Skywatch August 2009 (newest at top)

This is Dudley Observatory's Skywatch Line for Monday, August 31, and Tuesday, September 1, written by Alan French.

On Monday night a bright, gibbous Moon rises in the east southeast at 5:36 PM. Moon rise on Tuesday night is at 6:03 PM. Jupiter rises a half hour after the Moon Tuesday night and the pair will be a lovely sight in the darkening sky. They will be even closer together on Wednesday night.

At 11 PM the Summer Triangle is high overhead. This triangle of three bright stars provides an interesting lesson in star brightness.

If you look high in the south at 11 PM the first bright star you come to is Altair, the brightest star in Aquila, the Eagle. Altair is easy to recognize because it is flanked on either side by two “guard” stars of equal brightness. If you look a little past directly overhead, or turn around and look very high in the north, you'll find a pair of bright stars – Deneb and Vega. Deneb is the one toward the east and it marks the tail of Cygnus, the Swan. Vega, toward the west, is the luminary of Lyra, the Lyre. This obvious triangle of three bright stars quite conveniently points out three constellations of the summer skies.

A star's apparent brightness reflects both its intrinsic brightness and its distance from us. Altair, lying at a distance of 16.7 light years, is the thirteenth brightest star in the sky and one of our nearer neighbors. The light we see left the star in early 1993.

Vega is the fifth brightest star in the night sky and is also one of our nearer neighbors, lying at a distance of 25 light years. The light you see left the Vega in 1984.

The final star in the Summer Triangle, Deneb, ranks 19th in brightness among the stars in our night sky, but lies at a distance 1,425 light years. The light you see the star by left it way back in the year 581! As you can probably imagine, Deneb is intrinsically extremely bright. It is more than 54,000 times as bright as our Sun! If we moved Deneb to the same distance as Vega – 25 light years – it would be easily visible in the daytime sky.

This is Dudley Observatory's Skywatch Line for Friday, August 28, through Sunday, August 30, written by Alan French.

The Moon was at first quarter on Thursday so a waxing gibbous Moon dominates the evening sky over the weekend. The Moon sets thirteen minutes after midnight on Friday night. Each following weekend night adds another hour, so the Moon won't set until more than two hours after midnight on Sunday. The Moon will be Full on September 4.

The Moon's eastward motion relative to the stars will be very obvious this weekend as the Moon moves from Scorpius through Sagittarius. If you look toward the south at 9:00 PM on Friday you'll find the Moon well above the tail of Scorpius, the Scorpion. At the same time on Saturday night it will next to the top of the well know teapot shaped pattern of stars that outlines Sagittarius. By Sunday night the Moon will be to the east of the teapot's handle.

On last Monday and Tuesday's Skywatch Line I mentioned that a rare night launch of the space shuttle to the International Space Station (ISS) allows us to see the shuttle as it rockets up the east coast on its way into orbit. The launch has been postponed twice, and is now scheduled for Friday night..

To see the shuttle Discovery on its way into orbit you'll need a location with a very good view of the south southeastern horizon. Discovery will be very low and close to the horizon so your view should be unobstructed by trees or buildings. You'll also need clear skies free of clouds and haze near the horizon.
Discovery is scheduled to be launched at 11:59 PM on Friday evening. The light from its three main engines should be visible low in the south southeastern skies six to eight minutes later. If the sky is clear and free of haze, it will be as bright as the brightest stars. It will look like a pulsating, fast moving orange tinted star, and will be moving eastward faster than an orbiting satellite. Binoculars may reveal the contrail following the shuttle.

Of course this depends on Discovery being launched as scheduled. Keep you eyes on the news or NASA's television station to be kept up to date on the actual launch time. If your observing site is close to your house you can probably watch the launch and then get outside to catch it skim our south southeastern horizon six to eight minutes later. If the launch is postponed to another night slot simply look for it six to eight minutes after the new time.

