From the September 2005 issue

A conjunction for the ages

September 2005: A stunning sight awaits viewers in early September, when Venus and Jupiter have their most spectacular evening conjunction in more than 3 years.
By and | Published: September 1, 2005
Blazing beacons Venus and Jupiter appear striking as twilight falls in early September. Scan for them low in the west-southwest 30 to 45 minutes after sunset. The sky darkens quickly at this time of year, so the two brightest planets become more prominent as the minutes pass. But make sure you have an uncluttered horizon — otherwise, the pair will be lost behind trees or buildings.

Although Jupiter shines brightly, Venus dazzles in comparison. And while Venus gleams a pure white, Jupiter shines a few shades toward pale peach. Watch how their colors deepen toward orange, and even red, as they descend through Earth’s thick lower atmosphere.

The planets appear closest to each other September 1. Nevertheless, you should start looking during the last week of August to see Venus climbing away from the Sun while Jupiter slides in. Mark your calendar for September 6, when the waxing crescent Moon joins the duo to create a stunning trio. View the gathering with your naked eyes and binoculars. With this optical aid, you should see a fainter sparkle directly below Venus and to the Moon’s left: the bright star Spica.

Don’t miss this conjunction — the next nice one between the two brightest planets happens in February 2008.

Venus and Jupiter conjunction
Venus and Jupiter passed each other during dusk in February 1999, an arrangement they’ll repeat in early September.
Frank Zullo
Rusty-orange Mars now rises during mid-evening, surprising casual skywatchers because it shines almost as bright as Jupiter. Its increasing prominence results from Earth’s gradual approach, which makes Mars appear both bigger and brighter. Despite its brightness, Mars can be a bit of a disappointment for newcomers getting their first telescopic view. Experienced observers see a large disk brimming with subtle details under “good seeing” — when our atmosphere steadies and details come into sharp focus. A beginner needs to train his or her brain to recognize low-contrast dark patches on the tiny dot. Only time at the eyepiece can accomplish this. Another common mistake of novices is to observe Mars as soon as it rises, when Earth’s turbulent atmosphere usually erases all detail in a rushing blur. Wait until midnight for better conditions.

The Moon hides in the Sun’s glare at the start of September, then returns to form a lovely trio with Venus and Jupiter the evening of the 6th. Look for the gray shading on the dark side of the Moon. Astronomers call this light earthshine because the Moon is returning sunlight that has reflected off Earth.

Note the Moon’s path over the next several evenings. It crawls low across the south until it becomes Full the night of September 17 — the Harvest Moon. Four nights later, it joins Mars near the Pleiades cluster (M45).

Saturn, the bright yellowish “star” in the east as dawn breaks, also goes by the name of the Greek god Cronus. Across the millennia, Cronus has been confused with Chronos — father time. It doesn’t help that Saturn takes 29.5 years to complete a full circuit of the background sky, providing a handy measure of time’s passage. Indeed, it’s a celestial anniversary of one of this column’s authors, Alister Ling: “I first laid eyes on Saturn in November 1975, when it made a nice triangle with Castor and Procyon. I’ll never forget the view through my new 4.5-inch scope, aimed between the trees from the sidewalk. I’m sure it will stir more memories when I see Saturn in Cancer again.”

The distant gas-giant planet Uranus reaches its peak the night of August 31/September 1. At magnitude 5.7, it glows brightly enough to be spotted with the naked eye from a dark site. Find it first with binoculars next to the 4th-magnitude star Lambda (λ) Aquarii.

The deep sky

Barnard’s dim galaxy
Far from the crowded core of our expansive galactic empire lie dozens of fainter dwarf colonies. Instead of the hundreds of billions of stars that constitute a major galaxy like ours, most dwarfs contain only a few million. Astronomers are still trying to piece together the puzzle of the dwarfs’ origin and evolution. In some cases, the galaxies have already suffered a passage through the Milky Way that robbed them of their gas and flung their stars into long, trailing arcs.

