Allentown School District (ASD) Planetarium: Observing Eclipses

Observing a
Total Solar Eclipse

Gary A. Becker and Allen Seltzer

[ECLIPSE MAP]
[ECLIPSE MAP]



Eclipse Times for Aruba,
February 26, 1998

Event
(from Aruba)
Time
(Atlantic Standard Time)
First Contact12:38:51 p.m.
Second Contact02:09:48 p.m.
Third Contact02:13:22 p.m.
Fourth Contact03:36:02 p.m.
Maximum Eclipse02:11:36 p.m.
Duration3 min. 34 sec.




Youíre not in control. That you learn quickly. You are at the mercy of the elements that you have come to view. Clouds overtake you; as they scud overhead, the sun plays tag with them. But finally, pure light bathes you in its heat. Slowly, the light wanes- very imperceptibly- until the complete black disc winks out the sun. It is suddenly dark; the stars and Venus burn brightly. You realize then, how much you share in common with the first peoples who were truly in awe and frightened of the power.

If you really thought about that power, the power behind the eclipse and gravity, the sea and its mysteries, the slow inexorable change of land that sculpts mountains and canyons, then you would put your petty jealousies and problems behind you and be the best person you could be. Because the eclipse brings you face-to-face with your soul... You are meant for higher purposes, of noble stock, of the bright and positive and spiritual... You are at one with the power of the universe.

So yes, the eclipse is an event, but it is something else too. It is an experience of perception. It turns you, as surely as the North Star, to a sacredness that pertains to all nature. Once you see the blackened disc, the entrance or portal to this other reality, you are changed. Go back then to your daily round and remember.

The following thoughts were written by Susan B. Reisinger-Becker after observing the February 26, 1998 total solar eclipse off the coast of Curacao.

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Any eclipse can be an exciting event, but a total solar eclipse holds the special magic of seeing the sun "set" twice in one day, and the veil of darkness created by the moonís shadow rapidly descending all around you. As the moonís shadow approaches, it can be almost as if a giant thunderstorm is about to envelop you, but there is no rumbling and no smell of rain in the air. The minute or two before the eclipse becomes total can also be filled with an array of exotic optical effects: the pulsating lights of shadow bands, a darkening reddish hue cast upon objects still exposed to the sunís waning luminescence, weakening but very sharp ground shadows, and the whole sky rapidly sliding into darkness as if someone was controlling a giant rheostat which was dimming natureís light forever.

A total solar eclipse is, without doubt, one of natureís grandest light shows and it will leave you yearning for more. For there is never enough time to catch it all, to savor every event, or to get tired of the darkness and long for the return of the light. The sunís light will return soon enough, and you will probably be left with a feeling of celebration, as well as a craving to do it again, to repeat the phenomenon, to make another rendezvous with the moonís shadow at some future date.

The path of totality for the February 26th eclipse begins in the central Pacific and moves rapidly eastward across equatorial waters, making its first landfall over the northern edge of the Galapagos Islands. The moonís shadow races eastward traversing the border between Panama and Colombia before exiting into the Caribbean Sea from northwestern Venezuela. The moonís shadow passes over the islands of Aruba and Curacao about 2:10 p.m. Atlantic Standard Time, then continues eastward across the Caribbean Sea, overtaking the Leeward Islands of Montserrat, Antigua, and Guadeloupe just 20 minutes later. The eclipse ends at sundown, just west of the Canary Islands.

It begins simply enough with first contact, when the limb of the moon begins encroaching upon the moon. Itís a tireless advance which does not show, at first, any outward signs of visibility. It must be scrutinized with the use of filters or projection techniques.

As more and more of the sun becomes eclipsed, the sky darkens and the landscape takes on an eerie metallic quality, imperceptibly at first, then more noticeably as totality approaches. Shadows on the ground become sharper, the sky becomes more contrasty, and the air temperature drops sharply as the solar disk is reduced to a thin sliver. In the last few minutes before totality, the fading light drops off dramatically, and the scenery reddens as the cooler outer layers of the sunís photosphere now provide the last remaining illumination to the landscape. The coloration is similar to a ruddy sunset which occurs on a clear, cloudless day, an eerie deep red or orangy glow that is one of the most visually appealing moments of an eclipse preceding totality.

With the advancing darkness, it may be possible to glimpse a curious but often elusive eclipse phenomenon--shadow bands. They appear as alternately light and dark bands of varying thickness passing over the ground. The effect is similar to the wavy lines seen on the bottom of a pool, produced by refracted sunlight shinning through the ripples on the surface of the water. Shadow bands may be due to irregularities in the Earthís atmosphere augmented by the ever thinning crescent of sunlight from the eclipse. However, they are not always observed with every eclipse. When they are seen, they usually appear just minutes before the beginning of the total eclipse or for a few minutes following totality. Because of the greatly diminished light and because shadow bands are generally a low contrast phenomenon, a white sheet spread over the ground will greatly improve your chances of observing them.