Dudley Skywatch Line for Wed. and Thurs., Aug 26 & 27, 2009:
by Ray Bogucki

Last week's Skywatch line described a double shadow transit of Jupiter by its moons Io and Ganymede. Tonight (Wednesday) Jupiter will put on a repeat performance except that the shadows involved will be those of Europa and Ganymede, and the entire double shadow transit will occur after astronomical twilight when the sky will be as dark as it can be with the almost first quarter Moon preparing to set in the west. At 10:21 p.m., Europa's shadow will begin to cross Jupiter's surface. Twenty minutes later, Ganymede's shadow will follow Europa's shadow onto the face of Jupiter. The two shadows will continue to cross together until 1:12 a.m. Thursday morning, when Europa's shadow exits Jupiter's face followed by the departure of Ganymede's shadow about an hour later. Next week, for the third week in a row, there will be another double shadow transit on Jupiter following a rarely seen short period when Jupiter will appear to be alone, with none of its four Galilean moons visible. Details on this event will be given in next week's Skywatch line.

On Thursday evening, as the sky darkens, observers will find the first quarter Moon just about a half degree away from Antares, the supergiant red star in the constellation Scorpius, the Scorpion. In fact, a couple of hours earlier, at about 6 p.m., the dark side of the quarter Moon will have occulted Antares in broad daylight. Daytime lunar occultations are not normally visible to the unaided eye or even in binoculars, but with a telescope, a careful and persistent observer can actually watch such an occultation. For this event, one can find precise information about the occultation of Antares on the website of the International Occultation Timing Association at: www.lunar-occultations.com/iota Some years ago, this observer had the good fortune to watch a lunar occultation of Antares in daylight with an 8-inch Newtonian reflector. While it is a bit tricky to recognize the tiny spark of a star in the daylit sky, the result when you succeed is very satisfying, and well worth the attempt.

This is Dudley Observatory's Skywatch Line for Monday and Tuesday, August 24 and 25, written by Alan French.

When the space shuttle is launched on a mission to the International Space Station (ISS) its path into orbit brings it up along the east coast. When there is a rare night launch we have a chance to see the shuttle as it rockets into orbit. The writer was able to easily see the shuttle on the March 15 night launch. The launch early tomorrow morning may be our last remaining chance to see a night launch.

To see the shuttle Discovery you'll need to find a location with a very good view of the south southeastern horizon. Discovery will be very low and close to the horizon so the view should be unobstructed by trees or buildings. You'll also need clear skies from of clouds and haze near the horizon.

Discovery is scheduled to be launched at 1:36:05 AM on Tuesday morning. Its engines should be visible low in the south southeastern skies six to eight minutes later. By the time it is visible from our area, the solid fuel boosters will have dropped away, but we can see the light of the shuttle's three main engines. If the sky is clear and free of haze, it will be as bright as the brightest stars. It will be moving faster than an orbiting satellite, and will look like a pulsating, fast moving stars. The color will be yellow or orange. Binoculars may reveal the contrail following the shuttle.

There is a chance we might be able to see the main engine cut off. This is when the main engines shut off and the external fuel tank is jettisoned. The occurs a little less than 8 and a half minutes after launch, so try to follow the shuttle as long as you can. Binoculars will be very helpful.

Of course all this depends on Discovery being launched as originally scheduled. Keep you eyes on the news or NASA's television station to be kept up to date on the actual launch time. If your observing site is close to your house you can probably watch the launch and then get outside to catch it skim our south southeastern horizon six to eight minutes later.

The Moon has returned to the evening sky and is now visible as a crescent toward the southwest as the skies darkens. Jupiter continues to be the luminary in the southeastern skies as twilight falls.

This is Dudley Observatory's Skywatch Line for Friday, August 21, through Sunday, August 23, written by Alan French.

The Moon was new Thursday morning so the skies will be dark and moonless over the weekend. A slender crescent Moon will be visible with difficulty soon after sunset on Saturday and will be higher and somewhat easier by Sunday.

To see the crescent Moon and nearby Mercury and Saturn on Saturday evening you'll need to find a site with a good, unobstructed view of the western sky and you'll have to look for the trio at 8:20 PM. The Moon will be just a little south of due west and only two degrees above the horizon. With its low altitude and the twilight skies binoculars may be needed to spot it. Mercury can be seen about nine degrees to the right or north of the Moon and will be the same distance above the horizon. Saturn will be another six degrees north or right and slightly farther above the horizon.

