Skywatch July 2009 (newest at top)

This is Dudley Observatory's Skywatch line for Friday, July 31, through Sunday, August 2, written by Alan French.

The Moon was at first quarter this past Tuesday and will be full next Wednesday, so a waxing gibbous Moon will dominate the night sky over the weekend. It will set well after midnight.

Amateur astronomers who have caught some of the few recent clear nights have noticed quite a few meteors streaking across the night sky. Some have been quite bright. Although the Perseid Meteor shower does not reach its peak until August 12, some Perseids are already gracing the night sky.

Summer vacations often take people away from light polluted skies and they are often up late and notice the star spangled sky. Such nights provide a great opportunity to learn the brighter constellations. Not only is it fun to look up and recognize these ancient star patterns, but it can be useful when you want to find a comet or other celestial sight that is in the news.

The simplest and least expensive tool for learning the constellations is a planisphere. This is a cardboard or plastic sleeve enclosing a disk with all the visible bright stars and constellations. A window in the sleeve reveals the star visible at a specific time and date. The time and date is set by rotating the inner disk.

Planispheres are generally found at larger bookstores and science stores. Be sure to buy one that includes our latitude of 44 degrees. The usual version sold in this area covers latitudes 40 to 50 degrees. If you vacation at lower latitudes you'll see southern stars invisible from here and will need a planisphere covering the more southerly latitude.

Keep in mind that planispheres do not know daylight savings time. When daylight savings time started in the spring, we “sprung” the clocks ahead an hour. As a result our time is one hour ahead of “planisphere time.” When it is 10 PM EDT set the planisphere for 9 PM.

When you are out under dark skies it takes your eyes time to get used to the dark. Your eye's pupils open wider to let more light in. There is also a chemical change that greatly increases your eye's sensitivity to light. After about 30 minutes you can see much fainter stars and the Milky Way really stands out under dark skies. To preserve your night vision, avoid using a white light to see your planisphere. A dim red light will let you see it without ruining your dark adaption. You can buy one from on-line astronomy dealers or simply make one using red paper or plastic and a white light.

A popular book on learning the night sky is H.A. Rey's “The Stars.” It nicely augments a planisphere.

Dudley Skywatch Line for Wed. and Thurs., July 29 and 30, 2009:
by Ray Bogucki

Just 15 years ago, astronomers watched in fascination as several pieces of the broken up comet, Shoemaker-Levy (S-L 9) collided with Jupiter, leaving a series of dark scars on the giant planet's visual surface. S-L 9 had been torn apart by Jupiter's intense gravitational field in the previous pass when it swung too close to Jupiter's surface. The collisions were anticipated and recorded by hundreds of astronomers.

15 years later, in a marvelous coincidence, Australian astronomer Anthony Wesley, last week noticed a dark mark on Jupiter which was not there the previous night. His announcement was picked up and spread across our planet within minutes. Hundreds of astronomers have confirmed the sighting and also the fact that the spot looks remarkably similar to the scars left on Jupiter's surface by S-L 9. The Hubble Space Telescope team promptly suspended their ongoing testing procedures on the newly refurbished telescope and trained its powerful new Wide Field Camera 3 on Jupiter. The details in the images are remarkable. It is generally assumed that this scar was left by the impact of a comet or asteroid, but unlike S-L 9, this object was not anticipated or detected in advance. Some astronomers are puzzled by how an object large enough to cause an Earth-sized scar on Jupiter could have gone undetected from Earth. Others note that over the past eons, Jupiter has undoubtedly absorbed many objects which otherwise might have posed a threat to Earth, and send their thanks to our giant neighbor for taking the hit for us. More sober folks note that Jupiter's powerful gravitational field is a double edged sword and in distant past events has more than likely altered the trajectories of some incoming objects to set them on a collision course with Earth.

In an entirely separate anniversary event last July 18, NASA launched its new Lunar Reconnaissance Orbiter (LRO) just 40 years after the first human landing on the Moon. The purpose of the LRO is to search out promising landing sites for any future Moon missions. The LRO's polar orbit has it flying about 30 miles above the lunar surface. Whereas earth-based lunar photography cannot detect objects much smaller than approximately one mile in length, the LRO's Narrow Angle camera can detect objects as small as 3 feet across. In one of the early images sent back by the LRO, the Lunar Landing Module left on the Moon's surface by the Apollo 14 mission is clearly delineated with its long, square-ended shadow. 500 feet away, a light spot shows the location of the Lunar Surface Experimental Package set up by the astronauts. Most fascinating is the subtle darkening of the surface where the astronaut's boots wore a path in the dusty surface as they moved back and forth between the two objects. For more details and many spectacular images of both of these events, go to the website: www.skyandtelescope.com and click on the links to the stories "The Impact on Jupiter" and "Apollo Landers Seen on the Moon".

