by Paul D. Maley, NASA Johnson Space Center Astronomical Society and International Occultation Timing Association (IOTA)

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On August 21, 2017 a total eclipse of the Sun will occur over the continental United States caused by the Moon passing between Earth and Sun where the Moon’s shadow is cast upon the Earth. This will offer a unique opportunity for schools located near the edges of the eclipse path to participate in an experiment to determine one of the two “true” edges of the zone of totality and potentially updating the diameter of the Sun if successful measurements are made at the opposing edge about 130 mi/ 209km north of Minden, NE.   This citizen science effort is intended to help determine the accuracy of eclipse path prediction as well as to contribute to long term study to determine changes in the size of the Sun.  “The path of totality” is defined as that area on the ground that will experience a complete solar blackout.  This total eclipse can be seen from Oregon to South Carolina but only over a narrow area in gray as shown below.  The path defines the movement of the Moon’s shadow cast onto the Earth during a 90 minute trip and tracks from a west to east direction; the shadow is 61.5mi/ 99km in width as it first crosses the west coast in Oregon. Then it expands slightly to a width of  71.3 mi/ 114.8km wide where it exits North America at the coast of South Carolina. All of the Sun’s light is extinguished for a maximum time interval of roughly 2.5 minutes depending upon where in the narrow zone of totality you happen to be situated.  The farther you are in a perpendicular direction from the center (thin blue line on the map below) of this track, the less totality is seen until finally when you are at the precise edges, where there is no true total eclipse at all. Those outside the gray area see what is called a partial eclipse.   As you keep moving further from the center you enter a very expansive partial eclipse zone where there is  some amount of solar disc visible.   In general the weather in August tends to be less cloudy west of the Mississippi River; however, there is no guarantee of any specific weather condition far in advance.


Figure 1. “Path of the totality” is defined as the gray zone crossing the US in the figure above inside of which the Sun is totally eclipsed. Maps courtesy of X.Jubier.



Observations similar to what we propose have been attempted before–most notably at several eclipses including that of 1925 in New York City (total eclipse) and 1984 in Mexico (annular eclipse) where the groups for one reason or another (weather, hardware problems, data collection issues, etc.) were not able to satisfactorily determine changes in the Sun’s diameter.

A different early attempt in 1875 in Russia to measure the solar radius by positioning observers across both north and south limits did not succeed due to bad weather.  However, in 1983 Dr. John Parkinson organized 25 6th grade students along a 5mi / 3km road on the north coast of central Java, Indonesia.  They were divided into two teams straddling the north (Batang town) and the south edges (Bangil town) of the eclipse path with the groups separated by 120 mi /200km.  Each person’s role was to look at the Sun and say the word “Partial” (indicating the Sun remained visible) or “Total” indicating the Sun disappeared for some period of time however brief.  Both groups were successful and the conclusion was that the diameter of the Sun was 0.34 arc seconds smaller than predicted but the amount of error in the observations was likely larger than the precision that was desired.  In addition there was some confusion on the part of a few observers whose training was last-minute.


Photo 2.  The Parkinson-organized eclipse edge groups in Indonesia June 11, 1983.

At the very edge of the eclipse path and even just outside of it,  it may be possible for visual observers to actually see the Sun’s outer atmosphere (corona) with the naked eye as in the drawing below made during the 1871 solar eclipse.


Figure 3.  Drawing of the solar corona by A.R. Dawson December 12, 1871 from just outside the path of totality.

During the last century this experiment was attempted in New York City during the total solar eclipse of January 4, 1925.  Electric utility companies in that area were interested if any possible power impacts on the loads carried by the various substations would occur as a result of the eclipse.  New York Edison decided to assist scientists and sponsor a study by which the precise edge of the eclipse might be determined to correlate with power usage both within the zone of totality compared to that outside.  The edge of the eclipse was calculated as being at a certain point on the ground + or – 1 mile. To further define this it was decided to assign 149 observers into groups of 2 or 3 and place them on the roofs of various buildings (see black dots in the figure below). This zone covered about 63 city blocks at 73 locations. There were two types of measurements conducted where the one bringing in the best results involved an observer at each location specifying whether the Sun was completely covered or not.  It was to find that demarcation, between a full eclipse and not a full eclipse that was the primary goal.  The resulting distance between where it appeared that the eclipse was total and not total varied between observers from 225 to 750 feet separation.  Although the aim of this deployment was to determine the change in the diameter of the Sun at this eclipse, the expedition failed because half the data disappeared with the death of the expedition leader.


