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Saturn’s Moon - Enceladus: August 28 - September 3, 2006.
Saturn returns to the morning sky and Selene is back to rule the night. Follow along this week as explore the lunar surface and find all that is bright and beautiful under the stars. Saturn by Wes Higgins.
Monday, August 28 - On this day in 1789, William Herschel discovered Saturn’s Moon - Enceladus. The ringed planet is barely skimming the horizon to the east just before sunrise with brilliant Venus. Be sure to check IOTA as well, for the Moon and Spica will perform an occultation tonight.
Although we have traveled this road before, let’s go further south than last night’s lunar study and have another look at Furnerius. Shallower and less impressive than Petavius, Furnerius will fade to obscurity as the Moon waxes. This flooded old crater has no central peak, but a much younger crater has punched a hole in its lava-filled floor. Look for the long "crack" extending from Furnerius’ north shore to crater rim. Perhaps it was caused by the impact? Sharp-eyed observers with good conditions and high power will also spot a multitude of small craters within and along Furnerius’ walls. For binocular viewers, try spotting crater Stevinus to the north and Fraunhofer to the south.
Tonight the Moon sets just as the sky gets dark and presents a fine opportunity to continue our ascent along the Milky Way. Let’s start with a quick look at M11 almost precisely between 3.5 magnitude Lambda Aquilae and 4.1 magnitude Alpha Scutum. At low power it’s possible to get the "Big Picture" of this fine example of a dense Milky Way cluster in northern hemisphere skies. Range through all your eyepieces to bring out more and more stars as the background sky darkens and resolution improves.
After you find the one eyepiece that gives M11 the best view, shift over to Alpha Scutum and check east-northeast for neighboring 7.8 magnitude open cluster NGC 6664. Compare the view to Scutum’s other Messier open cluster - similar sized M26. As one of the faintest Messier clusters, it’s surprising his scope was able to reveal it at all! To locate M26 shift a little less than 3 degrees south-southeast of Alpha. Those with larger scopes should look for a strange void in the middle of the cluster.
Tuesday, August 29 - Need some astronomical inspiration? Then just have a look at the Moon and Jupiter caught together tonight in the starry sky.
On the lunar surface, head to the eastern shore of Mare Nectaris to catch an easily noticed broken black line. This is the western flank of the Pyrenees Mountains which stretch close to 350 kilometers north to south. The black line you see is a good example of a lunar scarp, a feature more like a cliff than a true mountain range. This scarp ends to the north in crater Guttenberg. Just south of Guttenberg, you will find high contrast Santbech.
The Moon is now becoming the "highlight" of the night sky. Try using "higher power" to diminish some of its glare. While southwestern Sagittarius is also high, why not observe some of its other globular clusters?
Center the scope on Epsilon and sweep less than 3 degrees north-northeast to find small 7.7 magnitude globular M69. M69 gives an appearance similar to that of other compact clusters - such as M28 and M80. Small and moderately bright, it appears coarsely textured through smaller instruments and requires larger scopes to bring out its brightest 14th magnitude members. This cluster sits near a blue 7th magnitude star which complicates seeing M69 through binoculars and finderscopes.
Now head a little more than a degree southeast, then north of a pair of 6th magnitude stars to locate NGC 6652 - a very small 9th magnitude globular. Go less than 2 degrees northeast to find brighter (8.1 magnitude), larger M70. Notice how more of M70’s light is concentrated in its core than M69. Continuing a little more than 3 degrees in the direction of Zeta we encounter M54. Through a modest scope, this 7.7 magnitude globular is small, very blue, and intensely concentrated at the core. Larger amateur instruments will only bring out a few 15th magnitude members out of this globular’s faintly glowing form.
Charles Messier discovered M69 and M70 on August 31, 1780 from Paris while trying to confirm a discovery made by Lacaille using a half-inch spyglass in South Africa. These two globulars lie within 2,000 light-years of each other and less than 30,000 light-years from Earth. Due to unusual richness in metal content - for astronomers, "metals" are any elements other than Hydrogen and helium - M69 may be a relatively young cluster. At some 90,000 light-years, M54 is the most distant Messier globular cluster - and may not be a globular at all - but the core of a dwarf Galaxy beyond the bounds of the Milky Way! In fact M54 is intrinsically larger (300 light-years in diameter) and brighter (magnitude 10.1) than any other globular within the Milky Way itself.
Wednesday, August 30 - On the lunar surface tonight, we’ll return to identify Metius, Fabricus and Janssen to the south. Southwest of this trio you will see a sharply defined small crater known as Vlacq. Power up to resolve its small central mountain peak. Angling off to the west and extending westward is multiple crater Hommel. Look especially for Hommel A and Hommel C which fit nicely and precisely within the borders of the older crater. Note how many individual craters make up its borders. Just north of Hommel is Pitiscus and to its south is Nearch.
Tonight with the Moon in Libra and low to the southwest, deepsky studies will still continue to only be mildly hampered. The main study for tonight will definitely improve once the Moon sets - so while we’re waiting, let’s drop by open cluster M29 less than 2 degrees south-southeast of Gamma Cygni. At lower power, or through small scopes, its handful of brightest members makes this 6.6 magnitude open cluster look more like an asterism than a real group. Lacking any sense of a core, higher power and larger scopes will bring out another dozen or so stars. Those with binoculars will enjoy seeing a few of M29’s brightest stars against a vague nebulosity.