NGC 6822
Local group galaxy NGC 6822, better known as Barnard’s Galaxy, lies 0.7 degrees from planetary nebula NGC 6818 in Sagittarius.
Astronomy: Roen Kelly
More distant dwarfs have maintained their independence, giving birth to new generations of stars. These are the ones backyard astronomers can best observe. Following the two Magellanic Clouds deep in the southern sky, the next-brightest dwarf lies in Sagittarius and goes by the name Barnard’s Galaxy (NGC 6822).

Discovered visually through a 5-inch refractor by famed observer E. E. Barnard in 1884, this modestly large, elongated patch of light can be teased out of the background sky only under the best haze-free conditions. Get well away from city skyglow, and seek it out at the beginning or end of September, when moonlight does not interfere. The galaxy’s long axis spans more than 10′, so use your lowest-power eyepiece to get a nice wide field of view. (In comparison, the Moon covers 30′ of sky.)

Start your search with the chain of stars that includes 54 (a wide double) and 55 Sagittarii, then slowly sweep north and east a bit less than 2°. Because the human eye is fairly sensitive to motion, you probably will find this dwarf galaxy easier to see if you nudge the telescope a bit.

NGC 6822 appears so diffuse, it tends to disappear into the background when viewed with a large telescope at high power. However, you’ll need the larger light grasp of a big scope to pick out some of its associated gas clouds. The brightest emission nebula in the galaxy is IC 1308, attached to the northeastern flange of the glow. Both UHC and OIII nebula filters will help you see it, but remember to use a dark hood to conserve all the photons coming through the eyepiece.

NGC 6818
The Little Gem Nebula (NGC 6818) lives up to its name, glowing gray-green and measuring just 22′ across.
Mitch and Michael Dye / Adam Block / NOAO / AURA / NSF
A little gem
You’ll have a much easier time finding NGC 6818, a planetary nebula in our own galaxy that lies just 0.7° north-northwest of Barnard’s Galaxy. Nicknamed the Little Gem Nebula, it looks like a 10th-magnitude star that seems a little “flat” when viewed at low magnification. Pump up the power to see a circular, gray-green disk of light 22″ across. From our earthbound perspective, this appears barely wider than the ball of Saturn, but in reality, it spans about half a light-year.

Near the end of a star’s life, it puffs off its outer layers, which glow from ultraviolet radiation emitted by the white-hot core that remains. William Herschel, who coined the descriptor “planetary nebula” for these objects, discovered the Little Gem August 8, 1787. A 6-inch scope will pick up NGC 6818 from a suburban backyard.

The planets

Early evening September 1 provides the setting for a dramatic encounter between Venus and Jupiter. Normally, Jupiter’s brilliance is enough to attract attention, but this time, it looks dim compared with Venus. Venus dazzles at magnitude –3.9. Jupiter, which lies just 1.2° above Venus, appears nearly 10 times fainter, shining at magnitude –1.7. Watch as the sky darkens, turning from orange through aqua blue to deep blue, and the brilliant planets sparkle like a pair of jewels.

A great way to remember the scene is to take a photograph. Set up your camera on a tripod, and use the self-timer or a cable release to fire the shutter. (This avoids jitter created by manually pressing the shutter.) The best pictures contain a scenic foreground object. When placed against the bright evening twilight, the foreground will form a beautiful silhouette.

Venus and Jupiter
The two brightest planets come together for a beautiful conjunction in the west-southwest during September’s first week.
Astronomy: Roen Kelly
The two planets also provide nice views through backyard telescopes. Careful viewing of Venus reveals a 75-percent-lit disk 15″ across. It’s much easier to see the disk during twilight because the contrast between a dark sky and bright planet produces lots of glare. Jupiter reveals little this low in the sky, but you should be able to make out its four bright moons.

