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As the Moon exits the early evening scene, we return to pick up some of the summer season's finest studies. This week's studies are planetary nebulae, galactic and globular clusters, as well as a look at history. So, get out your binoculars or telescopes, because... Here's what's up! NGC 6826: “The Blinking Planetary”
Monday, September 11 - Today celebrates the birthday of Sir James Jeans. Born in 1877, Jeans was an astronomical theoretician. During the early 20th century, he worked out the fundamentals of gravitational coalescence, contributing significantly to our understanding of the formation of solar systems, stars, and galaxies.
With the Moon out of the picture early tonight, let's head to northwestern Cygnus and the “Blinking Planetary” - NGC 6826. This 10th magnitude nebula is joined by a matched magnitude central star. The result is eye confusion. When you look at the star, the nebula brightens due to slight aversion, and when you look at the nebula, the star brightens by the same optical effect. Check it out for yourself. Find the pair of stars marking the Swan's western wing tip - Kappa and Iota. Extend the line between them continuing south east the same distance and you'll find it easily northeast of Theta. Enjoy!
Tuesday, September 12 - With early skydark, let's have a look at another planetary in Cygnus - NGC 7027. This one is as bright as the “Blinking,” yet contains no central star. You'll find it about three finger-widths southeast of Deneb and about half that distance northeast of Nu. Power up and pay attention to the irregular shape of this planetary. How would you describe it?
Now let's look at the most splendid planetary nebula in the night sky for the small scope or binoculars - the “Dumbbell Nebula.” M27 is unquestionably the brightest study of its kind. Easily located around a finger-width north of Gamma Sagittae, it's not the largest of all planetaries but is the largest of its kind on the Messier list. M27's expanse and luminosity suggest that it is quite close to our own system. Appearing like a pale green apple core, we'll be back to visit this one later!
Today in 1959, the USSR's Luna 2 scored a hit as it became the first manmade object to strike the Moon. Let's continue to enjoy the warm summer evening as Luna and it comrade - the Pleiades - rises and have a look at its successful landing area in Paulus Putredinus.
The most outstanding lunar feature tonight is mid-placed Copernicus. From Copernicus head northeast to Eratosthenes - caught on the “tail” of the Apennine Mountains. Trace the curve of the Apennines northeast to locate prominent Archimedes - with smaller craters Aristillus and Autolycus to the east. South of this pair, and trapped along the mountain range, is a dark grey, heart-shaped area known as the “Rotten Swamp” - Paulus Putredinus. Look for the Apollo 15 landing site near Mons Hadley on the swamp's northeastern shore. More than a decade before Apollo 15, Luna 2 landed in the region between southern Autolycus and Archimedes. Spaseba!
Wednesday, September 13 - Tonight we have more than an hour of skydark to return for another look at M27.
A fascinating aspect of this planetary is its “living” quality - something apparent in even modest scopes. Several factors, such as light passing through this 1000 light-year distant cloud, make it seem to subtly shift in orientation. There are also a number of faint stars whose light seems to waiver and flux as they come to the edge of resolution. The central star, magnitude 13.5, may be a source of polarized light - creating an intense magnetic field. Whatever the source of the effect, observers agree with Burnham. “The observer who spends a few moments in quiet contemplation of this nebula will be made aware of direct contact with cosmic things; even the radiation reaching us from the celestial depths is of a type unknown on Earth...”
Today in 1922, the highest air temperature ever recorded on the surface of the Earth occurred. The measurement was taken as Libya burned at a blistering 136ºF, but did you know that the temperatures in the sunlight on the Moon double that?
If you're out when the Moon rises tonight, then let's take a look at a sunlit feature as we head for the bright point of crater Euler. Beginning toward the north in the Mare Imbrium region, look for this small, but conspicuous, crater near the terminator. Euler is roughly the same size as two craters to the east - Lambert and Pytheas - but has a noticeably higher central peak. If the timing is right, you may be able to see the peak of Mons Vinogradov peeking above the terminator to the west.
Thursday, September 14 - Early evening dark skies mean a great opportunity to view the “Little Gem Planetary” and “Barnard's Galaxy” slightly less than a fist width west of Beta Capricorni.
At lowest power in large scopes, the pair can be spotted together in the same field. The blue/white NGC 6818 will be north of a large, faint shimmer of a 1.7 million light-year distant dwarf Galaxy - NGC 6822.
If you'd like to try something new, return to M27 and head 2 degrees west-northwest to find NGC 6830. This rich 7.9 magnitude, cross-shaped open cluster is a real treat. Continue another 2 degrees in the same direction to pick up 7.1 magnitude cluster NGC 6823. Those with large Telescopes should look for a faint sheen of nebulosity associated with this youthful open cluster!
Friday, September 15 - Tonight at skydark look for Mercury and Mars having a close conjunction. For observers in the northern hemisphere, look for the “Summer Triangle” overhead. Bright, blue Vega is now beginning its descent while Deneb approaches mid-sky. Close, bright Altair is reaching its highest point to the south. Overhead you will see eight bright stars - Sadr, Delta, Epsilon, Alberio, Deneb, Tarazed, Zeta and Altair. Lying on your back, with your head toward Polaris, it's time to use your imagination and discover a large asterism called “The Sword in the Stone.”
Telescopically, you can find small densely populated 7.8 magnitude open cluster NGC 6834 near the very center of this image set in stars. Visible as a faint splotch in binoculars three finger-widths northeast of Alberio, most Telescopes scopes should reveal a line of 10th and 11th magnitude stars within a subtle haze of fainter members.
Saturday, September 16 - While still well positioned overhead, let's revisit M57 to see how “low you can go” with a small telescope. Try a number of magnifications to determine which one gives the clearest view of the 13.0 magnitude “test” star to its edge. Now, use low power to locate 8th magnitude globular cluster M56. You'll find it in a rich star field a little more than halfway between Gamma Lyrae and Alberio. Once located, try the same magnification used to hold our “test” star and see if you can now resolve some of this globular's 13th magnitude stars!
Although M56 might appear to fall within the borders of Cygnus, it technically is the second Messier study in Lyra. Found by Charles himself on January 19, 1779, this cluster lies some 33,000 light-years distant and is 80 light-years in diameter. Like most all Class X globulars, its faint stars are difficult to resolve.
Now let's locate two faint stars in tiny Sagitta - Delta and Gamma. Almost precisely between them, binoculars or finderscopes will reveal M56's “twin” - 8.2 magnitude M71. Aside from brightness, size, and beauty of stellar field, these two globulars have very little in common. M71 is roughly one-third as distant as M56, and its brightest stars approach the 11th magnitude. Most smaller Telescopes can resolve a string of stars (reminiscent of M4) across its core. Very loosely structured, it would be more fitting as an “uncertain class,” but its stellar Chemistry of high metal content stars means M71 has a dual identity as both dense open cluster and globular!
Sunday, September 17 - Today in 1789, William Herschel discovered Saturn's Moon Mimas. Tonight we'll look at another kind of “Saturn” as we locate the centermost bright star in the northern half of the constellation of Aquarius - Theta.
Three finger-widths north of Theta you will see dimmer Nu, and one finger-width west of Nu is NGC 7009. Nicknamed the “Saturn Nebula,” this wonderful blue planetary is around 8th magnitude and is easily achievable in small scopes and large binoculars. At moderate magnification, you will see the elliptical shape giving rise to its moniker. With larger scopes, those “ring like” projections become even clearer!
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