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A Practical Guide to Viewing the Universe
photographs by Terence Dickinson
foreword by Timothy Ferris
also available: Paperback Hardcover
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Sky Measures

(from page 30)

Just as road maps have distance indicators between cities, our celestial guide maps denote distances between key stars and star groups -- not the distance from Earth to the stars but, rather, the apparent distance from one star to another. This measure is calibrated in degrees (360 degrees in a circle). Using this calibration on the sky is beautifully simple: just hold up your hand. At arm's length the width of the end of the little finger is almost exactly 1 degree -- wide enough to cover the Sun or the Moon, both about half a degree across. The two pointer stars in the bowl of the Big Dipper used to find Polaris are 5 degrees apart, the width of three fingers held boy-scout fashion at arm's length.

For larger sky angles, one fist width is 10 degrees, while 15 degrees is the span between the first and little fingers spread out. An entire hand span, from thumb to little finger, is about 25 degrees, the length of the Big Dipper. Larger dimensions can be measured as multiples of these. For general reference, the distance from the horizon to overhead is 90 degrees. Remember, these hand-reference measurements work only at arm's length.

The system is reasonably accurate for men, women and children, since people with smaller hands tend to have shorter arms. Only the hand-span measure seems to vary from person to person, because some people can extend their thumb and little finger more widely than others can. A quick check against the Big Dipper will indicate whether you have a span closer to 20 degrees than 25. Anyone can become proficient at gauging the distances in degrees from one star or star group to another in just minutes.

It doesn't matter in which season you begin; the Big Dipper diagram on page 34 can be used to locate several prominent stars almost instantly once you have a sense of the dimensions involved. This is the crucial first step toward becoming a backyard astronomer. Orion's seven brightest stars -- three in the belt and four in a surrounding quadrilateral -- are equally efficient as celestial guideposts. Orion's only drawback, compared with the Big Dipper, is that it is prominent in the evening sky only from late November to early April.

Backyard astronomy does not have to be a maze of formulas, calculators, grid lines, nomenclature, mythology and jargon. It can be easy and fun to find your way around the night sky. Most people want to be able to start finding celestial objects from their first night out. That's my goal here in layout out the most straightforward way to do it. In the next chapter, more detailed charts build on the same principles of using distinctive stellar guideposts to lead the observer around the sky. This is a gradual, painless way to come to know the starry sky.


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Herman Melville

Herman Melville

also available: eBook
tagged : astronomy
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