What is Eclipse Season? And Why Do They Come in Pairs?

What is Eclipse Season?
~~and~~
Why Do Eclipses Come in Pairs?
Or Even Threes?

by Dallas Doctor

Solar Eclipse

Eclipses are interesting phenomena and have been commanding our attention since we have been human (and probably even before that).  As long as our species has been documenting anything at all, eclipses have been an important part of our history.

A Syrian clay tablet records a solar eclipse which occurred 3,240 years ago (on March 5, 1223 B.C).  Chinese historical records of solar eclipses date back over 4,000 years.  And a megalithic monument in Ireland records an eclipse 5,357 years ago (on November 30, 3340 B.C) complete with the deposited charred bones from approximately 48 individuals that attest to possible human sacrifice to “save” the Neolithic “Sky God” (Sun) from dying as it descended to the “underworld.”

So what exactly is an eclipse, anyway?

A Solar Eclipse

An eclipse always involves the alignment of three celestial bodies.  The Greeks called it syzygy (meaning, “yoked together”).  It occurs whenever there is a straight-line configuration of three celestial bodies in a gravitational system.

A Lunar Eclipse

On Earth, we generally refer to eclipses as those that involve only the Sun, Moon and Earth, but many other combinations can and do, of course, occur.  (The giant planets in our solar system, which have many moons (Jupiter, Saturn, Uranus, and Neptune) all exhibit eclipse phenomena regularly.

ECLIPSE SEASON

For the Earth-Moon-Sun combination, Eclipse Season comes twice a year; the conditions repeat every six months.  Every time the plane of the Earth’s orbit around the Sun crosses with the plane of the Moon’s orbit around the Earth, we enter an Eclipse Season.  At least two, and at most three eclipses, will occur during every eclipse season.  This is because it is about 15 days between full moon and new moon and vice versa.  (If there is an eclipse at the very beginning of the season, then there is enough time — 30 days — to squeeze in two more eclipses.)

A solar eclipse is always paired with a lunar eclipse, because during the solar (moon-in-the-middle) eclipse a new moon crosses the ecliptic from south to north.  But a half orbit earlier, the full moon crosses at  the opposite node (earth in the middle) from north to south, encountering the Earth’s shadow along the way.  So a solar eclipse is always preceded by a lunar eclipse.

Here’s an interesting thing to think about:  IF the Earth’s orbit (around the sun) AND the Moon’s orbit (around the earth) were in the SAME PLANE, then we would get eclipses twice every month (every 27 days).  We would get a lunar eclipse every full moon, and a solar eclipse at every new moon.  AND: IF the orbits of both the Earth and the Moon were perfectly CIRCULAR, then each solar eclipse would always be the same type — total.

BUT that doesn’t happen, because the orbits are NOT circular and they’re NOT in the same plane (there’s a 5-degree difference).  As a result, eclipses are NOT common events.  In fact, solar eclipses (particularly a Total Solar Eclipse) can be extremely rare.  They can be decades apart, because totality exists only along a very narrow path on the Earth’s surface.

There are many kinds of eclipses (total, annular, hybrid or partial).  In a total eclipse, the disk of the Sun is fully obscured by the Moon (solar) or the Moon is completely shadowed by the earth (lunar).   In partial and annular eclipses, only part of the Sun or moon is obscured.

SOLARE ECLPISE

Interestingly, in the event of a total solar eclipse (the Moon passes between the earth and the Sun), the Moon is able to cover the Sun’s disc precisely because the Sun is about 400 times bigger than the Moon, and also about 400 times further away, meaning they have the same size in our sky.

Total solar eclipses (the rock star of all eclipses) are extremely rare (in any given location) although they generally occur somewhere on Earth about every 18 months on average.  But a solar eclipse in any specific location is likely to take place only once every 360 to 410 years.

Solar eclipses move very quickly (from west to east) and last only a few minutes at most.  The longest theoretically possible total eclipse is 7-minutes and 32 seconds and that number is decreasing over time.  The next total eclipse exceeding seven minutes in duration will not occur until June 25, 2150. (The longest total solar eclipse during the 11,000 year period from 3000 BC to at least 8000 AD will occur on July 16, 2186, when totality will last 7 min 29 s.)

Amazing that we can figure this stuff out – eh? 

NOTE:  While it might be safe (during totality only) to look at a total solar eclipse with the naked eye, it is NOT recommended, because most people are not trained enough to recognize the phases of an eclipse.  Looking directly at the sun (even a portion of it) can cause permanent eye damage and even blindness.   Special lenses or indirect viewing are always recommended when observing a solar eclipse.

LUNAR ECLIPSE

Lunar_eclipse_September_27_2015

A lunar eclipse (when the Moon passes behind the Earth) is safe to observe with the naked eye, because all the light is reflected.  Unlike a solar eclipse, this larger, safer, more common eclipse moves much more slowly and covers a large area.  A lunar eclipse can be viewed from anywhere on the night side of Earth.

A total lunar eclipse is one where the shadow of the earth completely blocks any direct sunlight, allowing only reflected light to reach the Moon.  If the Earth had no atmosphere, the moon would go completely dark during a total lunar eclipse.  But this doesn’t happen, because, sunlight is refracted through the Earth’s atmosphere into the shadow, causing the Moon to appear red for the same reason that sunsets are red — the blue light gets scattered as it passes through Earth’s atmosphere.

THE ECLIPSE THAT CHANGED THE WORLD

The most consequential (so far) eclipse in history is the one that turned Albert Einstein into a pop star.  It happened on May 29, 1919.  The moon blocked sunlight for more than six minutes of darkness sweeping across South America and across the Atlantic to Africa.   It was during that eclipse that Arthur Eddington (a British astronomer) measured the bending of light rays from distant stars that had been wrenched off their paths by the gravitational field of the sun.  Eddington’s measurements confirmed Einstein’s General Theory of Relativity and turned Albert Einstein into an international celebrity.

MAN-MADE ECLIPSES

Yes, they exist!  The crew of Apollo 12 took a famous photograph of the Earth eclipsing the Sun in 1969.

This photograph (above) was taken with a 16mm motion picture camera from the Apollo 12 spacecraft during its trans-Earth journey home from the moon.  The fascinating view was created when the Earth moved directly between the sun and the Apollo 12 spacecraft.

And (below) this incredible photograph — one of the most amazing ever — was taken in 2006, by the Cassini probe as it was positioned to observe Saturn eclipsing the Sun.

Saturn eclipsing the sun taken by the Cassini spacecraft on 15 September, 2006.

How Cool is that?

So enjoy your eclipses kids.  Always practice safe eye-care.  And remember: Every eclipse gives you a chance to share and revel in something that has been revered and wondered at by your ancestors since the very beginnings of your ancestors.  Think about that; it’s kind’a cool.


P.S.  I’d love to hear what you think.  Please leave a reply.  As long as it’s not spam or trolling, I’ll happily post it here for all to enjoy!  Thank you!

P.P.S. ALSO Here’s MY GoScienceGo Promise: If you EVER think I get something wrong — and if you can provide actual evidence  — (not anecdote, but verifiable EVIDENCE) — of such a thing, PLEASE let me know.  If your argument is valid, I’ll be thrilled to change my mind and acknowledge my error (because that’s the only honest way to be); all you have to do is give me a good reason…

©2017 GoScienceGo.com


For Further Reading:

http://www.astronomy.ca/3340eclipse/

https://en.wikipedia.org/wiki/Eclipse

https://en.wikipedia.org/wiki/Eclipse_season

https://www.space.com/37717-lunar-eclipse-prelude-to-2017-solar-eclipse.html

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