Figure 4. Locations of observers across Manhattan Island


Figure 5. The 1925 eclipse was observed by both photographic and visual means in winter.


Help make science happen by volunteering for a real research project.  For the 2017 eclipse the International Occultation Timing Association (IOTA) would like to refine that distance error even further by using smart phone video taken from locations perhaps as little 70 feet /22m apart (TBD) at consecutive sites perpendicular to the theoretical southern edge of the eclipse path.  If one projects the path of the total eclipse onto the surface of the Earth, the zone where we want to focus is that located south of the city of Grand Island, Nebraska at the town of Minden. We want to duplicate to the extent possible the visual observation method of the past and introduce video recording to corroborate the historical method.


Figure 6. The eclipse path over Nebraska centered on Grand island.  If you are in the grayed zone, you can see a total eclipse. If outside, it is a partial eclipse where perhaps 99% or less of the Sun is covered by the Moon.


Minden, NE is fortuitously located at the southern limit of the 2017 eclipse path.  The eclipse shadow will be moving from northwest to southeast at a speed of 1697 miles/hour.  Any science to be gained from this eclipse will occur at the true edge which crosses 31 Road amongst others.


Figure 7. A view along 31 Road looking north at the intersection of hwy 34/6.


Figure 8. A view along 31 Road looking south at the same intersection. Keep any site away from the railroad tracks as well as outside the highway intersection. This is the most “hazardous” point from the traffic standpoint along the eclipse observation road and should be blocked off, if possible, during the observation period to keep observers safe.


Figure 9. The predicted path of the southern edge over Manhattan in 1925.


If we look at the Sun normally we can see just the outer shell of this giant ball of gas. It is called the photosphere (visible surface of the Sun including sunspots) as shown below; it is a layer from the surface extending upward to 400km / 250 miles high. Above that layer is another one called the chromosphere that extends from 400km to 2100km/250 to 1300 miles. Beyond that is the outer atmosphere of the Sun called the corona which can extend many thousands of miles above the surface. The chromosphere and corona are only seen during solar eclipses when the blinding rays of the Sun are completely blocked from view.


Figure 10. The various layers of the Sun. From

The likely marker that lets one see where the edge of the solar eclipse path is located is when one can see the bright photosphere disappear and then the reddish chromosphere (superheated hydrogen is being burned off) appear very briefly. It is perhaps easier to spot this color change visually than through a cell phone video but that is partly what we intend to determine.  The start of ‘totality’ might best be described as the time of transition from the photosphere to the chromosphere and the end of totality would be the reverse transition from chromosphere back to the photosphere.


Figure 10A. The photosphere with sunspots as seen on a normal day as seen through a solar filter. IMPORTANT: you must never look directly at the Sun without a proper solar filter (except as directed).

At each eclipse limit there is a region on the Earth that can be referred to as the graze zone which is defined by the irregular shape of the lunar poles projected onto the Earth at the north and south edges.  This graze zone has been used for decades by members of IOTA to observe ‘grazing occultations’ of stars as they are periodically hidden and then revealed as the Moon advances around the Earth each month. Grazing occultations have been used in the past to determine heights of lunar features and to discover double stars during occultations which may last from a few seconds to several minutes or longer.  The region of total eclipse is slightly complicated by the presence of this graze zone where bits of sunlit continue to be seen before the Sun returns back to its normal brightness state.


Figure 11. The chromosphere is the pink portion in the upper left that can be seen at the beginning and end of the true total eclipse.


