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??EN A SOLAR eclipse whipped ?? ancient Asia in 585 B. C., the ?? and the Lydians supposedly ?? a five-year war with an immediated cease-fire and peace treaty.
?? though tomorrow's eclipse will probably not effect international politics much, millions of North Americans will be plunged into an eerie ?? afternoon twilight as the moon ??ks out the sun's light.
??ere in the Cambridge area, the ?? will cover some 96 per cent of ??sun-not quite enough to see the ??s faint corona, the shifting halo ??onized gases that extends millions miles from the sun's surface. But ?? Nantucket Island, the eclipse will match totality for about two minutes. ?? the sky is clear, thousands of New England sun-watchers will crowd the ?? antiquate ferry or fly out to the island ??or those two minutes. Executive Air-??nes regularly scheduled flights have been sold out for weeks, and several ?? ter airlines have assigned their en-??re flees to ferrying eclipse-watchers ??om mainland points to Nantucket.
At least two Harvard and M. I. T. groups plan to canoe to isolated Mon-??moy Island off Cape Cod and then like nine miles down the beach for ?? 45-second wink of totality.
?THESE preparations may appear ex-??me, especially since NBC and CBS ??th plan live color coverage from Mexico, but a total eclipse is one of the most spectacular of natural phenomena. For earth-bound observers, there are four major eclipse features to watch for:
At 12:31 p. m. here, the moon's disc will seem to touch the right hand edge of the sun and slowly cover most of the sun. At mid-eclipse in Cambridge, a thin crescent of sunlight will remain above the black moon. Clouds will take on a sunset appearance, and the shadow of totality, traveling at over 1000 miles per hour, may be visible from some offshore islands.
As totality approaches on Nantucket, the "Diamond Ring Effect" should be visible. A thin circle of light, capped by one bright spot, surrounds the moon's black disc and creates the impression of a ring. About this time, ripples of light (the so-called shadow bands) may race across the landscape as sunlight is refracted by irregularities in the earth's upper atmosphere.
Several seconds before totality, a few pinpoints of sunlight will remain along the moon's edge, as lunar valleys allow the last modicum of sunlight to pass through. This phenomenon is generally called Baily's Beads, although astronomers here claim that a Harvard professor noticed the beads some 56 years before Baily did.
At 1:47 p. m. the moon will completely cover the sun off the Massachusetts coast. The sky will grow so dark that photographers may need a flashlight to change their camera settings. Venus, Mercury, and some of the stars will be visible. The faint corona will appear to extend about four solar diameters from the sun's edge, and reddish prominence of glowing hydrogen gas will occasionally bubble up around the moon. Ground temperatures may drop ten or 15 degrees, and even in Cambridge, the partial eclipse may cause a drop of a degree or two. Greenhouse flowers may lose their petals. Some birds will fly around disoriented, while others will begin to roost.
After two minutes of totality, the entire process will be reversed, and by 2:57 p. m. the moon will uncover the last piece on the sun's left side.
AN ASTRONAUT looking down from space would see the eclipse's totality as a black circle about a hundred miles across that would first appear off the Pacific Coast of Central America and then race across Southern Mexico. The shadow would then pass over the southeastern U. S.. Nantucket, Nova Scotia, and Newfoundland before disappearing east of Greenland. This deep shadow or umbra is shaped like an inverted cone with its base on the moon and its narrowest point on the earth.
By coincidence, the moon's diameter will appear to be the same as the sun's tomorrow, but this is not always the case. Since the moon's orbit is not circular, there are times when the satellite passes in front of the sun but is so far from the earth that the cone of the umbra falls short of the earth's surface. When this happens, the moon will appear smaller than the sun, and at mid-eclipse, the sun will form a ring around the smaller moon-an annular eclipse.
The moon arrived at the closest point in its orbit at 5 a. m. this morning (223,600 miles from earth), and it will only be a few hundred miles farther away tomorrow. Thus? Saturday's eclipse will be total, not acicular.
