This document is about total solar eclipses, or more particularly, it includes; information about what to expect of a total solar eclipse; suggested preparations to make if you plan to observe and photograph an eclipse; and finally, suggestions for what to do during a total solar eclipse.
This article is one chapter in a series of documents that comprise an on-line solar eclipse "book", and probably a printed publication later on. Together, these chapters cover many fascinating aspects of solar eclipses, some of which have never been covered before. Check out the EclipseChaser web page for many exciting eclipse features, including cool 360 degree panoramic photos taken during total solar eclipses!
This chapter is intended to address the needs of the first time total solar eclipse observer and the veteran eclipse observer alike. It focuses on how to manage the equipment and procedures required to document an eclipse. Included are many useful tips to help you plan your eclipse encounter; whether you are planning a serious eclipse expedition or a simple "getaway" that includes an eclipse. Even if you only plan to look at the eclipse, you may still find some of this material useful. For those of you who are thinking about going to your first eclipse, this chapter begins some basic information about eclipses.
The still photography section of this paper includes information from a presentation I made at the 1991 Riverside Telescope Makers Conference entitled "Gadgets and Techniques for Total Solar Eclipse Photography". The basics of the present paper were presented at the 1996 Riverside Telescope Makers Conference. Some descriptions of the total solar eclipse experience in this paper are from the narration for my future eclipse video which will be entitled "A Quartet of Total Solar Eclipses".
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A total solar eclipse occurs when the moon moves directly between the earth and the sun, and when the moon is close enough to the earth that its apparent diameter is larger than that of the sun. During a total solar eclipse, the sky will become dark enough to allow the sun's corona to be observed. The sun's corona is obviously present all of the time, but it is relatively dim so it is usually obscured by the brightness of the normal daytime sky.
The plane of the moon's orbit is inclined about 5 degrees to the plane of the earth's orbit, so as seen from earth, the new moon will usually pass above or below the sun, rather than directly in front of it. A solar eclipse can only occur if the moon passes between the earth and the sun at such a time that the moon is near a point (or node) in its orbit where its orbital plane crosses the earth's orbital plane. This happens about twice a year; however, the moon's orbit is elliptical. During more than half of its orbit, the moon appears too small to completely cover the sun. If a central eclipse occurs at this time, the result is an annular eclipse. Due to all of these factors, a total solar eclipse can only occur somewhere on earth about every year and a half.
When a total solar eclipse occurs, it can only be observed from a very limited region. This is because the eclipse is only total within the the moon's conical shadow, or umbra. Depending on the eclipse, the width of the umbra at the earth's surface can vary from less than 1 km to over 260 km. An eclipse will generally last the longest when; the cross section of the umbra is large, the eclipse occurs near the equator, and when the eclipse occurs near local noon. The latter two factors lengthen an eclipse because; the curvature of the earth places the observer slightly closer to the moon, and; the rotation of the earth counteracts about half of the moon's orbital velocity, thereby slowing the ground speed of the umbra. The lunar umbra usually moves rapidly across the earth from west to east. The ground speed of the umbra can be as slow as ~2,000 km per hour, but it is usually much faster than that. Even though the lunar umbra can be quite large at the earth's surface, its rapid ground speed causes it to move its own width in only a few seconds or minutes; therefore, the duration of the total phase of an eclipse, or "totality" is quite short; typically from 1 to 5 minutes. Some eclipses can last longer (up to about 7-1/2 minutes) but such long eclipses are rare.
1.2 What is it like to see a total solar eclipse?
A total solar eclipse is truly an awesome experience. Many people (including myself) have become eclipse addicts (or to use a milder term, "eclipse chasers") after seeing our first eclipse. Right after the end of my first eclipse, my immediate thought was "when is the next one?" Once bitten by the eclipse bug, it is not unusual for a person to travel all over the globe just to be in the moon's shadow for a few brief, awe-inspiring minutes.
The partial eclipse phase begins at first contact, when the moon takes its first bite out of the edge of sun, (or more correctly, the solar photosphere, which is the brightest visible layer of the sun). The ambient light gradually dims as the moon covers the sun during the partial phase, which can last from between about an hour to an hour and a half. It is important to remember that the partial phase of the eclipse can only be observed with a proper solar filter, because it is not safe to look at the uneclipsed or partially eclipsed sun without a proper filter.