This is Dudley Observatory's Skywatch Line for Friday, July 24, through Tuesday, July 28, written by Alan French.

The Moon was new late this past Tuesday. As you probably know parts of Africa and Asia were treated to a total solar eclipse. Check astronomy web sites like www.spaceweather.com <http://www.spaceweather.com/> for photographs of the eclipse.

A slender crescent young Moon returned to the evening sky on Thursday. On Friday night look for the Moon just above the western horizon around 9:00 PM. Saturn will be above and a little left of the Moon and the star Regulus will be well to its right. By Saturday night the Moon will be higher and toward the west southwest. Monday evening will find the Moon toward the southwest and just below Spica, the brightest star in Virgo. The Moon reaches first quarter and we will see half of the sunlit face on Tuesday night.

There is a nice pass of the ISS over our area on Saturday night. It will be brighter than any of the stars, and will look like a bright star gliding across the sky. As you watch, think of the shuttle Endeavor docked to the station and the 13 astronauts now there. The space station will first appear at 9:02 PM in the west northwest. After moving upward it will be highest when 52 degrees above the southwestern horizon just before 9:05 PM. The ISS will vanish below the southeastern horizon at 9:07:35.

On July 19 amateur astronomer and Jupiter observer Anthony Wesley of Australia photographed a dark spot near Jupiter's south pole. The spot looked very much like the impact scars we witnessed when pieces of Comet Shoemaker-Levy slammed into Jupiter back in 1994. JPL verified that the spot was indeed to result of something hitting Jupiter and essentially creating a cloud of soot in the planet's atmosphere.

The spot is visible in modest sized amateur telescopes. It is best seen when in the middle of the planet and when Jupiter is highest in our skies. Right now Jupiter is highest around 3 AM. The spot crosses the center of Jupiter about two hours and six minutes before the famous Red Spot transits. You can get times for Red Spot transits at www.skyandtelescope.com <http://www.skyandtelescope.com/> and simply add two hours and six minutes to them. Your best bet for seeing the spot is when the resulting time is close to 3 AM. Keep in mind that the spot is quite far south, not far from the planet's south pole. For reference, look at the photos on the Sky & Telescope web site.

Dudley Skywatch Line for Wed. and Thurs., July 22 and 23, 2009:
by Ray Bogucki

About an hour after the Sun set in Albany on Tuesday, it was rising at the coast of India, near Mumbai, fully eclipsed by the New Moon, with the duration of totality about 3 1/2 minutes. Racing at thousands of miles per hour, the Moon's dark umbral shadow swept across India into China where it departed the Asian land mass at Shanghai, less than an hour after the eclipse began. The shadow continued racing eastward, darkening the island of Iwo Jima shortly before achieving its longest duration of totality of 6 minutes and 39 seconds, the longest in this century. The shadow then curved southeastward, darkening many tiny Pacific islands, until it crossed the equator and then the international date line far to the east of Australia. The eclipse finally ended when the Moon's shadow lifted from the Earth's surface as the fully eclipsed Sun set over the vast waters of the South Pacific. The entire event required only a little under four hours, but images and measurements will be pouring in for months as astronomers assemble the eclipse data in an attempt to better understand the behavior of our Solar System's own personal star.

Because we are still in the current eclipse season, when the next Full Moon rises near Jupiter on Wednesday, August 5, the Earth will return the favor for this week's solar eclipse by casting its own penumbral shadow on the Full Moon. While the Sun-Earth-Moon alignment is good, the timing is poor. The Earth's penumbral shadow is faint, although it is detectable in a dark sky. Unfortunately, this penumbral lunar eclipse is at its maximum right after sunset, when the twilight is very bright in the sky, making the lunar eclipse essentially invisible.