If you can't find the Moon on Saturday night, look again around 8:30 PM on Sunday evening. The sky will be a bit darker and the Moon will be almost five degrees above the west southwestern horizon. Spica, the brightest star in the constellation Virgo, will be just to the Moon's upper left.

Jupiter continues to dominate the southeastern sky in the early evening hours and is due south and best suited for telescopic observation just after midnight. Any telescope will show the four brightest Galilean moons of Jupiter.

On Friday night at 11 PM Ganymede will be to the west of the planet and Io, Europa, and Callisto will be to the east. (If your telescope does not have a drive to follow the stars, objects drift out of the west side of your view.) Io and Europa will be very close together – so close that they may look like one moon.

Saturday night at 11 PM will find Io and Ganymede to the west of the planet. They will also be very close together. Europa and Callisto will be to the east of Jupiter. On Sunday at the same time Europa will be to the west and Io, Ganymede, and Callisto will be to the east.

Weather permitting the Albany Area Amateur Astronomers will hold public star parties at Landis Arboretum on Friday and Saturday nights. The star parties will begin at 9:30 PM and a variety of telescopes will be set up to show guests celestial sights, including Jupiter. Directions to Landis Arboretum can be found at www.landisarboretum.org.

Star parties are canceled if the skies are mostly cloudy. To verify a star party is being help or to get further information call 374-8460.

Dudley Skywatch line for Wed. & Thurs., August 19 and 20, 2009
by Ray Bogucki

At star-watching gatherings this month, the first question from visitors is usually, "What's that bright object climbing in the southeastern sky?". The answer is "Jupiter". Next comes, "Is there anything interesting to see?" The best answer to that question is simply to turn the telescope to the gas giant and point out all the fascinating events occurring. For example, today - Wednesday -, while the Sun is preparing to set in the west, and before Jupiter has risen, the shadow of Ganymede, the third moon out from Jupiter, will begin to cast its shadow on its giant planet's surface. An hour later, at 7:46 p.m., the shadow of Jupiter's second moon, Europa, will also begin to cross the face of Jupiter. As the evening darkens, about 9 p.m., both shadows will be clearly visible in a telescope, with Europa's shadow slowly gaining on Ganymede's. The moons themselves will be transiting the face of Jupiter 20 or 30 minutes ahead of their respective shadows.

The moons themselves are usually very difficult to make out against the planet's bright surface, but at 9:45 p.m., as Ganymede's shadow is approaching the edge of Jupiter's disk, Ganymede will reveal itself as it emerges from in front of Jupiter's disk as a regular bright little moon, right next to its giant parent. 45 minutes later, Ganymede's shadow will leave Jupiter's face. At 10:21, Europa itself will emerge from the edge of Jupiter and continue its race to overtake Ganymede. Europa's shadow exits Jupiter's surface at 10:38 p.m. Europa finally does overtake Ganymede at about 1:48 a.m. when it passes behind Ganymede, a short distance west of Jupiter. For about 16 minutes, the two moons will appear as one, until Europa finally reappears ahead of Ganymede.

But wait! The competition between the two moons is not quite finished. At 2:04 a.m., while the two moons are slowly separating, Ganymede begins to cast its shadow on its small neighbor until Europa, 99% eclipsed, vanishes from our view until 20 minutes later, when it starts to leave Ganymede's shadow. During all of this activity, Io, Jupiter's closest moon was busy passing behind its giant parent, and slow-moving Callisto, the fourth moon, barely changed its position, far out to the east.

This is Dudley Observatory's Skywatch Line for Monday and Tuesday, August 17 and 18, written by Alan French.

The Moon was at last quarter last Thursday so a waning crescent Moon rises well after midnight, making the evening skies this week dark and moonless.

Neptune reaches opposition, the point where it is directly opposite the Sun as seen from Earth, on Monday evening. Neptune is now located three and a half degrees northeast of Jupiter but is too faint to see with the eye alone. It can be spotted in virtually any telescope, and finder charts can be found on the web or produced by any planetarium software.