Although the two planets appear close together in our sky, they reside at dramatically different distances from Earth. Venus lies 105 million miles away, while Jupiter comes in at a distance of 577 million miles.

On September 6, a crescent Moon joins the planets, now separated by 5°. This evening, the Moon sits 3° south of Jupiter and 4° west of Venus. You should also see a 1st-magnitude star 1.8° below Venus. This is Spica, the brightest star in the constellation Virgo the Maiden.

Venus continues to pull away from Jupiter, and by the 9th, both lie just shy of 5° from Spica. For the rest of September, Jupiter sinks lower in the west and sets earlier each night. Twilight begins to drown it out toward the end of the month. Venus remains visible, hugging the southwestern horizon. It passes 2° south of Zubenel-genubi (Alpha Librae) on the 24th. Through a telescope, Venus grows to 18″ across, while its phase shrinks to 65-percent lit by month’s end.

The last evening conjunction between Venus and Jupiter occurred in June 2002. However, in terms of their altitude, this month’s is the best evening conjunction since February 1999. The next good conjunctions between these two planets occur in the morning sky in February 2008 and in the evening sky in November 2008.

The blue-green coulds of Uranus are caused by methane gas, which absorbs red wavelengths of light.
Uranus reaches opposition and best visibility the night of August 31/September 1, when the 6th-magnitude planet lies a few degrees southwest of 4th-magnitude Lambda Aquarii.
Astronomy: Roen Kelly
Moving from the brightest planet to the faintest, Pluto. currently lies almost midway between Eta (η) Ophiuchi and Xi (ξ) Serpentis. At magnitude 13.9, you’ll need a transparent night and a dark observing location to spot it. Your best chance will come with a 10-inch or larger scope.

Glowing at magnitude 7.9, Neptune proves much easier to see, although you’ll still need a telescope to view its tiny 2.3″-diameter disk. The outermost gas giant reached its peak at opposition last month and remains well-placed for viewing. You can track its slow motion with binoculars as it treks westward through Capricornus the Sea Goat. It lies approximately midway between 29 and Theta (θ) Capricorni, edging closer to Theta.

Neptune’s inner cousin, Uranus, reaches opposition the night of August 31/September 1. You can find it between 3° and 4° southwest of the 3.7-magnitude star Lambda (λ) Aquarii. This star lies midway between the lower-right star of the Great Square of Pegasus, 2nd-magnitude Markab, and the 1st-magnitude star well south of it, Fomalhaut.

Uranus glows at magnitude 5.7, making it an easy binocular target that’s even visible to the naked eye under a dark sky. The challenge comes in identifying which faint point of light is the planet. Either use a good star chart with Uranus’ position marked on it or draw the field of view over 2 to 3 nights. Uranus will betray itself by its slow motion. Alternatively, aim your scope at the suspected planet; at medium power, you should see its 3.7″-diameter blue-green disk.

From now through year’s end, Mars appears better than at any time in the past 2 years. On September 1, it rises shortly before 11 P.M. local daylight time among the background stars of Aries the Ram. It comes up earlier each night through the end of the month.

Mars gleams so brightly and with such a distinct ruddy hue, you won’t confuse it with any other object. On September 21, Mars stands 5° south of a waning gibbous Moon. The next night, the planet crosses into Taurus. By the end of September, Mars lies less than 10° from the Pleiades star cluster (M45).

Mars closes on Earth fast and brightens considerably this month, climbing from magnitude –1.0 to –1.7. It easily bests the brightest star in this vicinity, Aldebaran. For those with telescopes, Mars’ phase and angular diameter both increase this month. The disk spans 14″ and appears 87-percent illuminated September 1. These numbers climb to 18″ and 93-percent lit by month’s end.

The Red Planet is better placed in the sky for observing than during its historic opposition 2 years ago. Although it won’t come as close to Earth as in 2003, its much higher altitude will greatly benefit observers in the Northern Hemisphere.

