Mad About Science: Eclipse

By Brenden Bobby
Reader Columnist

As baseball player Pete Rose once said: “It’s a round bat and a round ball, and you got to hit it square.”

An eclipse is a lot like baseball in this respect. It is the interaction of photons, traveling straight, interacting with a series of spheres and circles to create a rare and unique experience. Because of the complexity of so much interacting mathematics, I beg your forgiveness if some of the information in this article is slightly off.

A diagram of a solar eclipse (top) and lunar eclipse (bottom). Courtesy image.

However, the premise of an eclipse is fairly straightforward. It’s what happens when a celestial object is blocking the light of another celestial object from reaching the viewer. In most cases, we’re referring to solar and lunar eclipses, respectively — but this can occur in other star systems like our own.

A lunar eclipse is what happens when the moon passes through the shadow of the Earth, often giving the moon an eerie red hue and making it almost disappear in the night sky. You may be wondering how this differs from the cycles of the moon.

The moon orbits the Earth much slower than the rotation of the Earth. Additionally, the moon is tidally locked to Earth, which means that the same side always faces the surface of the planet regardless of its relative position. While the Earth is making a full rotation over the course of 24 hours, it takes the moon 27 days to orbit the Earth. 

The moon’s phases are based on its position relative to the sun, and the direction from which light from the latter is hitting the former. During a new moon, the sunlight is hitting the side of the moon we cannot see. During a full moon, sunlight is hitting the side that is facing us.

However, the moon’s orbit is not perfectly circular, or lunar eclipses would be an extremely common occurrence. The moon’s orbit is elliptical and also tilted by about five degrees, which leads to infrequent eclipses.

If your head is starting to spin, then I think you’ve begun to truly appreciate Mr. Rose’s baseball quote at the top of the page. 

The math involved in eclipses is already confusing enough, but there’s still some more complexity involved. There are two terms worth mentioning here: penumbral and umbral eclipses. A penumbra is essentially a partial eclipse, in which some of the Earth’s shadow is being cast across the lunar surface, but light is still able to pass through in sufficient quantities so as not to fully obscure its features. An umbral eclipse, sometimes called a total eclipse, occurs when the bulk of the Earth’s shadow is cast over the surface of the moon, blocking light from nearly the entire surface. 

Here’s the mindfreak: If you were standing on the surface of the moon during a total lunar eclipse and watching the Earth, you’d be viewing the sunrise and sunset simultaneously.

At this point, you’re certainly wondering why the light on the moon is red when it’s normally white. Red is the lowest visible wavelength of light in the color spectrum. As the light is passing through the densest amount of atmosphere on Earth, other wavelengths of light are either absorbed or reflected before reaching the surface of the moon, giving it that telltale red glow. This is nothing ominous, it’s simply a rare and interesting interaction with light and our atmosphere.

A solar eclipse is what happens when the moon passes between the sun and the Earth, blocking the daylight from reaching Earth’s surface and transforming huge swaths of the planet’s surface into a chilling twilight. 

The moon has virtually no atmosphere, so we do not experience a red glow during a solar eclipse — rather, we just experience the shadow of the moon.

Total solar eclipses are a bit of a rarity. The orbit of the moon, which we’ve already established is pretty funky, has to line up perfectly with the orbit of the Earth around the sun. Earth also has an elliptical orbit around its star, while also rotating at a whopping 1,037 miles per hour. Additionally, the Earth wobbles on its axis to allow either the Northern or Southern hemispheres to face the sun more prominently for a number of months, granting us our seasons. All of these factors have to line up perfectly in order for a solar eclipse to occur.

The next “annular” solar eclipse — when the moon will cover most, but not all of the sun — will occur over us on Oct. 14. The next total solar eclipse will occur for Mexico and much of the eastern United States on April 8, 2024. After that, we may not see another for at least a decade.

Would you like to learn more about eclipses from people that know considerably more about how the heavenly bodies move across the sky than I do? Stop by University of Idaho’s Sandpoint Organic Agriculture Center on 10881 N. Boyer Road on Saturday, June 29 from 6-8 p.m. Spacepoint will be hosting Dr. Matthew Bernards in a lecture and hands-on demonstration of a number of telescopes, including a model you can check out and take home from your local Library of Things.

This is a great opportunity to meet up with other people interested in astronomy in our community, learn a bit more about eclipses from people that have devoted their careers to the field and testing out some sweet hardware. I hope you’ll join me there.

Stay curious, 7B.