Jupiter continues to dominate the southeastern skies as the sky darkens, and it due south and superbly placed for telescopic viewing at 12:45 AM. If you don't want to stay up that late, Jupiter is high enough for a good view by 10 PM. At 10 PM on Monday night the moons Io and Europa will be to the west of Jupiter, and Callisto and Ganymede will be to the east. These four bright moons are visible in any telescope and in steadily held binoculars when well away from the planet. If you are watching Jupiter with a telescope at 12:54 AM Tuesday morning you can see Europa passing behind and being occulted by Jupiter.

If you turn a telescope toward Jupiter at 10:00 PM on Tuesday night you'll find all four moons to the planet's east. In order of distance, closest to farthest, they will be Io, Europa, Ganymede, and Callisto. At 11:02 PM Io will move in front of Jupiter, and eight minutes later Io's shadow will move onto the planet.

The Albany Area Amateur Astronomer's will meet at 7:30 PM on Tuesday night a Landis Arboretum in Esperance. The meeting is being held in the Meeting House, and includes the club's annual swap shop where members sell and trade astronomical items. Weather permitting, the meeting will be followed by a star party. At the star party a variety of telescopes will provide views of celestial sights to club members and guests. Jupiter is now well placed for viewing and you'll be able to see the transit of Io and its shadow described earlier. We'd also be happy to show you Neptune.

The club meeting is open to all ages and everyone is welcome. The Meeting House is up Lape Road about 100 yards beyond the farm house and main parking area. For directions visit www.landisarboretum.org <http://www.landisarboretum.org/>.

This coming weekend, August 21 and 22, the amateur astronomers will host public star parties at Landis Arboretum. They will also be held in the Meeting House field and will begin at 9:30 PM. These star parties are canceled if the skies are mostly cloudy.

This is Dudley Observatory's Skywatch Line for Friday, August 14, through Sunday, August 16, written by Alan French.

The weather here was not very cooperative for the peak of the annual Perseid meteor shower. Many observers reported cloudy or variably cloudy skies. Fortunately there is still a chance to see a few late Perseids over the weekend, and the Moon rises later allowing for some viewing under dark skies. The Moon rises just after midnight on Friday, but not until 1:07 AM on Sunday morning. Moonrise on Monday morning is at 2:18 AM. Observers on Saturday and Sunday nights will have several hours of darkness before the Moon rises.

In the early part of the last century, Albert Ingalls happened upon "A Poor Man's Telescope," by Russell W. Porter, in “Popular Astronomy.” The article told how the author made his own mirror for a Newtonian reflector. A later article told how some residents of Springfield, Vermont, under Porter's instruction, made their own telescopes. Further research by Ingalls revealed but one book on making your own telescope, "The Amateur's Telescope," by William Ellison, Director of Armagh Observatory in Northern Ireland. Obtaining a copy of the book and later contact with Porter, Ingalls made his own telescope.

Fortunately for amateur astronomers, Ingalls was an Associate Editor of “Scientific American”, and he got the idea of popularizing amateur telescope making. To test the waters, an article in the November, 1925, issue of “Scientific American” described a night under the Vermont skies with the amateurs inspired and instructed by Porter. The magazine received 368 requests for instructions, and so requested Porter to write instructions for making a telescope. The articles were published in the January and February, 1926, issues. A thin, 102 page book followed, which included Ellison's book and the two articles from the magazine. The 3400 copies were gone by 1928, and a new, expanded second edition was published. It eventually grew to three volumes, and articles about telescope making and reporting on amateur built telescopes were a regular feature of “Scientific American” for many years.

Up through the second world war building your own was the only option for many amateur astronomers. After the war commercial instruments and optics became more readily and reasonably available, but telescope making continued. Today we have a plethora of telescopes and high quality Newtonian optics, but some people continue making their own mirrors. There is a fascination and great satisfaction in viewing the heavens through a telescope made entirely by your own own hand.

