Weekend SkyWatcher’s Forecast: July 16-19, 2010

Greetings, fellow SkyWatchers! Are you ready for a rock the night weekend? Then come along as you won’t need a telescope to watch the movement of the planets and the Perseid meteor shower heating up your evenings! If you’d still like a challenge, then why not chase bright asteroid Ceres with binoculars – or look up a challenging globular cluster? If you still need appeal, then there are a couple of great stars that are worth observing… and learning about! Whenever you’re ready, I’ll see you in the backyard….

July 16, 2010 – Today celebrates the 1746 birth of Giuseppe Piazzi. Although we know Piazzi best for his discovery of the asteroid Ceres, did you know he was also the first to notice that 61 Cygni had a large proper motion? Nine days and 38 years later, the man responsible for measuring 61 Cygni, Friedrich Bessel, was born.

This would indeed be a great evening to check out asteroid Ceres for yourself. You’ll find it in Ophiuchus and well placed for either binoculars or a small telescope just above the “sting” of the Scorpion! Here’s a map to help you along the way…

Now let’s take a look at gorgeous 61 Cygni. You’ll easily locate it between Deneb and Zeta on the eastern side. Look for a small trio of just visible stars and choose the westernmost (RA 21 06 54 Dec +38 44 44). Not only is it famous because of Piazzi and Bessel’s work, but it is one of the most noteworthy of double stars for a small telescope. Of the unaided visible stars, 61 is the fourth closest to Earth, with only Alpha Centauri, Sirius, and Epsilon Eridani closer. Just how close is it? Try right around 11 light-years.

Visually, the two components have a slightly orange tint, are less than a magnitude apart in brightness, and have a nice separation of around 30″ to the south-southeast. Back in 1792, Piazzi first noticed its abnormally large proper motion and dubbed it the ‘‘Flying Star.’’ At that time, it was only separated by around 10″, and the B star was to the northeast. It takes nearly seven centuries for the pair to orbit each other, but there is another curiosity here. Orbiting the A star around every 4.8 years is an unseen body that is believed to be about 8 times larger than Jupiter. A star—or a planet? With a mass considerably smaller than any known star, chances are good that when you view 61 Cygni, you’re looking toward a distant world!

July 17, 2010 – This date marks the 1904 passing of Isaac Roberts, an English astronomer who specialized in photographing nebulae. As an ironic twist, this is also the date on which a star was first photographed at Harvard Observatory!

Tonight let’s have a look at a real little powerpunch globular cluster located in northern Lupus—NGC 5824. Although it’s not an easy star hop, you’ll find it about 7 degrees southwest of Theta Librae, and exactly the same distance south of Sigma Librae (RA 15 03 58 Dec –33 04 04). Look for a 5th magnitude star in the finderscope to guide you to its position southeast.

A Class I globular cluster, you won’t find any others that are more concentrated than this. Holding a rough magnitude of 9, this little beauty has a deeply concentrated core region that is simply unresolvable. Discovered by E.E. Barnard in 1884, it enjoys its life in the outer fringes of its galactic halo about 104 thousand light-years away from Earth and contains many recently discovered variable stars.

Oddly enough, this metal-poor globular may have been formed by a merger. Research on NGC 5824’s stellar population leads us to believe that two less dense and differently aged globulars may have approached one another at a low velocity and combined to form this ultra-compact structure. Be sure to mark your observing notes on this one! It also belongs to the Bennett catalog and is part of many globular cluster lists.

July 17, 2010 – Celestial scenery alert! Are you watching the planet dance as Mars heads towards Saturn? You don’t need a telescope to enjoy the early evening trio of bright Venus along the western horizon – or the duet just above it! While you’re out enjoying a relaxing evening, keep your eyes on the skies. The early activity of the annual Perseid meteor shower is really heating up and you can expect to see several “shooting stars” an hour!

Tonight let’s begin with the 1689 birth of Samuel Molyneux. This British astronomer and his assistant were the first to measure the aberration of starlight. What star did they choose? Alpha Draconis, which oscillated with an excursion of 39’’ from its lowest declination in May. Why choose a single star during an early dark evening? Because Alpha Draconis—Thuban—is far from bright.

At magnitude 3.65, Thuban’s ‘‘alpha’’ designation must have come from a time when it, not Polaris, was the northern celestial pole star. If you’re aware that the two outer stars of the ‘‘dipper’’ point to Polaris, then use the two inner stars to point to Thuban (RA 14 04 23 Dec +64 22 33). This 300-light-year distant white giant is no longer main sequence, a rare binary type.

Now head to binary Eta Lupi, a fine double star resolvable with binoculars. You’ll find it by staring at Antares and heading due south two binocular fields to center on bright H and N Scorpii— then one binocular field southwest. Now hop 5 degrees southeast (RA 16 25 18 Dec –40 39 00) to encounter the fine open cluster NGC 6124. Discovered by Lacaille, and known as object I.8, this 5th magnitude open cluster is also Dunlop 514, Melotte 145, and Collinder 301. Situated about 19 light years away, it shows a fine, round, faint spray of stars to binoculars and is resolved into about 100 stellar members to larger telescopes. AlthoughNGC6124 is low for northern observers, it’s worth the wait to try at culmination. Be sure to mark your notes because this delightful galactic cluster is also a Caldwell object and counts for a southern skies binocular award.

Until next week? Keep capturing photons!

This week’s awesome images are (in order of appearance): 61 Cygni, NGC 5824, Alpha Draconis and NGC 6124 are from Palomar Observatory, courtesy of Caltech. Maps are courtesy of “Your Sky”. We thank you so much!