A few minutes before the total phase of the eclipse, or "totality", the ambient light dims rapidly, and it is often possible to see the moon's shadow (or umbra) in the sky as it races toward you. The light level continues to drop until it is as dim as what you would normally see about half an hour after sunset! If you are alert and know to look around, the speed of this transition to apparent twilight will be mind boggling; and this is just the beginning!
The real "star" of the show is the sun; particularly its atmosphere, or "corona", which becomes visible at the beginning of totality, or second contact. During the brief duration of totality, it is safe to look directly at the corona without any filtration, and it is a beautiful sight! Totality ends at third contact, and a second partial eclipse phase follows, ending at fourth contact, when the moon no longer eclipses any part of the sun. A more detailed description follows:
The eclipse begins: As the moon takes the first bite out of the sun, there is little effect on the local lighting. Nonetheless, one can begin to become excited with anticipation, for that bite out of the sun means that the eclipse has begun! As the partial phase of the eclipse progresses, the ambient light begins to progressively dim. By about 15 minutes before the total phase of the eclipse, or "totality", the light is noticeably dimmer than usual and the colors around you appear to "gray out" a little.
The ambient temperature may have dropped since the beginning of the eclipse, and it may continue to drop over the next several minutes. At this time, it is not uncommon for a noticeable breeze to blow for a few minutes. As the lunar umbra approaches, this "eclipse wind" typically blows in toward the cooling (and contracting) air near the center line of the eclipse, though it is possible to experience this wind even from sites right on the center line. In some climates, this wind can be caused by factors other than localized contraction.
The eclipse progresses: A few minutes before totality, the sun appears to be a crescent shape and the ambient light is substantially dimmer than normal. By this time, the shadow (umbra) of the moon can usually be detected as a dark gray-blue area low in the sky near the western horizon. The color may be similar to that sometimes seen under late afternoon storm clouds.
If the sky is clear and one is VERY, VERY careful, it may also be possible to detect some of the moon's outline against the sun's inner corona through a small telescope by stopping it down to about 2 cm aperture and placing the crescent sun a little outside the edge of the field of view.
By this time, more terrestrial phenomena may have become observable. Subtle shadow bands may appear on the ground and on sunward walls. Their appearance may vary between straight bands that are stationary or that move in a constant direction, to twisted shadows which wander aimlessly like those sometimes seen on the bottom of a swimming pool.
About two minutes before totality, the light intensity begins to drop fast enough that you can barely detect it is getting darker second by second. The crescent sun is getting thinner and thinner at an unmercifully fast rate! If the sky is clear, brighter stars and planets will become visible. The lunar umbra gradually appears to get larger, and a pale yellow color may become visible near the horizon on either side of it.
It's getting exciting now! By one minute before totality, only a small sliver of the sun is still visible, and the light intensity begins dropping almost as fast as when the lights are dimmed in a theater. In clear weather, the blazingly bright crescent sun stands alone against a perceptibly darkening blue sky, and there is very little localized glare around it. It may be possible to detect some or all of the moon's outline against the sun's inner corona (though you should not try to observe this directly because it is not safe to look at any part of the nearby crescent of the solar photosphere without proper filtration). I "accidentally" saw this effect for a second or so in 1994, when I was so sleep deprived that I forgot to follow my own advice! It was fascinating to see, but do not plan to look at it again! I described it so you won't have to look at it!
By this time, the moon's umbra may cover up to one quarter of the sky, and its diffuse leading edge may be observable as it moves across the sky, "eating up" the brighter blue sky as it goes. (This motion is typically easiest to see relatively near the horizon, particularly if the umbra is projected on a distant cloud bank). By now, the trailing edge of the umbra will have moved above western horizon, and some yellow or orange color may be visible along the horizon below and to either side of it. The upper boundary of the umbra gradually becomes too diffuse to discern with the naked eye, though it may still be detected with a wide angle viewer such as a fisheye door peeper. The sky overhead can begin to take on a deep blue color, which gradually continues to darken as totality approaches.