Figure 12. The Moon (shown as solid black) is depicted above with a spherical limb as it is covering the Sun. But because the surrounding edge of the Moon is actually irregularly shaped (jagged curve below the black disc) it will gradually cover up the Sun. The point where total eclipse begins is when the last bits of Sun (dotted curve) are covered. The graze zone is then the area where bits of sunlight poke through and around the jagged portion of the Moon at central eclipse. The depth of that zone may be thousands of feet wide on the ground and is unique from eclipse to eclipse depending on lunar librations and the specific lunar mountains and valleys contributing. The goal of the experiment is to find 1) the spot on the ground to within an accuracy of the site to site spacing where all sunlight is extinguished and 2) the site just to its south where one or more bits of sun always remain visible.

If one is located inside the graze zone during a total eclipse you can see tiny points of light forming, merging, disappearing over a span of 1 to 3 minutes. These points of light are referred to as Baily’s Beads, named for Sir Francis Baily who first documented an explanation for the phenomenon in 1836.


Figure 13. The bright points of Baily’s beads above as seen through cloud. As long as you can see points of light of any size, the eclipse is not total. From Minden the beads will be seen at the bottom (southern) edge of the Sun.

These beads will be visible at the south edge of the Moon/Sun intersection first just before the eclipse becomes total and then reappear some seconds afterward as the Moon continues to slide slowly across the Sun.  If you are exactly in the graze zone, the beads may not disappear at all.  Since about 1980 under the direction of Dr. David Dunham, the International Occultation Timing Association has attempted to record this phenomena at both total and annular solar eclipses with the objective of establishing a trend in the expansion/contraction of the Sun itself.


Figure 14. The author organized this group observation at the eclipse edge in Kwikila, Papua New Guinea in November 1984.  This is one of a series of edge expeditions the author has led to both annular (ring) eclipses and total eclipses with the objective of determining variations in the solar radius including Indonesia (1983), China (1987), Curacao (1998), Turkey (1999) and Uganda (2010).


Figure 15. The author (left) and his guide are shown in the photo above; this expedition was set at the southern edge of the eclipse path at Gulu, Uganda for the January 2010 annular solar eclipse. One of the challenges is to keep each site private and free of distractions such as onlookers seen here. 


Figure 16. Baily’s Beads seen here at the author’s site on a small view screen are recorded along with GPS time. This eclipse was NOT a total eclipse so you will not see a crescent surrounding the Moon as in the illustration here.  It is intended to show that using a video system, you can record quite excellent detail.  There is a neutral density 5 solar filter placed in front of the telescope that allowed this video to be recorded safely.  P. Maley photo. 


At about 12:58:50pm CDT, central eclipse is predicted to occur at Minden, Nebraska. At this time the Sun will be located 60 degrees (i.e. 2/3 of the way from the horizon to the overhead point) above the south-southeast horizon (azimuth 160 degrees).  Depending upon where one is standing, the duration of total eclipse will vary from zero seconds at the southern limit to perhaps as long as 47 seconds at the local airport which is a number of miles north of the southern limit. However, just south of Sycamore St on 31 Rd is where the critical point of 0 seconds of totality is to be expected. As the path crosses through the town it is not along a direct west-east line but in fact, canted by 59 degrees from the vertical and 21 degrees from a west-east line.  We propose to place a line of observers on 31 Rd.  See figure 19 for a possible placement zone which will be updated later with more detail on specific placement of each site.  The number of observers will be determined based on the actual volunteers participating with smart phones.  If 31 Rd is not found to be suitable there are other north-south roads on the east side of town such as S. Minden Ave, 33 Road, 34 Road, or 35 Road (30, 29 or 28 Road to the northeast) that would make a potential substitute.  The observer line needs to be along a common roadway that is free from traffic and other potential hazards. Safety is the number one concern.  It would help if local police were to block traffic along the chosen road in both directions from 1230 to 110pm on August 21 as well as to place signs announcing the upcoming road closure a few days in advance if needed.

