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DECEMBER 7, 2014: Christmas and Telescopes
Telescopes and Christmasóthey go together like bread and butter, 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, simply stay away. Telescopes are essentially light buckets, designed to bring to an exact focus more light than the human eye can collect. The more light, the deeper into space you will be able to view. The eye, acting as the receptor of the photons being gathered by the telescope, is essentially enlarged to the area of the light-gathering lens or mirror. Telescopes also need to deliver crisp, vivid images so the observer can actually see detail on the moon, planets, or other sky objects that are being scrutinized. They must also produce acceptable fields of view, so that the object under examination can be seen in its entirety. This is partly a function of eyepiece design. Any telescope will come with an acceptable eyepiece or two, but nothing special. Your scope must also be attached to a sturdy mounting system to dampen unwanted vibrations when it is moved around the sky or if the wind kicks up. When all of these criteria are met, then the topic of magnification can be discussed; but there are still limits. Any telescope will not tolerate more than about 50-power per inch of aperture. Therefore, a telescope with a 4-inch lens or mirror should not be pushed beyond 200-power. Where can you find a first-rate, fairly priced instrument? Iím sorry to say that K-Mart, Wal-Mart, or any department stores should not on your list. I would first suggest Orion Telescopes which produce economically priced instruments that meet astronomical criteria. Go to www.telescope.com and search for a type of reflector called a Dobsonian. This will be your best bang for the buck. More about Dobsonian telescopes next week...
DECEMBER 14, 2014: Dobsonians: Biggest Bang for the Buck
In 1967 a Vedantan (Hindu) monk by the name of John Dobson (1915-2014), intrigued by astronomy and telescope making, left the order and co-founded (1968) the San Francisco Sidewalk Astronomers. Dobson had been building telescopes for decades and bringing astronomy to the public near his monastery, but as a Sidewalk Astronomer, Dobson and his telescopes became a national sensation among amateurs. The telescope, a simple reflector, was nothing new. The design had been conceived and first built by Isaac Newton in 1668/9. It consisted of a parabolic mirror at the bottom of a tube which sent its converging light beam back up the tube to a piece of aluminized glass. The flat secondary reflected the light cone through a hole in the upper portion of the tube where a focuser, which held an eyepiece, was located. What made Dobsonís telescopes so special was the simplicity of its mount, a box-like structure which rotated and allowed the telescope to pivot up and down at its balance point. It was so simple and easy to make that Dobson often built one of his scopes in just a dayís time. Dobson never patented his invention, and as a result, its design was free to be modified and enhanced by amateurs and commercial entrepreneurs alike. Before Dobson, a portable telescopeís size was limited by the bulky, heavy mounting system which supported the instrument. After Dobson and the technology which kept thin mirrors from flexing, the size of the light-gathering primary mirror was essentially limited by the dimensions of the van or SUV that was used in its transportation. Iíve looked through 17-, 20-, 25-, 30-, and even 36-inch Dobsonian telescopes that had been easily transported to the remote site where they were being used. Start off with an eight or 10-inch model and several eyepieces; and youíll have a splendid Christmas gift that will not only be cost-effective, but will provide a lifetime of observing pleasure.
DECEMBER 21, 2014: Winter Solstice: Low Sun, High Hopes
How low can the sun go? It all depends upon where you live, your location north or south of the equator; however, for us in the Northern Hemisphere, the noontime sun will be at its lowest yearly altitude in the sky on December 21. Itís simple arithmetic to calculate the daily high sun for your location. Keep in mind that the Earth is essentially a sphere, and as you move north or south, the sun will reflect your motions. If the noontime sun is south of your position as it is now for all of the US, and you move southward, the sun will get higher in the sky. Moving northward will decrease the sunís altitude. Here is a simple way to calculate how low the noontime sun will be on the winter solstice. Subtract 90 degrees from your latitude position, and then add or subtract the latitude position over which the zenith sun is shining. If you are in the Northern Hemisphere, south of the equator is negative, and north of the equator is positive. You now have your own personal noontime calculator of the sunís altitude on December 21. I live at approximately 40 degrees north of the equator, so 90 degrees minus 40 degrees minus 23.5 degrees (the sun is over the Tropic of Capricorn at 23.5 degrees south latitude) equals 26.5 degrees. That will be the noontime winter solstice altitude of the sun at 40 degrees north latitude. If I lived in Fairbanks, Alaska, 65 degrees north of the equator, the calculation would be 90 degrees minus 65 degrees, minus 23.5 degrees which equals 1.5 degrees. The sun would transit due south at noon only 1.5 degrees above the horizon. Yuck! It would actually be closer to two degrees because the atmosphere causes objects near to the horizon to appear higher than they actually are. Thatís still a big yuck! In Miami, at 26 degrees north latitude, the noontime altitude of the sun will still be only 40.5 degrees, but the warmer waters surrounding Florida will make all of the difference. Hereís hoping for a higher sun real soon.
DECEMBER 28, 2014: 2015: A Good Year for Astronomy
Looking ahead to the New Year is always a fun activity, and although 2015 will not be as spectacular as 2017, when a total solar eclipse sweeps diagonally across the US (August 21), it does hold the promise for some very enjoyable sights including the highlight of the year, a total lunar eclipse on the evening of Sunday, September 27. First contact with the Earthís main shadow happens at 9:07 p.m., EDT; totality occurs between 10:10 and 11:24 p.m., and final egress from Earthís umbra happens by 12:27 a.m. Monday. The altitude of the moon ranges from 26 degrees at the onset of the eclipse to just over 50 degrees at its conclusion, so finally after many years of witnessing morning, tree-hugging eclipses, weíll have a lunar eclipse that takes place at a relatively decent hour, and at a height where trees and buildings should pose few problems. If you want to see planets, the first half of 2015 is perfect. Jupiter is in prime evening viewing from January through June, and Saturn from mid-May through early September. Both Venus and Mercury have beautiful evening apparitions during the spring. On May 7 Mercury sets nearly two hours, and Venus almost four hours, after sundown. During twilight, Mercury, Venus, and Jupiter will be strung out like glistening pearls against the darkening evening sky. By June 30 Venus and Jupiter stand only 1/3rd degree apart, a splendid visual or telescopic sight. Venus is also visible in the morning sky throughout much of the fall, but between October 26 and November 3, Venus, Mars, and Jupiter do-si-do high in the dawn sky. Meteor showers with respect to morning moonlight are nearly perfect for 2015. Perseid meteors fly August 13, one day before new moon; the Orionids, October 21, one day after first quarter; the Leonids, November 18, with a six-day old moon in the sky, and the Geminids, December 14, with a thin waxing crescent moon. To tell you the truth, 2015 is really not that bad. Clear skies to everyone in the New Year!