Protect Your Eyes

Total eclipse (photo by n0ll)

June 15, 763 BC: A total solar eclipse is recorded by Assyrians. Assyria was located in the northern half of Mesopotamia on the upper Tigris River. Because we have the time and place of the eclipse, using mathematical calculations from the current time, we can place the chronology of Mesopotamian history accurately.

A solar eclipse occurs when the Moon passes between the Sun and the Earth. There are three types of eclipses: 1) total, where the Sun is completely hidden by the moon, 2) annular, where the Moon appears smaller than the Sun and a ring of light shows around the entire edge, and 3) partial, where the Sun is not exactly in line with the Moon and so is not adequately obscured.

The Sun is about 400 times larger than the Moon and about 400 times farther away from Earth than the Moon. This synchronicity means that they appear the same size to us. Orbits are not circular, but rather elliptical so that the sizes are not always in sync. The Moon’s orbit around the Earth is inclined 5º when compared to the Earth’s orbit around the Sun. This all means that there can be up to a 6% difference in the appearance of size.

Lunar eclipses can be seen from anywhere on the night side of the planet. Solar eclipses are less accommodating. The shadow cast by a total solar eclipse is seen only in a particular area. Total eclipses are rare with one occurring every 18 months somewhere on the planet. For a particular place, a total eclipse occurs once every 370 years, on average. The longest a total eclipse can last is 7 minutes and 40 seconds, but most are shorter in duration. In each millennium, fewer than 10 last more than 7 minutes.

By studying the pattern of eclipses, two cycles have been found. The Saros cycle lasts about 18 years and is a more stable and consistent cycle. After a Saros cycle, and Inex cycle that is more volatile and less well defined runs its course. By using complex mathematical computations we can determine when past eclipses occurred and plot them into the calendar we currently use.

“Insurrection in the city of Ashur. In the month Sivan, the Sun was eclipsed.” – from The Assyrian Chronicles

“The Sun was eclipsed, a thing of very evil omen. Then the Moon became small, and now the Sun became small. . . . For the Moon to be eclipsed is but an ordinary matter. Now that the Sun has been eclipsed – how bad it is!” – from the Shih-ching

“Nothing there is beyond hope, nothing that can be sworn impossible, nothing wonderful, since Zeus, father of the Olympians, made night from mid-day, hiding the light of the shining Sun, and sore fear came upon men.” – Archilochus

“You’ve got to be careful when you look at the sun at anytime. Today is no different. The solar eclipse itself doesn’t generate anymore unusual a phenomenon.” – Paul Delany

Also on this day:
King “Soft-sword” John “Signs” on the Dotted Line – In 1215, King John of England signs the Magna Carta.
Not Spock – In 1844, vulcanization was patented.