In the Shadow of the Moon: Solar Eclipse 101

Monday will be the first time in almost 100 years a solar eclipse has passed over the entire U.S.

For more information from NASA – eclipse2017.nasa.gov

For interactive maps – eclipse2017.nasa.gov/eclipse-maps

For live streaming of the eclipse – eclipse2017.nasa.gov/eclipse-live-stream

5 questions answered about the solar eclipse

Editor’s note: Shannon Schmoll, director of the Abrams Planetarium at Michigan State University, explains why and how it happens, and what we can learn from an eclipse.

How do we know when an eclipse is going to happen? How do we know in advance where it will be visible?

Solar eclipses happen when our view of the sun is blocked by the moon. When the moon lines up between the sun and Earth, the moon will cast a shadow onto Earth. This is what we on the ground observe as a solar eclipse.

We know when they’ll happen because over centuries astronomers have measured very precisely the motions of the Earth, moon and sun, including their orbital shapes, how the orbits precess and other parameters. With those data about the moon – and similar information about the Earth’s orbit around the sun – we can make mathematical models of their movements in relation to each other. Using those equations, we can calculate tables of data that can predict what we will see on Earth, depending on location, during an eclipse as well as when they will happen and how long they last. (The next major solar eclipses over the U.S. will be in 2023 and 2024.)

How often do eclipses happen?

A solar eclipse happens, on average, a couple times a year. The moon passes between the Earth and sun every 29 days, a time we call the “new moon” – when the moon is not visible in Earth’s nighttime sky. However, the moon’s orbit and the sun’s path in our sky don’t match up exactly, so at most of those new moon events, the moon appears above or below the sun.

Twice a year, though, there is a period where the moon and the sun line up with Earth – astronomers call this an eclipse season. It lasts about 34 days, long enough for the moon to complete a full orbit (and then some) of the Earth. During each eclipse season, there are at least two eclipses visible from some parts of the Earth. At the full moon, there will be a lunar eclipse, when the moon passes directly behind the Earth, resulting in a darker, reddish-colored moon. And at the new moon, there will be a solar eclipse, when the sun is blocked by the moon.

Can we learn anything from eclipse events, or are they really just oddities that happen in nature?

We can definitely learn things from eclipses. The outermost layer of the sun, known as the corona, is difficult to study because it’s less bright than the rest of the sun – so we have trouble seeing it amid the rest of the sun’s brightness.

When the moon blocks the sun, we can see the corona, the famous visual of the halo of light around the dark disk of the moon. Currently astronomers study this by creating an artificial eclipse with a mask built into special instruments on telescopes called coronagraphs. This is great, but doesn’t allow the best pictures. Eclipses give scientists opportunities to get more data to study the corona in depth.

We can also learn about Earth itself. In an area affected by an eclipse, the darkening of the sun leads to a sudden drop in temperature. NASA-funded studies during this eclipse will look at the effects from the eclipse on our atmosphere as well as what happens on land. Previous studies observed animal behavior during an eclipse in 2001 and noted some animals went through their night routines as the sun disappeared while others became nervous.

And we can learn about the whole universe. Less than 100 years ago, an eclipse proved a prediction Albert Einstein had made about gravity. That success helped make him a household name. In his general theory of relativity, Einstein had predicted that gravity could bend the path of light. The effect he predicted was very slight, so it would best be viewed as the light passed a very large celestial body as part of its travels across a very long distance of space.

Sir Arthur Eddington, an astronomer who helped further the study of general relativity and whose work is a major piece of our modern understanding of stars and black holes, used the darkness provided by a solar eclipse to look at the position of the stars’ light during the day, when it passed the sun. He then compared those positions to their known positions at night. He saw that the gravity of the sun had bent the path – exactly as, and in the precise amount that, Einstein had predicted.

How weird is it that the moon can basically exactly block out the sun?

It is very unusual that the moon and the sun just happen to be at the right distances and sizes to appear to have the same size in our sky. This allows the moon to perfectly block the sun’s disk, while also showing us the corona. Venus and Mercury, for instance, can also pass in front of the sun from our perspective. However, they appear as small specks moving across the sun.

What would someone standing on the moon see happen on Earth? Would Earth get dark?

If you were on the moon, you would be able to see the effects of the solar eclipse on Earth only if you were standing on the moon’s night side, the side facing the Earth. You would see a round shadow cast onto the Earth. This particular eclipse will first hit the Pacific Ocean, then move into Oregon, cross the U.S. to South Carolina and end in the Atlantic Ocean. This path the shadow takes is called the path of totality.

Solar eclipses are not new phenomena. They have happened since the dawn of time, and astronomers have been looking at these shadows for nearly 4,000 years and more, by some estimates.

On Monday, all of North America will be treated to an eclipse of the sun. A curving path from Salem, Oregon to Charleston, South Carolina will experience a total eclipse. A total eclipse, according to Jason Seffen, assistant professor of physics and astronomy at the University of Nevada-Las Vegas, happens every few years, but mostly over oceans. To have one that goes across the entire continental U.S. is quite rare.