Fortunately, we have better luck tomorrow (Thursday) evening when Jupiter's moons put on a great show. From a site with an unobstructed view to the east-southeast, Jupiter should be rising about 9:30 p.m. as the sky grows dark. A telescope will reveal that all four moons are to the west of Jupiter. The moons Io, Europa and Callisto (numbers 1, 2 and 4 in distance from Jupiter) will be arranged in a tiny triangle close to Jupiter, while Ganymede (number 3) lies farther out. Io and Ganymede, at the westernmost end of their apparent harmonic motion back and forth across Jupiter will appear essentially motionless for a couple of hours. Callisto, however, is in front of Jupiter, moving rapidly westward toward Ganymede, while Europa is behind Jupiter moving even more rapidly eastward toward the giant planet. These motions should be readily apparent within 10 or 15 minutes. Notice that the motions allow you to identify all four moons unambiguously. This is the kind of action of Jupiter's moons that kept Galileo's eyes glued to his telescope night after night 400 years ago!

This is the Skywatch Line for Monday and Tuesday, July twentieth and twenty-first.
by Joe Slomka

The Sun sets at 8:28 PM; night falls at 10:32. Dawn breaks at 3:30 AM, ending with sunrise at 5:36.

Saturn remains the solitary evening planet, which appears lower daily. Saturn sets shortly after nightfall.

As astronomical twilight ends, Jupiter and Neptune make their appearance. For a brief time, one can see them and Saturn at opposite ends of the horizon. But all three are very low and easily hidden by trees or hills. By midnight, Jupiter and Neptune are high enough for detailed telescopic observation. Binocular users can track the four Galilean moons - astronomical websites and magazines provide tables and charts to help identify these satellites.

Uranus is also high enough for the telescope user. It remains below the Circlet of Pisces.

The first hints of dawn bring Mars and Venus on the scene. Mars and the Pleiades treat early risers to a beautiful spectacle to either the naked eye or binocular observer. Mars and the Pleiades lie about six degrees above the red star Aldebaran, the "Bull's Eye" of Taurus. Compare Mars and Aldebaran. In a telescope, Mars is a small red ball, while Aldebaran is a red pinpoint of a star. White Venus blazes about eight degrees to Aldebaran's left.

If we look south at about 10:00 PM, a hazy white band of light stretches from the North Pole to horizon. This band is commonly called "The Milky Way". Examination of the Milky Way with binoculars or telescopes reveals it to be a continuous band of stars or clouds of dust or gases. Our galaxy is a gigantic pinwheel, with several arms. Our planet is located in one of these arms. When we look at the Milky Way, we are seeing through this arm out into space. From Lyra to Sagittarius the Milky Way seems to divide in two. A giant dust cloud causes this "Great Rift". We can see these dust clouds on other galaxies. If we follow the Milky Way to the horizon, we come upon the constellation Sagittarius. The center of our galaxy is located in that constellation, but we cannot see it due to dense star and dust clouds.

Clear Skies
Joe Slomka

This is Dudley Observatory's Skywatch Line for Friday, July 17, through Sunday, July 19, written by Alan French.

On Saturday and Sunday mornings a slender old crescent Moon will join the planets Venus and Mars in the east northeastern sky. Look for this pretty grouping around 3:30 AM. On Saturday morning the crescent Moon will be to the upper left of Mars, and the lovely Pleiades star cluster will be to the Moon's upper right. Venus will be shining brightly closer to the horizon. By Sunday the Moon's eastward motion among the stars will have brought it down close to Venus. With a good choice of foreground, either grouping would make a pretty photograph.

The Moon was full last Tuesday so a waning gibbous Moon will rise well after midnight over the weekend. Moonrise on Friday night will be at 1:24 AM. By Saturday night the Moon will not rise until 2:19 AM, and Sunday night will add a bit over another hour of dark, moonless skies.

The Albany Area Amateur Astronomers will take advantage of the dark skies to hold public star parties at Landis Arboretum in Esperance on Friday and Saturday night. At star parties club members set up a variety of telescopes to provide guests with views of nebulae, galaxies, star clusters, and other celestial showpieces. Star parties are open to all and children are welcome.

The star parties begin at 10:00 PM in the Meeting House Field. Entering Esperance from the east on Route 20, take the first right onto Charleston Street. The is a large “Landis Arboretum” sign at this intersection. Follow the Landis Arboretum signs for about one and a half miles to the arboretum. Once you reach the farmhouse on your right and parking area on your left, continue up Lape Road about 100 yards. On your right as you reach the top of the steeper part of a short hill you will see the Meeting House driveway. Turn right and drive in. There will be a reflective sign marking the driveway.

