Skywatchers’ Guide for August 2010

HIGHLIGHTS: Annually one of the best shooting stars shows, the Perseid Meteor Shower is unhindered by moonlight, making for one of the best times in recent memory to view what should be the year’s best meteor shower (peak nights on August 11/12 and 12/13). August 2010 again features the trio of Venus, Mars and Saturn in the western evening twilight for much of the month, and close groupings or ‘conjunctions’ of planets and stars. Brilliant Venus continues as our ‘evening star’ in the west. Venus groups with the planet Saturn (August 5-6), the planet Mars (August 18-20) and with the star Spica (August 30-31). Mars and Saturn are closest in our sky on August 1-2, while Venus, Mars and Saturn group more tightly later in a triangle around August 8-9, just before the Perseid Meteor Shower. Mercury might be visible (use binoculars) as the bottom member of this planetary ‘line-up’ the first few days of the month, but is much lower in the west. In the morning sky Jupiter continues to brighten towards its 12 year best show: The gas giant is overhead in morning twilight, but is also easily visible at 9 p.m. the last week of August. Joining Jupiter and making for a trio of planets for those viewing with telescopes is faint Neptune and brighter Uranus, the latter paired 2-3 degrees from bright Jupiter.

A GREAT YEAR TO SEE THE PERSEID METEOR SHOWER

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.

The annual Perseid meteor shower (the Perseids) occurs this year on the nights of August 10th-14th. The Perseids are often the best meteor shower of the year, with at least 10-30 meteors per hour visible even for beginning stargazers. The peak rates of meteors (also called shooting stars) will be seen on the nights of Wednesday, August 11th into Thursday, August 12th, and Thursday, August 12th into Friday, August 13th, with as many as 50 meteors per hour or more visible in a clear, dark sky. The new moon this year on August 10 creates an opportunity each night for perfect viewing, if the weather cooperates. If monsoon clouds interfere, viewers will also be able to see meteors in numbers on the nights of August 10-11 and August 13-14. Meteor watchers should seek out a dark sky several miles away from city lights and gaze in a wide area of sky high in the eastern and northern sky and overhead after 10:00 p.m. To see the shower well, observers should view until well after midnight (or 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 and the Tucson mountains west of town. Observers should expect to drive 30 minutes to out of town, away from city lights, to get good views of the shower.

The debris causing the meteor shower is from a comet that 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.

To help the public learn about this meteor shower, the Mount Lemmon Sky Center will offer two special viewing nights on the summit of Mount Lemmon on August 11 and 12. Click here for more information.

For more information visit the news article in Flandrau’s astronomy news section.

PLANETS

This sky chart shows the Mercury, Venus, Saturn, Mars and the star Spica in the western evening sky on August 1, 55 minutes after sunset from the Desert Southwest. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico. This sky chart shows the Moon, Venus, Saturn, Mars and the star Spica in the western evening sky on August 12, one hour after sunset from the Desert Southwest. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico. This sky chart shows the Moon, Venus, Saturn, Mars and the star Spica in the western evening sky on August 13, one hour after sunset from the Desert Southwest. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico. This sky chart shows Venus, Saturn, Mars and the star Spica in the western evening sky on August 23, one hour after sunset from the Desert Southwest. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico.

August 2010 should be the last month for viewing the rings of Saturn in a telescope as Saturn is losing altitude and sinking low in the western evening twilight. Saturn is currently the dimmest it will be this year at magnitude 1.1, but because it’s so far away from Earth this is not much dimmer than it was at opposition. However, compared to previous years the ringed planet is somewhat dimmer this year because its rings are more edge-on. The best bet to see Saturn and its rings is early in the month, starting 30-45 minutes after sunset. Saturn is found in the constellation Virgo the Virgin (though well west of Spica, Virgo’s brightest star).