Between 30 and 15 seconds before totality, as the solar crescent fades to a thin filament of light, it does not go out instantaneously, but instead breaks apart into a succession of brilliant explosions of light, called Bailyís beads. The beads received their name from the vivid description of them written by the English amateur astronomer, Francis Baily, after he observed them during the total solar eclipse of May 15, 1836. The phenomenon is the result of sunlight streaming through the valleys between the mountain peaks along the moonís limb. As totality approaches, the lunar mountain peaks will appear to touch the preceding limb of the sun, breaking the remaining thin crescent into a beaded pattern. Coincident with the appearance of the last of the beads is the sunís inner corona. Together, the single glistening bead of light and the inner corona surrounding the lunar disk create a beautiful diamond ring effect. The duration of the diamond ring usually lasts for about 5-10 seconds. You should remove any viewers or filters used to observe the partial phases of the eclipse at this time.

As the last of the sun's bright light disappears (2:09:48 p.m., AST), the moon's shadow appears to descend upon the earth with incredible speed. The dark blue sky changes rapidly to gray or dull purple, and darkness overwhelms the scene very dramatically. You will understand why the "natives grew restless" when a total solar eclipse suddenly appeared. You will probably be compelled to make some type of spontaneous verbal comment, not from a feeling terror, but from the sheer exhilaration of the moment, and the beauty which has now enveloped you and your companions. A small tape recorder is a handy device which will allow you to help capture the moment permanently so that you can relive the excitement and share it later with other friends. The beginning of totality is often referred to as second contact.

The darkness which prevails during totality varies greatly, but it is never as black as night. There are several reasons for this. First, the solar corona, which is about twice as bright as the full moon, adds a considerable amount of light to the sky. Also, the sky near the horizon, which lies outside the moonís shadow, is still brightly illuminated. This horizon glow, appearing yellowish or reddish like the colors of sunset, contributes further to the overall brightness of the sky. A hazy atmosphere will also scatter and reflect more light into the shadow zone too. Expect the sky brightness to be about the illumination of 6-8 full moons. Planets and some of the brighter stars will be visible if you can draw your attention away from the camera or the eclipsed sun to take a look.

The sky during totality, February 26, 1998. From Astronomy magazine





Another layer of the sunís atmosphere visible during a total eclipse is the chromosphere. It lies between the photosphere and the corona. Invisible in full daylight, the chromosphere appears as a thin red arc for a few seconds at the beginning and near the end of totality. From the chromosphere are seen red flame-like structures called prominences. These arcs of fluorescing hydrogen gas follow field lines which usually propagate from magnetically active regions in the photosphere, where sunspots can often be found. Larger prominences, such as the ones seen during the July 1991 total solar eclipse, can be viewed with the unaided eye, but here also, binocular and telescopic views will enhance the enjoyment.

The most conspicuous feature of any total solar eclipse is the corona. The corona is the outer atmosphere of the sun which extends for several million miles above the sunís visible photosphere. It is a rarefied collection of very hot, highly ionized gases and atomic particles. The corona first makes its appearance immediately before the extinction of the sun during the time of the diamond ring effect. It appears as a delicate pearl-tinted halo, often with brushes and petals of light, streamers, and spikes surrounding the black disk of the moon. Under very transparent sky conditions the corona has been seen to extend four to five solar radii and sometimes even farther.

During periods of sunspot minimum, asymmetries in the corona are most pronounced. Generally, there tend to be long equatorial streamers and relatively short polar brushes. At sunspot maximum, the corona is usually in its most symmetrical form. Sunspot totals bottomed in 1996, so activity is just now beginning to build. Look for a fairly asymmetrical corona for the February í98 eclipse, hopefully similar to the solar eclipse in 1991, which was visually the most spectacular of the twentieth century.

After three minutes and 34 seconds of darkness, the moon will begin to uncover the sun. Third contact, which occurs at 2:13:18 p.m., AST for Aruba, marks the end of totality. The chromosphere, prominences, corona, and stars rapidly fade from view as the moonís shadow races away. The diamond ring and Bailyís beads are repeated, but in reverse order and on the opposite limb. Again, it may be possible to see shadow bands, but it will be probably very difficult to concentrate. Some people will cry, some will just stand silently around with that "itís all over look," upon their faces, but most individuals will want to communicate immediately their thoughts with each other. This is another good time to have a tape recorder running. The remaining partial phases will continue for another hour and 13 minutes. Most people wonít care, but itís really a great time to continue your photography and reflect in writing your feelings and facts while they are still fresh in your mind. Fourth contact happens at 3:36:02 p.m. local time when the lunar and solar disks separate, denoting the end of the eclipse.


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