Dudley Skywatch Line for Wed. and Thurs., August 12 and 13, 2009:
by Ray Bogucki

The celestial events closest to the Earth this week are the Perseid Meteor Showers. This meteor display occurs when the tiny particles of debris left in our orbit by the comet, Swift-Tuttle, collide with our upper atmosphere at speeds near 130,000 miles per hour. By the time the particles have penetrated to about 100 miles above the Earth's surface, the high speed collisions with molecules and atoms in the upper atmosphere have heated the particles to incandescence. The energy radiating from these white-hot particles excites the nearby atoms and molecules to fluoresce and glow. It is this rapidly moving cylinder of glowing gas that we actually see from the Earth's surface as a meteor. The Earth is now moving through the densest part of the particle stream so that the peak of the meteor shower will occur Tuesday and Wednesday nights into the early morning hours. The last quarter Moon will be rising about 11:30 Wednesday night and will brighten the sky enough to wash out some of the fainter meteors. Turn your back to the Moon, or find a tree or building to shade the Moon so it is not a distraction. Also, note that it would be worthwhile to continue watching Thursday and Friday nights because the Moon will rise an hour later on each successive night and its crescent will be diminishing and producing less of a sky-brightening effect.

Farther out in the Solar System, Saturn, the bright planet farthest from the Sun, and Mercury, the planet closest to the Sun, appear close together very low in our western sky this week. From a site with an unobstructed view to the west, look for Saturn near the horizon a half hour after sunset, with Mercury a little below and to the right. Because the sky will still be bright with twilight, binoculars will be a big help. By Saturday, Saturn will be directly above Mercury and will not be easily visible again after this week until next October, when it will be rising in the east as a morning star, an hour before sunrise.

Early risers on Friday will be treated to the sight of the waning crescent Moon successively occulting several stars in the Pleiades cluster in the hour before sunrise. Also note that Mars and Venus have finally parted company in the early morning sky with Mars rising about 1:30 in the constellation, Taurus. Venus rises almost 2 hours later in the constellation Gemini.

This is Dudley Observatory's Skywatch Line for Monday and Tuesday, August 10 and 11, written by Alan French.

The annual Perseid meteor shower is now nearing its peak. The best times to catch some Perseids will be on Tuesday and Wednesday mornings. Unfortunately a bright waning gibbous Moon will hamper the views and the fainter meteors will be lost in the moonlight. Fortunately the Perseids usually include many bright meteors. Also astronomers are predicting a burst of activity – perhaps up to 200 an hour – between 3 and 5 AM on Wednesday morning. It might be worth setting your alarm for a very early hour before you go to bed on Tuesday night.

If you do go out for a Perseid watch on Wednesday morning you'll find the Moon, sixty five percent illuminated, in the southeastern sky. Although the trails of Perseid meteors all point back toward the constellation Perseus, high in the east northeast, the meteors can appear in any part of the sky. The best meteor watching might be toward the northwest, away from the bright Moon. A comfortable lawn chair makes meteor watching more enjoyable, and a light blanket will protect you from the damp dew that often forms in the early morning hours. I also suggest being prepared for mosquitoes.

Saturn, like our Earth, is tipped on its axis, with a tip of almost 27 degrees. As Saturn make its twenty nine and a half year journey around the Sun our view of the rings changes. Back in late 2002 and early 2003 Saturn's southern hemisphere was tipped directly toward us and the rings were wide open. We had a superb view of their southern face. Since then Saturn's rings have been closing and they are now almost edge on. They appear tipped a little less than one and half degrees.

The Earth and Saturn are in slightly different orbital planes, so the view of Saturn from the Sun is somewhat different. On Monday Saturn's rings will be exactly edge on to the Sun, so sunlight will no longer be lighting the southern face of the rings but will be shining on the edge of the rings. When this happens the rings will essentially disappear and not be visible in a telescope.

Beginning on August 11 the Sun will be shining on the northern face of the rings, but we will still be looking – although poorly – at the now unlit southern face. Of course sunlight can shine through the rings although there is considerably variation in the density of material in different parts of the rings.