Star parties are canceled if the skies are mostly cloudy. As I write this the weather forecast is not promising. If the conditions are uncertain and questionable, call 374-8460 after 7 PM to verify that the star party is being held.

The Albany Area Amateur Astronomers will meet at 7:30 PM on Tuesday night at the Schenectady Museum on Nott Terrace Heights. Club member Ted Close will give a program on his experiences attending Dick Parker's mirror making workshop and making a mirror for his own telescope. Telescope mirrors, more accurate than the finest machining, can be made by hand with simple tools and a good dose of time and patience. The program is open to all ages and there is no admission charge.

Dudley Skywatch line for Wed. and Thurs., July 15 and 16, 2009:
by Ray Bogucki

This week, our own Solar System is the stage for a number of interesting and even spectacular observations. Tonight, as the sky begins to darken an hour after sunset, look for Saturn shining at first magnitude, low in the west below Leo the Lion. The next few weeks provide the last chance to observe the ringed planet before it becomes lost in the glare of the setting Sun. Its rings continue to close down presenting a thinner appearance each successive night.

As Saturn sets in the west at about 10 p.m., giant Jupiter, shining 36 times brighter than Saturn, rises in the southeast in the constellation Capricornus. For the next couple of months, Jupiter will present its equator as well as the orbital planes of its four large Galilean moons to our line of sight. As a result, the moons will cast their shadows not only on the enormous face of their mother planet but on each other, as they pass back and forth in front of and behind each other, causing numerous occultations and eclipses. An excellent table listing times of events can be found in the July issue of Sky & Telescope on page 52, with accompanying explanations. Also, note that during the month of July, Jupiter serves as an unerring guide to the elusive, farthest, large planet, Neptune. Although not visible to the unaided eye, Neptune can easily be found in binoculars or telescope just about one Moon-width above, or north of Jupiter, appearing as a pale blue-green dot readily distinguishable from the sharp pinpoints of surrounding stars.

By far the most spectacular event is the total solar eclipse that occurs at New Moon in the evening of Tuesday, July 21 (EDT). This will be the eclipse with the longest period of totality for any eclipse during this century. The reason is that the Sun is still near its farthest distance from the Earth, so that its disc is 1.6% smaller in diameter than its average size. By an unusual coincidence, the Moon will be only a few hours from perigee, its closest approach to Earth in its current orbital cycle. This close approach will cause unusually high tides as well as making the Moon appear 7.5% larger than its average diameter.

This combination of unusually small Sun and exceptionally large Moon will result in a maximum duration of totality of 6 minutes and 39 seconds. Typical durations are closer to 4 minutes. Also because of the nearness of the Moon, the roughly 150-mile diameter of the Moon's dark umbral shadow on the Earth's surface will be larger than usual and sweep a wider path of totality. Because the path of totality begins at the coast of heavily populated India and exits the Asian land mass at Shanghai, China, this total eclipse will most likely be observed by the largest number of people in the history of our planet. Alas, because we live on the wrong side of the planet, we will not be part of that favored group, unless we make the trip. The next total eclipse to cross the U.S. will occur on August 21, 2017.

This is the Skywatch Line for Monday and Tuesday, July thirteenth and fourteenth.
by Joe Slomka

The Sun sets at 8:33 PM; night falls at 10:42. Dawn breaks at 3:20 AM, ending with sunrise at 5:30.

Shortly after sunset, Saturn appears in southwestern skies. The planet remains near Leo's hindquarters. A telescope user will note that Saturn's rings continue to gradually close to near invisibility.

Nightfall witnesses the rise of two other planets: Jupiter and Neptune. Both rise shortly after 10 PM and separated by a Moon diameter. One can see both Jupiter and Saturn at opposite ends of the horizon. Astronomy websites and magazines provide charts for observation of both planets' satellites.

The twenty-one-day-old Moon rises at 11:18 Monday night and 11:41 Tuesday night. Monday night sees the Moon under the circlet of Pisces. The fourth gas giant planet, Uranus, lies about thirteen degrees to the Moon's right. Nearly sixth magnitude, Uranus is visible in binoculars, but a telescope reveals its planetary nature. The Moon becomes Last Quarter at sunrise Wednesday morning.