Smart phones are quite common and people at young ages are skilled at using them. We suggest that this medium be used to automatically record 3 consecutive minutes of video according to the timeline below.  The phone should preferably not be hand-held but aimed directly at the Sun and set securely in a position where it will not fall over or be disturbed in any way during the recording process.  This frees up the phone owner to simply activate / deactivate the phone at the proper times and concentrate on other things during the critical 3 minutes.  The Sun should be placed in the center of the field of view and zoomed in to maximize its image.  Most important is to consider to set up a support “structure” to serve as a smart phone holder perhaps made of stiff cardboard; the structure should be designed for a 30-degree angle to a level surface (such as a sidewalk, table top, etc.) so as to point to the 60 degree altitude of the Sun. Then, once placed on the ground/other flat surface, an observer would just need to rotate the structure to the proper azimuth of the Sun.  Do not worry if after you turn on the phone and set it in photo mode that the image on the screen seems way overexposed when pointed at the Sun. As the eclipse progresses it should produce the desired video results.


Figure 17. Moon (and Sun) size in an IPhone 6S unmagnified. The Moon and Sun are about the same apparent size as seen from Earth. You can see how small the Moon appears in this unmagnified view.


Figure 18. Moon magnified using an IPhone 6S–a much better image scale.


After examining roads in and around Minden we suggest that 31 Rd be considered as the primary road to be used for the experiment team.  The precise number of sites to be staffed will be determined by the number of volunteers and the spacing; we suggest no more than 2 volunteers per station to avoid distractions and unnecessary noise. No children, animals or onlookers! The spacing of consecutive sites is currently planned to be inside two points 1100 ft/325m north and south of the PROPOSED ACTUAL LIMIT marked in the figure below. In the region of + or – 550 feet/160m from the PROPOSED ACTUAL LIMIT we would possibly set stations 70 ft/22m apart. From north of 550 ft and south of -550 feet we would set stations 140 ft/44m apart. Again, this is subject to change.  The minimum number of stations would be 15 (30 volunteers). If enough additional volunteers are available then the separation of sites could be uniformly 70 ft/22m apart for a total of 31 stations (62 volunteers).


Figure 19. Proposed location of observers on 31 Rd is between the UPPER LIMIT and LOWER LIMIT points. Based on the lunar profile expected during central eclipse, it is believed the actual south edge is located at the PROPOSED ACTUAL LIMIT and not the red line although we expect to refine this closer to the eclipse date.  Range of observations suggested by X. Jubier. 

For this experiment to properly work, it is also suggested that a second observer at each site be equipped with a pair of “eclipse shades” which will allow safe viewing of the Sun during the partial eclipse process. Although this “one power”–no magnification–pair of glasses is safe to use any day, it is likely that any beads of sunlight remaining just before the eclipse becomes total can be detected at the southern edge of the Sun/Moon intersection. [Note: if one is located farther north where the total eclipse will definitely occur, it is safe to take OFF the glasses and look directly at the Sun as long as no sunlight can be seen!! This only occurs during the short duration of totality.]


eclipse shades_web

Figure  20. Eclipse glasses/eclipse shades are thin cardboard items that are worn similar to 3D glasses in a movie theater. There are two thin mylar / polymer film strips — one for each eye– that protects the eyes from the Sun’s dangerous rays. The glasses are folded so that the ends attach above each ear.  These are “one power” meaning that there is no magnification. Always wear these glasses for the experiment.

Solar eclipse glasses can be obtained inexpensively from Rainbow Symphony, a well respected manufacturer, at Regardless of the source, each pair should be inspected for tiny pinholes. If such a defect is located, the glasses should not be used. After receiving the glasses the wearer should take care of them to ensure they are kept in a safe place that would minimize the chance of damage to the lens surfaces.  Order early as supplies will be exhausted as the eclipse date gets closer.

