Much talk is in the media these recent days about the upcoming North America solar eclipse. Anyone following the world of astronomy for the past year at least has been aware of it, but suddenly the mass population is waking up to the pending reality of the event too. Their focus is on traffic jams and hotel rooms and possibly defective solar glasses.
Having prepared for August 21st months ago, I am now waiting just like most of you, and watching the weather forecasts with an interest usually not provided to the television personalities. I will not be using glasses, in part because I enjoy doing things differently than most. So while millions will gaze up with open mouths at the Moon and Sun with their 3D-esque eyewear, I will be leveraging my telescopes along with simple cardboard holdouts to measure the event.
This waiting time is a good time to reflect on the eclipse and what it means beyond the covering of the Sun. The eclipse will bring darkness and with darkness comes stars. I am in the 88% coverage range and have no idea what it will look like, though I assume at least bright Venus towards the West will be visible.
Those in the path of totality will have a special treat as the sky should go dark to the point stars appear. It was this phenomena that helped prove Albert Einstein’s General Theory of Relativity true, or at least as a superior theory to explain the universe over Isaac Newton’s gravitational theories. If you want to read the details of how it was done, do an Internet search for the 1919 solar eclipse to find many articles. Here is one from space.com that summarizes it nicely.
I am neither astrophysicist nor physicist, just a backyard astronomer. But I feel I know enough to explain the 1919 solar eclipse experiment in the simplest terms. Consider first a typical clear evening on the planet Earth, with stars shining and the Sun well out of the way on the other side of the globe.
With no large cosmological objects in the way, starlight in aggregate gets to Earth mostly on a straight line. Whether Einstein was correct or not was not crucial for this part. There is a path of light from a star to here, and we can assume a straight line for this path.
Now consider what happens during a solar eclipse. The Sun (and Moon) have gotten into the path of some of that starlight, but for other stars their light will skirt past the Sun and still reach Earth. Einstein asked, “will the gravity of our massive Sun alter course of light from those stars?” His theories said yes, and the 1919 eclipse was used to prove him and his theories correct.
Figure 2 shows a few things happening. First, the Moon is between the Sun and Earth, hence blocking the Sun’s light. The Sun of course is enormous in size compared to the Earth and Moon, but the Moon’s proximity to us and the Sun’s distance make them approximately the same apparent size in the sky. If one were to make an argument that the ancient gods set up the universe so that their sizes looked the same, you would probably have difficultly coming up with a sound rebuttal for why this is so, beyond coincidence.
Next, the Sun blocks some, a very small amount, of starlight that is directly behind it. I suppose you could say that the Earth, Moon, Sun, and any stars hidden behind the Sun will be in conjunction on August 21st.
Lastly, there is starlight with paths that will approach the Sun. As proven in 1919, the Sun’s gravity will effects this starlight as it travels past the Sun, altering the starlight’s course. This is happening all the time in the daylight, but we cannot observe it due to that -27 magnitude star close by.
When the masses of millions look at Monday’s eclipse, few will be thinking about Einstein. But some yearning, bright individuals will. Perhaps the next Einstein will be among them, awaiting the inspiration to change our fundamental understanding of the cosmos once again.