Eclipses by Hugh Jones, Black Science

What causes solar and lunar eclipses?

According to my friend Alex Torres “Lunar and solar eclipses are both wonderful phenomenons. They can either light up the sky or put it out completely. But they are two different things.”  I have to agree with him.

A solar eclipse is caused when a new moon gets directly in between the Earth and Sun.  In other words, the Earth and moon are both in the sun’s plane at the same time.  A portion of the sun’s light ends up hitting the side of the moon that we don’t see from Earth (new moon), leaving a small part of Earth covered by the moon’s shadow.  Everyone who happens to be in the moon’s shadow during the eclipse experiences a total eclipse, which lasts for a few minutes and then becomes a partial eclipse.  Partial solar eclipses may even look kind of like a diamond ring.   Total solar eclipses are less common and occur about once every 18 months.  Lunar eclipses tend to be more common.  

Video of a total solar eclipse by the BBC.

A lunar eclipse is also caused when the Earth and moon are in the sun’s plane at the same time, only this time the full moon gets caught in part or all of the Earth’s shadow.  You might think that this would cause a full moon to become invisible to us during a lunar eclipse.  However, since the sun is larger than the Earth some sunlight can still reach the moon, giving it a red/orange tint.  Lunar eclipses tend to occur about once every six months, total (full) or partial.

How come we don’t have eclipses every new moon and full moon?

There are multiple ways to explain why we don’t experience eclipses every new and full moon.  It is easier to explain with visuals.  In class we began by using a quarter (taped to a stick) as the moon, a model as the Earth and a small lightbulb as the sun.  Mr. Battaglia created a solar eclipse for us by moving the quarter into the sun’s plane.  There was a shadow on the surface of the model Earth where the quarter was blocking the light (See Example 1).  Mr. Battaglia also created a lunar eclipse for us by moving the quarter behind the model Earth.  Mr. Battaglia did not move the quarter directly behind the Earth, only partially behind.  A small part of the model Earth’s shadow was hitting the quarter’s surface, creating a partial lunar eclipse (See Example 2).

Next in class Mr. Battaglia used a model he had made with clay.  The model used a thin, clear disc with a clay Earth model at its center to describe the moon’s revolution path around the Earth.  At one tip of the disc was a clay moon.  The moon’s orbit is only tilted about 5 degrees from Earth’s orbit around the sun.  However, to make this model easier to understand, the disc showing the moon’s orbit path around the sun is tilted at about 30 degrees.  Using a lightbulb as the sun, Mr. Battaglia had the Earth model revolve around the lightbulb, along with the moon model revolving around the Earth.  After a few seconds, he would look and see if there was either a solar or lunar eclipse by observing the model’s shadows on an index card.  If only the Earth’s shadow was visible, then an eclipse had happened at that position.  If the Earth’s shadow and the moon’s shadow were visible on the piece of paper, the model’s position would not represent an eclipse.  You can look below at Examples 3 and 4.

In summary, an eclipse is caused when either the new or full moon and Earth are both in the sun’s plane at the same time.