This second observer can record also on a smart phone whether he/she sees the Sun completely disappear or not. It is a binary decision. The moment when the Sun is no longer visible should be called out and then the moment when the Sun can be seen again is the second data point needed. The farther north one is located along the eclipse observation road, the longer the duration of the total eclipse is expected.  The second observer can also call out a time hack at the top of the minute to indicate a calibrated reference on his/her smart phone so that the continuous recording will have a time anchor.  Before terminating the recording a second time hack (at the zeroth second) of a successive minute should be called out.  The observer can start recording before the top of the minute and then call out “Mark. 12:58:00” with the word “Mark” being mentioned as the seconds go from 59 to 00.

The results of the video can be downloaded from each smart phone (using a standard smart phone to USB chord) to a central PC once the eclipse is complete. Each video file must be confirmed to be related to a particular site/observer; then assign a video file name that identifies the site number and observer last name as it is downloaded.   If there are, e.g. 15 sites, the first video would be assigned a file name such as where “1” is the site number, “SMITH” is the last name of the observer and “.mov” is the typical file extension from a smart phone video.  The original videos need to be retained in case there is a problem later with the analysis.  The videos can be transferred by using a Google Drive account which is free of charge.  We can then access the data after it has been loaded.  Note that smart phone video files are quite large, perhaps 200MB and so we recommend that each file be examined carefully before uploading. Even though 3 minutes of data was recorded, a maximum of 90 seconds of video should be uploaded beginning 45 seconds prior to the time of predicted central eclipse.  For stations where the Sun is fully eclipsed, this period of total eclipse should be easily recognized. It is expected that the Sun will saturate the screen until it is completely covered by the Moon at central eclipse. At some stations bright points of sunlight will pop in and out (Baily’s Beads) making the time of central eclipse to be better determined.



Figure 21. Total eclipse from Svalbard as seen on our 43rd solar eclipse expedition March 20, 2015. Ruben Ruiz photo composite.

The sequence of images above shows the progression of the Moon in front of the Sun from left to right. It takes about 1.5 hours from the moment the partial eclipse begins until central eclipse. Use eclipse shades to watch the partial phase (images where crescents are shown).  As the crescent sun keeps getting smaller eventually it turns into a bright area (see image below) which diminishes into bead structures. Once the beads disappear, the pinkish chromosphere appears and that is the start of the total eclipse.



Figure  22.  This is the orientation that can be seen from Minden.  The view is facing south.  The crescent sun will shrink until you see bits of the Sun remaining as the Moon moves in the image above from left to right. The last “bit” is actually the 4th image from the top. Images 5 and 6 define the total eclipse and will likely not be seen in the eclipse shades. 


Volunteers: younger persons have better eyesight generally than older adults. We encourage volunteers be from the high school level. No more than 2-3 persons per site and no small children or animals or anything else that can cause distractions. At each site one person (VIDEO RECORDER) will set up a smart phone, point it at the Sun, and activate it/deactivate it at the proper times. A second person (VISUAL OBSERVER), also with a smart phone, will look at the Sun for a 2 minute period using just the naked eye per the time line below; prior to that time and following the eclipse volunteers must use eclipse shades to view the Sun. The VISUAL OBSERVER will announce the start time using an app below to begin recording at 12:58:00, then watch as the solar crescent becomes smaller and smaller keeping track of any bits of Sun remaining. The idea is to use as few words as possible but enough to indicate the moment that no bits are seen, then to indicate when bits become visible. Use the eclipse shades continuously during that period without interruption.  The VIDEO RECORDER should also be on the lookout preceding the time of central eclipse for any problems from oncoming vehicles, etc. and deflect them before they impact the experiment. Those impacts including vibrating the roadway possibly causing the smart phone recording process to be interrupted or to cause distractions to the VISUAL OBSERVER who must be focused on the Sun during those two critical minutes.