The south pole of Mars currently tilts in our direction, giving us a good view of the south polar cap. However, the cap will shrink throughout the apparition as Mars’ southern summer continues.

Mars rises before midnight this month, opening a prime viewing window that will last through the end of the year.
Astronomy: Roen Kelly
Martian features closer to the equator become visible as Mars rotates. Mars has a period close to Earth’s, so each night, nearly the same face of Mars points in our direction. An hour or 2 after Mars rises during September’s first week, Solis Lacus will be visible. By mid-September, Sinus Sabeaus lies near the meridian. On September 20, wedge-shape Syrtis Major, perhaps the most recognizable dark feature on Mars, can be seen for a short period. It soon rotates out of view but remains visible longer as September comes to a close. By the end of the month, Syrtis Major comes around the limb at 1 A.M. EDT and remains visible the rest of the night.

Keen-eyed observers occasionally spot clouds on Mars. September is a good month to watch for orographic clouds near the Tharsis region. Such clouds form when mountains force moisture-laden air to rise, creating clouds on their downwind side. With massive peaks like Olympus Mons and the other Tharsis volcanoes, such clouds may become visible. You can improve their visibility by using blue or violet eyepiece filters to enhance their contrast.

Mars will make its closest approach to Earth at the end of October and reach opposition November 7.

Saturn lies near the Beehive star cluster (M44) during September. Between the 10th and 20th, the two objects appear together in the same low-power field of view. On September 28, a waning crescent Moon joins the scene. Saturn rises more than 2 hours before the Sun in early September and, by month’s end, appears high in the east well before twilight begins.

Innermost Mercury makes a fine appearance in the early morning sky during the first week of September. On the 4th, it lies 1.1° north of Regulus, Leo’s brightest star, although the latter is barely visible in the brightening twilight. At magnitude –1.4, Mercury shines much brighter than Regulus.

By the 9th, Mercury rises only 40 minutes before the Sun. Although it shines brightly at magnitude –1.6, its visibility becomes limited against the glowing twilight. After this date, it will be hard to follow.

Meteors and moons

A pair of Aurigids

September traditionally ranks low on most meteor observers’ calendars. Certainly in comparison to August’s high activity, September tends to be overlooked. The month’s many minor showers all tend to be under-observed.

With a Full Moon occurring during the third week of September, meteor watchers should get their best views early in the month. The Alpha Aurigids, a minor shower that typically produces a meteor every 10 minutes, remains active from August 25 to September 8. It peaks, if that phrase can be used for such a minor shower, September 1.

The meteors rank among the fastest — slamming into Earth’s atmosphere at 41 miles per second. During the past century, backyard observers have recorded three Alpha Aurigid outbursts (in 1935, 1986, and 1994), when rates reached 1 meteor nearly every 2 minutes. Although astronomers don’t anticipate such activity this year, the possibility can’t be discounted.

Mount Hadley
Mount Hadley lies at the northern end of the lunar Apennines, not too far east-southeast of the large crater Archimedes.
Consolidated Lunar Atlas (LPL / UA)
Apollo 15
Apollo 15 astronaut Jim Irwin works at the lunar rover as he and Dave Scott prepare to explore the rim of Hadley Rille in 1971. Mount Hadley looms behind the rover.
The Delta Aurigid shower overlaps with its neighbor, with activity running from September 5 to October 10. Observers can monitor the first part of the shower, but the bright Moon will affect the view later in the month. Rates typically run near the background level of sporadic meteors — around 5 meteors per hour. The radiants for both showers rise by 11 P.M. local daylight time and climb higher throughout the rest of the night.

Spotlight on Hadley

On July 30, 1971, Apollo 15 astronauts Dave Scott and Jim Irwin landed near a rille located not far from Mount Hadley. Although the lunar lander is far too small to be seen using telescopes on Earth (or in orbit, for that matter), the region provides plenty of nice features to observe with a backyard telescope. Mount Hadley lies near the northern end of the lunar Apennine Mountains. Three distinctive craters reside nearby on the Mare Imbrium plain: Archimedes, Aristillus, and Autolycus.