Baily's beads: By about 20 seconds before totality, the ambient light dims so fast that you may feel as though something big is coming down on top of you. It is exciting! The remaining sliver of sun appears to shorten at a faster and faster rate, and a rim of dimmer light can be seen extending from its ends, barely making a complete ring of light, with the bright sliver making up one side. This dimmer light is the inner corona. The remaining sliver of the sun continues to shorten, and its ends begin to break up into small pieces, briefly making it appear like a shrinking arc of beads.
The diamond ring: Finally, only a small, contiguous group of beads are left. They appear to be as though they are a bright diamond set against the rim of dimmer light. This is often called the "diamond ring" effect. Often, the small group of beads making up the "diamond" may appear to be surrounded by a localized diffuse circular or oval glare which is caused by atmospheric scattering. This makes the diamond ring effect even more dramatic. The beads quickly dim and go out until only one is left. As the last bead of light continues to dim, the rim of light around the moon appears to brighten and widen as your eyes adjust to the dimmer light. Before you know it, all of the direct sunlight disappears and totality begins! At this point, it IS SAFE to look directly at the eclipse!
Totality! The solar corona is visible around the entire dark outline of the moon, even though a rapidly shortening arc of bright pink light remains near the point where the last bead of sunlight was. This arc of pink light quickly disappears. It was the solar chromosphere.
To the naked eye, the corona appears to be a pearly white ring of light around the dark, round, outline of the moon. At the first casual glance, the corona may appear to be a featureless and irregular ring of white light, extending out to an angular distance equivalent to about one lunar radius from the dark edge of the moon. If the sky is clear, a more extended observation of the corona will reveal that there is a soft quality to its light and that it has streamers radiating out from its center. The corona may extend out at least one solar diameter in all directions. Some of the eastern and western coronal streamers may extend well beyond two diameters. During eclipses which occur near sunspot maximum, some polar streamers may appear be nearly as long as the equatorial ones. The corona appears absolutely stationary, though passing thin clouds may rarely produce the illusion that it is scintillating or has subtly changing colors.
Bright pink blotches of light, called "prominences", may also be visible around the edge of the moon. These solar prominences may look small as seen from earth, but in reality they are quite large; it is not unusual for them to be over 20,000 km high!
Through binoculars or a low power telescope, the streamers in the corona will appear to be very sharp, almost as though they were etched with a fine blade. Some radial polar streamers appear fanlike, and some of them contain myriads of incredibly fine radial lines. If your telescope or binocular is on a stable mounting, the detail in the corona and any visible prominences will be breathtaking, particularly at magnifications between 15x and 25x. At lower magnifications, it is sometimes even possible to see major features on the surface of the moon which are illuminated by earthshine.
The sky overhead is a dark gray-blue color, and some brighter stars and planets may be visible. The area occupied by the moon appears to be about the same color and brightness as the grayish blue sky immediately surrounding the corona. Most of the horizon all around you is ablaze with the yellow and orange colors of a sunset! It is not completely dark during totality, but it is dark enough to make reading difficult. During this time, an incident light meter will typically read an exposure of one or two seconds at f/4 with ISO 100 film.
The end of totality: As totality nears an end, the western sky gradually gets brighter. A bright slice of bright pink light (the chromosphere) begins to appear at the western edge of the moon. It gradually lengthens until it appears to wrap around about 60 degrees of the moon. Then, a tiny part of the sun's photosphere appears through a valley on the edge of the moon. It appears blazingly bright and quickly increases in brightness. It is now time to look away from the sun, because it is no longer safe to look at it without proper filtration!
For a few seconds, the corona remains visible around the moon as the photosphere emerges. This the second "diamond ring". A few seconds more, and the sky appears bright again, though it may still be possible to detect some of the moon's outline against the inner corona for another minute or so (though again, you should not try to observe this because it is not safe to look directly at any part of the solar photosphere). Soon, the sky grows so bright that there is no longer any trace of the corona. For a few seconds or minutes, the lunar umbra may be visible as a slowly shrinking dark area near the eastern horizon. It is soon gone and the entire sky appears to be normal again, even though there may still be a strong partial eclipse remaining. In cases where the ambient temperature dropped before totality, it may continue to remain relatively low for several minutes. Over the next hour or so, the moon gradually retreats from in front of the sun, and the eclipse ends.
