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Galaxies of spring. What’s Up this Week - June 19-25, 2006.


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Virgo Galaxy Cluster.
Virgo Galaxy Cluster - Credit: NOAO/AURA/NSF.

Get ready to rock as the week opens with the another stream of the Ophiuchid meteor shower and summer studies begin in the Milky Way. Venus teams with the crescent Moon and we’ll go globular as we head out to party under the stars, because....

Before you read this week’s What’s Up, I just wanted to remind you that What’s Up - 365 Days of Skywatching now has a blog of its own. You can access it by going to http://www.astrowhatsup.com
We’ll be adding many more features, with cool photographs for every day, so come check it out.

Now, on to the week.
Monday, June 19 - The galaxies of spring have now progressed to the west. Rich in variety and prodigious in number, they are now giving way to the star clusters and intragalactic nebulae of summer. Doesn’t it make sense to bid adieu to what could be the last of them before turning binoculars and Telescopes elsewhere? If you could revisit one Galaxy in particular which would it be?

Tonight, before that vast assembly of "island universes" rides off into the sunset, head out with scope on mount and charts in hand. Make an evening of parting company with those great whirling vortices of light others may call "home"...millions of light-years away!

Tuesday, June 20 - With very little Moon in pre-dawn hours, we welcome the "shooting stars" as we pass through another portion of the Ophiuchid meteor stream. The radiant for this pass lies nearer Sagittarius and the fall rate varies from 8 to 20 per hour, but the Ophiuchids can sometimes produce more than expected!

Ready for a new direction in observing? Then look no further than the tail of the Scorpion and get ready to head south - then north. - The Summer Milky Way is upon us!

Let’s start with a "bright star and globular cluster" view. Some of the most easily found studies in the night sky are ones residing in the same field with bright, recognizable stars. And, some the most difficult things to observe in the night sky are - you guessed it - faint studies lying near overwhelmingly bright stars! But there are compromises...

Less than 3 arc minutes east of 3.3 magnitude G Scorpii (the tail star of the Scorpion) is 7.4 magnitude globular cluster NGC 6441. No challenge here. This 38,000 light-year distant compact cluster is around 13 thousand light-years from the galactic core. It was first noted by James Dunlop from southeastern Australia in 1826.

Around two and a half degrees northeast of G Scorpii (and NGC 6441) is another interesting deep sky twosome - bright open cluster M7 and faint globular NGC 6453. M7 was first recorded as a glowing region of faint stars by Ptolemy circa 130 CE. Located 800 light-years away, the cluster includes more than half a dozen 6th magnitude stars easily resolved with the least amount of optical aid. Through telescopes, as many as 80 various stars can be seen.

Now head northeast and the faint haze of 31,000 light-year distant globular cluster NGC 6453 will reveal itself to mid- and large-sized scopes. Like NGC 6441, this globular was discovered from the southern hemisphere, in this case by John Herschel on June 8, 1837 while observing from the Cape of Good Hope, South Africa.

Wednesday, June 21 - Dark skies continue tonight and we’ll continue following the great expanse of the Summer Milky Way.

Our first stop will be the "Butterfly Cluster" - M6. About the size of the full moon, this scattering of 7 to 12th magnitude stars looks like its namesake. The "wings" are easily seen as two lobes east and west of the cluster’s main body. Around 75 blue and blue-white stars are visible at low power.

Want more? Head northeast a little more than one degree to reveal the expansive, 5.5 magnitude open cluster NGC 6383. Continue to sweep west at low power to find what might be expected as a very faint sheen of stars - 9th magnitude NGC 6374. What’s that? You can’t find it? Then you’ve just learned an invaluable lesson - some things in J. L. E. Dreyer’s catalogue simply don’t exist!

Thursday, June 22 - Celestial Scenery Alert! Although no one likes to get up early, the morning skies will be quite worth it. The Moon, loaded with earthshine, and brilliant Venus will be dancing just ahead of sunrise.

Today celebrates the founding of the Royal Greenwich Observatory in 1675 - 331 years of astronomy in a single location! Home to Flamsteed and Halley, the observatory was established by King Charles II to study human and sidereal time. We know it as the landmark for the Prime Meridian of the Earth and the universal time (UT) standard. Also on this date in history (1978), James Christy of the US Naval Observatory in Flagstaff, Arizona discovered Pluto’s satellite Charon.

Originally discovered in Gemini, Pluto is now about a full moon’s width southeast of 55 Serpentis. At magnitude 13.9, the planet can just be detected in a mid-size scope, but recognizing the "God of the Underworld" is another matter. It takes very careful chartwork.

Tonight let’s resume our trip north from Scorpio’s "tail." Starting with Antares, head east-northeast less than a fist width to put yourself in the general location of M19. With a visual magnitude of 6.8, this bright globular cluster can be seen with small binoculars, but requires a telescope to take on form. Discovered by Messier in 1764, M19 is the most oblate globular known. Harlow Shaply, who studied globular clusters and cataloged their shapes, estimated that M19 has about twice as many stars along the major axis as the minor. This "stretch" is due to its proximity to the Galactic Center - a distance of only about 5,200 light-years. Very rich and dense, even small Telescopes can pick up the cluster’s faint blue tinge.

