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Galactic star clusters: October 16 - October 22, 2006.
As dark skies return at a sane hour, we'll spend this week checking in on galactic star clusters and nebulae. No scope? No problem! The brilliant Venus is back just before dawn and the week ends with one of the year's most reliable meteor showers. So turn an eye towards the sky.
Monday, October 16 - With early evening dark skies, let's return to the region of Cas A and see what else we can find. Although Cas A itself is invisible in amateur equipment, it is known to be associated with a 10,000 light-year distant supernovae remnant related to an unnoticed event occurring more than 300 years ago. The remnant itself has now expanded to a region filling some 10 light-years of space and has been imaged using orbiting X-ray observatories.
The closest deepsky study to Cas A is the dense and compact open cluster NGC 7510. This diminutive, magnitude 7.9 study can be just glimpsed as a hazy patch in large binoculars and small scopes, with a few of its brightest 10th magnitude members resolvable at higher magnifications. Doubling the aperture brings out a dozen or so 12th magnitude stars against the teeming glow of numerous fainter members. Double the aperture again, and 60 stars to magnitude 14 are possible. Many amateurs have discovered that the combination of a small rich field refractor, a 6″ apochromatic refractor, and 12″ newtonian makes for the ultimate in observing equipment...but don't forget those binoculars!
Tuesday, October 17 - Tonight the large, bright and scattered open cluster M39 is in favor just after skydark. Located between Deneb and Lacerta, this 4.0 magnitude cluster can be seen as a faint haze unaided and easily resolves into over a dozen stars through binoculars. Since we've visited with this one before, let's use it as a touchstone and look around to see what else is up there!
A degree and a half south of M39 is its “echo” - the large, faint, 7.2 magnitude open cluster NGC 7082. Easily overlooked within a V-shaped array of brighter stars, this cluster takes some concentration, along with a larger scope, to perceive resolve it as physical members based on its two dozen or so faint components.
Returning to M39, head two finger-widths southwest in the direction of Deneb to seek 6.8 magnitude IC 1369. Mid-sized instruments will show a dozen or so 12th and 13th magnitude members within a misty haze.
Look for Regulus accompanying tonight's Moon!
Wednesday, October 18 - If you're up before dawn have a look at two brilliant points of light - Venus and Spica. Today in 1959, Luna 3 began returning the first photographs of the Moon's far side. Also today - but in 1967 - Venera 4 became the first spacecraft to probe Venus' atmosphere.
Today Venus lies within 3 degrees of the Sun and 4 degrees of Mars - some 108,000,000 kilometers from Earth. The proximity of Venus and Mars to the Sun was thought of as a form of “combustion” by ancient Astronomers - many of whom also practiced alchemy and astrology. Today we no longer think of the Sun as actually renewing the planets by fire, but we know that trying to observe Mars and Venus under such circumstances is hazardous to the health of our optical orbs!
Instead, let's return tonight to use M39 as our touchstone and seek out something well-away from the blinding Sun. Starting with M39 head less than two finger-widths east-southeast to a 7.2 magnitude open cluster. This one is associated with the 12th magnitude “Cocoon Nebula.” Collectively known as IC 5146, this cluster with nebulosity consists largely of 12th magnitude stars, and is around mid-sized. Barely detectable in a small scope, this 4000 light-year distant cluster needs aperture to come out and play. Large scopes may make the nebula possible - although an appropriate filter may be necessary from most observing sites. To assist in finding the Cocoon, look for the stream of the obscuration nebula B168 touching its eastern frontier.
Thursday, October 19 - Not only is the Moon furthest from Earth right now, but it will also occult asteroid Juno at approximately 18:00 UT.
Dark skies mean the perfect chance to have another look at the “Saturn Nebula” now well positioned at skydark. At magnitude 8.0, the Saturn Nebula - NGC 7009 - can be located through binoculars, but due to small apparent size, may not be easily recognized. Here's your opportunity to use a small scope at low power and make a study of two fine nebulae - NGC 7009 and M57. Your assignment, should you decide to accept, is to view them using both binoculars and a low power telescope to see how they fit in with brighter stars in their fields. This will improve your sense of the way larger planetary nebulae look through binoculars.
Friday, October 20 - We are now slipping into the stream of Comet Halley and one of the finest meteor showers of the year. If skies are clear tonight, this would be the perfect chance to begin observations of the Orionid meteor shower. But get to bed early and rise well before dawn!
