August 2009 (update 5)
Skywatchers’ Guide for August 2009
HIGHLIGHTS: The Perseid meteor shower peaks on August 11-13, with bright meteors visible through moonlight. Saturn is losing altitude in the western evening twilight, with last chance viewing of its rings edge-on. Starting Aug. 10 the Sun passes through the ring-plane of Saturn allowing for a rare ‘dark line’ view of the rings. Jupiter, recently impacted by a comet or asteroid, is at opposition on August 14, when it’s visible all night long. Around this date Jupiter is near its brightest and largest in a telescope this year. Two bright planets, Venus and Mars, are widely spaced in the eastern half of the morning twilight sky. Jupiter, during the first half of the month, is also visible in the morning twilight above the western horizon.
PLANETS
 This sky chart shows Saturn and Mercury in the western evening twilight about 55 minutes after sunset at 8:10 p.m. on August 5 (All times Mountain Standard-MST).  This sky chart shows Jupiter and the Moon on August 5-6 at 8:30 p.m. This sky chart is also useful throughout much of North America during early and mid-August around 8:30-9:30 p.m.  This sky chart shows Venus, Mars and the Moon on August 18 about 1 hour before sunrise (or about 4:45 a.m. MST for the Desert Southwest). The Moon is also shown for Aug. 17. |
Early August 2009 offers the last chance evening telescope views of Saturn this year with unusual views of its ring system edge-on. The ringed planet sets early, and is only 10 degrees above the western horizon one-hour after sunset on August 5. By the second half of August Saturn sinks near the horizon and near elusive Mercury. Saturn moves into the glare of the Sun during the last week of August. The young 2 day old waxing crescent Moon will lie nearest (but 9 degrees to the southeast) of Mercury on August 22. Saturn and Mercury will lie both just four degrees above the horizon that same evening, 45 minutes after sunset (at 7:45 p.m. for southern Arizona). Starting Aug. 10 the Sun passes through the ring-plane of Saturn allowing for a rare, but difficult to see ‘dark line’ view of the rings. After August 10 the rings will be difficult to see, if at all, because Saturn is so near the horizon.
Bright Jupiter continues to gain altitude and rise early by 8:15 p.m. during the first week of August in the southeastern sky. Then, on August 14, Jupiter is at opposition (opposite from the Sun in the sky) when it rises at sunset and is visible all night long. Around this date Jupiter is also near its brightest and largest in a telescope this year. Jupiter is high enough for quality telescopic viewing starting 2.5 hours after its rise time, while up to four of its bright Moons can be seen in binoculars. All August long the giant planet is also easily seen over one hour before sunrise, just above the western horizon. Jupiter has recently been impacted 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 is difficult to see in high quality amateur telescopes. Jupiter is in the same low power telescope field (2 degrees wide) with faint, bluish Neptune at the start of August. However the two are moving apart in our sky and separate to a binocular field apart (at 4.5 degrees separation) by the end of August. Jupiter and Neptune are both located in the constellation of Capricornus, the Sea Goat, while bluish-green Uranus is some 30 degrees east of Jupiter in Pisces, the Fish. The waning gibbous Moon will rise closest to Jupiter above the east-southeastern horizon on the evening of August 6. The best views of any planet should be when it is highest in the sky, but viewing 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.
The brilliant planet Venus is now at its peak altitude this year, in Gemini, the Twins. At the start of August it’s about 23 degrees above the eastern horizon, 1 hour before sunrise. Venus moves near the Beehive Cluster in Cancer, the Crab around 2 hours before sunrise next month on September 1-2. Faint Mars lies some 17 degrees to the west of Venus on August 1. The two drift farther apart each day to reach 32 degrees apart in our sky by the end of August. Mars is still a long ways off from Earth (hence its faintness compared to Venus) and so is currently an unremarkable object in a telescope. The waning crescent below and nearest Mars this month in the morning twilight of Sunday, August 16. Also, look for the waning crescent Moon (26 days old) above Venus on Monday, August 17, while a thinner 27-day-old Moon will lie below Venus in our sky in the dawn twilight of Tuesday morning, August 18.
Visitors to Flandrau’s 16-inch telescope should note that Jupiter is visible in the telescope during the later public hours, by 9:15 p.m. on August 1 and by 8:30 p.m. on August 12. Saturn will not be visible because it is too low in the sky. 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.
Perseid meteors visible through the moonlight
 The Perseid meteors become visible as the radiant (the path where the meteors seem to originate) rises. This graphic shows the sky on August 11-12, at midnight from the southwestern USA. Planets are not shown. |
The annual Perseid meteor shower, one of the best meteor showers of the year (and the one everyone likes to see), peaks on the nights of August 11-12, 12-13 and 13-14. Perseid meteors can also be seen for the few nights before August 12 and after August 15, but in much reduced numbers.
