OCTOBER  2011

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789    OCTOBER 2, 2011:   The Handy Planisphere

With the temperate and clearer evenings of fall now upon us, I’d like to suggest a handy little tool that will make your sojourns under the vault of the heavens more enjoyable. The device is known as a planisphere, and it is the most efficient, non-computerized way to create a personalized portrait of the heavens for your travel destinations or the backyard. They are inexpensive, about $10-$20 in a plastic version, and flat, so they pack well or store efficiently on a bookshelf. And most importantly, they work. An inner circle containing the 24 hours of the day rotates around an outer fixed circle which contains the days of the 12 months. The view of the heavens is oval-shaped, showing the sky in all directions. If you match the hour of the night with the day of the year, a correct representation the sky at that moment is achieved. To use a planisphere, simply look down upon it, holding the direction in which you are viewing closest to you. The heavens in front of you will be mimicked on the planisphere quite accurately, but much smaller in size than the real sky. Planispheres always give the standard time representation of the firmament. Since most of us are on Daylight (Saving) Time, subtract one hour on the planisphere to achieve the most accurate results. If it’s 11 p.m., EDT, set the planisphere for 10 p.m. which would be the correct standard time. Planispheres are also designed for specific latitudes which cannot be altered. If you are planning a trip to Australia, a planisphere purchased for 40 degrees north latitude would be useless in Oz. Also forget about planispheres with glow-in-the-dark stars. They don’t work very well and you will still need a flashlight for illumination. Bookstores like Barnes and Noble always carry a few planispheres on their science shelves. My favorite is the huge blue and yellow Levy planisphere, 16 inches in diameter. Good sky watching!

790    OCTOBER 9, 2011:   Comet Garradd on the Loose

There is a comet roaming the heavens, and as soon as the moon’s brightness clears the early evening sky next week, it should become visible to observers with telescopes and binoculars who live in suburbia and darker locales. Comet Garradd, also named C/2009 P1 (Garradd), was discovered with the 0.5-meter Uppsala Schmidt telescope in Australia at Siding Spring Observatory, 235 miles NW of Sydney on the evening of August 13, 2009. I spent three weeks photographing from that observatory in February 2000. Orbital calculations showed that Garradd would brighten significantly, passing closest to the sun on December 23, 2011 and then passing closest to the Earth on March 5, 2012. At that time Garradd’s distance will be 1.27 astronomical units or 118 million miles. One AU equals the Earth-sun distance of 92.8 million miles. What makes Garradd unusual is its very long period of brightness which began in September and will continue into next spring. It is a big comet that is traveling in a sideways path nearly perpendicular to the plane of the solar system and which favors the northern hemisphere. Unfortunately, there is a “but.” Garradd gets no closer to the sun than Mars’ average solar distance of 1.5 AU. This means that we have a grand view of the comet for a long, long time, but it doesn’t get really bright enough to become an easy naked eye target for the average person. When Garradd passes closest to Earth in March of 2012, and is at its brightest, it will already be headed away from the sun. After this time the comet fades rapidly, never to be seen again. Garradd is in a hyperbolic orbit which means that it is destined to wander the galaxy, kicked from our solar system nest by the gravitational tugs and pulls of the planets. More about Comet Garradd next week...

791    OCTOBER 16, 2011:   Christmas for Garradd

Christmas Day is the new target for C/2009 P1, Garradd’s, closest approach to the sun, but the comet itself will be next to impossible to observe because it will be setting just about the same time that it will be dark enough to see it. It will be visible at dawn about two fists, held at arm’s length, above the eastern horizon. Binoculars will always be needed to view Garradd, which at that time will be close to the star Delta Herculis. But wait, I’m getting ahead of myself. Garradd will be visible with binoculars in the west as soon as the bright light from the moon is gone, and that could be as early as Sunday when the moon rises about 9:00 p.m. Beyond that time there will be nearly a three-week window in which the comet should be viewable right after darkness if weather conditions permit, and humongous trees are not hogging your western sky. The problem with Garradd is that it is bright as comets go, but just at the threshold of the average person’s ability to spot it. Garradd is also located in a no man’s zone of the sky where the stars are not very bright. On the positive, Garradd has been extremely well behaved as comets go, brightening almost exactly as predicted. If you manage to catch Garradd as a fuzzy, elongated object, you’ll be looking at two components which make it shine. One is subsurface ice which warms from the absorbed energy of the sun, vaporizes, and cracks the comet’s exterior. This gas jets into space and fluoresces (glows) from the ultraviolet light emitted by the sun. The gases absorb this invisible component of the sun’s spectrum, and then reemit energy in wavelengths of light that we can see. The second part is the dust mixed with the ice. It is pushed into space by the jetting action of the gases. This dross reflects and scatters sunlight back in our direction, also making the comet shine. It’s a very “cool” process. An online map locating Garradd changing position is at the URL below.

