September 2009
Skywatchers’ Guide for September 2009
PLANETS
HIGHLIGHTS: Bright Jupiter dominates the evening sky as the brightest star like object visible this month in the evening hours. More brilliant Venus is in the morning sky, with the bright winter constellations. September is a great month for sporadic or chance meteors (shooting stars) and the Milky Way is prominently visible after sunset in reasonably dark skies away from city lights. The fall or autumnal equinox occurs for Tucson and much of Arizona in the afternoon hours of Tuesday, September 22.
Bright Jupiter continues to gain altitude in the evening southeastern sky. Because Jupiter was at opposition last month (opposite from the Sun in the sky, and rose at sunset on August 14) it is high enough for quality telescopic viewing starting 2.5 hours after sunset in early September, and during twilight in late September. Also up to four of its bright Moons can be seen in binoculars. Jupiter is setting earlier each morning: In early September the giant planet sets by 4:15 a.m. above the western horizon but by 2:15 a.m. on Sept. 30. Jupiter was impacted on July 19 by a small asteroid or comet (the first such impact since the Shoemaker-Levy Comet of 1994, discovered by Flandrau Adjunct Scientist David Levy), but the impact (a smear as of early August) should have faded from view by September.
Jupiter is in the same wide binocular field (5 degrees wide) with very faint, bluish Neptune at the start of September. However the two are moving apart in our sky and separate to 7 degrees apart by the end of September. Jupiter and Neptune are both located in the constellation of Capricornus, the Sea Goat. The nearly full waxing gibbous Moon will rise closest to Jupiter above the east-southeastern horizon on the evening of September 2.
The best views of any planet should be when it is highest in the sky, but viewing of Jupiter, its cloud belts, and festoons is dependent on atmospheric stability and conditions, and of course, the quality and size of the telescope used. Large, high quality amateur telescopes in good “seeing” (stable atmospheric conditions) will best reveal any features on a planet’s disk. However to view Jupiter’s moons, a good pair of binoculars is all that’s needed.
The brilliant planet Venus is losing altitude this month, moving from Cancer, the Crab into Leo, the Lion. At the start of September it’s about 18 degrees above the eastern horizon, 1 hour before sunrise, but sinks to 12 degrees in altitude by September 30. Venus moves near the Beehive Cluster in Cancer, the Crab around 2 hours before sunrise on September 1-2. Also, look for the waning crescent Moon (27 days old) nearest Venus in our sky on Wednesday, September 16.
Mars, now near 1st magnitude in brightness, lies some 32 degrees to the west of Venus on September 1. The two drift farther apart each day so that Mars is overhead by the end of September with Venus far away above the eastern horizon. Mars is still a long ways off from Earth (hence its faintness compared to Venus) and so continues to be an unremarkable object in a telescope. The waning crescent Moon is nearest Mars this month in the morning sky of Sunday, September 13.
Mercury and Saturn are both invisible due to the glare of the Sun during much of September. By the end of the month Mercury might be visible in binoculars just a few degrees above the eastern dawn horizon, 45 minutes before sunrise (Saturn will lie below Mercury, and is still too close to the Sun to spot easily in binoculars). Look for these two planets to group with Venus above the eastern dawn horizon later in October.
Visitors to Flandrau’s 16-inch telescope should note that Jupiter is visible in the telescope during the later public hours. Other celestial objects will be shown in the telescope, weather permitting. Although Flandrau’s main exhibit hall and planetarium is now closed to the general public due to state budget cuts, school groups can arrange for field trips and the Mineral Museum is open Friday and Saturdays from 9:00 a.m. to 5:00 p.m. (and by appointment). Our Observatory remains open for viewing during public hours from 7-10 p.m., weather permitting, Wednesday through Saturday nights (excluding select holidays). Finally, remember that in spotting planets there is a general rule: ’stars twinkle, planets don’t’. This is because stars are point sources of light; therefore starlight is easily disturbed and shifted by air currents in the Earth’s atmosphere. However when looking at Mercury or Mars this month, note that they appear to twinkle somewhat; however, this twinkling is of a slower nature than that of the bright stars.
SEPTEMBER EVENING STARS
 This chart shows the sky overhead around the Summer Triangle for much of the first half of the night in September.  The Big Dipper will start to sink from view as seen from southern Arizona by around 9:30 p.m. in middle September. This chart shows the northwestern and northern sky at 9 p.m. in early September, and at 8 p.m. in mid September from the Desert Southwest. |
This chart shows the southern evening sky for much of the USA in early September at 8:30 p.m. and in middle September at 7:30 p.m. (MST) This sky chart is useful throughout all of the southern USA and northern Mexico. This chart shows the sky overhead around the Summer Triangle for much of the first half of the night in September. The Big Dipper will start to sink from view as seen from southern Arizona by around 9:30 p.m. in middle September. This chart shows the northwestern and northern sky at 9 p.m. in early September, and at 8 p.m. in mid September. This sky chart is useful throughout the USA, and northern Mexico and southern Canada.