The eclipse experience will probably leave you in awe, and like many others who have been bitten by the eclipse bug, you will probably want to know: "When is the next one?!" The moon covered the sun, yet you saw the sun in a way you have never seen it before!
1.3 What is difficult or unusual about photographing an eclipse?
Some may wonder: "Why go to so much bother preparing for something that lasts such a brief time?" Answer: The very brevity of the total eclipse is what makes preparation so important! Most people can't just "wing it" if they are to carry out even a modest photographic program in the short time available, particularly if they want to have time to look at the eclipse. If the photographic program is relatively ambitious, one could be orchestrating the taking of over 30 pictures per minute with a quartet of cameras!
The duration of totality is short, and photographing some aspects of an eclipse can be challenging; and most of all, you don't get a second chance! Even though it is not obvious visually, the brightness of the corona near the edge of the moon is typically over 1,000 times brighter than the outermost ends of the longest coronal streamers. A wide range of exposures will be required to record the full brightness range of the corona. For landscape photos, the light intensity just before totality can drop as fast as three f/ stops per minute, and auto exposure will not always produce the best result. In addition to all of this, the eclipse may cause you to become excited! (It can be easy to "lose your cool" if you have problems before and during totality, particularly if the eclipse has already caused you to lose most of it already!) And there's more! You may have to observe a total solar eclipse from a remote and unfamiliar site that lacks creature comforts and good shelter; and then of course, there's always the weather... Obviously, you cannot do a great deal during the short duration of totality, especially if you want to have time to LOOK at the eclipse, but good planning and preparation will allow you to accomplish much more than you could have otherwise!
In spite of all of the above difficult factors, it is important to remember that eclipse photography can be done; and that good planning, practice, and documentation is what can facilitate its being done successfully!
1.4 How do I get good photos and/or video of a total solar eclipse?
It is not particularly difficult to take a few "good" photos of the corona. Lenses as short as 200 mm will do an acceptable job, and 600 mm to 1000 mm lenses will work really well. With ISO 100 film and an f/8 lens, exposures of 1/250 second, 1/60 second, 1/8 second, 1/2 second, and 2 seconds will usually give you good pictures of prominences and of the inner, middle, and outer corona, even if you do not have a clock drive. If you want to photograph more than just the corona, things can become more involved. Totality is so short lived that you probably will not have time to change camera lenses or film; therefore, it is usually a good idea to bring one camera body for each lens or film type you want to use. This can be costly, but you can lower the cost by renting or buying used equipment.
In order to be successful at documenting multiple aspects of an eclipse, most if not all of us should, at least in principle, deal with the task in much the same way as a business would deal with engineering its products. More particularly, you should set your goals or objectives, (what you want to accomplish); determine your requirements, (how much to spend, what your instrumentation must be capable of and how portable it must be, how much setup and program execution time you have, etc.); define applicable problems, (determine what you want to do that your current instrumentation is not capable of, and what instrumentation you need to gain the capability, how and when to acquire or construct necessary instrumentation, how to get yourself and your equipment to the eclipse, and how to reliably complete your eclipse program in the available time, etc.); solve the applicable problems, (planning, acquiring instrumentation, practicing, etc.); and then go to the eclipse and perform your eclipse program; all while still enjoying the eclipse.
In short, if you want to photograph more than one aspect of an eclipse, it may take a lot of preparation. The more demanding your eclipse program, the more you should prepare for it. The more you prepare, the more successful you will probably be. In general, you will reap what you sow.
The goals of some seasoned eclipse chasers may even require that they design and fabricate your own custom instrumentation. This may seem extravagant, but remember that the right equipment can simplify one's procedure at the eclipse, while at the same time extending one's capability. In addition, such equipment can be used over again at other eclipses, etc.
