August 2008
Skywatchers’ Guide for August 2008
The Perseid meteor is mostly washed out by moonlight on August 11-12 until well after midnight
 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 U.S. |
One of the best meteor showers of the year (and the one everyone likes to see) the annual Perseid meteor shower peaks on the nights of August 11-12 and 12-13. Perseid meteors can also be seen for the few nights before August 10 and after August 14, but in much reduced numbers. The shower should peak on the night of August 12-13, with August 11-12 also a secondary prime night for the shower. Unfortunately this year, until after midnight, the shower is washed out by the large, gibbous Moon which does not set until 1:35 a.m. on the peak morning of August 12 (12:44 a.m. on August 11).
The large moon this year will brighten the sky, reducing the amount of shooting stars one 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 on the nights of August 11-12 and 12-13 then look for one of the year’s best annual sky shows starting at 12:30-1:30 a.m. (when the moon is near setting time). If monsoon clouds interfere, viewers will also be able to see meteors in numbers on the nights of August 10-11th and August 13th-14th, after the Moon sets. 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 before sunrise in dark skies, 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 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.
PLANETS
HIGHLIGHTS: Four planets at one time might be glimpsed with the unaided eye in bright evening twilight this month, with five possible in binoculars, but three of the four (Saturn, Mercury, and Venus) will be very low and challenging. Venus, Saturn and Mercury group tightly but very low in bright evening twilight from August 12-15. All three are so low that only Venus will be visible to the naked eye, with Saturn (after Aug. 3) and Mercury requiring binoculars. Venus and Mercury then leave Saturn and pair up much of the rest of the month. Also, the Perseid Meteor shower on August 11-13 is washed out by moonlight until 12:30-2 a.m.
Bright Jupiter dominates the 2008 August sky for the first half of the night. Jupiter appears as a very bright, almost brilliant white star-like object, high above the southern horizon on August evenings. Jupiter was closest to Earth and farthest from the Sun (at opposition) on July 8 and is still bright and large in a telescope in August. In fact, weather permitting, August is the best month to view it this year in the convenient evening hours just after sunset. Look for bright, whitish Jupiter just east (or roughly ‘left’) of the Teapot of Sagittarius: It’s the brightest star like object well up in the late night sky this summer. Jupiter is easily found 1 hour after sunset in the southeast. The giant gas planet is highest (at around 30 degrees in altitude for much of the Desert Southwest, 34 degrees for southern Arizona) and due south around 10:30 p.m. in early August, at 9:30 p.m. in mid-August, and at 8:30 p.m. in late-August. Look for the waxing gibbous Moon to be near and west of Jupiter this month in the southern sky on Tuesday evening, August 12, the peak night of the Persied Meteor Shower.
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. Jupiter in early August is still close to its brightest this year (at magnitude -2.6) and largest in a telescope (at 45 arc seconds wide). The giant gas world, although dimming slightly, remains nearly this bright in the skies of Earth all month long. August 2008 continues to be a good time for viewing the giant planet as it appears well up in the southern sky this year during the convenient evening twilight. When looking at Jupiter in a telescope to view its cloud belts and festoons, the sharpest views should be in evening twilight, when it’s highest. 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.
Mars was closest to Saturn in our sky from July 9-11, but now the two start August over 11 degrees apart, and Mars is moving 0.5 degrees per day away from much lower Saturn (moving out of Leo, the Lion and into Virgo, the Virgin). To determine which is which, note that cream-white Saturn appears much lower in our sky and looks like a first magnitude star-like object in early August or about as bright as the brighter stars in the summer sky. Orange-red Mars will appear less than half as bright as Saturn. Saturn will move into the glare of the Sun and become increasingly difficult to see with the unaided eye after August 3. The razor thin waning crescent Moon will be just above the western horizon and below Saturn on Saturday evening August 2, and nearer to Mars on Sunday evening August 3.
Although not very bright (at around magnitude 1.8), Mars is more easily visible than Saturn this month starting around 45 minutes after sunset in the western sky in evening twilight. However the Red Planet continues to shrink in apparent size (from a tiny 4.1 to an even smaller tiny 3.9 arc seconds) and is almost magnitude 1.8 in brightness). Mars is too small in apparent size for viewing of surface contrast features, even in large, high quality telescopes.
The brilliant planet Venus very gradually moves out of the glare of the Sun above the western horizon and into the evening twilight this month, but being so low, it won’t be easy to find. Look for Venus to be easier to see later this fall. Venus is grouped close to Saturn and Mercury from August 12-15 but the three are so low that only Venus will be visible to the naked eye, with much dimmer Saturn and Mercury requiring binoculars. Because Venus is so low in the sky a clear horizon is needed to spot it, as well as Saturn and Mercury. Venus and Saturn are paired closest on August 12-13 with Venus paired with dimmer Mercury much of the rest of the month. Look for Mercury to group with brilliant Venus starting around August 17 through August 26. Venus starts August just a few degrees above the west-northwestern horizon about 30 minutes after sunset. It does not get much easier to see because it drifts southeast in our sky each day, hugging the western horizon.
As mentioned previously, the elusive planet Mercury and the ringed planet Saturn both group tightly with Venus from August 12-15, with Mercury and Saturn closest from August 14-15. However, the glare of the Sun brightens the sky and eliminates naked eye viewing for Mercury and dimmer Saturn: Use binoculars to find them. Mercury will be brighter than Saturn at magnitude -0.4 but fades each evening slightly and is only 0.0 magnitude by late in the month. Mercury is then paired with brilliant Venus above the western horizon starting around August 17 through August 26.
Visitors to Flandrau’s 16-inch telescope should note that only the planet Jupiter is visible this month in the telescope after it opens at 7 p.m. 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.
AUGUST EVENING STARS
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!
 The bright star clouds of the southern Milky Way surround the Teapot of Saggitarius (planets are 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 first new moon in August occurs on Friday August 1. Also on Friday August 1, Earth’s first total solar eclipse since March 29, 2006 occurs over north polar regions such as Eurasia, extreme northern Canada, and Siberia, but ends in more habitable regions of northern China. The second new moon in August occurs on Saturday, August 30. The August first quarter Moon will occur on Friday evening, August 8. The August Full Moon, whose names include the Full Sturgeon or Full Red Moon, rises on the evening of Saturday, August 16 and sets on the morning of Sunday, August 17. That night a deep partial lunar eclipse occurs for Europe, Africa, the Indian Ocean, and parts of Asia. This eclipse is not visible in North America, but may be seen rising in partial eclipse from South America.
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