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Observing - Basics of Astronomy 2 A hand at arm’s length, a star chart, and the ability to remember simple shapes and lines puts you right on target. |
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The key ingredient in finding objects that are either barely visible or invisible (hiding) to the naked eye is to use brighter (bigger) objects for reference points. For example:”Go about two thirds of the way past Walmart toward McDonalds and take a right at the phone booth; go down to the end and turn left. Go about fifty feet and you’ll see the a six foot tall pink flamingo wearing sunglasses; that’s the place!” |
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1 - Learn Angular Size & Distance relative to the outstretched hand. Angular Size & Distance is the length, width, and/or diameter of a celestial object as seen against the sky. |
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The ANGULAR size of the tip of a pinky finger is is 1(one) degree. |
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The ANGULAR size of the tips your ring, middle, and index fingers together is 5 degrees. |
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The ANGULAR size of your fist from pinky to thumb inclusive is is about 10 degrees. |
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The ANGULAR size of your hand stretched out from pinky tip to thumb tip is 20 degrees. |
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2 - Transpose angular sizes and distances of objects from charts and lists A telescope with an eyepiece that yields 35X magnification has approximately a 2 degree field of view; a 8 X binocular or typical telescope finder scope has approximately an 8 degree field of view. The greater the magnification, the narrower the field of view; and as power increases, the concentration of light diminishes as it is visually spread over a larger area. It is important at this point for you to understand why most astronomical viewing is done at low powers - well below the capability of the telescope. The more you magnify an image, the broader it’s light is distributed over the view through the eyepiece; and the smaller that field of actual view becomes. Limit use of higher powers only to reveal small details and small objects. The angular size of the moon is 1/2 degree, so you can easily cover it with your pinky finger extended to arm’s length. Many objects in the night sky have much larger angular size than the moon. A few galaxies in our local group and even more nebulae in the Milky Way galaxy are larger than (1) one degree. The Great Andromeda Galaxy - M31 is three degrees long and one degree wide - much larger than the full moon. The Hercules Globular Cluster - M13 is 1/4 degree or 15 minutes in diameter - half the angular size of the full moon at . When I point out objects, I use degrees and describe geometric shapes or imaginary lines which point to the object. I point out a star and say “go west 10 degrees and then 3 degrees south”, or “”those 3 stars for a right triangle; imagine a line between the two southernmost stars and look at a point 1/3 of the way along that line from the east.” If you don’t have someone to point things out, just remember what you see on your chart and then identify (within a few degrees) nearby stars. Considering the wide field of 7 X to 10 X binoculars and finder scopes, finding many objects invisible to the naked eye quickly gets easier. For dim objects, use the lowest magnification eyepiece in your telescope.
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Demonstrations of described methods are just one part of our public astronomical observation program. Join the fun. |
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