Solar Eclipse in Layman's Terms

A Solar Eclipse is something that occurs when the moon passes directly in between the Earth and the sun.  When this occurs, the moon partially or completely blocks out the sun (depending on where you are located on Earth). A partial blocking of the sun is called a Partial Eclipse and it causes partial darkness.  A total blocking of the sun is called a Total Eclipse and causes total or night-like darkness. 

I will attempt to further explain things using common questions you might have regarding Solar Eclipses.

Q. How can the moon block out the sun when the sun is much much bigger than the moon? 
 
A. The sun is billions of miles farther from the Earth than the moon...so from our point of view here on Earth...the disc of the moon is almost the same size as the disc of the sun.  For example...imagine you are holding a pingpong ball close to your face.  Now imagine there's a basketball several meters away from you.  Can you completely block out your view of the basketball by moving the pingpong ball in front of it in your line of sight?  The answer is yes, it's quite easy to block out the view of the bigger but much farther basketball using the smaller pingpong ball which is held closer to your eyes.  This same principle applies to the moon and the sun. 


Q. How often do solar eclipses occur? Shouldn't they occur once a month since the moon goes around the Earth once a month and can potentially block out the sun once a month?

A. Solar Eclipses happen about twice a year.  The moons orbit around the Earth is not on the same plane as the Earth's orbit around the sun.  If it was...then we would indeed have Solar Eclipses once a month. However, the moons orbit is tilted about 5 degrees away from the plane of the Earth's orbit around the sun. This small tilt causes the moon to be directly in between the Earth and the sun only about twice a year. 


Q. How come some part of the world experience a Total Eclipse while other parts of the world only get a Partial Eclipse?

A. This is because the Earth is much bigger than the moon and different places on Earth have a different "line of sight" from their location to the moon, and then to the sun.  So only the parts of the Earth that are in perfect alignment with the moon and sun at the same time get a Total Eclipse.  Also not even all people in the area of the Earth directly under the moon will experience a Total Eclipse.  This is because only those people directly under the moon's "umbra" or darkest, most focused shadow will see the Total Eclipse.  Think of a tennis ball in your hand and  of someone holding a bright spotlight pointed at the ball several meters away.  Now think of a globe or bigger ball in your other hand.  The shadow the tennis ball will cast on the bigger ball will not be uniformly dark.  The center of the shadow will be darkest, surrounded by ever lighther shadows.  So basically in a Solar Eclipse...those under the moon's darkest shadow experience a Total Eclipse.  Those under the moon's ligher shadow experience a Partial Eclipse.  Those not under any part of the moon's shadow at all experience no eclipse.


Q. How do I view a Solar Eclipse without damaging my eyes?

A. There are several way to safely view a Solar Eclipse:

1. Pinhole method - get two pieces of white cardboard. Punch a small pinhole through one of them.  Let the sunlight fall through the pinhole into the other piece of cardboard.  Move the other cardboard back and forth until you get a good image of the sun on it. 

2. Solar filters - you can usually buy these online or at observatories or specialty astronomy shops.  They are simple to use...just hold it in front of your eyes.  Some are even in the shape of shades so you can just wear them.

3. Welder's Goggles - if you are lucky enough to know a welder or have one of these handy...they are great for viewing Solar Eclipses.

4. Fully exposed and developed black and white film - Kodak Tri-X or Pan-X black and white film, which have a layer of silver on them when developed are good enough to protect your eyes when viewing a Solar Eclipse.  To create a filter out of the film, fully expose the film to the sun and have it developed.  Use the negatives as a solar filter.  It is suggested to use at least 2 layers of negatives to view a Solar Eclipse safely. 

DO NOT USE COLOR FILM NEGATIVES! DO NOT USE CHROMOGENIC BLACK AND WHITE NEGATIVES! These kinds of films do not have the protective silver coating and will not protect your eyes.