Dawn hours find Jupiter and Neptune high in the South. The Moon and Uranus lie to their left in Pisces. The Red Planet Mars lies about five degrees from the Pleiades - a nice binocular view. Venus is easternmost, lowest and brightest. It occupies the horns of Taurus. Venus, at minus four magnitude, contrasts with dimmer Aldebaran, the Bulls' Eye. Telescopic views show Venus 67 percent illuminated, while Aldebaran appears as a red dot.

At nightfall, Scorpius lies due South and obvious to a sky watcher. Scorpius is one of the oldest constellations; its origins lie in the sands of Babylon. Star names betray its history. Sumerians and Babylonians gave us the Zodiac and gave them names in their languages.

Antares is the name for the red star that marks the Scorpion’s heart. The word Antares means “rival of Ares,” the Greek version for the Roman god, Mars. The two do look alike. Two stars on either side of Antares were called “Al Niyat,” Arabic for “the Arteries.” Stars in the head, were called Graffias, Deschubba and Jabbah. The stinger’s stars are Shaula and Lesath – again Arabic names. Stars that form the tail are called by Sumerian names: Girtab and Sargas.

Clear Skies
Joe Slomka

This is Dudley Observatory's Skywatch Line for Friday, July 10, through Sunday, July 12, written by Alan French.

The weekend starts with a fine pass of the International Space Station, or ISS, over the Capital District on Friday night. The pass occurs just after the end of civil twilight, so only the brightest stars will be visible. Over time, more parts have been added to the ISS and it has gotten larger. With more area to reflect sunlight down to those of us in darkness, it has also gotten brighter. On Friday night it will approach magnitude -3, brighter than any stars, and should be easy to spot gliding across the sky.

The times given for the ISS will be for Schenectady, but they should be close enough for anyone in the Capital District and surrounding areas. The difference in the times would be only a few seconds. Some times will be given in hours, minutes, and seconds.

The ISS will first appear rising up from the west southwestern horizon just before 9:12 PM tonight. It will be highest when 71 degrees above the north northwestern horizon just after 9:14. If you missed it rising up from the horizon, look very high in the north northwest at 9:14 and watch for a bright star moving toward the northeast. The ISS will vanish below the northeastern horizon at 9:17:32.

The Moon was full on Tuesday so a waning gibbous Moon will make an appearance before 11 PM over the weekend. Moon rise on Friday night is at 10:16 PM, and each weekend night will add only another 20 minutes of dark, moonless skies.

Saturn remains the lone planet gracing the early evening skies. It is low toward the west as darkness falls, lying below the back end of Leo, the Lion. From our viewpoint, the rings are now tipped less than three degrees. Through a small telescope magnifying at least 30 times they appear as thin lines to either side of the planet. The tip will gradually decrease even more until September 4, when Earth will be pass through the ring plane and the rings will be edge on. Alas, on September 4 Saturn will be very low in the sky as darkness falls, and will set just over 30 minutes after the Sun. We will not have a good view of Saturn's edge on rings. The next ring crossing in 2025 is also unfavorable.

Jupiter now rises at 10:18 PM and is due south and highest at 3:30 AM. The best views of the planets are had when they are south and highest because we are looking through as little of our atmosphere as possible. Unfortunately, Jupiter is well south of the ecliptic and only gets a bit over 33 degrees above the southern horizon. In spite of this, any modest telescope should reveal some of the darker belts in Jupiter's atmosphere and the four brightest moons. Io, Europa, Ganymede, and Callisto were discovered by Galileo and are often called the Galilean moons. They are visible in any telescope, and can even be seen in steadily supported binoculars when they are well away from the planet. It is fascinating to watch their changing positions from night to night, and to think what a puzzle these companion stars were to Galileo at first.

DUDLEY SKYWATCH LINE FOR WED. AND THURS., JULY 8 AND 9, 2009:
by Ray Bogucki

In last week's Skywatch Line, we described the globular cluster, M4, which shines just one degree west of the bright supergiant red star, Antares, in the constellation Scorpius. For a final look at Scorpius we can move to the back end of the Scorpion, following the curved line of stars along the Scorpion's back, until we come to two bright stars close together that form the "stinger" at the end of the Scorpion's curved tail. Moving eastward from the stinger, we encounter a bright smudge of light about halfway between the stinger and the spout of the well known "Teapot" asterism in adjacent Sagittarius. This smudge of light, which sparkles in binoculars, is an open or galactic cluster of stars designated as M7 in the Messier catalog. Open star clusters are very different from globular clusters in several ways. To begin with, open clusters are much smaller and have many fewer stars than globular clusters. They also are usually much closer and younger than globular clusters. Comparing M7 and M4 will illustrate these differences.

