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Ceola Roefaro
For the 1919 eclipse, only a few stars (identified by the marks in the photo shown here) were visible on the photograph through the glare of the bright solar corona. The photo was large enough to cover both the eclipsed solar disk and the surrounding stars within 1.5 degrees of the sun. Even so, the measurement was at the very limit of what could be done given atmospheric distortion, star twinkling, and the unfavorable scale of the image for making such a precise measurement.
The blue objects are the image of a single, more distant, spiral galaxy that has been lensed by the multiple gravitational fields in the foreground cluster of galaxies. The cluster, called CL0024 1654, is located 4 billion light years away towards the constellation Pisces.
Einstein published his theory and predictions in 1915, and in 1919 the British physicist Sir Arthur Eddington took advantage of a total solar eclipse to attempt to detect the shifting images of stars near the limb of the sun. The problem was that during totality the sky does not get perfectly dark, and only a handful of stars were visible near the sun from which to make the measurement.
What will the sky surrounding the eclipse look like at the time of totality? Will there be many stars close to the sun that you can measure? This will determine whether you have enough star deflection measurements from which to detect the shift! Here is what the sky will look like near the sun at totality, for the sun located at Right Ascension 10hours 03minutes and Declination +11degrees 56minutes in the constellation Leo. The viewing location for the simulated sky scene image is near Carbondale, IL. (Credit: TheSky software).
The eclipse will take place not far from the bright star Regulus in the constellation Leo. As you can see from this figure, there are quite a few stars near the limb of the sun, but these stars are between magnitudes of +7 and +10. This means they are between 3 and 40 times fainter than the faintest naked-eye stars you can easily see at night from a clear location. Only Regulus will be easily seen during totality without a telescope, but at its distance from the sun, which amounts to a projected distance of 5.3 solar radii, its image will only shift by about 1.75/5.3 = 1/3 arcseconds. The many fainter stars such as HIP49158 will show a much larger deflection of over 1 arcsecond, but the challenge is that these faint stars may be completely lost in the glare of the solar corona!
This experiment will require a telescopic photograph to detect and measure enough stars. Only with a telescope will you be able to detect the faint stars, and have a large enough magnification across the image so that you can make measurements near the required limit of 1 arcsecond.
Make sure you take at least a few images of the eclipsed sun while you are photographing the star field. Ideally, the width of the star field you photograph should span about 3 to 5 times the solar radius. You will have to select a telescope and eyepiece combination that allows for this level of field coverage and magnification.
You will need to test-out your method long in advance of the eclipse, preferably by photographing the star field near Regulus during the weeks before the eclipse. For your telescope-camera combination, find a magnification that lets you capture a digital image about three degrees across. During the eclipse, you will have to make many short-exposure images, but not so long that the corona burns out the entire image field. Experiment with your exposures until you can just capture enough of the fainter stars near 8th magnitude to make at least three or four measurements. Because the sky brightness resembles the twilight sky just after sunset, you might want to try photographing faint stars in the twilight sky to see what kinds of exposure times you need. You might also experiment using filters that reduce skyglow.The eclipse only lasts 2.6 minutes so you can use this time to make 5 or more exposures of 30 seconds or longer so long as the corona light is not a problem. Ideally, you would like ten images that you can measure to improve your estimate of the average positions of the reference and target stars.
For best results, you need the photograph to have a resolution of about 1 arcsecond per pixel because the effect you are trying to measure is not much more than this under ideal conditions. That means the sun will appear to have a diameter of 1800 pixels in the image. That also means that for most megapixel-format cameras, you may not be able to capture images of distant reference stars if they are more than a few solar radii from the center of the sun and keep the image scale high enough to detect this deflection for the inner-most stars. Also, the solar corona will be bright enough that most faint stars will not be visible through the diffuse coronal light nearest the solar limb so you will have to use only bright stars, which are generally fewer in number.
