Selecting an Observation Site

Selecting an Observation Site

The partial phases of a total solar eclipse are usually visible over a wide area. But only within the path of totality can you see the spectacular and striking effects. The difference between experiencing a total eclipse and a partial eclipse is, literally, "the difference between night and day." Those who live within the path or take the opportunity to travel there have the chance to be rewarded with one of the most fleeting and beautiful visions of Nature's grandeur.

Your choice of a site within the path should be guided by three main factors:

(1) Duration of totality at the site
(2) Unobstructed view of the Sun
(3) Chances for clear skies

First of all, you need to be located within the path of totality during the time of the eclipse in order to be able to see the corona. For any given locale within the path of totality, a point nearer the central line of the eclipse has more time in totality; this is because the Moon's shadow, which forms an ellipse on the surface of the Earth, is wider nearer the center of the path. If you are located just within the path, totality will not last very long -- less than a minute. However, the "edge phenomena" of a total eclipse (Baily's beads, diamond-ring effect, and view of the chromosphere) will last longer there.

To ensure an unobstructed view of the eclipse, you need to know approximately where the Sun will be in the sky. You don't want any trees or mountains, for example, blocking your view. An easy way to find this out is to look for the Sun from your vantage point a day or two before the eclipse at the same time of day totality occurs. This will tell you if anything is in your way. Also, if you're on a hill or tall building with a good view of the west, you may get a chance to see the approach of the Moon's shadow as it races toward you over the Earth.

The third factor in choosing a site is the weather. Unless you fly above the clouds to observe an eclipse, you'll always have to take some risk on the weather. But there is a lot you can do to optimize your chances to see the eclipse. The meteorological term for cloudy skies is "sky cover." It is measured in numbers from 0 to 10, with each number representing a tenth. (For example, a sky cover of 3 indicates 30% overcast, or 70% clear.) Weather Bureau records will show the average sky cover for different places along the path at the time of year of the eclipse.

However, sky cover predictions are only general estimates covering large areas. Local weather conditions can be very different for places a short distance apart. You'll want to avoid places likely to have fog; also, stay away from mountain ridges where clouds tend to gather. But perhaps the greatest asset in finding clear skies for an eclipse is mobility. Driving a few miles to a clearer location at the last minute could save the day for you.

** Material adapted from ECLIPSE by Bryan Brewer ($14.95 plus S&H). ECLIPSE Book Order Form. **

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