Items required:

  1. marking devices such as small flags or stakes to identify each site uniquely with a number on each one
  2. one smart phone per VIDEO RECORDER set to airplane mode
  3. one smart phone for VISUAL OBSERVER set to Emerald Time or another app such as TIME THE SAT which displays exact time in hours, minutes, seconds
  4. timeline of information showing when to begin, end recording
  5. observer should have a vehicle in order to reach the site; if a wind is blowing the vehicle should be used to block wind
  6. a prop such as stiff cardboard that is preset to a 30 degree angle on which to place the smart phone during the eclipse. The prop can be placed on the vehicle or other flat surface where it will not be disturbed during the recording process. Or you can be creative and use other methods.
  7. team members: bring a chair on which to comfortably lie, preferably a folding lounge chair which will allow you to lay back and look up at a 60 degree angle.
  8. compass that can be used to align the smart phone prop (item 6) to be accurately aligned in the direction of the Sun.


Figure 23. a bad smart phone prop to achieve a solid 30 degree angle from the horizontal: NOT A GOOD IDEA!



Figure 24. A good smart phone prop: a 30 degree angle wedge. When the smart phone is set on top, it will point to a 60 degree angle from the horizontal. Some rubber door stops may be of this design. 


Figure 24a.  Another way to construct a smart phone prop is to stack/align one or more books of any type as in the image above. It would be good to measure the elevation angle and adjust books to ensure the proper angle.  This is normally done with an inclinometer.  A phone app such as can be downloaded to help.


Figure 24b. The proper compass with degree markers around the periphery can be used to confirm the proper azimuth angle.  Note that the smart phone/prop must be aligned to azimuth of 160 degrees (south-southeast),


Figure 24c. Do not use this type of compass.


  1. Local Coordinator: Person(s) in Minden who is/are in charge of the overall deployment effort. Will insure overall safety of the sites, make sure enough volunteers are able to staff each site and that all data will be immediately stored and properly save. Define a date for a simulation of this activity before the day of the eclipse to shake out any problems.  
  2. Supervisors: mature adults who can ensure that volunteers are located where they are supposed to be, have the proper equipment set at the correct angles and are trained to do their jobs. They will then serve as a focal point for post eclipse data collection and reporting.  Supervisors are the best hope for ensuring data will be taken through the scientific method process and should ensure each site is properly numbered from 1 to N where N is the highest site number based on the number of volunteer teams enlisted.
  3. Video Observers: as defined above
  4. Video Recorders: as defined above

Time required: volunteers should be at their assigned station no later than 30 minutes prior to central eclipse (totality) in order to set up the smart  phone and be sure it is in a stable configuration. Phones should be fully charged for this experiment and NOT used for any other purpose until after the recording process is over. That means no phone calls sent or received and no internet or game access (set to AIRPLANE MODE).

Time correlation: in order to know precisely when to begin recording, observers should download a phone app such as “Emerald Time” for IPhones.  If this does not work for Android phones, try an app like “Simple Second clock”.  If the time of central eclipse is predicted to be 12:59pm then recording should begin just before 12:57 and end at 1:01pm.  If the phone is being used for video recording it will not be possible to verify the stop time unless one either has a second cell phone (2 people at each site) or a separate calibrated digital watch as described above.  All phone apps should be checked that the time (to the nearest second) is the same on every phone once the app is installed and before being used for the eclipse.


Figure 25. “Emerald time” may be downloaded free of charge from the Internet and displays accurate time in hours: minutes: seconds. 


AUGUST 1, 2017: Names and contact information for all volunteers provided to local coordinator no later than this date

AUGUST TBD:  SUPERVISORS conduct briefing and training session for all observers; confirmation of VIDEO RECORDER and VISUAL OBSERVER at each site. Assign sites. Measure exact location of each site with GPS in prior to August 21. Verify that all 2 person teams have smart phones, a prop to set them to 60 degree elevation and compass to align to 160 degrees azimuth, and that the apps on ALL phones show the same time to the nearest second. Training is vital. All team members must be able to demonstrate that they can execute the plan properly and in a timely manner.

Simulating the Sun: one idea is to use the Full Moon as the Sun in order to line up the smartphone in the proper direction and to zoom in and verify the Moon is in the center of the field of view. This can be performed March 12, April 10, May 10, June 9, July 8, or August 7.