Unfortunately Saturn is now very poorly placed for telescopic observation and the Sun's ring crossing will not be well seen from Earth. When the Sun sets at 8:04 Saturn will only be 15 degrees above the western horizon. By the end of civil twilight at 8:47, you should be able to spot first magnitude Saturn, but it will be only seven degrees above the horizon. When we look at objects low in the sky we are looking through a very thick layer of atmosphere, and the views are often poor.

On September 4 Saturn's rings will be edge on as seen from Earth. Saturn will be even lower in the evening sky and viewing the planet will be even more difficult.

This is Dudley Observatory's Skywatch line for Friday, August 7, through Sunday, August 9, written by Alan French.

The Moon was full this past Wednesday so a waning gibbous Moon will dominate the night sky over the weekend. The Moon will rise at 8:43 on Friday evening. Each following weekend night will make moonrise only 20 minutes later than the previous night.

In spite of the bright moonlight, amateur astronomers have been watching early members of the Perseid meteor shower streak across the sky. Some have been quite bright. These meteors are caused by debris from Comet Swift-Tuttle. As comets travel around the Sun small bits of material are lost and left in the comet's orbit. When our Earth travels through the orbit of Comet Swift-Tuttle we get treated to a meteor shower as these high speed bits of material enter the Earth's atmosphere and are heated and vaporized as they compress and greatly heat the air ahead of them.

Astronomers have used observations from the annual Perseid meteor shower to map the debris left in Swift-Tuttle's orbit. This allows predictions of when the Earth will pass through a more concentrated area of debris than usual. This year they are predicting we may get a burst of activity – perhaps twice as high as normal – between 4 and 5 AM on Wednesday morning, August 12. It might be worth getting up a little early on Wednesday morning to see it their predictions are correct. A good meteor shower is always a treat. Perseus will be high in the east and the meteors can appear anywhere in the sky. The trails of members of the Perseid meteor shower will all point back toward Perseus.

By 11 PM Jupiter is well up in the southeast. Its four brightest moons, Io, Europa, Ganymede, and Callisto are all easily seen in virtually any telescope. From our vantage point they appear to shuttle back and forth from one side of the planet to the other. Sometimes they pass in front of the planet and cast their shadow on it. Sometimes they pass behind the planet and are either occulted or eclipsed. An occultation is when a moon simply passes behind Jupiter's limb. An eclipse is when a moon moves into Jupiter's shadow and vanishes from view. Moons can also reappear from occultation or eclipse.

On Friday at 11 PM telescope users will find Ganymede to the west of Jupiter, and Io, Europa, and Callisto will be to the east, in order from closest to farthest. By Saturday night at 11, Ganymede and Io will be to the west and Europa will be to the east. Callisto will be passing in front of the planet and difficult to see. Callisto's shadow, appearing as a small dot against Jupiter, should be easy to see. Sunday night will find Europa and Callisto close together and west of Jupiter, and Io and Ganymede to the east.

Dudley Skywatch Line for Wed. and Thurs., August 5 & 6, 2009:
by Ray Bogucki

This month, the planet to watch is Jupiter. Our giant neighbor will come to opposition in mid August, when it will rise in the east as the Sun sets in the west, and be visible throughout the night Jupiter is closest to us at opposition and its giant sphere will show a diameter of 48 arc-seconds and a brilliant magnitude of minus 2.9. The fascinating movements of Jupiter's four Galilean moons are worth following any time you are out at night with a telescope. Also keep an eye out for the dark scar left on Jupiter's surface when a large object collided with Jupiter around July 19, as reported in last week's Skywatch Line. Next week, we will be treated to the sight of thousands of collisions of small particles left in our orbit by the passage of Comet Swift-Tuttle. These collisions appear as the Perseid Meteor Shower which will be visible all next week with a maximum number of meteors appearing on Tuesday and Wednesday nights.

