Why don’t we see solar eclipses more often?

(Courtesy: Sudekum Planetarium Adventure Science Center)

NASHVILLE, Tenn. (WKRN) – By now, most of you know that an eclipse of the Sun is caused by the moon literally getting in the way of our view of the Sun as the moon orbits around the Earth.

But why don’t we see this more often?  It’s been over 500 years since a total solar eclipse occurred here in Middle Tennessee.  And a lunar eclipse, or an eclipse of the moon, occurs more often and can be seen by so many more people than a solar eclipse.

“A lunar eclipse occurs when the moon falls within the Earth’s shadow, and a solar eclipse occurs when some people fall within the moon’s shadow,” explained Derrick Rohl, Planetarium Manager of the Adventure Science Center.

He continued, “Now, the Earth is much, much larger than the moon,  so the entire moon can actually fit within the Earth’s shadow.  When that happens, everyone on that half of the Earth that can see the moon can see the eclipse.  So literally, an entire side of the Earth gets to see a lunar eclipse all at once.  But when you have a solar eclipse happening, the moon’s shadow is only about 60 to 70 miles wide by the time it reaches Earth.  So only a lucky few falls within that much smaller and very fast moving shadow.”

Another reason solar eclipses are rare is the fact that the orbit of the moon around the Earth and the orbit of the Earth around the Sun are not completely level with each other.

(Courtesy: Sudekum Planetarium Adventure Science Center)

There’s actually about a five degree tilt between the Earth’s orbit around the Sun and the moon’s orbit around the Earth.  That means that even if the moon is almost between the Earth and Sun, sometimes it’s a little bit too low, or a little bit too high for that shadow to actually touch the Earth.

When they do cross each other, there’s also an amazing coincidence that allows a total solar eclipse to occur.

“The moon is much, much smaller than the Sun, but the Sun is also much, much further away from the Earth, so we have this beautiful coincidence in the sky that the moon and the Sun appear almost exactly the same size as viewed from Earth,” Rohl said.

He added, “ So what that means, is when we have a total solar eclipse, the moon is just the right size to block all the light from the Sun.  If the moon were just a little bit further away from Earth, it wouldn’t block enough sky for us to have a total solar eclipse.  So it’s just a really beautiful coincidence up there in the sky.”

Middle Tennessee is lucky because during some solar eclipses, the moon is too far away. The moon’s orbit around the Earth is not a perfect circle.  It’s elongated, or an ellipse.  The means when the moon is farther away, it appears smaller, and does not completely cover the Sun, leaving a ring of the surrounding Sun, which is called an annular eclipse.

“Lucky for us, this isn’t an annular eclipse.  This will have the entire surface of the sun blocked.  That means we can take those glasses off, and look directly up and see that sun’s atmosphere.”

Visit wkrn.com/eclipse for all the resources and information you need.