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Welcome again to our monthly newsletter with features on exciting celestial events, product reviews, tips & tricks, and a monthly sky calendar. We hope you enjoy it!

• Eclipse at Dawn
  Lately most of the lunar eclipses visible in North America have been evening events. This month we’re in for a change: a morning eclipse!
     
• Star Charts for Planning Observations
  Geoff Gaherty describes the method he uses to generate all-sky charts.
     
• August Meteor Shower Will Be 'A Great Show'
  The annual Perseid meteor shower is expected to put on a great show this year, peaking in mid-August with a display of dozens of shooting stars each hour.
     
• Constellation in Focus: Lyra
  Bright stars, quadruple stars, and one of the best known planetary nebulas.
     
• Astrophoto of the Month
  Graeme Quinn shoots the Southern Globular Cluster Omega Centauri
  

On the morning Tuesday August 28 there will be an eclipse of the Moon, visible in part over most of North America. The full eclipse will be visible west of the Rockies; the rest of the continent will see the beginning of the eclipse, but the Moon will set before it is finished.

Lunar eclipses are caused by the shadow of the Earth falling on the Moon. They can only occur at Full Moon, but not at every Full Moon because usually the Earth’s shadow passes above or below the Moon. A couple of times a year, Sun, Earth, and Moon line up exactly, and we get a lunar eclipse.

The Earth’s shadow has two parts, called the penumbra and the umbra.

The umbra is the central part of the shadow, where the Sun’s light is completely blocked except for the dim reddish light refracted through the Earth’s atmosphere, the light of all the world’s sunrises and sunsets.

The penumbra is the outer part of the shadow, where at least some of the light comes directly from the Sun. The whole effect is like a bull’s eye: the dark central umbra surrounded by the lighter penumbra.

Many eclipses are called “partial” because the Moon is never completely immersed in the umbra, but this eclipse is total, with the Moon passing almost through the centre of the umbra. This makes it one of the longest total lunar eclipses possible, with totality lasting a full 90 minutes.

Lunar eclipses take place at exactly the same time, wherever you observe them from, but appear to take place at different times because of the rotation of the Earth, causing the local times to be different. This table shows the local times for the major time zones across North America. It also shows the local times of moonset for major cities in each time zone, which will cut the eclipse short.

I’ve shaded the times of parts of the eclipse which won’t be visible in a particular time zone because the Moon will be below the horizon. The important events in an eclipse are as follows:

P1: Penumbral first contact: when the very first shading appears on the Moon.

U1: Umbral first contact: when the dark central umbra first touches the Moon.

U2: Umbral second contact: total eclipse begins.

Greatest: Greatest eclipse: when the Moon is closest to the middle of the umbra.

U3: Umbral third contact: total eclipse ends.

U4: Umbral fourth contact: when the umbra leaves the Moon.

P4: Penumbral fourth contact: very last shading leaves the Moon.

Notice how more of the eclipse is visible the farther west you go. People in the Pacific time zone will see the entire eclipse, while people in the Atlantic zone will see a partially eclipsed Moon set.

In every case, the Sun will begin to rise just as the Moon sets, as always happens at Full Moon.

The Eclipse in Starry Night®

Starry Night® can depict the lunar eclipse really well. I’ve set the location to New York, NY, which automatically shows the view from Central Park. The time is set to 5:30 a.m., with the Moon about a third of the way into the umbra. Under Options:Solar System:Planets-Moons I can set Starry Night® to display the Earth’s shadow and outline the edges of the umbra and penumbra. This is the result:

By advancing time, I can see the Moon move deeper into the shadow until it sets just to the left of the twin skyscrapers at right, deep in eclipse.

Observing the Eclipse

A lunar eclipse is an event for every stargazer! Whether you observe it with your unaided eyes, with a binocular, or with a small telescope, you will have a beautiful view. Because this eclipse carries the Moon particularly deep inside the Earth’s shadow, we can expect deep and beautiful colors.

It’s interesting to see how dark the Moon gets during totality by comparing it to the brightness of the stars; here it helps if you normally wear strong glasses so that, by taking them off, both the Moon and the stars will appear as fuzzy blobs!