According to NASA’s website, the last time a total eclipse touched the U.S. was in 1979, and the last time a total eclipse spanned the entire continental U.S. was in 1918.

What is an eclipse

Solar eclipses happen when the moon moves between Earth and the sun. You might think that this should happen every month since the moon’s orbit, depending on how it is defined, is between about 27 and 29 days long.

Our moon’s orbit is tilted with respect to Earth’s orbit around the sun by about 5 degrees. It doesn’t seem like much, but the moon itself is only about half a degree in width in the sky, about half the width of your pinky finger held at arm’s length. So, sometimes the moon misses too high and sometimes too low to cause a solar eclipse.

Only when the sun, moon and Earth line up close to the “line of nodes,” the imaginary line that represents the intersection of the orbital planes of the moon and Earth, can you have an eclipse.

Steffen said there are three types of eclipses. A partial eclipse, a total eclipse and an annular eclipse. On Monday, a total eclipse will occur along the path of totality, and other areas will experience a partial eclipse.

A partial eclipse, is what can be seen in Kingman and the surrounding area. This is when the moon covers only a part of the sun’s disk.

In Kingman, the peak eclipse will be 69 percent at approximately 10:29 a.m. Golden Valley will experience 68 percent eclipse around 10:28 a.m. Dolan Springs and Yucca will experience between 66 and 69 percent coverage at 10:29 a.m.

Fourteen states will experience what is known as a total eclipse. This happens when the moon completely covers the sun. Totality can last for no more than about seven and a half minutes, but is usually less than three minutes long. For this eclipse, the longest period when the moon completely blocks the sun from any given location along the path will be about 2 minutes and 40 seconds.

Safety

It is universally acknowledged that looking at the sun for an extended period of time is dangerous. The simplest way to experience the solar eclipse would be to purchase solar glasses. As of Tuesday, most of these were unavailable online.

Another option Steffen suggested is to look up videos online to create pinhole projection. For example, cross the outstretched, slightly open fingers of one hand over the outstretched, slightly open fingers of the other, creating a waffle pattern. With your back to the sun, look at your hands’ shadow on the ground. The little spaces between your fingers will project a grid of small images on the ground, showing the sun as a crescent during the partial phases of the eclipse. Or just look at the shadow of a leafy tree during the partial eclipse; you’ll see the ground dappled with crescent suns projected by the tiny spaces between the leaves.

It is also possible to create a projector out of a telescope or binoculars, Steffen said. This would create a projection onto a piece of paper through which the eclipse could be viewed. He also said that a cellphone camera would likely not be able to capture the event or “survive the event.”

Christie Vanover, public affairs officer for the Lake Mead National Recreation Area, said it is important for those driving to make sure their headlights are on during the eclipse and suggests people carry a flashlight in the event it becomes darker than expected.

You can experience the eclipse safely, but it is vital that you protect your eyes at all times with the proper solar filters. No matter what recommended technique you use, do not stare continuously at the sun. Take breaks and give your eyes a rest. Do not use sunglasses: they don’t offer your eyes sufficient protection.

Local events

For people who have the day off, Lake Mead National Recreation Area is holding a free viewing party at the visitor center from 9 a.m. to noon. Vanover said the park rangers will be giving a presentation and be available to answer questions throughout the event. There will be solar glasses available for purchase for those who wish to experience the event on their own. There will also be a solar telescope for people to look through at the ranger station.

Vanover said a second opportunity for people to view the eclipse is by rafting down the Colorado River with Black Canyon River Adventures. The Aug. 21 tour departs at 10 a.m. Guests are asked to check in by 9:30 a.m. at the Lake Mead RV Village, located at 268 Lakeshore Road, Boulder City, Nevada. The cost for adults (16 years and older) is $97.

It’s also possible to simply step outside to view the eclipse, as long as safety measure are followed.

This event has naturally drawn a lot of attention nationwide. Vanover said she believes the rarity of these events are what drive the hype.

“It’s been nearly 40 years since the last one,” Vanover said. “It would be a fantastic morning … stepping outside and enjoying nature for a minute.”

Local schools are also being involved. Celeste Lucier at Kingman Academy said she will be taking students out with pin holes in index cards and will be playing the NASA site throughout the day for students to watch. Michelle Burkes at Manzanita was able to obtain safety equipment and is planning a solar eclipse viewing. Burkes is also planning to cook using a solar oven Thursday. Even kindergarteners at Cerbat Elementary will get a chance to view the eclipse.

Steffen said the event is an amazing phenomena.

“You have a blazing hot ball of plasma, one million times the volume of the Earth and 10,000 degrees Farhenheit,” Steffen said. “It is briefly blocked by a gigantic, self-gravitating rock the diameter of North America. The shadow is cast 250,000 miles away onto another ball of rock, this one with a slice of habitability less than 10 miles thick and upon which there are 7 billion members of a species able to both appreciate how beautiful the situation is and understand how it all works. I think that being humbled by the universe inspires gratitude for life – and gratitude is good medicine for whatever ails you.”