Here is a close-up of the field near the eclipse that you will see through your telescope adjusted so that the scale of the image allows you to measure the arcsecond-sized shift in the star images. The two brightest stars in the field are HIP-49158 (+7.8) and HIP-49328 (+7.1) which are seventh-magnitude stars. The rest are unusable faint stars that have magnitudes between +10 and +11 that will most certainly be lost in the glare of the corona.
At least in principal, once you have the photograph, you need to measure the positions of the available stars in terms of their pixel locations. Usually you can import images into programs such as Photoshop, use the cursor to center on a star image and read-out its x and y location. Because the amount of the deflection depends only on the radial distance from the center of the sun, you need to keep track of how far the target star was from the center of the sun at its closest point. That means it will be convenient to line up the short edge of the image you take with the solar limb so you can use this edge as a distance reference point when you measure the deflections.
Once you have made these measurements on as many limb stars as you can detect, you now need to make a measurement of where these target stars are when the sun is not there. To do this, photograph the same star field at night and repeat the relative measurements again to get the position of your target stars when the sun is not there.
Amateur astronomers are, in fact, gearing up to make this very difficult, but not impossible, gravitational deflection observation. Here is an article in Sky and Telescope magazine by Donald Bruns that describes his preparations for making this measurement. -and-telescope-magazine/beyond-the-printed-page/my-do-it-yourself-relativity-test/
A partial solar eclipse last October that covered parts of the Western U.S. offered a test run of sorts. In a December report analyzing the grid impacts of that eclipse, the California Independent System Operator said it was able to manage a nearly 60 percent drop in solar generation during the event by curtailing some solar during the ramp up, importing more energy and ramping up battery storage and other resources.
That means grid planners have had plenty of time to prepare for the celestial event, even though forecasting continues until the final hours and minutes to get a sense of cloud cover and weather conditions. A cloudy day means that there will be less solar generation before the sun gets blocked, meaning there will be less of a decline for operators to have to manage.
The New York ISO predicts that as the path of totality goes over the northern part of the state, total solar generation could drop by 3,110 MW on a clear day, with sufficient resources to accommodate the drop, the ISO said.
On Saturday, 4/6/24, I set up 2 WSPR transmitters in my back yard. These will hopefully operate uninterrupted through sometime Tuesday afternoon, 4/9/2024. This should provide good baseline information before and after the solar event.
NASA scientists and other professional and amateur space engineers will consolidate data from amateur operators around the world to help understand how this rare event impacts the various layers of the ionosphere.
WSPR is a one-way digital communication protocol using VERY low power (less than .2 Watt or 200 mW). I usually set the transmitters to much lower power than that (.02 Watt or 20 mW) because the weaker signal is more likely to reflect subtle changes in either the antenna or the atmospheric conditions. The sending station transmits a beacon on a specific frequency for each band. The digital package sent by the transmitter contains the callsign of the operator, grid square location and transmitted power in milliwatts. The message is sent slowly and repeated several times. Then, there is a pause and it starts again.
Several websites are available to extract the data or view it in map format. All of the ones I use are free and do not require a login. The ones I most frequently use are listed below, but there are others. In general, use my callsign (KY4KK) as the transmitting station, leave the receive station blank and select either 20 or 40 meters.
It also shows the most distant contacts and can display a map
Specifically, I will use this to look at individual stations that recorded me several times during the day. Where was the eclipse during each of the recordings, and did my received signal significantly change?
Also, I will look for differences in how the two bands will be affected.
=KY4KK&timelimit=1d
The interface takes some getting used to, but to start, go to the search button, select the number of spots to show, the time frame (10 minutes if you want to see immediate activity only), band (20m or 40m) and TX Call (KY4KK) and click Search. Then you can click map and it will show all of the contacts the station has made in that time frame.
Final Disclaimer: When doing a test like this over several days, a lot of things can go wrong. Batteries die in the middle of the night, a dove crashes into my antenna, the dog runs away with one of my antenna radials (all of these have happened). If I see something has interrupted the transmission, I will try to correct it as soon as possible.
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