Physics Photo of the Week - October 20, 2023
Partial Solar Eclipse of October 14, 2023
Partial Eclipse photos by Jeremy Allen
Students, teachers, and parents in the Swannanoa Valley in Western North Carolina were celebrating the grand opening of an addition to the ArtSpace Charter School last Saturday. I set-up an eclipse watch at the festivities providing a solar-filtered telescope, solar viewing goggles, and a special telescope. Parent Jeremy Allen obtained this excellent color photo of the partial eclipse, caused by the Moon passing in front of the Sun, blocking out about 1/3 of the Sun's visible "disk". The eclipse event was partially hampered by clouds that had moved in during the event, but opened briefly to admit the sunshine in limited patches of clear sky. The clouds actually aided Jeremy's camera, as the clouds probably passed only about 1/10 the full sunlight - preventing heavy over-exposure. Students, parents, and teachers were awed by viewing the partially eclipsed Sun with special solar-viewing goggles, and with a simple pinhole camera (see the PPOW for October 6, 2023).
The photo at right shows another of Jeremy's photos with a longer focal length setting (zoom factor). This photo is interesting because we also see the silhouettes of the clouds as well as the more distant Moon partially blocking the Sun. Both photos show subtle colors created by sunlight shining through the microscopic cloud droplets.
Solar eclipses occur relatively rarely when the Moon, in its monthly orbit about the Earth, passes almost directly between the Sun and the Earth. It takes the Moon about 2 1/2 hours to transit across the Sun's visible disk. The transit began earlier than this photograph when the Moon's silhouette began to take a "small bite" out of the lower-right (southwestern) portion of the Sun's disk. During the early afternoon, the Moon slowly drifted across the "bottom" of the Sun's disk, and eventually left the position of the Sun's disk off the lower-left (southeastern) portion of the Sun.
On most lunar orbits, the Moon passes north or south of the Sun and completely misses the Sun because the Moon's orbit is tilted at a small inclination angle (about 5 degrees) from the Earth's orbit around the Sun. See the animation in this link.. From within a narrow path (about 40 miles wide) that traversed the southwestern United States observers could see Moon's disk completely within the Sun's disk. That left a narrow "ring of fire" that the observers in this narrow path could observe with their solar eclipse goggles. The "ring of fire" that people in the narrow path could see is called an "annular eclipse" - where the un-eclipsed Sun becomes a narrow ring because the Moon was too far away from Earth and its angular size was smaller.
The Moon's orbit is an ellipse, not a perfect circle. Sometimes when the Moon transits the Sun (solar eclipses) the Moon is closer than it was last Saturday. When the Moon is close enough the Moon's disk completely covers the Sun and produces a very rare Total Solar Eclipse. A total solar eclipse is a spectacular event! The sky gets dark as night. The Sun becomes totally eclipsed, and we can look directly at the totally eclipsed Sun and see the faint corona. The complete blockage of the Sun's light only lasts at most a few minutes.
I obtained the image (left) of the solar corona during the 2017 North American total solar eclipse along the narrow path that crossed the US from Oregon to South Carolina coast. That totality lasted only 2 minutes.
The next total solar eclipse in the United States will take place Sunday, April 8, 2024 - less than 6 months from now. Find the narrow path of totality with the help of an internet search for "Solar Eclipse 2024". Again the path of totality will only be about 40 miles across. If you wish to observe it, you should get to a location that is totally within the narrow band of totality. It is not good enough to get to a place that has only 99 % totality. The complete blackout of the Sun occurs only within the narrow path of 100% totality. Anywhere else the Sun will be too bright to observe without eye-protection.
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Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature interesting phenomena in the world around us. Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to dcollins@warren-wilson.edu.
All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion. These photos and discussions may be used for private individual use or educational use. Any commercial use without written permission of the photoprovider is forbidden.
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