Greetings, fellow SkyWatchers! Has everyone enjoyed the Apollo revival? I certainly have – and now the Moon is gently returning to evening sky and offering us great opportunities over the coming evenings to do a little bit of study with binoculars and telescopes. Look for its slender crescent just after sunset! This weekend we’re going to try an open cluster you may never have seen that works well for small optics and a Herschel object with a real twist. Need more? Then we’ll check out a beautifully colored double star, too… But not the one you expect! Grab your telescopes and binoculars and I’ll see you in the back yard…
Friday, July 24, 2009 – Today let’s start with the 1853 birth on this date of Henri-Alexandre Deslandres. Do you recognize his name from our lunar studies? He invented the spectroheliograph to photograph the Sun in monochromatic light! Deslandres also observed the spectra of planets and stars and measured their radial velocities. Did you see the very young crescent of the Moon during twilight? The Moon played an important role in history on this date. The Apollo 11 astronauts splashed down from their return from the Moon on this date in 1969! Only 15 years before, in 1954, the sound of a human voice had been reflected off the Moon’s surface and returned to Earth. James H. Trexler at the Naval Research Laboratory spoke into a microphone at the laboratory’s Maryland facility, and the sound was relayed back 2.5 seconds later. Although ‘‘Operation Moon Bounce’’ was only a repetition of vowel sounds, Trexler felt the project held promise as a communications and radar intercept device. It might be worth it to point out that many radars are very close to the theoretical possibility of contacting the Moon, and hence the practicality of building a system capable of intercepting these systems by reflections from the Moon is not beyond the realm of possibility.
Tonight we start with a group of young stars beginning their stellar evolution and end with an old solitary elder preparing to move onto an even ‘‘higher realm.’’ Open cluster IC 4665 is easily detected with just about any optical aid about a finger-width north-northeast of Beta Ophiuchi (RA 17 46 18 Dec +05 43 00). Discovered by Philippe Loys de Cheseaux in the mid-1700s, this 1,400 light year distant cluster consists of about 30 mixed-magnitude stars all less than 40 million years of age. Despite its early discovery, IC 4665 did not achieve broad enough recognition for Dreyer to include it in the late nineteenth-century New General Catalog (NGC), and it was later added as a supplement to the NGC in the Index Catalog of 1908. Be sure to use low power to see all of this large group.
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Saturday, July 25, 2009 – Today we celebrate a success of the U.S.S.R. space program with the achievement of cosmonaut Svetlana Savitskaya, the first woman to walk in space (in 1982 on this date) and only the second female to go into space, preceding Sally Ride. Today is also the date of the 1973 launch of Soviet Mars 5 probe. Although it didn’t complete its full mission, it did send back 60 photos of the Martian Southern Hemisphere!
Although poor position makes study difficult during the first few lunar days, be sure to look for the ancient impact Vendelinus. Spanning 150 kilometers in diameter and with walls reaching up to 4,400 meters in height, lava flow has long ago eradicated any interior features. Its old walls hold mute testimony to later impact events such as crater Holden on the south shore, larger Lame on the northeast edge, and sharp Lohse northwest. Mark your challenge list!
Tonight’s challenge is Herschel I.44, also known as NGC 6104, a 9.5-magnitude globular cluster around two finger-widths northeast of Theta Ophiuchi and a little more than a degree due east of star 51 (RA 17 38 37 Dec –23 54 31). Discovered by William Herschel in 1784 and often classed as ‘‘uncertain,’’ this halo object has been pegged by today’s powerful as a Class VIII and given a rough distance from the galactic center of 8,800 light-years. Although neither William nor John could resolve this globular and listed it originally as a bright nebula, studies in 1977 revealed a nearby suspected planetary nebula named Peterson 1. Thirteen years later, further study revealed this wasn’t a nebula at all but evidence of a symbiotic star. Symbiotic stars are a true rarity—not a single star at all but a binary system. A red giant dumps mass toward a white dwarf in the form of an accretion disk. When this reaches critical mass, it then causes a thermonuclear explosion, resulting in a planetary nebula. Although no evidence exists that this object is located within metal-rich NGC 6401, just being able to see it in the same field makes this journey both unique and exciting!
Sunday, July 26, 2009 – On this date in 1969 in a vacuum-sealed room, the very first sample return of Moon rocks was studied.
Our own vacuum of space awaits as we view the area around Mare Crisium to have a look at this month’s lunar challenge—Macrobius.
You’ll find it just northwest of the Crisium shore. Spanning 64 kilometers in diameter, this Class I impact crater drops to a depth of nearly 3,600 meters—about the same as many of our Earthly mines. Its central peak rises to 1,100 meters and may be visible as a small speck inside the crater’s interior. Be sure to mark your lunar challenge lists, and look for other features you may have missed before!
Since the moonlight will now begin to interfere with our globular cluster studies, let’s waive these for a while as we take a look at some of the region’s most beautiful stars. Tonight your goal is to locate Omicron Ophiuchi, about a finger-width northeast of Theta (RA 17 18 00 Dec –24 17 02). At a distance of 360 light-years, the Omicron system is easily split by even small telescopes. The primary star is slightly dimmer than magnitude 5 and appears yellow to the eye. The secondary is near 7th magnitude and tends to be more orange in color. This wonderful star is on many doubles’ observing lists, so be sure to note it!
Are you wanting to keep an eye out for those dark markings of the Jupiter impact, too? Well, they’re there! Just remember if you’re new to astronomy that features on Jupiter rotate as the planet turns and we’re turning, too. Seeing the new “spots” requires some calculations and these areas will rotate into meridian view about 2 hours and 6 minutes after the Great Red Spot makes an appearance. Also remember that our own atmospheric seeing conditions play a great role as well! If it just so happens the dark spots will be making their appearance will Jupiter is still very low on the horizon, chances are your luck with seeing them in a small telescope won’t be high. But, don’t let that discourage you from looking! It doesn’t take long for a planet to rise to good observing height and the spots will stay visible for several hours as they rotate in and out on either side of your computed appearance time. (And don’t forget galiean moon shadow transits can also cause dark markings… but these will be very round!)
Until next week? Enjoy your observations and keep reaching for the stars!
This week’s awesome images are (in order of appearance): Henri Deslandres (historical image), IC 4665 (credit—Palomar Observatory, courtesy of Caltech), Vendelinus (credit—Alan Chu), NGC 6401 (credit—Palomar Observatory, courtesy of Caltech), Macrobius on the edge of Crisium (credit—Greg Konkel) Omicron Ophiuchi (credit—Palomar Observatory, courtesy of Caltech) and Jupiter (credit-Sky & Telescope: Sean Walker). We thank you so much!