ANNULAR and partial eclipses of the sun are not very interesting to scientists because the remaining two or three per cent of the ?? disc completely drowns out the coro?-a halo that is 500,000 times fain??er than the rest of the sun. It is possible to study the corona without an ??clips by using a coronagraph-a met?? disc held in front of telescope to create an artificial eclipse. However, interplanetary dust and sunlight scattered in the upper atmosphere obliterate the corona's fine details.
In the past, eclipse observations have uncovered some important facts about the sun. For instance, after comparing the corona's shape and intensity from eclipse to eclipse, nineteenth century astronomers realized that ?? changed over an ?? The element helium ?? usual ionized states ?? also first detected from ?? corona's light. The disc??? ions, such as Iron??????? led to a remark ?? corona's tempera ??? reach at least ?? ?? heit in order to pro? ?? When parties are ?? sun they pro? ?? shock waves ?? these ??
The ?? Theo? ?? from ?? When ?? tions ?? during ?? stars ?? predict? ?? theory ?? bent th? ?? the ap? ?? ??
DURI? ?? astronomers ?? will make ?? ?? new comets th? ?? the sun to be ?? fact, enough ti? ?? a new comer's ?? and a second ?? ?et for its orbit ??
?? is a prize plum for any as? ?? since his discovery is auto? ?? named after him.
?? ?h? astronomers who will be ?? along the eclipse path ?? ?ct such dramatic results. ?? ?servtions should prove ?? for a more complete ?? the sun. As their data ?? models of the sun im? ?? ?tivity and the earth's ?? become more predict? ??
?? of astronomers from ?? ?llege Observatory and ?? ?neighbor, the Smith? ?? ?physical Observatory, will ?? ?ng our major experi? ??
international team including ?? M. Reeves and William H. ?? ?son, lecturers in Astronomy, ?? have two ultra-violet light de? ?? ?s aboard one of the 33 rockets ?? ?NASA inteds to fire from Wal? ?? Island. Virginia, tomorrow. The ?? ?ll be used to photograph the ?? or chromosphere as ?? ?ls into the eclipse ?? ?? of light ?? rocket's cameras ?? ?he chemical finger? ?? identify the reactions ?? that region of the sun. ?? ?mosphere is only visible for a few seconds during a total eclipse before the moon covers up the thin layer.
The same group of Harvard astronomers will use their ultra-violet experiment aboard the Orbiting Solar Observatory VI satellite to make simultaneous observations of the sun.
In the Mexican village of Miahuatlan, another group-headed by Donald H. Menzel, Paine Professor of Practical Astronomy-will make ground-based observations of the sun's corona. Jay M. Pasachoff '63, research associate in Astrophysics, will photograph the corona's visible light with a special telescope.
Another group, under Winfield W. Salisbury, lecturer in Astronomy, will take television pictures of the corona to study the light waves orientation or polarization and calculate variations in the sun's magnetic field in the corona.
PASACHOFF had also proposed that NASA and Air Force use the SR-71, a high-flying reconnaissance plane, during the eclipse. Since the SR-71 can attain speeds of at least 2000 miles per hour-several hundred miles faster than the eclipse shadow at some points-it could prolong eclipse observation-time by an hour or more. The jet could also position itself anywhere within the moon's shadow. Sci? ?? ?? ?? ??
Cruising at a heig? ?? the SR-71 would also be high e? ?? to observe some ultra-violet and infrared wavelengths of light that the atmosphere obscures at lower altitudes.
Federal budget stringencies apparently prevented the project this time, but shortly before leaving for Mexico. Pasachoff said that an SR-71 or SST modified for eclipse work may well fly within the next few years.
Two instrument-laden jets will be following the eclipse tomorrow but traveling at 600 mph, they are too slow to extend totality by more than a few minutes.
FOR most earthlings with less exotic plans, a total solar eclipse is a once-in-a-lifetime experience. It occurs only once every 360 years at any one place on the earth's surface, and the eastern U. S. can't expect another one in this century. "So we recommend that any one within comminuting distance of Nantucket or Norfolk. Virginia, make it," Pasachoff said, in a burst of enthusiasm that is typical of the spacemen who populate Observatory Hill. "Don't settle for 98 per cent."
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