LAST Aug. 21, the Moon cast its darkest shadow on a part of the Earth. Along with millions of people from around the world, my family and I went to where this shadow fell to witness a total solar eclipse. For many who witnessed it, and certainly for me, it was an out of this world experience.
A total solar eclipse happens when the darkest part of the Moon’s shadow, the part called the umbra, touches the Earth’s surface. For those standing within the Moon’s umbra, it would appear as if the Moon is completely blocking the Sun’s disk, causing the darkness of night to fall in the middle of the day. Those within the umbra are experiencing what is known as totality.
Because of the Moon’s distance from us, the umbra is not very big when it reaches Earth. (The largest the umbra can get is about 260 km across. It’s usually smaller than this.) Because the Moon moves around the Earth, the umbra moves across a part of the planet during a total solar eclipse. The path the umbra takes is called the path of totality. Those outside this path will not experience totality.
Last Aug. 21, the path of totality went across the continental United States, passing through parts of 14 states. My family and I went to Casper, Wyoming, which was one of the cities in the path of totality. There, totality lasted for a mere 2 minutes and 25 seconds. But what a breathtaking 2 minutes and 25 seconds those were!
Maybe you’ve seen a partial solar eclipse and think you know what I’m talking about. A partial solar eclipse happens when the Moon only partially blocks the Sun. This kind of eclipse when the less dark part of the Moon’s shadow called the penumbra hits the Earth. The most recent partial solar eclipses visible from the Philippines happened on March 9, 2016 and May 10, 2013. The next one will happen on December 26, 2019.
However, a partial solar eclipse is very experience from totality. How different? Totally different.
During a partial solar eclipse, you need certified eclipse glasses to safely view the Sun. When you are looking at the Sun through such glasses, you will see a circular chunk taken out of its disk. That would be the part of the Moon blocking the Sun.
During a total solar eclipse, on the other hand, those along the path of the umbra can experience totality. During totality, and only then, you can take off your eclipse glasses and safety look at where the Sun should be. However, instead of seeing the disk of the Sun, you will see the Moon’s shadow. The only part of the Sun you will see is the corona. The corona is the Sun’s thin atmosphere which extends for millions of kilometers from its surface. We don’t usually see it because the photosphere, the layer just below it, is so much brighter.
When you are looking at a partial solar eclipse through eclipse glasses, you are seeing the part of the photosphere that is not blocked by the Moon. The only time you can see the solar corona is during totality. To the naked eyes, the corona looks like the ghost-thin petals of a frail white flower or the feather, wispy extensions of a dandelion seed. The sight of it in the sky is a vision like no other.
Aside from the corona, some planets and the brightest stars can be seen during totality. Because the Solar System is relatively flat, the visible planets will approximately line up with the Sun and Moon. The sight can transport you to a view of the Solar System from outside.
If that sounds mind boggling, you are not alone. Many observers say that animals behave strangely during totality, as if baffled by the sudden disappearance of the Sun.
Total eclipses are not very rare. On average, one can be seen in a part of the Earth every 18 months. The next one will happen on July 2, 2019, followed by another one on Dec. 14, 2020. Both can be seen from South America. However, because the path of totality includes a very small part of the Earth, a given part of the world experiences totality only once every 375 years.
There is nothing quite like witnessing totality. For those reading this who could afford it, do yourself a huge favor by planning a trip to see the next ones. A trip to witness totality is not just a trip to witness a spectacle; it is a celebration of fact that the universe is governed by rules, and the astounding fact that we humans have understood these rules well enough to predict such occurrences to great precision.
Pecier Decierdo is resident physicist and astronomer of The Mind Museum.