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Cat's Eye Nebula: July 3 - July 9, 2006.


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Plato and Vallis Alpes - Credit: Ricardo Borba.

This week we travel across the Moon, probe Jupiter's close approach, see the after effects of a recent supernova, and celebrate the lives of some prominent astronomers. All in all, it's an exciting week, so get outside.

Monday, July 3 - It might be hard to believe, but right now the Sun is farthest from the Earth.

Tonight, let's take a quiet journey on the lunar surface as we view an area highlighted by sunrise - the Caucasus Mountains. Easily spotted in both binoculars and small telescopes, this range towers some 5182 meters above the surrounding plains - making its peaks as high as Mount Ararat. As the shadows throw the rugged terrain into bold relief, take the time to enjoy watching the terminator move along the lunar surface. As time passes you can follow the mountain's shadows shortening and details emerging in Crater Cassini. It's a very peaceful experience...

Despite bright skies, let's observe 6.6 magnitude M62. Located roughly halfway between Alpha and Lambda Scorpii, this ordinarily bright cluster deserves a fine, dark night, but it's fun to locate. Distorted by its proximity to the galactic core, M62 is 22,000 light-years away. This globular cluster is intrinsically twice as bright as M10 and M12, and much more centrally condensed at Class IV.

Tuesday, July 4 - Today is the suspected date when Chinese Astronomers first noted the bright supernova event that corresponds with the Crab Nebula - M1. Well, it might not be a supernova, but something cool will happen tonight...the Moon will occult Spica! Such a bright star is quite fun to watch disappear behind the lunar limb and requires no special equipment to enjoy - just the right location. Be sure to check IOTA for times and areas.

If you explore the lunar surface this evening, you will find a very curious feature we've studied before known as the Alpine Valley. Located near the terminator in the north, look for a long, narrow scar creasing the foothills between Mare Frigoris and Mare Imbrium. Running a distance of 177 kilometers and ranging between 1.6 to 21 kilometers wide, this gash through the Montes Alpes includes tiny crater Trouvelot to its south. Stable conditions at high power will also reveal a narrow fissure on its floor.

If you'd like more, then let's revisit M19 through the less welcoming skies of moonlight. Many amateurs like to make a study of how seeing affects views in the night sky. Relocate other studies as well and see the difference!

Wednesday, July 5 - For SkyWatchers, have a look at the Moon tonight... Jupiter is very nearby.

Tonight at first glance, the most prominent features on the Moon will be the descending series of "rings" - Ptolemaeus, Alphonsus, and Arzachel. Between, and west, of Alphonsus and Arzachel you will discover a selenographer's delight! Power up to have a close look at Alpetragius. At 25 miles in diameter and 9800 feet deep, the sharp young crater has a massive central mountain peak precisely at its center. This huge, symmetrical dome towers 6200 feet above the crater floor and rivals neighbor Arzachel's central peak. While part of the crater may still be dark, be sure to look at the dazzling west wall and the summit of Alpetragius' fantastic mountain.

Ready to climb to greater heights? Then look north... Tonight one of the finest, bright planetary nebulae - NGC 6543 - calls for attention. At magnitude 8.1, the "Cat's Eye Nebula" is small and intense. On a still night - with or without the Moon - this feline beauty simply absorbs all the magnification you can send its way. About the only thing "wrong" with this planetary is how difficult it can be to find! High magnification is needed to distinguish it from a star - but the greatest challenge is the navigation skills needed to track it down. Start at Gamma Draconis and extend a line past Xi twice the distance between them. This leaves you about one degree south of NGC 6543. Now sweep the sky north-northeast until you make out that bright, but fuzzy star. Power up. As you observe this 3600 light-year distant planetary, think about how the "Cat's Eye" looks almost directly down from the north pole of the solar system. A view very similar to the "circles within circles" used by Ptolemy to explain the layout of planetary orbits!

Thursday, July 6 - Today in 1687, Isaac Newton's Principia was first published with the help of the Astronomer Royal of England - Edmund Halley.

Tonight on the lunar surface, previous study Copernicus will draw attention to itself, but let's head to the north and look for prominent little Class I Pytheas. Like a bright little ring standing alone in the southern half of dark Mare Imbrium, this high contrast feature will catch the eye. Just a bit more to the north is Lambert. Although it is marginally larger, notice how much darker it appears. Lambert stands on a great lunar ridge winding its way up from grand Eratosthenes, 250 miles southeast, and continues on for another 150 miles. As you observe, you may notice the ridge is just slightly lighter than the background. While Lambert is not as grand as its neighbor to the east - Timocharis, you might catch the sunlight reflecting off the hollowed-out remains of its central peak. It is believed that this is a collapsed area of a "rebound dome." A formation created when the crater formed during a particularly nasty impact.