Comet Garradd makes its best autumn appearance during the month of October. Use binoculars to view Garradd as soon as it gets dark and without any moonlight in the sky. The first good night is October 16th. Unfortunately Comet Garradd will not be bright enough to be visible to observers in major metropolitan areas. Map by Gary A. Becker using Software Bisque's, The Sky.

792    OCTOBER 23, 2011:   Seasons Lag Behind Sun

We are living on borrowed time. Everyone has watched as the amount of sunlight has decreased, and night has become the dominant period of time in our “days.” In fact, that threshold was crossed over one month ago on September 23. Trees, flowers, and even the grass have taken their cues from this shrinking amount of daylight. Weather patterns have also been changing, modified by successions of Canadian weather fronts ushering in fresh clean air from the north. Gone are those muggy periods of summer where the sky appears bleached denim or simply white. Those endless days of “grunge” have been replaced by windier conditions and crisper skies, often accompanied by deep blues near the zenith and lighter shades of turquoise near the horizon. Daylight has taken on warmer hues as the sun has moved into the southern hemisphere and appears lower in the sky each day. The air filters shorter wavelengths of light, such as the blues and greens, but allows the yellows, oranges, and reds to pass less impeded. A lower sun increases this effect, translating into warmer hues which also help to accentuate the colors of the changing leaves. Yet through all of these transformations, light jackets or no jackets are still the attire of the day. The sun will not return to its same noontime position until mid-February and we all know what conditions will be like by then. Why are circumstances so temperate now and so harsh in February, when astronomically speaking, the sun is exactly in the same position? The answer lies in the lag of the seasons. Mid-latitudes reach their highest temperatures in late July and their coldest periods in late January. Although conditions are now cooling, there is still plenty of summer heat leftover to moderate circumstances right into early November. By November’s end, however, the heat will be gone and so will those temperate days of autumn.

Changing Sunset Directions: These two images were taken from the same location atop the Collier Hall of Science in Bethlehem, PA. Note the change in sunset direction between September 13 and October 8. The sun will keep setting farther and farther to the left (south of west) until the winter solstice on December 22. Photos by Gary A. Becker...

793    OCTOBER 30, 2011:   Christmas and Telescopes

Telescopes and Christmas—they go together like ham and cheese, but most people buying a scope for under the tree will make the wrong decisions. All telescopes are a compromise in one way or another, but all experts agree that scopes are not built strictly for magnification. If a manufacturer hypes the power that a telescope can attain as the chief reason for purchasing the scope, stay away from that item like the plague. The most important aspect of a telescope is its ability to gather light and to bring that light to a sharp focus in as comfortable a manner as possible. The eye, acting as the receptor of the photons being gathered by the lens or mirror, is essentially enlarged to the diameter of the light-gathering element of the telescope. Telescopes also need to produce crisp, vivid images of what the viewer is observing. This requires optics that meet criteria for producing astronomically acceptable images. I’m sorry to say that K-Mart specials or scopes sold at Wal-Mart stores are a joke. Telescopes need to produce quality images so the observer can actually see detail on the moon, planets, and other objects in the sky. They also need to produce acceptable fields of view, so that the object under scrutiny can be seen in its entirety. A telescope must also be attached to a sturdy mounting system to dampen unwanted vibrations when moved around to find sky objects or to hold steady if the wind kicks up a little. When all of these criteria are met, then the topic of magnification can be discussed; but there are still limits. A good telescope will not tolerate more than 50-power per inch of aperture. A quality, reflecting telescope with a 4-inch mirror should not be pushed beyond 200-power. Where can you find a first-rate, fairly priced instrument? I would first suggest Orion Telescopes which produce economical scopes that meet astronomical criteria. Go to www.telescopes.com.