September evenings are an excellent time to see the bright constellations of the summer months (especially Scorpius and Sagittarius), along with the Milky Way. To see the brightest areas of the Milky Way in the south, look before 10 p.m., as the star rich regions in Scorpius and Sagittarius start to lose altitude in Arizona skies early. Start by finding the brightest star in Scorpius: Antares. These evenings, its orange-red twinkling enlivens the southern sky, giving reason to its name “the rival of Mars”. From the southern United States Antares does not get very high, only about 30 degrees (or three fists held at arm’s length) above the southern horizon, because of its position in the southern sky. Antares is the brightest part of a most impressive scroll of stars, sort of like a long letter “S” fallen halfway forward. And in this case the “S” stands for the constellation it is part of: Scorpius, the Scorpion.
To the ‘left’ or east of Scorpius is the “Teapot” of Sagittarius. Not technically a constellation, the Teapot is actually part of the larger constellation Sagittarius, the Archer. Like steam emerging from the spout of a real teakettle, look for bright portions of the Milky Way off the spout of the Teapot. This region marks the central area of our galaxy and is fascinating to scan in binoculars. High power binoculars and telescopes reveal the Milky Way to be clouds of stars, millions of them, with attendant star clusters and gas clouds making up some of the “fuzzier” spots you’ll see.
Overhead in the September evening sky look for the bright stars of the Summer Triangle: Vega, Deneb, and Altair. Each night every September the widely spaced triangle of Vega, Deneb, and Altair brighten the evening sky. Vega, Altair, and Deneb are each the brightest stars of three constellations that make up the Summer Triangle. Vega is the brightest star in the small constellation of Lyra, the Lyre (a small ancient harp). Vega, one of the closer stars to Earth (only 25 light years away), was the Pole Star (our North Star) some 12,000 years ago, and will again be the North Star in 12,000 A.D. when Earth’s cyclical wobbling motion brings in near the pole once more. Deneb is the tail of Cygnus the Swan, but also marks the bottom of the cross-shaped pattern whose other name is the Northern Cross. Deneb is a huge super-giant star over 1,600 light years from Earth. Aquila, the Eagle, is the home of the bright star Altair, the first star of the three in the triangle to set late at night and the closest of the three to Earth at only 16 light years distant. Aquila looks more like a diamond or kite than an Eagle. Aquila and Cygnus (or the Northern Cross) mark some of the brightest areas of the northern Milky Way.
The Big Dipper sets early in September, low in the northern half of the evening sky. Look for the Big Dipper low in the north starting 1 hour after sunset. Take the two end stars off of the bowl (the ‘pointer stars’) and point down to Polaris, the North Star. Polaris is a star of ordinary brightness, and marks the end of the handle of the Little Dipper. Polaris can also be found about 30 degrees (or 3 fists) above the northern horizon. Polaris stays put in the sky; to the eye it doesn’t appear to move. This is because Earth’s axis is pointed toward Polaris in space.
The Milky Way Prominent into the Late Night Hours!
The brightest portions of the Milky Way are near the Teapot of Sagittarius and Scorpius, the Scorpion. Sky chart valid around 8:30 p.m. in early September 2009 and at 7:30 p.m. (MST) in middle September from Arizona.
Look for the Milky Way after the end of evening twilight on moonless September evenings, as its brightest portions ride high in the southern sky. You’ll need to look right after the end of evening twilight as these bright regions of our home galaxy (around the constellation Scorpius, the Scorpion) set early. The Milky Way, the galaxy of stars, gas and dust our solar system resides in, is prominent all summer long, but its brightest portions in Scorpius and Sagittarius are best seen around 8 p.m., through 9 p.m. in September when they are highest in the sky. Additional bright portions can be seen overhead into the late night hours around the ‘Summer Triangle’ of bright stars: Vega, Deneb, and Altair. To see the Milky Way, you’ll need to get away from city lights to a dark location, and look on a night when there’s not much interference from the moon. Our home galaxy will appear as a “cloudy” band stretching clear across the sky. High power binoculars and telescopes reveal the Milky Way to be clouds of stars, millions of them, with attendant star clusters and gas clouds making up some of the “fuzzier” spots you’ll see.
September 22nd marks the Autumnal Equinox, The Start of Autumn for Arizona
Fall begins for Tucson and much of Arizona in the afternoon hours of Tuesday, September 22 at 2:19 p.m. MST (Mountain Standard or Tucson time), as the sun, in Virgo, stands directly overhead from the equator at noon. Fall now begins for the northern hemisphere (and spring for the southern hemisphere) as the Sun heads south of the equator, losing altitude in our northern hemisphere sky.
MOON PHASES
The September Full (Fruit/Harvest) Moon will rise on the evening of Friday, September 4 and set on the morning of Saturday, September 5. The September last quarter Moon occurs on Friday morning September 11. The September new moon occurs on Friday, September 18. The September 2009 first quarter Moon will occur on Friday evening, September 25.
Note: Additional information can be accessed by phone at Flandrau Science Center’s Astronomy Newsline at (520) 621-4310 or as a menu option at 621-S-T-A-R.
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