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Greetings, fellow SkyWatchers! Are you ready for another weekend? As the seasons slowly begin to change for both hemispheres and the Moon grows more full, look for an optical phenomena known as a “nimbus” – or halo around the Moon. While it’s nothing more than a thin layer of ice crystals in the upper troposphere, it is a wonderfully inspiring sight and was once used as a means of weather forecasting. If you see a nimbus, try counting the number of stars visible inside the halo and see if it matches the number of days before bad weather arrives! In the meantime, follow me as we head out on our next weekend journey into the night…
On this date in 2001, the Genesis Solar Particle Sample Return mission was launched on its way toward the Sun. On September 8, 2004, it returned with its sample of solar wind particles – unfortunately a parachute failed to deploy, causing the sample capsule to plunge unchecked into the Utah soil. Although some of the specimens were contaminated, many did survive the mishap. So what is “star stuff?” Mostly highly charged particles generated from a star’s upper atmosphere flowing out in a state of matter known as plasma.
Despite tonight’s Moon, let’s study one of the grandest of all solar winds as we seek out an area about three fingerwidths above the Sagittarius teapot’s spout as we have a look at the magnificent M8.
Visible to the unaided eye as a hazy spot in the Milky Way, fantastic in binoculars, and an area truly worth study in any size scope, this 5200 light-year diameter area of emission, reflection, and dark nebulae has a rich history. Its involved star cluster – NGC 6530 – was discovered by Flamsteed around 1680, and the nebula by Le Gentil in 1747. Cataloged by Lacaille as III.14 about 12 years before Messier listed it as number 8, its brightest region was recorded by John Herschel, and dark nebulae were discovered within it by Barnard.
Tremendous areas of starbirth are taking place in this region, while young, hot stars excite the gas in a region known as the “Hourglass” around the stars Herschel 36 and 9 Sagittarii. Look closely around cluster NGC 6530 for Barnard Dark Nebulae B 89 and B 296 at the nebula’s southern edge…and try again on a darker night. No matter how long you choose to swim in the “Lagoon” you will surely find more and more things to delight both the mind and the eye!
Under this lighting, the bright ring of this class V walled plain extends 83 kilometers in diameter. Even though it looks to be quite shallow, it still has impressive 2150 meter high walls. To its south is a feature not often recognized – the Montes Archimedes. Though this relatively short range is heavily eroded, it still shows across 140 kilometers of lunar topography. Look for a shallow rima that extends southeast across Palus Putredinus toward the Apennines. Mark your challenge notes!
Now let’s go have a look at a star buried in one of the spiral arms of our own galaxy – W Sagittarii…
Located less than a fingerwidth north of the tip of the teapot spout (Gamma), W Sagittarii (RA 18 05 01 Dec -29 34 48) is a Cepheid variable that’s worth keeping an eye on. While its brightness only varies by less than a magnitude, it does so in less than eight days! Normally holding close to magnitude 4, nearby field stars will help you correctly assess when minimum and maximum occur. While it’s difficult for a beginner to see such changes, watch it over a period of time. At maximum, it will be only slightly fainter than Gamma to the south. At minimum, it will be only slightly brighter than the stars to its northeast and southwest.
While you watch W go through its changes – think on this. Not only is W a Cepheid variable (a standard for the cosmic distance scale), but it is also one that periodically changes its shape. Not enough? Then think twice… Because W is also a Cepheid binary. Still not enough? Then you might like to know that recent research points toward the W Sagittarii system having a third member as well!
Sunday, August 10, 2008 – Today in 1966 Lunar Orbiter 1 was successfully launched on its mission to survey the Moon. In the days ahead, we’ll take a look at what this mission sent back! Tonight keep a very close watch on Selene as Antares is less than a degree away. Check for an occultation event!
Keep an eye out for the beginnings of the Perseid meteor shower and a futher report! Wishing you clear skies and a great weekend…
This week’s awesome images are: Nimbus – Credit: Shevill Mathers, Hipparchus: Credit: Tammy, M8 – Credit: NOAO/AURA/NSF, Archimedes – Credit: Wes Higgins, Walter – Credit: West Higgins and Eta Sagittarii – Credit: Palomar Observatory courtesy of Caltech. Thank you for sharing!
Man, I remember the first time I ever saw a nimbus, it freaked me out 🙂