We are about five days away from a total solar eclipse that will be passing over South America. For several years, I’ve been looking forward to amazing images of the Solar Corona shining brightly over some of the world’s greatest landscapes in Patagonia and Chile. While most tourist trips have been canceled, we expect there to still be images coming to us from scientists who are looking to once again recreate Eddington’s amazing images of stars appearing in distorted locations thanks to the light bending actions of the Sun’s gravity. 

By taking images when six months apart, when the Sun appears in front of a constellation and when the constellation hangs unblocked in the nighttime sky, astronomers can use precise measurements of stellar positions to map how gravity acts like a lens to bend light, with more bending occurring for stars closer and closer to the edge of the Sun.

The thing is, no matter how many times we do these measurements, there is error, and while the results match expectation, that error leaves room for some other variable to be involved, and it turns out sometimes scientists just forget to account for all the variables. 

When light passes through something, whether it be a pane of glass or a cloud of gas, that something will refract, or bend, the light. Our Sun has no distinct surface but rather transitions from a convecting layer to a magnetically active atmosphere that thins with distance. That atmosphere and its associated refraction add just the tiniest of terms, but it is something the Parker Solar Probe may be able to verify in 2025. This work appears in Radio Science and was done by Jacob Fokkema and Peter van den Berg. We now have one more reason to look forward to the 2025 Parker Solar Probe observations and one more reminder that there is often room for one more thing in your observations’ error bars.

More Information

Eos article 

“On the Electromagnetic Propagation Paths and Wavefronts in the Vicinity of a Refractive Object,” Jacob T. Fokkema and Peter M. van den Berg, 2020 Nov 15, Radio Science.