Saturn’s rings still appear nearly as ‘narrow’ as they did earlier this year, due to our vantage point on Earth. The ringed world continues drifting eastward with ‘direct’ motion in August, but its much slower motion allows Venus to move close to it in our sky. The two group with Mars on August 8-9 in a fairly compact triangle. Look for Saturn about 5 degrees from Mars on August 9, with Venus 3 degrees from Saturn in the triangle (a spectacular view in binoculars). The razor thin waxing crescent Moon slides below the three on the evening of August 12 and left (southeast) of the trio on August 13.

Viewing of Saturn will be best when it is highest in the sky, probably in bright twilight early this month, 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 continues losing altitude this month, and, like Mars, is moving rapidly against the background stars. Venus passes out of Leo, the Lion and into Virgo the Virgin by early August. In addition to the triangular grouping with Saturn and Mars around August 8-9 (see Saturn text), Venus groups more closely with the planet Mars (August 15-17) and with the star Spica (August 30/31). Again, also look for the razor thin waxing crescent Moon to slide below Venus on the evening of August 12 and left (southeast) of Venus, Mars and Saturn on August 13.

As noted previously, orange-reddish Mars groups very closely with the brighter planet Saturn and brilliant Venus (see above). Orange-reddish Mars is now at minimum size and brightness for the year (1.5 magnitude in brightness, 4.7 arc seconds in apparent diameter). This is because Mars is now twice the distance that the Earth is from the Sun (at around 186 million miles from Earth) making the Red Planet an unremarkable object to the eye and in a telescope. Mars, like Venus, is moving rapidly against the background stars as Earth continues to recede from it in our solar system.

Jupiter continues to gain altitude and rise earlier each night in the east-southeastern sky. In the morning sky Jupiter continues to shine brightly and is overhead in morning twilight. The gas giant is also easily visible above the eastern horizon at 10:30 p.m. in early August and by 8:30 p.m. the last week of August. As it becomes more prominent in our sky Jupiter also comes closer to Earth, and swells in size to 49 arc seconds in apparent diameter in a telescope by the end of the month. Jupiter is slowly nearing its opposition date on September 21, when it will be opposite from the Sun in the sky and nearly the brightest and largest it will be in a telescope this year. Also in the morning sky faint Neptune lies far away from brighter Uranus, which continues to be paired 2-3 degrees from bright Jupiter. Finally look for the thick waning gibbous Moon to rise at around 7:53 p.m. well above Jupiter (about 5 degrees northeast) on the evening of August 26 (the giant gas planet rises about 30 minutes later that evening from southern Arizona).

Mercury is still visible in the first week or so of August as the lowest and most difficult to see of the planets lined-up in the west. Because Mercury is low and not that bright, binoculars may be needed to spot it. The elusive planet is best seen early in the month when it is brightest and highest. On August 1, Mercury, a 0.2 magnitude bright object, might first be visible 50 minutes after sunset when 5 degrees above a crystal clear western horizon. By August 11, the razor thin 2 day Moon is less than 2 degrees ‘left’ or west of the now fainter planet (now at 0.66 magnitude in brightness). However, the Moon that evening is even lower than Mercury being at the horizon 50 minutes after sunset, and so may be impossible to view. Mercury fades and sinks into the glare of the Sun after this date.

Visitors to Flandrau’s 16-inch telescope should note of the planets Saturn is visible in the telescope during public hours, and other celestial objects will be shown in the telescope, weather permitting. Flandrau’s telescope 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 may appear to twinkle somewhat; however, this twinkling is of a slower nature than that of the bright stars.

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!

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 last quarter Moon occurs on Sunday morning, August 1. The August new moon occurs on Monday, August 10,  allowing for unhindered view of what may be the year’s best meteor shower. The August 2010 first quarter Moon will occur on Monday evening, August 16. The August Full “Red/Sturgeon” Moon will rise on the evening of Tuesday, August 24 and set on the morning of Wednesday, August 25.

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: Graphics done using Starry Night Pro, Starry Night Enthusiast and Adobe Photoshop. To purchase Starry Night Pro or Enthusiast, go to http://StarryNight.com