If you’re observing with high power binoculars or a small telescope, you can record the times when craters are immersed in shadow and when they emerge; timings to the nearest tenth of a minute are adequate.

Every eclipse is a major photo opportunity, and this one will be particularly so because, for much of the continent, the Moon will be low in the western sky.

Ordinary cameras can make as good pictures as telescopes of a lunar eclipse, but remember, if you normally keep a filter over your lens, to remove it for the eclipse. Filters often cause unwanted reflections, and I once ruined a set of eclipse pictures by leaving my filter on!

Be sure to post your eclipse reports and images on the Starry Night® Yahoo Group for all of us to enjoy:

• tech.groups.yahoo.com/group/StarryNight/

Geoff Gaherty
Geoff has been a life-long telescope addict, and is active in many areas of visual observation; he is a moderator of the Yahoo "Talking Telescopes" group.

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Even though Starry Night® offers a great system for generating lists of objects to observe, I’ve personally always found a graphical presentation more useful.

I’ve never really cared for the 180° all sky charts which you see in most books and magazines, and which Starry Night® generates automatically. I find the scale too small and the constellations appear distorted. I prefer to generate a set of four larger scale charts, each depicting a quarter of the sky, centred on the four points of the compass and each showing the sky from horizon to zenith.

Let’s suppose I want to observe objects from Messier’s catalog around 10 p.m. on New Moon night, August 12, from my farm in Coldwater, Ontario. I start by setting Starry Night® to this time and date. On the Options pane, I add the things I want on my chart: the constellation stick figures and boundaries, and the Messier objects. Since I’ll be observing with a Dobsonian, I also turn on the Alt-Az Grid.

The major trick I’ve discovered is how to generate a chart which includes exactly 90° from left to right and also from horizon to zenith. Here’s how to do it.

First open the pane on the left side of the screen; it doesn’t matter which tab you click. Between the pane and the tabs is a very narrow vertical blue strip with a single short vertical line in its middle. This is the handle which lets you adjust the width of the pane, but it also allows you to adjust the dimensions of the viewing window.

Put your mouse on this narrow strip and experiment with dragging it to the left and right.

As you do so, observe what happens in the Zoom window at the far right end of the tool bar. Strangely enough, the “width” dimension stays the same (100° is the default) while the “height” dimension changes. Adjust it until the two numbers are the same (100° say) and leave the blue strip there.

Now click on the arrow on the right side of the Zoom box and select 90° from close to the bottom of the menu. Drag the sky image downwards with the mouse until the two tiny arrows forming a circle appear at the top of the screen. Back up a tiny bit until they just disappear. Your window is now set to display 90° of the sky from east to west, and 90° from horizon to zenith.

To get four exact quadrants of the sky facing North, West, South, and East, turn on the scroll bars under the View menu. If you slide the scroll slider all the way to the right of the scroll bar, you will be viewing North. Print this chart with the following settings <N.pdf>:

• 1 Pane ON
• “Full Sky” Chart (180°) OFF
• Fill page when printing OFF
• Use current settings ON
• Print legend ON

Now click once in the scroll bar to the left of the slider. The chart will now be centred on the Western sky. Print this chart <W.pdf>. Click again to the left of the slider, and you’ll get the Southern view. Print <S.pdf>. A final click will move the view to the East. Print the final chart <E.pdf>.

I find charts in this format extremely easy to use in planning my observations. I concentrate first on the objects towards the bottom of the South chart, because these are low in the sky and will never get any higher. Then I look for objects low on the West chart because they too will be setting soon. I can be more relaxed looking for objects on the East chart, and leave those on the North chart for last, because they are mostly circumpolar.

I avoid objects right at the tops of the charts because these are in “Dobson’s Hole,” the part of the sky hard to reach with a Dobsonian mounted telescope. In an hour or two, these objects will have moved to a more comfortable position.

I use charts like these for all my observations, for example plotting all of the variable stars currently on my observing program. I can prioritize my observations in seconds, and easily see which objects will be conveniently close to each other for observing.

When I was observing the Herschel 400 deep sky objects, I put together a customized Starry Night® observing list of the objects I had yet to observe, and then removed the ones I’d observed each morning after I finished an observing session.