The open cluster M7 has about 80 stars, born at about the same time in a collapsing cloud of gas and dust 800 light-years away, about 220 million years ago. By comparison, the globular cluster M4 contains many thousands of stars that formed a giant ball of stars some billions of years ago. It is currently some 10,000 light-years away. The famous globular cluster M13, in the constellation Hercules, has perhaps a half-million stars which are very ancient, going back close to 13 billion years. While globular clusters all have roughly the same shape, with thousands of stars concentrated at a roughly spherical center, stars in open clusters are scattered in random ways. M7, viewed in large binoculars or a small telescope, shows the very recognizable pattern of a "cross" of stars, looking like a tiny miniature of the great "Northern Cross" in Cygnus, the Swan. Another open cluster in Scorpius, about 3 degrees northwest of M7, carries the designation M6, but is known by most astronomers as the "Butterfly Cluster" because they can imagine the shape of a butterfly with outstretched wings in the arrangement of stars in the cluster. One of the great pleasures in observing open clusters lies in seeing what shapes suggest themselves to you while you are enjoying the sparkling images in binoculars or a telescope.

This is the Skywatch Line for Monday and Tuesday, July sixth and seventh
by Joe Slomka

. The Sun sets at 8:36 PM; night falls at 10:49. Dawn breaks at 3:11 AM and end with sunrise at 5:24.

At sunset, Saturn remains a solitary planet. If it looks fainter than usual, your impression is correct. Saturn is receding and, consequently, appearing smaller. Also, its rings are closing up, reducing their contribution to Saturn's brilliance. It sets at about 11:30 PM.

The Moon rises before sunset, but sets at sunrise, when it officially becomes "full." Monday night sees the Moon near the handle of Sagittarius. Tuesday night places the Moon between Sagittarius and Capricornus.

As night falls, Jupiter and Neptune rise in Capricornus. It is possible to see Jupiter, Neptune and Saturn at the same time, but they are very close to their horizons and easily hidden.

The only easy objects are Jupiter and Neptune. The hours between midnight and dawn are the best times to see Jupiter and Neptune. Both fit within the same binocular view; Jupiter is big and bright, Neptune is small and blue-green. Astronomy magazines and websites provide details of Jupiter's four Galilean Moons. Neptune is only thirty arc minutes away from Jupiter, roughly the size of a full Moon. High power views show it as a ball, but little else. Uranus rises before midnight in Pisces and is well placed for pre-dawn viewing.

The hours before sunrise show the Moon, the Jupiter-Neptune pair, Uranus and the Venus-Mars pair. Venus and Mars are separated by six degrees, just fitting within the same binocular view. The beautiful Pleiades star cluster also accompanies them - a grand sight for early risers.

This past month has seen poor weather for sky watchers. Other planets also experience weather. An amateur telescope shows weather bands and the Great Red Spot, a gigantic hurricane, on Jupiter. The Hubble and Cassini telescopes show similar weather bands and storms on Saturn. Uranus and Neptune have also displayed storms - as seen by research telescopes. With daily reports from Martian rovers, planetary weather observers look for clues that help understand earthly weather patterns. Solar specialists generate Space Weather reports, vital to satellite and power line operators, and astronauts, since powerful solar emissions could endanger these operations.

Clear Skies
Joe Slomka

This is Dudley Observatory's Skywatch Line for Friday, July 3, through Sunday, July 5, written by Alan French.

The Moon was at first quarter on Monday so a waxing gibbous Moon will dominate the night skies over the weekend. On Friday night the Moon will be very close to Antares, the brightest star in Scorpius, the Scorpion. As the night progresses, the lunar orbs eastward motion among the stars will slowly move it closer to Antares. They will be closest together at moon set, which occurs at 2:42 AM Saturday morning. Residents of Hawaii and Japan will get to see the Moon occult or move in front of Antares at 6:00 AM our time.

Many people with an interest in astronomy eventually buy a telescope. We recommend attending a star party and seeing a variety of telescopes and what they can show before buying anything. This weekend we'll talk a bit about telescopes and their attributes.