Have a large scope and want a challenge? Try the 10th magnitude, “bright” reflecting nebula NGC 7023. To locate this difficult study, start at 3.0 magnitude Beta Cephei and head southwest less than two finger-widths to 5.2 magnitude T Cephei. What? No T? It makes sense - this one is a Mira-type variable capable of going “deep” - to magnitude 11.3! Instead center on a solitary 7th magnitude star (SAO 19158) and avert your vision to scan around. Look for an oriental fan-shaped nebulosity to the south. This is the brightest portion of the nebula itself. Very large amateur scopes will also begin to reveal the very faint cluster now condensing out of this nebulous cloud of gas and dust.
Saturday, October 21 - Be sure to be outdoors before dawn to enjoy one of the year's most reliable meteor showers. The offspring of Comet Halley grace the early morning hours as they return as the Orionid meteor shower. This dependable shower produces an average of 10-20 meteors per hour maximum, and best activity begins before local midnight on the 20th, and reaches its peak as Orion stands high to the south about two hours before local dawn the 21st. With only one day to go until New Moon, this looks to be the year's premier meteor shower!
Although Comet Halley has now departed the inner Solar System, its debris trail remains well organized - allowing us to predict when this meteor shower will occur. The Earth first enters the stream at the beginning of October and does not leave until the beginning of November. This makes your chances of “catching a falling star” above average! These meteors are very fast, and although faint, occasional fireballs do leave persistent trails.
For best success, get away from city lights. Face south-southeast, relax and enjoy the stars of the Winter Milky Way. The radiant is near Betelguese, but may occur from any part of the sky. The meteor watching experience is much more comfortable if you include a lawn chair, blanket, and thermos of your favorite beverage.
Clouded out? Don't despair. You don't always need eyes or perfect weather to keep the watch. Tune an FM radio to the lowest frequency that doesn't receive a clear signal. An outdoor FM antenna pointed to the zenith increases your chances - but isn't essential. Simply turn up the static and listen. Those hums, whistles, beeps, bongs, and occasional snatches of signals are distant transmissions being reflected off a meteor's ion trail!
Sunday, October 22 - Something very special happened today in 2136 B.C. A solar eclipse occurred and it had been predicted by Chinese astronomers. A good thing, because royal Astronomers were executed for failure!
Today is the birthday of Karl Jansky. Born in 1905, physicist Jansky was also an electrical engineer. His pioneering discovery was non-earth-based radio waves at 20.5 MHz. This serendipitous discovery occurred while investigating radio noise in 1931 and 1932.
In 1975, Venera 9 kept busy for almost an hour sending Earth its very first look at Venus' sharply-etched surface of flat rocks and angular stones.
Tonight is New Moon: it's the perfect time to revisit the Veil Complex and North American Nebula. Having trouble aiming at the zenith? Then let's leave these two nebulae for an hour and head off to revisit the “Cluster and Galaxy” pair that are well positioned at skydark in Cepheus - dense open cluster NGC 6939 and 9th magnitude face-on spiral NGC 6946. Take the time to travel a fist width northeast of Deneb for M39 as well.
Interested in something new while we're waiting? Try M73 - a faint asterism of stars in southern Aquarius - and its neighbor M72 - the faintest of Messier globular clusters. Like double star M40, the asterism M73 is an anomalous study whose nebulous appearance qualified for Messier's list of comet-like objects. Through a modest scope, this asterism appears to be a small triangle of three 10 to 12th magnitude stars. The brightest is south, mid is north and the dimmest is to the west between the two brighter members. High power will show the 12th magnitude star to be double - separated by about 10 arc-seconds. Larger scopes will hold all four stars in the asterism direct. Most observers agree these four stars seem to be related.
M72 was discovered on the night of August 29, 1780 by Pierre Méchain. This 55,000 light-year distant globular is the most challenging of the 29 Messier globular clusters. At magnitude 9.2, and 7 arc minutes in apparent size, Class IX M72 is almost beyond detection at low power through average scopes. Small, dim, and not particularly condensed, it's amazing that Méchain managed to detect it, but you'll find them both southwest of Nu Aquarii.
May all your journeys be at light speed... Tammy Plotner with Jeff Barbour.
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