September 2007
Skywatcher’s Guide for September 2007
PLANETS
Bright Jupiter is still visible in the September sky, but is losing altitude in our evening sky. Jupiter appears as a very bright, almost brilliant white star-like object, above the south-southwestern horizon in the early September evening twilight. By late September Jupiter moves lower into the southwestern sky and by late October Jupiter sets fairly early above the southwestern horizon. Sinking in altitude this month, Jupiter sets above the southwestern horizon by 11:20 p.m. in early September, by 10:20 p.m. in middle September, and by 9:40 p.m. in late September (all times Mountain Standard or MST). To find Jupiter simply look for a very bright white star-like object above the south-southwestern horizon at 8 p.m. The largest planet in our solar system, Jupiter is the brightest star-like object most often seen in the night sky, although Venus is substantially brighter, and Mars can be brighter every 15 years or so. The giant gas world, although dimmed somewhat from June, remains very bright in the skies of Earth all month long. When looking at Jupiter in a telescope to view its cloud belts and festoons, the sharpest views should be in bright evening twilight, when it’s highest this month. As with any planet, viewing is dependent on atmospheric stability and conditions, and of course, the quality and size of the telescope used. However to view its moons, a good pair of binoculars is all that’s needed. Finally, the waxing crescent Moon can be seen well below Jupiter on the evenings of September 17 and 18.
Mars continues to brighten and is approaching zero magnitude in brightness by middle September. Mars is 0.1 magnitude and almost 9 arc seconds in diameter by September 15, so it’s worth looking at in high quality telescopes at high power. Mars is now overhead, at about 70 degrees in altitude, one hour before sunrise and drifts eastward from Taurus the Bull and into Gemini, the Twins this month into next. Mars is rising now above the east-northeastern horizon at around 11:15 p.m. in middle and late September. On the morning of Sept 4. the last quarter Moon will be found not far, and north of Mars in our sky after midnight.
Currently a Mars hoax e-mail might still be found making its way around the Internet, stating that Mars will be at its closest to the Earth in 60,000 years. Please go to our Mars hoax news story for more information.
The brilliant planet Venus is our ‘morning star’ this month in the east and gains altitude rapidly in the pre-dawn twilight. It rises about 90 minutes before the Sun does in early September but over 3.5 hours before the Sun by the end of the month. As Venus is now receding from Earth it slowly shrinks in apparent size in a telescope and its thin crescent now thickens. To the unaided eye Venus appears as an intensely bright white star that does not twinkle and is found fairly low in early September above the eastern horizon in the bright dawn twilight. By late September Venus is high above the eastern horizon, 45 minutes before sunrise. The thin waning crescent Moon is north (left) of Venus on September 10 but is found closest to Venus (and Saturn) and above it on Sunday morning, September 9.
Saturn emerges from the glare of the Sun in the morning twilight above the eastern horizon in mid to late September as a slightly brighter than 1st magnitude star-like object. It may be visible in bright twilight by September 8, 45 minutes before sunrise, just a few degrees above the eastern horizon. Located in Leo the Lion and near its bright star Regulus, Saturn rises earlier and creeps higher above the eastern horizon in September. Saturn is found far below Venus, not far above the eastern horizon in the morning twilight, starting 45 minutes before sunrise. The thin waning crescent Moon is found closest to Saturn and above it on Sunday morning, September 9 (binoculars might be needed to spot Saturn).
Mercury is currently lost in the glare of the Sun and not easily visible to the naked eye in the northern hemisphere.
Visitors to Flandrau’s 16-inch telescope should note that only Jupiter is visible when the telescope opens at 7 p.m. during early September. Jupiter is too low in our sky for viewing by 8:30 p.m. mid-month, so visitors should come see it by 7:30 or 8 p.m. Otherwise, no planets are currently visible in the telescope during normal operating hours. The telescope normally closes at 10 p.m.
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 right now, note that it may appear to twinkle somewhat; however, this twinkling is of a slower nature than the bright stars.
Aurigid meteors may shower
 The Aurigid meteors appear from a point not far from the bright star Capella. Sky is shown for 4:45 a.m. (MST) on Sept. 1. |
The little known Aurigid meteor shower is predicted to outburst by meteor astronomers Peter Jenniskens (SETI Institute’s Carl Sagan Center), Jérémie Vaubaillon (Caltech) and meteor astronomer Esko Lyytinen of Finland, near the start of dawn twilight for Arizona on September 1. Dr. Jenniskens predicts the Aurigid meteor shower may have a very brief one hour burst of activity especially favored for western North America (Hawaii is less favored) of about 20 to 30 bright meteors per hour or more on the morning of Saturday September 1st, starting around 4 a.m. Dr. Lyytinen predicts possibly 100 or more meteors per hour, with a peak at 4:20 a.m. while Dr. Jenniskens’ predicted peak is at 4:37 a.m. (all times MST). Any predicted peak may be off by at least 30 minutes, so meteor gazers should start observing at 3:30 a.m. to make sure they see any shooting star show that occurs. Sunrise for most parts of Arizona is at 5:59 a.m. (MST), so the shower can be seen well until around 4:50 a.m. with most bright meteors still easily visible until around 5:15 a.m.
Usually the Aurigids are a minor meteor shower ignored by the general public and most astronomers, and only produce 2-5 meteors per hour. In fact so few astronomers have observed Aurigid outbursts, the only outbursts of the shower seen were in 1935, 1986 and 1994. Also, some astronomers are skeptical that the Aurigids will shower earth with bright meteors: World famous comet hunter and Flandrau Adjunct Scientist David Levy remarks he is ‘mildly skeptical’ about a bright outburst of Aurigid meteors. However, there’s no way to know for sure beforehand if Earth will run into the main stream of rubble particles (which also orbit the Sun in our solar system). The meteor particles causing this annual shower that Earth will run into are from the lengthy debris tail of Comet Kiess, which last passed by the Sun in 1911. Size estimates usually given of most meteor shower particles are as small dust sized grains (not typically visible), to pea or pebble sized rocky material.
If there is an Aurigid meteor shower outburst, meteors are expected to be as bright as the brightest stars in the sky (magnitude 0) with some as bright as -2.0 (or about as bright as the planet Jupiter). Many meteors should therefore be visible through the bright moonlight that morning, weather permitting. The waning gibbous Moon, at 79 percent lit, means that a dark sky won’t be possible for any shower that may occur. However, as with most night sky events, an area away from localized light sources and light pollution should be sought out by anyone attempting to see a meteor shower, to get the best view possible. To see the shower simply look overhead and also slowly scan the sky high above the eastern and northern horizons. Meteors will appear to originate from a point near Capella, the bright winter star of Auriga the Charioteer. Meteors will appear to originate from a point near Capella, the bright winter star of Auriga the Charioteer.
SEPTEMBER STARS
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 o0 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!
Look for the Milky Way after the end of evening twilight on moon-less 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.
Sept. 23rd marks the Autumnal Equinox, The Start of Autumn for Arizona
Fall begins for Tucson and much of Arizona in the pre-dawn hours of Sunday Sept. 23 at 2:54 a.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 last quarter Moon will occur on Tuesday morning, September 4th, when it can be found not far, and north of Mars in our sky after midnight. The September new moon occurs on the night of September 10 into September 11. The September first quarter Moon will occur on Wednesday evening, September 19th. The Full Harvest Moon occurs on the night of Wednesday, September 26.
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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