The single most important factor in what a telescope will show you in the night sky is its /aperture/ - the diameter of the main light collecting optical element. For the refractor, this is the diameter of the lens at the front of the tube. For the Newtonian reflector it is the diameter of the primary mirror at the bottom of the tube. For an SCT or other compound telescope it is generally the diameter of the front optical element.

Aperture determines how much detail you can see in objects. A larger telescope will reveal more detail on the Moon and planets. Aperture also determines how much light the telescope collects and a larger instrument will provide brighter views and show fainter objects. Keep in mind, however, that the steadiness of the air often limits the detail you can see, and you need dark skies to see really faint galaxies and nebulae.
Focal length determines how much of the sky you can see. Telescopes with shorter focal lengths can provide low power, wide field views of the sky. The extreme example is binoculars, which can provide wider views of the night sky than most telescopes and are wonderful for exploring the sky from a lawn chair.

If you look at the advertising for telescopes available in some local stores and discount catalogs you may get the idea that magnification is the most important quality of the telescope. As we have said, the most important property of a telescope is its aperture, which limits the magnification. As a general guide the optimum power you can use is about 30 power per inch of aperture, so the common 60mm (2.4") refractor has an optimum power of 72x. With the highest quality optics and steady skies you can double this, so the highest power would be 144x. This is far less than the 400 power or more that is sometimes advertised for these scopes. In our area powers beyond 250 to 300 power rarely can be used to advantage.

We recommend staying away from any telescope that promotes high powers. Telescopes should be advertised by their aperture and focal length, not by a maximum magnification.

The best value for the money and *a *popular starting scope is a Newtonian reflector on a Dobsonian mount (often just called a "Dobsonian"). This is an excellent choice if you are interested in visual observing and have no interest in astrophotography. We suggest a 6" or 8" as a first scope. This is enough aperture to start showing a lot of lunar and planetary detail, and enough light grasp to do a good job on nebulae, galaxies, star clusters, and other "deep sky" objects. Many consider the jump to an 8" well worth the extra expense.

DUDLEY SKYWATCH LINE FOR WED. & THURS., JULY 1 & 2, 2009:
by Ray Bogucki

Last week's Skywatch line described the mythological and physical evolution of the constellation, Scorpius, the Scorpion.  This constellation is the brightest summer grouping of stars, while Orion holds this distinction in the winter sky.  However, while Orion lies astride the celestial equator and thus rises high in the southern sky from our mid-northern latitude, Scorpius lies far south of the celestial equator and never gets very high above the southern horizon.  Stars near the horizon appear considerably fainter than they would appear near the zenith because the thicker atmosphere near the horizon absorbs much of the star's light before it reaches our eyes.  For New Zealanders, Scorpius passes through the zenith, presenting a much more glorious appearance than we can ever see from here. 

Nevertheless, Scorpius contains enough wondrous sights to make it worth our while to search them out.  The unmistakably brightest star in Scorpius is orange-tinted Antares, a massive red supergiant star shining on us from a distant 600 light years away whose name means "Rival of Mars".  Mars and Antares are rivals in a couple of ways.  The planet Mars, in our own Solar System, is never very far away, and its cold, rocky surface shines only by reflected sunlight.  Because Mars' rocks contain large quantities of iron oxide, otherwise known as "rust", they reflect sunlight with a rusty orange tint.  Antares, on the other hand, shines with the energy of its own interior nuclear furnace, but unlike the brilliant, young, hot, blue-white stars, Antares is very old and has expanded out to a gigantic diameter, thus causing its surface temperature to drop to a very cool 3,000 degrees K, which also gives off an orange-tinted light.  Antares is so large that, if placed at the location of our Sun, its outer atmosphere would extend well beyond the orbit of Mars, into the asteroid belt.  With regard to magnitude, or apparent brightness in our sky, Antares is currently a little brighter than Mars, but on a roughly 26-month cycle, Mars will make its closest approach to Earth at opposition, and at these times, Mars greatly outshines its stellar rival.  

One of the finest telescopic sights in Scorpius is the globular cluster M4, which is found just about one degree, or two Moon-widths, due west of Antares.  Once you have found it, be sure to move your field of view far enough to the west to exclude Antares itself, whose brilliance would detract from your ability to see the subtle aspects of M4.  Unlike the globular clusters, M3 and M13 discussed on June 10, M4 is not so highly concentrated at the center.  This makes it possible to view many more of the individual stars toward the outer edge of the cluster.  Also, check the other bright stars in the constellation.  Several of them are elegant double stars.