Based on my own experience at the 1979 eclipse, I do not recommend taking a lot of sophisticated equipment to one's first eclipse. The enjoyable thing to do is LOOK at the eclipse! This may prove to be useful too, since you have to SEE an eclipse before you can know how to properly print your pictures of it. Once you have seen the corona, you will realize that no one photograph can capture what it REALLY looks like. After you experience your first eclipse, you will have a better idea of which (if any) aspects of the next eclipse you want to photograph.
Things to remember: The most important things to remember are simplicity, planning, practice, and documentation, or SPPD. If you decide not to heed the recommendation for simplicity, the other recommendations of planning, practice, and documentation will become even more essential. If you intend to have several eclipse projects, it is important to prioritize them. Giving one project high priority and considering most of the rest discretionary will go a long way toward keeping you relatively calm and organized during the eclipse.
It is important to remember, at least in regard to planning, that even looking at the eclipse should be considered a "project", with its own dedicated block of time. Trying to look at the eclipse only while you do other projects is not a good idea, since you can't take it in very well if you are distracted by other things, not to mention the fact that the eclipse may distract you from your projects! A short glimpse of totality typically isn't enough. You may travel a long way to see an eclipse; don't you want to remember it?
Practice makes perfect! Once your eclipse procedure is planned and documented, it is a good idea to practice until you have it memorized so well that you can do it correctly without referring to your documentation. When you practice, use a timer and stay with your schedule. It may also be helpful to synchronize an edited eclipse video with your timer when you practice. This may help you feel a twinge of the anticipation and excitement that you may feel at the real eclipse, and it will demonstrate the fact that when totality is over, it's over! Additional recommendations are summarized below. Adhering to them can potentially save your eclipse photography program if things go wrong, for example:
When I went to Bolivia for the 1994 eclipse, I had a relatively ambitious program; operating 6 still cameras and 3 video cameras, obtaining contact timings and incident light intensity measurements, and observing the eclipse through my telescope. This was not a "simple" program, but I had built special instrumentation for the task and had practiced my procedure a lot.
While in Bolivia, circumstances beyond my control caused me to become ill, stressed out, and more sleep deprived than I had been in 20 years. By two days before the eclipse, I could not practice my procedures nearly as fast as usual and there was little prospect of recovering in time, so I canceled some of my program. By eclipse day, I was uncoordinated and so "out of it" that I did not even remember how to set up some of the gadgets I brought, or the notable fact that Venus would appear right next to the eclipse! To make matters worse, I had Montezuma's revenge and I was surrounded by some relatively well to do local people who disturbed and obstructed my equipment, took flash pictures, and continuously asked me questions.
More or less operating on "autopilot", I set up my equipment according to my prepared list and performed the eclipse procedures I had practiced, referring to my written schedule when I had to. When the eclipse was over, over half of my work had been done properly. While half is not a good ratio, my condition at the time was so bad that if I had not planned, practiced, and documented my procedure, it is unlikely that I would have had any good results at all. This was an extreme situation, but it does show the value of planning, practice, and documentation!
The 1995 eclipse in Thailand was a more "normal" experience. As in Bolivia, I had a relatively ambitious program; operating 5 still cameras, 2 video cameras, obtaining incident light intensity measurements, and observing the eclipse through binoculars. In regard to the relatively short duration of totality, (1 minute 41 seconds) the procedure was even more intensive than that for the Bolivian eclipse. In Thailand, the logistical and demographic circumstances were very favorable, and practically EVERYTHING I had planned to do at the 1995 eclipse was successful.
In preparation for this eclipse, I tried something different. As usual, I practiced my procedure one last time the day before leaving the U.S., then packed my equipment as I disassembled my setup; but this time I left all of my equipment packed until I set it up at the eclipse site. Not only did this save time, but it also allowed me to maintain a low profile before the eclipse. At all previous eclipses except my first one, I had set up my equipment and practiced my procedures shortly after arriving in the country or region where the eclipse would occur. Both of these approaches have their advantages.
To modify a popular phrase; practice makes perfect when circumstances are favorable, and practice can prevent failure when circumstances are unfavorable.
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© Copyright 1995, 1996, Jeffrey R. Charles, All Rights Reserved.
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