Even though skies are bright, we can still study double stars - and we have a "double-double" in mind. Along with Orion's "Trapezium," Epsilon Lyrae is probably the most well-known multiple star system in the night sky. Just about any magnification, even binoculars, will resolve the main pair - but don't stop there. Drop in the power and look carefully as each of the wider members splits again. Any telescope capable of modest magnification will do the trick - but as in most things celestial - sky conditions rule. Note in particular the matched pair Epsilon-2 to the south and the disparate pair (Epsilon-1) to the north. On marginal nights of seeing, the pair of mismatched brightness (magnitudes 4.6 and 6.3) can be a tough split while the twins (magnitudes 4.9 and 5.2) may require little effort. Look for the "Double-Double" less than 2 degrees northeast of brilliant blue Vega.

Friday, July 7 - Tonight we'll observe a lunar feature near the southern terminator often overlooked for its grander neighbor - Clavius. Just take one step northwest and let's power up to study Longomontanus.

Named for Danish Astronomer and assistant to Tycho Brahe, Christian S. Longomontanus, this splendid mountain-walled plain shows a broken border on its north and an off-center mountain peak. Notice how its smooth sands have eroded its edges over time. Just outside its eastern wall, look for the remains of a much older crater destroyed when Longomontanus formed. Just to its north are the remains of Montanari, and the double strike of crater Brown to the northeast.

Before we call it a night, let's have a look at disparate double star Delta Herculis. A tough resolve for a small scope, this one promises to be a challenging double for mid-sized instruments. Bright Delta A glows at magnitude 3.0, while dim Delta B is at 8.1. The separation on this pair is 11 arc-seconds. We'll bring you back to this double later, along with other pairs to be observed over the next few nights. What a difference a dark sky will make...

Saturday, July 8 - While the gibbous Moon dominates the night sky, why fight it? Let's study it instead, as we head toward some challenging craters.

Start by identifying the long narrow ellipse of crater Schiller on the terminator to the south. Head further south along the terminator and look for a line of four prominent craters. Their interiors may be black, but the southwest walls will be brilliantly illuminated. The most striking of this quartet is Zucchius and depending on libration may be very shadowed. To its east is Bettinus, and at power you will see central peaks in both craters. Further southeast is Kirchner and to its east is the very old Wilson.

Just north of Bettinus and - at an angle to Zucchius - you will see a strange, walled, V-shaped area curving back to Schiller. This odd area is one of the Moon's older surface features. An aeon or two ago, this was part of a much larger structure which can be traced here and there amidst later forming craters. Since all that is now left is some hills and ridges, no one is certain if the area formed geologically or was caused by an impact.

But this isn't the only mystery in the universe. Why are so many stars in the night sky doubles? Do double stars form together? Are they created separately then later are gravitationally attracted? Or are doubles and multiple stars all that's left of an open cluster after the Milky Way pulls them apart through tidal forces? Who needs theory when these twosomes and threesomes make for such fine views!

Let's have a look at another "Herculean pair" - 3.5 magnitude Mu Herculis. Keep a sharp eye and use only enough power to darken the bright moonlit sky. Look for a dim 9.8 magnitude companion some 30 arc-seconds west-southwest of a golden 3.4 magnitude primary. During the current bright lunar phase, very small Telescopes will have difficulty with this one, but we'll be back.

Sunday, July 9 - On this day in 1979, Voyager 2 approached within 721,670 kilometers of Jupiter's cloudtops for its very closest pass. To see Jupiter tonight as Voyager II did, you'll need 207X magnification! As the sky darkens enough to locate this -2.3 magnitude "star," turn your scope on Jupiter - for what could be your last best look at the giant planet. Using 207X on the Moon gets you a lot closer than 721,670 kilometers. That magnification puts you within 1800 kilometers of the regolith. Now let's power up and have a close look at what is known to be one of the most transitory features on the lunar surface. To find it, begin by revisiting bright Aristarchus and note Promontorium Heraclides on Sinus Iridum's western tip. Just to the west and near the terminator you will see a small bump on the surface. This particular feature may not appear particularly striking in itself, but note how much brighter it is on its eastern slope. You are looking at Rumker - an object that cannot be seen at any power unless it lies near the terminator. Yet tonight it can be detected with binoculars! Rumker is an example of a lunar dome - a feature thought to be the remains of an ancient shield volcano.

Ready for another challenge? Then let's take on one of the toughest, and most beautiful, doubles in the night sky - Antares. This splendid, first magnitude red giant - "Rival of Mars" - is now high enough in the early evening to try to spot its 5.4 magnitude green companion. Like winter's Sirius, the Antares pair needs especially still - but not necessarily dark - skies. It also requires a well-chosen magnification - one high enough to separate the two close stars (2.9 arc seconds), but low enough to concentrate the fainter star's (magnitude 5.4) light.




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