For the adventurous, there are two more. Magnitude 8.2 NGC 6293 is less than a finger-width east-southeast of M19 and far brighter than you might expect. Note how much more round and concentrated the core appears to be. About the same distance north-northeast of M19 is fainter NGC 6284 - similar apparent size, but more loosely constructed.

Friday, June 23 - This evening, we’ll return to Scorpio from Ophiuchus and locate three globular clusters at the head of the Scorpion - Antares.

M4, located one degree west of Alpha (Antares) is one the most easily located of all globular clusters and provides a fine view with binoculars or scopes. First noted by Philippe Loys de Chéseaux in 1746, M4 is one of the nearest globulars - at some 7200 light-years. At magnitude 5.9, it approaches unaided visibility. This misty looking globular improves with both aperture and magnification, revealing a chain of 11th and 12th magnitude stars across the cluster’s core.

Less than one degree east-northeast of M4 is large and faint NGC 6144. Because of its position in the same low power field with Antares, it’s a 9.1 magnitude, low surface brightness challenge!

A challenge of a different type is M80 - one of the most densely packed globular clusters in the Milky Way. Located about halfway between Antares and Beta Scorpii, this 33,000 light-year distant cluster defies resists resolution. An original discovery of Charles Messier, in 1781, William Herschel was the first to resolve it into individual stars - and with the right scope and conditions, so can you!

Saturday, June 24 - On this day in 1881, Sir William Huggins made the first photographic spectrum of a comet (1881 III) and detected cyanogen (CN) emissions at violet wavelengths. This discovery caused near mass hysteria some 29 years later when Earth passed through the tail of Halley’s Comet.

Tonight is a near New Moon and a good time to pack the scope (and family) for a late night out among the stars. Before you head out to your favorite star party locale consider this: It’s summer and the richest part of the Milky Way is going to softly illuminate the sky from corona Australis in the south to Cepheus in the north. That means bring everything you can - from small hand held binoculars, to a big dob!

If you will be attending with other amateurs, here are some star party hints: Cover your dome and trunk lights with translucent red filter paper. Try to arrive just after sunset, but if you get there late, stop for a moment on the side of the road. Turn off your bright lights, allow your eyes to dark adapt, then drive into the parking area using parking lights only. If you don’t have a scope to set up, park well away from where others are stationed. Before opening car doors, turn off any music or news, then allow your eyes to further dark adapt so you can find your way around safely.

Amateur Astronomers are some of the friendliest folks you’ll ever meet!

Sunday, June 25 - Today celebrates the birth of Hermann Oberth. Born in 1894, Oberth is the father of modern rocketry and space travel. But you won’t need a rocket to travel skyward as we celebrate tonight’s New Moon.

The constellation Ophiuchus is the unrecognized "thirteenth sign of the Zodiac" and like any "zodiacal" constellation represents an "animal" - in this case a man; the Snake Charmer. Flanking Ophiuchus on both sides is a serpent (Serpens). To the west is its head (Serpens Cauda - Ser1), and to the east, its tail (Serpens Caput - Ser2).

The premiere study of Serpens Cauda is M13’s northern hemisphere rival - M5. In the far less recognizable Serpens Caput is an even less recognizable open cluster - M16. Between M5 and M16 are four fine globular clusters - M10, M12, M14, NGC 6539, and a large open cluster - NGC 6604. Let’s learn more about this mysterious region of the sky by visiting with them all...

The brightest star in Serpens Cauda is 2.8 magnitude Alpha. Just southeast is 3.8 magnitude Epsilon. Use these two stars to point you southeast to 3.0 magnitude Yed Prior (Delta Ophiuchi) and 3.3 magnitude Yed Posterior (Epsilon Ophiuchi). Look a fist width east of Epsilon, to locate the condensed 6.6 magnitude globular cluster M10. First resolved by William Herschel, Messier described this cluster as a nebula without stars on discovery May 29, 1764. It might appear that way in binoculars, but even small scopes pick stellar members out of M10 and neighboring M12 with ease.

To locate M12, look about two finger-widths northwest of M10. At first glance through binoculars or a modest telescope, this pair looks very much alike. Both have cumulative magnitudes of 6.6 and apparent sizes of 15 arc-minutes. Despite numeric similarities, there are differences. It’s a bit more difficult to tease resolution out of M12 at lower magnifications, while M10 has a slightly more blue coloration. For those with large aperture, this will help you note difference in class structures. M12 is class IX and M10 is class VII.

To locate 7.4 magnitude M14, head west-northwest about a fist width. M14 is roughly twice the distance from the Earth as M10 and M12 - and this is apparent when attempting to resolve individual members. Like M10 and 12, M14 was discovered by Messier during one of his comet sweeps of the ecliptic in late spring 1764. The brightest stars in this cluster are of the 14th magnitude - revealing the quality of William Herschel’s handmade reflector that resolved it in 1783. Smaller yet than the previous pair, M14 is right in the middle at Class VIII.

If you’re feeling adventurous, head southeast and visit two more - Class IV NGC 6517 between Nu and Tau and Class X NGC 6539 the same distance northeast of Tau. If this faint globular weren’t so obscured by dust it would be 7 times brighter than M14!




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