Friday, February 25, 2011

Weekend SkyWatcher's Forecast - February 25-27, 2011

Written By Tammy Plotner

Greetings, fellow SkyWatchers!

Well, if you're not buried in snow, blown away by tornadoes, or just suffering under clouds and rain, why not take advantage of mostly dark skies and enjoy some astronomy! Whether you use binoculars, a small telescope, love to astro-image or just like to kick back and stargaze - there's something here for everyone to enjoy!

Now, relax. And let's journey...

Friday, February 25, 2011 - The absence of early evening Moon is a great time for obscure objects requiring dark skies. Locate Epsilon Monocerotis and
head three finger-widths northeast for a vast complex of nebulae and star clusters. Variable binary S Monocerotis is easily visible, and small binoculars will find the beginnings of a rich cluster surrounding it: NGC 2264 (RA 06 41 00 Dec +09 53 00). Larger binoculars and small telescopes will detect a distinct wedge of stars—the 2-million-year-old Christmas Tree Cluster. Its nebulosity is beyond a small telescope, but the brightest portion is the Cone Nebula.

The northern region—the photographic-only Foxfur Nebula—is part of a vast complex extending from Gemini to Orion. Northwest are several regions of bright nebulae. Best suited to the average scope is large, faint NGC 2245, which accompanies an 11thmagnitude star. Fog-like NGC 2247 is a circular patch of nebulosity around an 8th magnitude star. IC 446 is for larger aperture, appearing comet-like with nebulosity fanning away southwest. Even to a large scope, the ‘‘barely there’’ IC 2169 is most difficult of all!

Return to Epsilon Monocerotis, and move a finger-width east for another star field with an interesting companion. NGC 2244 (RA 06 31 54 Dec -04 56 00) is a galactic cluster embroiled in a reflection nebula commonly called the ‘‘Rosette.’’ The cluster stars heat the nebula’s gases to nearly 10,000 degrees Celsius, emitting light in a process similar to fluorescence. A huge percentage of this light is hydrogen-alpha; backscattered from its dusty shell and polarized. You won’t see any red hues, but with good seeing, small telescopes can detect a broken, patchy wreath of nebulosity around the well-resolved symmetrical concentration of stars crowned by the yellow jewel of 12 Monocerotis. Larger scopes, and filtered ones, will make out separate areas, which also bear their own distinctive NGC labels. The entire region is one of the best for winter skies!

Saturday, February 26, 2011 - Today we celebrate the birth on this date of many astronomers, starting in 1786 with Francois Arago, who discovered the solar chromosphere and made astonishingly accurate estimates of planetary diameters. Arago’s experiments proved the wave theory of light and contributed to the laws of polarization. Following in 1842 was astronomer and author Camille Flammarion, who studied multiple stars, the Moon, and Mars. Although erroneous in some observations (‘‘May we attribute to the color of the herbage and plants which no doubt clothe the plains of Mars, the characteristic hue of that planet...’’), Flammarion was entrusted with a personal copy of the Messier Catalog, including the author’s notes, which he later revised. Last is the 1864 birth of John Evershed, who contributed mightily to solar physics when he photographically discovered that gases in sunspots flowed horizontally from the center toward their edges, an effect now named for him!

Let’s celebrate them all by kicking up some stardust about 5 degrees south of Alpha Monocerotis and into Puppis for M46 (RA 07 41 42 Dec -14 49 00).

Containing around 150 resolvable stars, and possibly involving as many as 500, this cluster appears faint and compressed to binoculars, but one star seems brighter than the rest. Through the eye of a telescope, you’ll soon discover the reason! In its northern portion, the 300-million-year old M46 contains a planetary nebula known as NGC 2438, first noted by Sir William Herschel. While it would appear to be a member of the cluster, the planetary nebula is just a little closer to us than the stars. Be sure to mark your notes. There’s a lot to find in just a little area!

Afterwards, relax and enjoy the Delta Leonid meteor shower. Burning through our atmosphere at speeds of up to 24 kilometers per second, these slow travelers will seem to radiate from a point around the middle of Leo’s ‘‘back.’’ The fall rate is rather low at around 5 per hour, but they are still worth keeping a watch for!

Sunday, February 27, 2011 - Today let’s celebrate the 1897 birth on this date of Bernard Lyot, master of optics. He invented the polariscope, and produced the first solar coronagraph. He also made the first motion pictures of solar prominences. Lyot was an astute observer, and realized that the lunar surface had similar properties to volcanic dust. He didn’t see canals on Mars but observed sandstorms there, as well as atmospheric conditions on other planets. The Lyot filter is well known, and so is his micrometer, a device used to make precise distance measurements, especially those between close double stars. By all accounts a wonderful and generous man, Lyot sadly died of a heart attack while returning from seeing an eclipse.

Honor Lyot’s work by studying two open clusters, found about a fist-width north of Xi Puppis. The brighter of the two— M47 (RA 07 36 36 Dec -14 29 00) —is 1,600 light-years away and a glorious object for binoculars.

Filled with mixed-magnitude stars that resolve fully to aperture, M47 features the matched-magnitude double star Struve 1211 near its center. For all its bright beauty, this stellar swarm has the most ironic of histories. Probably discovered first by Hodierna but kept secret, it was independently recovered by Charles Messier, but its position was logged incorrectly. Later, it was cataloged by both William and Caroline Herschel. . .and yet again by John Herschel, who said: ‘‘This cluster has not since been observed. It is probably very loose and poor one.’’ Even Dreyer had a hard time nailing it down! Funny, considering it has only been there for 78 million years...

While M47 is a Herschel object, look just slightly north (about a field of view) to pick up another cluster that borders it, NGC 2423 (RA 07 40 45 Dec -19 09 00). This compressed cluster contains more than two dozen faint stars with a lovely golden binary at its center. By comparing the two clusters telescopically, you are also expanding your own studies by viewing two different types of stellar evolution: M47 is very similar to the Pleiades, while NGC 2423 more closely resembles the Hyades.

Have a great weekend!

Astronomical Image Credits - Palomar Observatory, courtesy of Caltech. Historical Images are Public Domain.

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