To find the region, first center these three craters in a low-power eyepiece. Then locate a small lava plain to the east of Archimedes, bounded by mountains on the eastern side, and switch to a higher-power eyepiece. Set within the mountain range itself is a single small crater, Conon, which spans 14 miles. The area to its north, the small lava plain noted earlier, is called Palus Putredinis (or Marsh of Decay).

Under good seeing conditions, you should see a complex network of rilles here. The Sun rises over the region September 11, providing sharp shadows and exquisite views.

Apollo 15 introduced the lunar rover, helping to make this one of the most exciting visits to the Moon. The rover spent two of its three excursions exploring Hadley Rille.

Comets and asteroids

Deep Impact’s legacy
A year ago, it looked as though we were headed toward a famine of bright comets, leaving only faint, challenging fuzzballs for dark-sky enthusiasts. Then one night, Don Machholz discovered a comet that would give us 6 months of good views. Now, as we head into the final few months of 2005, no comet brighter than 11th magnitude looms on the horizon. Let’s hope we get lucky again.

Tempel 1
Comet 9P/Tempel 1 skims south of Antares in early September. Observers hope the effects of being hit by the Deep Impact spacecraft will keep the comet brighter than predicted.
Astronomy: Roen Kelly
One possibility could be Comet 9P/Tempel 1. Normally, it would be glowing somewhat feebly at 11th magnitude, but it still may be feeling the effects from its July collision with the massive copper projectile launched by the Deep Impact mission. If so, there could be freshly exposed, pristine ices causing the comet to glow a couple of magnitudes brighter. To find it, you’ll need a good site outside the city with a clear southern horizon. And you’ll need to look during September’s first week, when the Moon’s out of the sky. Because Tempel 1 is sliding south of Antares in Scorpius, it sets fairly early. Try searching for it before total darkness sets in.

Comet 161P/Hartley-IRAS should glow around 11th magnitude this month. It remains visible all night between the handle of the Big Dipper and Arcturus in Boötes.

Because moonlight doesn’t affect digital imagers as much as it does visual observers, see if you can capture 12th-magnitude Comet 37P/Forbes as it slides by two globular star clusters north of the Teapot asterism in Sagittarius. The comet passes 8th-magnitude NGC 6544 September 10 and 9th-magnitude NGC 6642 the 20th.

Jumping on the Scales
The solar system’s largest asteroid, 1 Ceres, measures 595 miles across. Not surprisingly, it was the first asteroid to be discovered. Although it currently plies the modestly rich star fields of Libra the Scales, Ceres glows at 9th magnitude, so it remains brighter than the typical background star in this area.
Asteroid Ceres continues to move eastward against the background stars of Libra. This 9th-magnitude object should be easy to spot through small backyard scopes.
Astronomy: Roen Kelly
To find Ceres, jump from Gamma (γ) Librae southward through the Zeta (ζ) triplet to the area depicted on the finder chart at right. Then zoom in on the big rock’s track. Chances are the first point of light you see close to the predicted position will be Ceres. To be sure, make a quick sketch of the region and return a night or 2 later to confirm that your suspect object has moved slightly.

Although watching an asteroid blot out the light from a distant star for a few seconds used to be a rare event, it now occurs almost monthly. No, such events aren’t becoming more common, we just can predict them for fainter stars and asteroids thanks to improvements in star catalogs, accuracy of asteroid orbits, and computer speed. Steve Preston’s web site,, contains an easy-to-browse list of upcoming events with maps showing the area and time. Thanks to his finder charts that zoom in on the exact location, it’s a snap to get ready.

Martin Ratcliffe is former president of the International Planetarium Society. Alister Ling is a meteorologist for Environment Canada.