It gave me a sense of accomplishment to see the plotted objects gradually disappear until all were gone, and I’d completed the list!

Geoff Gaherty
Geoff has been a life-long telescope addict, and is active in many areas of visual observation; he is a moderator of the Yahoo "Talking Telescopes" group.

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The Moon will be out of the way, leaving dark skies for good viewing as Earth plunges through an ancient stream of comet debris. Little bits, most no larger than sand grains, will vaporize in Earth's atmosphere, creating sometimes-dramatic "shooting stars."

"It's going to be a great show," said Bill Cooke of NASA's Meteoroid Environment Office at the Marshall Space Flight Center in Alabama. "The Moon is new on August 12, which means no moonlight, dark skies and plenty of meteors."

Chuck Hunt captured this image over the dark sky near Mansfield, Ohio on August 12, 2006. He writes “Observed for an hour, this meteor came at 10:05 PM. The Moon wasn't up yet. It seemed to be a slow mover and appeared orange. Beginning of trail has a rainbow of color.”

How many?

This year the Perseid meteor shower could deliver one or two visible streaks every minute during peak times, Cooke said in a statement yesterday. Urban skywatchers will see fewer due to local light pollution.

The meteors in this shower all appear to emanate from the constellation Perseus. The best times to watch will be late night Aug. 12 through dawn Aug. 13.

"The August Perseids are among the strongest of the readily observed annual meteor showers, and at maximum activity nominally yield 90 or 100 meteors per hour," said Joe Rao, SPACE.com's Skywatching columnist. "However, observers with exceptional skies often record even larger numbers."

Observing Tips

To see the show, one need only find a comfortable spot with a clear view of the northeast horizon, away from local lights. A dark rural location is best. Lie back on a blanket or lounge chair and scan the entire sky. In the late evening, starting around 9 p.m. local time, sharp-eyed observers might see "earth-grazing" meteors that skim the northeast horizon.

"Earth-grazers are long, slow and colorful," Cooke said. "They are among the most beautiful of meteors." But don't expect more than a handful in an hour, he said.

Later and during the overnight hours, the shooting stars will be higher in the sky as Perseus rises. Some skywatchers enjoy counting the number of meteors they see per minute, per hour or during a 15-minute interval and comparing notes.

Telescopes and binoculars are no help, as the meteors move too swiftly and are best observed with the naked eye.

The cosmic rivers of debris have been laid down for millennia by the comet Swift-Tuttle, which passes through the inner solar system every 130 years. Perseid meteoroids are exceptionally fast, entering Earth's atmosphere at roughly 133,200 mph (60 kilometers per second) relative to the planet, slamming into the air like bugs hitting a windshield.

• Top Ten Perseid Meteor Shower Facts
• Perseid Meteor Shower Images 2006
• Perseid Metero Shower Images 2005

Robert Roy Britt
Senior Science Writer, space.com

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Lyra is currently well placed for observation. Overhead during and after dusk, it passes through the zenith around midnight.

Vega is the northern hemispehere's second brightest star; only Sirius, at a magnitude of -1.5, is brighter. Because the Earth's spin is slightly imperfect, its axis carves a circle on the sky every 26,000 years. The phenomenon, called precession, means that as time progresses each pole, north and south, points to different stars. 13,000 years ago, Lyra was directly above our north pole and therefore acted as our Pole Star. And in another 13,000 years or so, it will once again act in that capacity.

One of the best known planetary nebulas is M57, lying roughly half way between Sheliak and Sulafat. Its cosmic bagel structure is apparent even in a 3" scope and, with larger apertures, only becomes clearer and more detailed. Try several levels of magnification.

M56 is a fairly dispersed globular cluster.

Finally, Epsilon Lyrae is one of the most beloved double star systems. It's fairly easy to split the first double, but higher magnification reveals that each component is itself a binary system.

Sean O'Dwyer
Starry Night® Times Editor

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Southern Globular Cluster Omega Centauri
Graeme Quinn took this photo from suburban Adelaide in South Australia. Taken with a Canon 350D at prime focus of a Takahashi FS-102 on an EM-10 mount. A combination of 23 4-minute exposures.

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