The best times for highest rates of meteors are predicted to be on the morning of August 12, and the night of August 12-13. This year, the shower is partially washed out by the gibbous Moon that will rise at 10:40 p.m. on the peak evening of August 12, and by 11:25 p.m. on August 13. The large moon this year will brighten the sky in the late night hours, reducing the amount of shooting stars novice stargazers can see in moon-lit skies to maybe 10 or 20 shooting stars an hour from a dark sky location overhead. However, if clear weather is available then look for one of the year’s best annual sky shows starting soon after sunset. If monsoon clouds interfere, viewers will also be able to see meteors in numbers on the nights of August 11th-12th and August 14th-15th, some before the Moon rises, but more in the late night hours when the constellation Perseus (from which the shower is named) is high overhead.
Meteor watchers should seek out a dark sky several miles away from city lights and look high in the eastern and northern sky and overhead after the moon sets. To see the shower well, observers should view in the hours after sunset and before moonrise, far away from city lights. Good locations for viewing include the east end of Speedway at Saguaro National Park East or areas far west of Tucson such as the Tucson mountains and Saguaro National Park West. Observers should expect to drive 30 minutes to out of town, away from city lights, to get good views of the shower. Clear dark sky views without moonlight may reveal upwards of 40 to 50 meteors an hour. Again bright meteors will still be seen through the moonlight, but in much diminished numbers. Meteor watchers should scan the skies to the east, north and overhead. All that’s needed to see the shower are clear skies and a lawn chair.
The next major meteor shower for casual observers, that is visible without interference from moonlight, is the Geminid shower in December (usually peaking on December 13-14 each year). In addition, as in 2006, there’s always the possibility of seeing an Earthgrazing meteor. The best chance to see an Earthgrazing meteor will start near the end of evening twilight (or starting around 8:30 p.m.). For more information on Earthgrazing Perseid meteors see the 2006 NASA news story. Causing the Perseid meteor shower is debris from a comet which last passed Earth in 1992 named Comet Swift-Tuttle. The debris consists of tiny particles of rock, some thinner than a hair and most no larger than a grain of sand. Nearly all the particles of a meteor shower burn up in Earth’s atmosphere. Comets are the source of nearly all meteor showers. Comets are bodies, often potato shaped and less than 6 miles in diameter, made of a loose aggregate of rock and ice that is in orbit around the Sun. As comets come in close to the Sun, they begin to evaporate off dust particles, gases and water vapor, leaving a long tail behind them. This tail leaves a trail of tiny debris in space, which Earth can pass through, resulting in a meteor shower.
AUGUST EVENING STARS
 This chart shows the southern evening sky for much of the USA in early August at 9:45 p.m. (times Mountain Standard-MST), and in mid-August at 8:45 p.m. The Moon is not shown.  This chart shows the sky overhead for much of the night in August, from around 10 p.m. - 4 a.m. in early August, from 9 p.m. - 3 a.m. in mid August, and from 8 p.m - 2 a.m. in late August.  Once bright Arcturus is found “speed on (or ‘spike’) to Spica”. This chart is useful around 9:30 p.m. in early August, and at 8:30 p.m. in mid-August. |
August 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 August evening sky look for the bright stars of the Summer Triangle: Vega, Deneb, and Altair.
Each night every August 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 supergiant 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.
Finally, the Big and Little Dippers are only briefly visible in the August evening sky. The Big Dipper will start to sink from view in from southern Arizona by around 9:30 p.m. in early August. Take the pointer stars and point to Polaris, our North Star (a star of ordinary brightness, but one that hardly moves at all in our sky).
The Milky Way Prominent in the Late Night Hours!
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This chart shows the southern evening sky for much of the USA in early August at 9:45 p.m. (MST), and in middle August at 8:45 p.m. (all times Mountain Standard-MST). The Moon is not shown. |
The summer Milky Way is brightest towards the south in the late night hours in August. This sky chart shows the southern sky from southern Arizona at around 11:30 p.m. in early August, 10:30 p.m. in middle August, and 9:30 p.m. in late August. Look for the Milky Way to rise late on moonless August evenings; It will be brightest around the constellation Scorpius, the Scorpion. The Milky Way, the galaxy of stars, gas and dust our solar system resides in, is prominent all summer long, but is brightest after midnight in August. To see it, 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. The Milky Way 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.
MOON PHASES
The August Full (Red/Sturgeon) Moon will rise near Jupiter on the evening of Wednesday, August 5 and set on the morning of Thursday, August 6. The August last quarter Moon occurs on Thursday morning August 13. The August new moon occurs on Thursday, August 20. The August 2009 first quarter Moon will occur on Wednesday evening, August 26. These dates and times are for southern and central Arizona, and are not necessarily Greenwich Mean Time dates, the moon phase dates used for calendars.
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. Graphics done using Starry Night Pro, Starry Night Enthusiast and Adobe Photoshop. To purchase Starry Night Pro or Enthusiast, go to http://StarryNight.com