A Sliver of Golden Light

Oftentimes astronomy can seem like a distant field. We do not study specimen in petri dishes or mix chemicals in a lab. Instead we turn our telescopes to the remote heavens and rely primarily on the light we receive from the universe. Yet sometimes the distant has a profound local impact. This is distinctly seen during a solar eclipse. As one of my friends remarked, it is only at times like this that you really think about how fast the Earth rotates.

On August 21st, 2017, the shadow of the moon swept across the continental United States and inspired millions of people to look up and contemplate the motions of celestial bodies. Here in Bloomington, Indiana, a CelestFest was held on campus. Despite the pesky clouds, questionable music, and shortage of solar glasses, the sight was still impressive.

The shadow of the International Space Station passing across the sun while partially eclipsed by the moon.
Image credit: NASA/Joel Kowsky

It was a hot day, in the low 30s Celsius, with a steady breeze that didn’t really cool us off. Even when the clouds rolled in, we were sweating; only when the moon was covering most of the sun were we not melting. Although we did not experience totality, the temperature drop was noticeable.

In addition to the temperature, the sky darkened around us. The saturation of the world decreased and the contrast slider similarly modified on a cosmic photoshop. The color shift was subtle; I would not have noticed if I did not know to look for it, but the differential was enough to cause the automatic street lamps around campus to turn on.

The sun partially eclipsed by the moon, but also obscured 

partly by clouds. Image credit: Jennifer Sieben

Looking through the solar glasses, it was possible to see a thin sliver of golden light unobscured by the passage of the moon. The crescent slowly shifted from the left side, up around the top and then to the right. I did not have great luck recording with my video camera, a combination of poor focus and a haphazard filter left an oversaturated image that only had a well defined crescent when dimmed by passing clouds.

However, we were able to make different pinhole cameras, even using just our hands to produce a crescent of light on the table. My favourite was seeing the many crescents from my sunhat dotted across my leg. This worked the same as a pinhole camera, showing a small version of what light is passing through the tiny hole. Since the sun is the dominant light source, that is what we see through the hole.

Through the holes in my sunhat 

I was able to see thin crescents of light from the partially 

eclipsed sun against my leg. Image credit: Jennifer Sieben

For added science, our table set up a solar panel to track the energy output of the sun. A large arrow rotated to show the decrease in energy. As of this writing I have not seen the data yet, but it dropped by at least 50%. Cloud cover dropping it to zero made it hard to judge by eye.

Unfortunately since I could not see totality, I was not able to see the corona. The corona is analogous to the outer atmosphere of earth–a gaseous envelope of highly charged particles. Telescopes such as SOHO regularly study the corona and look for coronal mass ejections such as those seen in the image below. Not every ejection is on this scale.

Masking the majority of the sun allows instruments such as the Solar and Heliospheric Observatory (SOHO) to study the corona of the sun. This image shows a large coronal mass ejection (CME) from 6 November 1997. Image credit: SOHO (ESA & NASA)

During the eclipse, the one opportunity for humble earthlings to see the corona for themselves, there was a modest sized prominence at about two o’ clock. Prominences are caused by disturbances in the magnetic field deeper down in the star. This stirs up material and sometimes it escapes from the surface of the sun to arc into space.

At nearly complete totality only a sliver of light is still seen of the photosphere on the right edge of the sun. Solar prominences are seen bursting forth from the surface of the sun as a result of turbulent magnetic fields. Image credit: Robert Stephens

Despite not seeing totality, I was nonetheless thankful that the clouds parted to allow for a view of the distant incandescent crescent. I do plan to chase down totality in seven years, but I will still have good memories of my first solar eclipse.