There was a total solar eclipse visible in the U.S., August 21, 2017. Lebanon, Tennessee was in the path of totality.
A solar eclipse happens when the earth, moon & sun line up with the moon in the middle. This happens at new moon! There is not a solar eclipse every month because the moon usually goes above or below the sun. Whereas lunar eclipses are seen by everyone on the night side of the planet, solar eclipses are local. Eclipse chasers travel to stand in the moon's shadow.
It is a coincidence that the sun and moon appear to be the same size. The sun is 400 times larger than the moon but 400 times further away.
Both the earth and the moon cast shadows into space. The moon casts a small shadow, so a solar eclipse lasts only a few minutes. The path of totality can be thousands of miles long and only 70 miles wide. The moon's shadow travels 1000 miles an hour.
The moon orbits the earth from west to east, so it makes contact with the sun on the sun's western edge. In half an hour, the sun is half covered. The sky has a metallic look. The moon's shadow approaches and the sun is suddenly a crescent. Baily's Beads flicker as light passes through lunar valleys. The beads were named after Francis Baily. We see the diamond ring and the corona! Then, totality! There is a black disk in our sky! We are in the moon's shadow! Look around! There are stars and planets. The experience is eerie! The temperature drops, and birds go to their nests. The sky brightens in the west, and totality ends.
On August 21, the moon's shadow touched down in the Pacific Ocean. It crossed the United States from the northwest to the southeast. It crossed Oregon, Idaho, Wyoming, Nebraska, Missouri, Illinois, Kentucky, Tennessee, & North and South Carolina. It passed into the Atlantic Ocean and left our planet near the Cape Verde Islands. I was in Lebanon, Tennessee, where the duration of totality was 2 minutes, 35 seconds. The crowd reacted! It is strange how the moon's shadow is treated as if it were a tangible thing. In reality, it is the absence of something: sunlight.
Kate Russo, in her book "Total Addiction," explains what a total solar eclipse is. It is a situation where the moon moves between the earth and the sun. For a short time, the moon's shadow traverses a long, narrow strip of the earth's surface. Observers along the path see the sun covered by the moon and its light blocked. Mercury and Venus are seen. The sun's corona, or outer atmosphere, appears around the moon's black disk. Total solar eclipses happen at new moon unlike lunar eclipses, which occur at full moon. TSEs vary in duration, the longest being 7 minutes, 31 seconds. There is one every 18 months.
GREAT AMERICAN ECLIPSE: August 21, 2017
A total eclipse of the sun occurs during new moon. New moon is when the moon moves between the earth and the sun. The night side of the moon faces us, so the moon is invisible. When the earth, moon & sun form a straight line, there is a total solar eclipse somewhere. An eclipse does not occur every new moon because the moon's orbit is inclined to the ecliptic. Generally, the moon passes above or below the sun. During a total solar eclipse, the moon covers the sun, plunging us into darkness. Eclipses vary in duration depending on the moon's distance from Earth. It is a perfect fit, the only 2 discs in the sky, one on top of the other.
The sun's diameter is 400 times larger than the moon's. The sun is also 400 times farther away. These facts make total solar eclipses possible. The sun is about 93 million miles away. The moon is about 240 thousand miles away. The moon was created when an object collided with the early earth, sending debris into orbit. The debris coalesced over time to form the moon. The moon was once much closer. It is slowly drifting away, and there will be a time when it will not appear large enough to cover the sun. There will be no more total solar eclipses.
The Great American Eclipse began in the Pacific Ocean. The moon's shadow touched land in Oregon and cut a diagonal path across the United States. Lebanon, Tennessee, 30 miles east of Nashville, was the ideal place. I lived in Lebanon in the 1970s and 80s and knew the town. There were 2 minutes, 35 seconds of totality. From Tennessee, the moon's shadow crossed Charleston, South Carolina, and moved into the Atlantic Ocean.
The partial phase began just before noon. Totality occurred at 1:28pm. The eclipse ended at 3pm. I had eclipse glasses for the partial phases. Only during totality can eclipses be viewed without glasses. The corona is visible at that time. The corona is the sun's atmosphere and made of plasma, the 4th state of matter. It is delicate & pearly white. The moon is a black disc covering the sun with the corona surrounding it.
Before and after totality, Baily's Beads and the Diamond Rings are seen. Baily's Beads are the sun's rays passing through mountains and valleys on the moon. The Diamond Rings are the last bead before totality and the first Bead after totality. This eclipse lasted 3 hours.
All solar eclipses are different. The path of the Great American Eclipse was 70 miles wide. It was a ribbon stretching across the United States, and people wanted to be as close to the center as possible. The moon's shadow came from the west.
August 21, 2017
My cousin and I rode out to Lebanon that morning to Cedars of Lebanon State Park, where a group of eclipse chasers were gathered. There were big fluffy clouds but by eclipse time, the sky was clear. It was hot! The eclipse began around noon and looking through my glasses, it looked like a bite had been taken out of the sun's western edge. It was the night side of the moon encroaching on the sun. As the bite got bigger, it looked like a vinyl record next to a banana. The crescent sun continued to shrink as the moon moved across it. It got smaller and smaller until totality occurred at 1:28pm. It was noticeably cooler, and the sky had darkened although it never got pitch black. I saw the white corona. It looked like a paper mache flower! I spotted Venus. I never noticed Baily's Beads or the Diamond Rings. Totality passed quickly, and we left as the reverse partial phase began. Perhaps my expectations were too high. We saw shadow bands through tree leaves as we returned to the car.