Each person set smart phone alarms as shown below. It will be easy to watch the smart phone clock to know when to start recording/observing but more distracting to keep track of when to stop. When the 12:49:00 alarm goes off the VIDEO RECORDER can spring into action; when the alarm for 1:00:00 goes off, both people at the site will know it is time to stop their activity. Test your alarm during previous days to be sure it can go off exactly at the top of the minute. If it goes off a number of seconds early, then you need to consider some other reliable way to know when to stop recording.

8:00am CDT: markers placed at all stations. Recommend stakes or small flags such as those found at Home Depot for placement at each site.  Confirm all smart phones are fully charged and that an alarm is set for 12:49:00 PM and another for 1:00:00PM when data collection is set to stop.

TBD: “Go/No go” time. NOTE: if weather is predicted to be definitely bad with no hope of clearing, the experiment organizer will notify all participants by email prior to this time for cancellation of the effort.

TBD: All personnel meet at ______ for last minute instructions and deployment to sites.

11:33am: Partial phase begins when the Moon’s disc first begins to touch the Sun. Use your eclipse shades (eclipse glasses) beginning at this point or at any time prior to 12:58pm to check the progress of the eclipse.

12:30pm: all observers in place no later than this time; assure all smart phones set to airplane mode!

12:30pm: road closure if possible

12:49pm:        VIDEO RECORDER: prop smart phone up onto a 30 degree angle support so the phone points up at an angle of 60 degrees. Point the prop until it lines up with a compass set to 160 degrees azimuth (southsoutheast direction).  This will ensure the Sun will be in the field of view! BE SURE THE SMART PHONE IS POINTED TO THE SUN AND NOT IN THE REVERSE DIRECTION!!!  

12:50pm:        VIDEO RECORDER:  center smart phone on the Sun and ensure Sun is in the center of the field of view, zoom in the image to the maximum.. Do not worry if the Sun seems overexposed on the screen.

12:57:30pm: VIDEO RECORDER: start smart phone video recording.  IMPORTANT: if you see any cars/trucks coming toward you, flag them down to stop until the video recording ends!! This may not be needed if police have blocked the road.

                          VISUAL OBSERVER: start your smart phone as an audio recording device

12:58:00pm: VISUAL OBSERVER: calls out “Mark 12:58:00”

                           VISUAL OBSERVER:  begin looking directly at the Sun for the next two consecutive minutes without eclipse glasses. Use common sense. If the Sun looks too bright, use your eclipse glasses! If you can see any piece of the Sun say “PARTIAL”; if the bits of Sun disappear completely say “TOTAL”. Keep up this running commentary until 1:00 pm.

12:58:50pm: total eclipse occurs at the edge for a few seconds

1:00:00            VISUAL OBSERVER: calls out “Mark 1:00:00”

1:00:30pm:    VIDEO RECORDER: stop cell phone video recording.

                           VISUAL OBSERVER: stop looking directly at the Sun without eclipse glasses. Turn off recording.

1:10pm: Open road to traffic.

Collect site markers and return to a common meeting point after the eclipse is over.

2:26pm: End of partial phases. The Sun regains it normal appearance as the Moon is no longer visible in front of its disc.

~5:00pm: or as soon as possible after the eclipse,

                           VIDEO RECORDER: provide smart phone video to the person designated to download all the videos.  That person should download each video to a central PC. Be sure to set the file name with the station number followed by the first initial and last name of the VIDEO RECORDER. Example: indicates station #1 and observer’s last name is Smith. Email indication to (TBD) that file has been shared via Google Drive.  We recommend that everything be done the same day so as not to delay data capture and sharing of the video and to minimize the chance to lose specific details. The VIDEO RECORDER must retain the original video in case it needs to be examined later and in case something happens to the downloaded video copy.

                           VISUAL OBSERVER: report to the organizer whether the eclipse was TOTAL or remained PARTIAL throughout the audio recording.