The remainder of this Skywatch Line will continue the theme of planetary impacts by foreign objects. In the Skywatch Line for October 15 and 16, 2008, we reported on a mini asteroid, about the size of an automobile, which was detected on a collision course with Earth. The asteroid was designated 2008TC3 and it collided with our upper atmosphere, as predicted, over the desert in Sudan. At an altitude of about 23 miles, it exploded with the energy of 1,000 or more tons of TNT, producing a flash and sonic booms across the area. Normally, little remains after such a collision, and any tiny fragments that reach the surface usually disappear into the ocean or other uninhabited places. This case was different because the remnants of the explosion would be charred and black, and if they fell on the light, tan colored desert, they might be recoverable.

With this idea in mind, Peter Jenniskens, a meteorite specialist with the SETI Institute contacted a professor of Physics at the nearby University of Khartoum to organize a search party. Within a couple of weeks they had assembed several busloads of students and staff. Using the global coordinates reported for the exploding asteroid, the volunteers were arranged in a very long line, spaced about 50 feet apart. They moved forward as a front, scanning the ground carefully, and within hours had recovered many small, black, porous stones which stood out against the tan surface. After a couple of later forays, the team had collected 280 specimens, from small pebble-sized to fist-sized, weighing about 11 pounds in total. Their appearance and composition identified them unmistakably as having come from the same recently heated source. The specimens, which are very unusual in structure and composition, are being studied and analyzed at several different laboratories. This event marks the very first time in astronomical history that an asteroid was first observed approaching the Earth, then monitored when it exploded, and finally recovered as remnants of the original object.

This is Dudley Observatory's Skywatch Line for Tuesday, August 4, written by Alan French.

The Moon, nearing full, rises at 7:32 PM and will not set until 5:21 tomorrow morning. Full Moon occurs tomorrow.

Jupiter is easily visible above the southeastern horizon by 11 PM. Even a modest astronomical telescope or spotting scope may reveal two dark bands crossing the planet. These are simply darker regions in the planet's atmosphere. At 11 PM all four a Jupiter's bright Galilean moons will also be visible through a modest telescope. Io will be very close to one side of the planet, while Ganymede, Europa, and Callisto will be on the opposite side. Callisto will be considerably farther from the planet than Ganymede and Europa.

Every night dozens of satellites are visible crossing the night sky. The ISS or International Space Station is the brightest and most obvious because it is very large. There are other satellites that are bright enough to be easily spotted. Lacrosse 4 passes high in our sky tonight and will be as bright as the brightest stars in the Big Dipper. The Lacrosse satellites are radar imaging reconnaissance satellites – spy satellites that use synthetic aperture radar to create high resolution photographs of features on the Earth.

The times for the satellite will be given in hours, minutes, and seconds. Lacrosse 4 will first appear at 9:57:37 PM coming up from the north northwestern horizon. It will highest at 10:02:27 when 75 degrees above the east northeastern horizon – essentially appearing right overhead. Lacrosse 4 will move into the Earth's shadow and vanish from sight at 10:04:31 when 34 degrees above the southeastern horizon.

The path of Lacrosse 4 will bring it up past the front of the Big Dipper, through the Little Dipper and Draco, the Dragon, and through Cygnus, the Swan. It will then past close to Altair, the brightest star in Aquila, the Eagle. Just after passing Altair, as it moves toward the Moon, the satellite will move into the Earth's shadow and fade from view.

This is Dudley Observatory's Skywatch Line for Monday, August 3, written by Alan French.

The Moon, approaching Full, will be in the southeast as the Sun sets. The Moon lies just east of the constellation Sagittarius, the Archer, which is easily recognized because its brighter stars nicely outline a Teapot. The handle of the Teapot is toward the east and the spout is toward the west. The Moon is at apogee – its farthest distance from Earth – at 9:00 PM this evening and will set at 4:18 AM Tuesday morning.

The constellation Perseus, the radiant or apparent origin of the Perseid meteor shower, will be above the horizon by 11 PM and skywatchers may catch a few of the brighter early Perseids against the moonlit skies. The shower will peak during the morning hours on Wednesday, August 12, through the morning hours of Thursday the 13th . Although all Perseid meteors do not start streaking across the sky in Perseus the trails will all point back toward Perseus.

Venus dominates the east northeastern sky in the hour before morning twilight and is visible long into the brightening sky. A telescope now reveals a gibbous phase.

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.