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PAGE 14 - PLAINDEALER - FPIDAY, JULY S, I»77 0 ^ Think ^ Pfaindealer V 0 ISp Kill when ASTRONOMY FROM *50® ; *-<*•V; Charles Schweighauser Sangamon State University ECUPSES OF THE MOON: WHY AND WHEN During a full moon, when the Earth is between the Sun and the moon, an eclipse of the moon is possible: As the moon revolves around the Earth it first enters the penumbra of the Earth's shadow. The penumbra is the partially shaded portion of the N shadow that surrounds the dark umbra. We can not usual­ ly notice a difference in the light reflected from the full moon during the penumbral part of the eclipse because- there is too much light in this part of the Earth's shadow. - When the moon enters the umbra, a curved shadow will begin to creep across the brightly lit full moon. The curved shadow on the moon's surface demonstrates the curva­ ture of the Earth; this phenom­ enon was one of the proofs of the spherical shape of the Earth cited by Aristotle. Totality is the condition when the moon is completely in the umbra of the Earth's shadow. It can last for a maxi­ mum of an hour and 40 min­ utes. The moon i$ never com­ pletely dark during totality be­ cause sunlight is refracted through the Earth's atmo­ sphere onto the surface of the moon: Light reflected from the sur- face of the moon can range from a dark reddish color to a lighter coppery color;variation in color is due to weather conditions^] the Earth's atmo­ sphere ^Ifgire the sunlight passes through, as well as to the amount of particulate mat* ter from volcanoes and pollu­ tion. •• y There are three kinds of lunar „ eclipses: penumbral eclipses occur when the moon passes through the penumbra of the Earth's shadow and completely misses the umbra; a PENUMBRA •r I L *>- '* !**V|2 ECLIPSE OF THE MOON BUSINESS CARDS LETTER HEADS ENVELOPES Ctons Papers Styled By ' 0 ^ f ' ' 4 Come in and view our fine selection ̂ The McHenry Plaindealer 3812 W. Elm St. McHenry 385-017ft rH 'j Rayi of tunlifht refracted In paving through aarth's atmosphere partial eclipse occurs when the moon passes through only part of the umbra without go­ ing entirely into the dark part of the shadow; and a total eclipse, when the moon is com- % * letely inside the umbra. Obviously, an eclipse of the moon can occur only during a full moon. Since there is a full moon each month, we would expect to see one of the three kinds of eclipses each month. However! we know that an eclipse of the moon does not -occur each month. The reason is that the moon in its path around the Earth most fre­ quently passes either above or below the Earth's shadow; only occasionally will the moon move directly into the Earth's shadow. * • If the sky is clear, a lunar eclipse can be seen from all oyer the Earth where the full moon is visible. The next eclipse of the moon will be a„ penumbral eclipse on the night of Sept. 26 and 27, 1977. Professor Schweighauser invites questions from interested read­ ers. One question each month will be selected for discussion in this column. • Write: Charles Schweighauser Sangamon State Univ. Springfield, IU. 62708 Next week: Eclipses of the Sun: Why and When Canned Seafood From time to time the Food and Drug Administra­ tion receives repents from c o n s u m e r s w h o b e l i e v e they've found glass in canned seafood,, especially shrimp. Examination however, us­ ually reveals it isn't glass but "struvite"--crystalline magnesium ammonium phos­ phate to the chemist--which occasionally forms naturally in canned seafood. Here's a simple test to dis­ tinguish between struvite and glass--simply place the crys­ talline material in warm vine­ gar. The struvite crystal will dissolve; glass of course, won't. Cosmetic Labels The Food and Drug Ad­ ministration has announced that all labels affixed to cos­ metic and toiletry products after April 15, 19/7 must list the ingredients in the product in descending order of predominant ,̂ laEf & S ...M dm kirn Woodstock, Illinois mchenry, Illinois semi-annual clearance sale During our store-wide clearance of nationally known famous brands, there's savings in every department. Some items reduced as much as 50%.Since this is a clearance safe, not every style in every size and color is available, however, there is still an outstanding selection. suits regularly'90.00 *68.00 regularly '115.00 .'86.00 regularly '135.00 '104.00 regularly '155.00 .'118.00 regularly '175.00 '136.00 i / * walking shorts - regularly'11.00 ...< '8.44 1 regularly'13.00 J. »9.88 regularly'15.00..„ . 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