                           VIDEO RECORDERRETAIN THE ORIGINAL SMART PHONE VIDEO. DO NOT DELETE IT. If possible back it up to another safe location.

                           VISUAL OBSERVER: RETAIN THE ORIGINAL SMART PHONE AUDIO RECORDING. DO NOT DELETE IT. If possible back it up to another safe location.

SUPERVISORS: collect all data based on a predetermined plan from all participants.


We encourage photos to be taken at each site with observers present and equipment in their proper placement.  A drone might be used to fly over the entire line of stations between 1230 and 1245pm in order to capture the deployment perhaps even with a large number placard set up (numbers 1- N) face up for the drone on which to focus.  Another more interesting drone experiment would be to see if the drone (perhaps equipped with a Go Pro type camera) could actually capture the edge of the shadow on the ground at Minden.  The school could even consider developing their own web page to make instruction and guidance easier.


Figure 26. Drone view of small town

We fully expect that the Sun will not disappear to the south of the actual southern limit but where is the question.  Visual observers located there should note that if the Sun is too bright when looked at without eclipse shades, to put the eclipse shades back on unless/until the brightness diminishes to where it does not hurt your eyes. An observer in South Carolina and one in Oregon will witness the true edge to be at slightly different locations relative to the predicted edge from Nebraska.  At the northern edge, we also expect identical experiments to be attempted but the ease in which the edge is defined is likely going to be much more favored at the southern limit where the lunar mountains are higher and valleys deeper allowing Baily’s Beads to be far more pronounced and recognizable.


People have tried using various crazy devices as substitutes for safe solar filters. Looking through CD’s and X-ray sheets are examples of things NOT SAFE for viewing the Sun.  We caution everyone especially if you are passing the word to friends and family that the only safe filters are a pair of eclipse shades/eclipse glasses, or a number 14 welders’s glass or a neutral density 5.0 solar filter.  The filter should be used at all time to view the Sun on eclipse day EXCEPT during the brief period when all portions of the Sun are covered up and the total phase of the eclipse is visible.

There are a number of other safe ways to observe the eclipse–by projecting the image of the Sun, by using eclipse shades or by direct telescopic/binocular observations with proper filters in front of the lenses.  See: 


Are there other locations along the path where similar experiments might be conducted? The answer is “yes”.  Examples of these towns through which the eclipse SOUTHERN edge passes include:

Blue Ridge GA

Murfreesboro TN

St. James MO

Kansas City MO

Wheatland WY

Emmett ID

Redmond OR

Examples where the NORTHERN edge experiment might be conducted include:

Camden / Lugoff SC

Brevard SC

Warhammer TN

Oak Ridge TN

Bowling Green KY

Central City IN

St. Louis MO

Belleville MO

Moberley MO

Lincoln NE

Canby OR

The above cities and towns are not the only ones where access to either the south or north edge can be attempted. Yet these are locations where the line actually passes through the urban area proper.

Good luck to all observers. We look forward to a fantastic solar eclipse process.


Account of the 1925 solar eclipse edge measurement:

C. Sigismundi (2011) “High precision ground-based measurements of solar diameter in support of PICARD mission”:

A. Raponi (2013)  “The Measurement of Solar Diameter and Limb Darkening Function with the Eclipse Observations”:

D. W. Dunham (2016) “The 2017 Solar Eclipse: IOTA effort, outreach, & sites; discussion “:

G.Mallen-Fullerton (1992) “The Observation of the 1984 Eclipse in Mexico” Research amateur astronomy; Proceedings of the Symposium, ed. S. J. Edberg, ASP Conference Series (ASP: San Francisco), vol. 33, p. 7.

G. Thuillier et al.  (2005) “Past, present and future measurements of the solar diameter” Advances in Space Research vol. 35 pp. 329–340

J.H.Parkinson et al. (1988) “The constancy of the Solar diameter over the past 250 years”, Nature vol. 288 pp.548-551

O. Sattaur (1983) “The Day We Measured the Sun”,The New Scientist, June 23, 1983, pp.875-882.

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