It’s coming. August 21st. The slowly progressing cycles of Earth and Moon orbits around the sun brings us closer to a special triple alignment every minute. A dedicated group of observers who literally ‘chase’ these special alignments across our planet, wait patiently but plan thourougly their next expedition to bask in… the dark of the moon. This special alignment, called a solar eclipse, is visible from someplace on Earth about every 18 months - that’s two total eclipses every three years. Often described as the most spectacular astronomical event to be seen from Earth, I recommend that no human should leave the planet without seeing a solar eclipse. Mabel Loomis Todd, a close friend of Emily Dickenson and an avid eclipse chaser in the 19th century, said this after witnessing the May 28, 1900 total solar eclipse at Tripoli, North Africa:
“I doubt if the effect of witnessing a total eclipse ever quite passes away. The impression is singularly vivid and quieting for days, and can never be wholly lost. A startling nearness to the gigantic forces of nature and their inconceivable operation seems to have been established. Personalities, towns, and cities, and hates and jealousies, and even mundane hopes grow very small and far away.”
Your next chance to see one? August 21st. Don’t miss it!
There are three types of solar eclipse visible from Earth; total, partial, and annular. While the first two types seem pretty straight-forward, that last one might be a bit challenging to understand. But before we figure that one out, let’s start at the beginning: What is a solar eclipse?
A solar eclipse is an astronomical event observed on Earth when light from the sun is blocked by the moon. Eclipses are all about the alignment of these three objects, which one is blocking the sun’s light, and the shadows they create. When the moon lines up directly between the Sun and the Earth, it blocks sunlight from reaching a narrow strip of Earth for a few hours. It’s a narrow strip and there’s a time element involved because the earth and the moon are in constant motion. This event is a total solar eclipse; the sun is ‘eclipsed’ - completely blocked - by the moon. If the moon doesn’t exactly line up in front of the sun, only part of the sun is eclipsed and the event is a partial solar eclipse. Then there’s the very special case – the annular eclipse, where the moon lines up directly in front of the sun but isn’t big enough to completely cover the sun. In this case a ring of sunlight encircles the moon as it stands in front of the sun.
Sound complicated? They can be but for the casual observer, it’s just light and shadows. Try this experiment: Stand outside in bright sunlight. Allow your shadow to fall on a nearby person, plant or pet. Your body, blocking light from the sun, creates a shadow, causing a solar eclipse for whatever is in your shadow. Exactly the same as the moon; blocking light from the sun, it creates a shadow, causing a solar eclipse for whatever is in its’ shadow. Get it? That’s all an eclipse is! For scientists who study eclipses, they are incredibly complicated and each solar eclipse has its own signature.
In the next installment, eclipse mechanics and why they don’t happen every month!
This five-part series will look at why eclipses don’t happen every month, a brief history of observing eclipses, how Einstein used an eclipse to prove his theory of general relativity, and of course, how you can become an eclipse observing expert just by holding a spaghetti strainer!