Now let’s see what the "I" can "C"... Less than 2 degrees southwest of M29 (just south of 5th magnitude P Cygni) lies another open cluster of similar brightness and size to M29 - IC 4996. How do these two compare? The less conspicuous IC 4996 lies in a richer Milky Way field and consists of fewer and more compact bright stars. Smaller scopes see this one as a patch of nebulosity.
Now for M55. Found in the far reaches of eastern Sagittarius, and west-southwest of Zeta, M55 is one of the coarsest globulars known. At magnitude 7.0, M55 can be seen as a large pale ghost of luminosity in binoculars or finderscopes. This is one very open globular cluster! A multitude of fine, easily resolved stars spread oblately over the mid-power field. Long exposure photos show this to be a true globular glowing with the combined light of almost 100,000 suns.
Thursday, August 31 - Watch as the Moon and Antares slow dance together tonight. Be sure to check IOTA for an occultation...
Tonight’s prominent lunar features are also Astronomical League challenges. Look southwest of previous study Theophilus for the huge form of Maurolycus. Its cratered floor may be either partially lit or fully disclosed depending on your observing time. Note especially Maurolycus’ multiple central mountains. North of Maurolycus you will see the well-eroded remains of Gemma Frisius. Its broken walls will show well under current illumination. Finally look carefully for crater Goodacre which has destroyed Gemma Frisius’ northern wall.
Tonight we begin entering the stream of the Andromedid meteor shower, which peaks off and on for the next couple of months. For those in the northern hemisphere, look for the lazy "W" of Cassiopeia to the northeast. This is the radiant - or relative point of origin - of the stream. At times, this shower has been known to be spectacular, but let’s stick with an accepted fall rate of around 20 per hour. These are the offspring of Beila’s Comet, one that split apart leaving radically different streams. The Andromedids have a reputation for red fireballs with spectacular trains, so watch for them in the weeks ahead.
If you decide to take the scope out tonight, now would be an excellent opportunity to revisit your southern summer sky favorites!
Friday, September 1 - In 1859, solar physicist Richard Carrington observed the first flare ever recorded. Naturally enough, an intense aurora followed the next day. 120 years later in 1979, Pioneer 11 made history as the first probe to fly by Saturn.
Tonight the waxing Moon will be above the Scorpion’s tail. Its most notable features will be the vast area of craters dominating the south-central portion near and along the terminator. Now emerging is Ptolemaeus - just north-northeast of Albategnius. This large round crater is a mountain walled plain filled with lava flow. With the exception of interior crater Ptolemaeus A, binoculars will see it as very smooth. Telescopes however can reveal faint mottling in the surface of the crater’s interior, along with a single elongated craterlet to the northeast. Despite its apparent uniformity, close inspection has revealed as many as 195 interior craterlets within Ptolemaeus! Look for a variety of interior ridges and shallow depressions.
With the Moon low to the southwest, we have a chance to go northeast to Cepheus for a new study - NGC 7160. At magnitude 6.1, this small open cluster is easily identified in scopes and may be seen as a faint starfield in binoculars. You’ll find it about a finger-width north of Nu Cephei.
Saturday, September 2 - On the lunar surface tonight, we’ll start by following the southward descent of large crater rings Ptolemaeus, Alphonsus, and Arzachel to a smaller, bright one southwest named Thebit. We’re going to have a look at Hell...
Just west of Thebit and its prominent A crater to the northwest, you see the Straight Wall - Rupes Recta - appearing as a thin, white line. Continue south until you see large, eroded crater Deslandres. On its western shore, is a bright ring that marks the boundary of Hell. While this might seem like an unusual name for a crater, it was named for an Astronomer - and clergyman!
Once you’ve been to Hell, let’s go to the heavens for NGC 7235. Locate the star crowded area of Epsilon Cephei which will also include this 7.7 magnitude open cluster in the same low power field. Give it a try. Look for a small, rectangular assortment of 10th magnitude and fainter stars west-northwest of Epsilon.
Sunday, September 3 - Today in 1976, the Viking 2 lander successfully touched down on Mars. By today’s technological standards, the type of equipment aboard Viking 2 would be considered antiquated, so why don’t we visit a couple of "antique" lunar features tonight?
Due south of mighty Copernicus on the eastern edge of Mare Cognitum, you will see a ruined pair of flattened craters. They are Bonpland and Parry - with Frau Mauro just above them. The smallest and brightest of these ancient twins is the eastern Parry. Have a look at its south wall where a huge section is entirely lost. It was near this location that Ranger 7 ended its successful flight in 1964. Just south of Parry is another example of a well-worn Class V crater. See if you can distinguish the ruins of Guericke. Not much is left save for a slight U-shape to its battered walls. These are some of the oldest visible features on the Moon!
If you’d like to head for something very young, have a look at 6.8 magnitude open cluster NGC 6811 in Cygnus. This mid-sized, unusually dense open cluster is found less than finger-width north-northwest of Delta - the westernmost star of the Northern Cross. Like most open clusters, the age of NGC 6811 is measured in millions, rather than billions, of years. Visible in binoculars on most nights, Telescopes should show a half dozen or so broadly-spaced resolvable stars overlaying a fainter field. Be sure to return again on a moonless night, and have another look a disparate double Delta!
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