&T: Sean Walker

    Mercury is hidden in the glare of the Sun.

    Venus (magnitude –3.9, in Leo) shines low in the east before and during dawn. Look for Regulus, much fainter, below it. Regulus climbs closer to Venus each morning; they'll have a close conjunction on the 20th.

    Mars (magnitude +0.9, in Gemini) rises around 1 a.m. and is high in the east before dawn. In a telescope it's still only 6 arcseconds wide: a tiny, fuzzy blob, though noticeably gibbous. Mars is on its way to an unremarkable opposition late next January, when it will grow no larger than 14 arcseconds wide.

    Jupiter (magnitude –2.8, in Capricornus) comes into view in the southeast as twilight fades — the first "star" to appear after sunset. It's higher in better telescopic view by 9 or 10 p.m. Jupiter shows more observable apparent surface area (square arcseconds) than all the other planets combined.

    July's impact mark on the planet has faded from view; see our article.

    Jupiter on the evening of Sept. 2, 2009

    This year, Jupiter's Great Red Spot has been nicely bordered by the thick white line of the Red Spot Hollow, which indents the dark South Equatorial Belt. Note the very dark red barge following behind the pale Red Spot. The North Equatorial Belt is full of turbulence, including a big blue plume. Far to the right (celestial east), Ganymede and Europa are in conjunction. S&T's Sean Walker took this image at 1:15 UT September 3, 2009. South is up. Stacked-video images like this show much more detail than you're ever likely to see visually on Jupiter.

    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.

    S&T: Sean Walker

    Saturn is hidden behind the glare of the Sun.

    Uranus (magnitude 5.7, just below the Circlet of Pisces) is well up in the southeast by 10 p.m.

    Neptune (magnitude 7.8, in Capricornus) appears 6° east of Jupiter — and nearly 20,000 times fainter. See our finder charts for Uranus and Neptune.

    Near Uranus is the asteroid 3 Juno, now close to opposition at magnitude 7.6. This is the brightest Juno will become until 2018! See the chart in the September Sky & Telescope, page 55.

    Pluto (14th magnitude, in northwestern Sagittarius) is still well up in the south-southwest right after dark. See the finder chart in the June Sky & Telescope, page 53. Good luck.

    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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