gsw@pegasus.UUCP (05/15/84)
A safe and cheap way to observe the eclipse is to use welder's glass of the proper shade. Here is a quote from Sky and Telescope, November, 1983, p403: "One safe way to look at Sun is to hold a rectangular welder's glass of the proper shade in front of the eyes. In a major study of radiation hazards to the eye in `Applied Optics', January, 1973, pages 1-33, D. H. Sliney and B. C. Freasier noted that a shade density of AT LEAST No. 13 (visual transmission 1 part in 130,000) is required for viewing the Sun. Shade No. 14, the densest made, provides glarefree viewing comfort during the partial phases, even when the Sun is high in a clear sky. But for the details of the beads of sunlight at the limb during annularity a No 13 shade may be preferred." I bought a No. 13 and a No. 14 shade a few weeks ago. They cost me about $1.40 each from S.O.S. Gases in Middlesex, New Jersey. Most welding suppliers stock welder's glass, though only two of the four I tried stocked the shades necessary for viewing the Sun. The glass comes in two sizes the smaller of which is sufficient for viewing with both eyes at once. They measure 2" by 4 1/4". WARNING: If you prefer to use over-exposed negatives as suggested in the A.P. article (and I don't) DO NOT use color negatives as they are transparent to infra-red. Observing the "Diamond Necklace" -------------------------------- The A.P. article says: > Because of their positions in the sky, the moon appears to be a tiny > bit smaller than the sun when it moves in front. If the moon's > surface were smooth, a simple ring of light would then form at the > heigt of the eclipse. > But instead, the moon has mountains and valleys. And in the seconds > just before the maximum eclipse, light shining between the peaks > gives the appearance of bright beads around the moon, a ''diamond > necklace in the sky,'' as some have described it. > But the best place to view it will be in the Southeast, along a path > from just north of New Orleans to just south of Richmond, Va. Indeed, > Ms. Cleere noted that Interstate 85 nearly parallels the path of the > eclipse for more than 600 miles from Georgia to Virginia. > Along that line the eclipse will be nearly total, with 99.8 percent > of the sun covered by the moon. Across the rest of the United States > and Mexico, a partial eclipse will be visible - with less of the sun > blocked out farther from the line. In order to see the "diamond necklace" you must be somewhere on the path described above. This path is 6 miles wide when it arrives on the Louisiana coast line at 12:02 CDT and is only *3* miles wide when it leaves the Viginia coast at 12:49 EDT. If you are intend travelling to view this phenomenon, known as an annular eclipse, you will need to know exactly where to go. It is probably too late to write but the U.S. Naval Observatory will supply (for free) a set of maps and reams of data for this eclipse by asking for Circular 166 at the U.S. Naval Observatory, Washington, D.C. 20390. Alternatively you can telephone me during the evening on (201)671-7780. I will photocopy the maps you require and mail them the following day (also for free, fool that I am.) Finally, meteorologists for the Observatory estimate that there is only about one chance in three that the sky would be clear enough along most of the path of annularity, though this can be significantly improved if you are mobile. I will be standing where Route 1 crosses Interstate 85 about 6 miles west of Petersburg, Virginia. See you there? Gordon Watson, AT&T Information Systems, Lincroft, New Jersey.