Many thanks to Jim Craig (2017 Science Guest) of Planet of Mystery Productions for writing this guide to next Monday’s eclipse (8/21).
THE GREAT AMERICAN ECLIPSE AND YOU
It’s the middle of the day.
But it’s dark.
The temperature drops.
Birds start to roost.
A shadow falls across the land.
Don’t panic.
It’s not the end of the world. It’s just…
THE GREAT AMERICAN ECLIPSE!
Unless you study astronomy, you probably have a lot of questions about the eclipse.
- What is an eclipse and how do they happen?
- Where can I go to see the eclipse?
- What can I expect to see?
- How can I view it safely?
- What’s the big deal? Don’t these happen all the time?
Part I – What is an eclipse and how do they happen?
Objects in space, such as moons and planets, cast shadows, just as you do. An eclipse happens when one of these objects casts a shadow on another.
But it’s not as simple as that.
Remember that space is huge and objects are very far apart. In order for an eclipse to occur, things have to line up just right. Here on Earth, that only happens a couple of time each year.
When the earth casts its shadow on the moon, the moon goes dark and we experience a lunar eclipse.
The earth makes a pretty big shadow compared to the size of the moon. If the shadow covers the entire face of the moon, we experience a total lunar eclipse. But you can only see it if you’re in the right place.
Luckily, that’s a pretty big place. You just have to be on the nighttime side of the earth when the eclipse is happening.
The moon’s shadow on the earth isn’t as big at only about 70 miles across. So in order to see the sun eclipsed, you have to be somewhere along that narrow path that the shadow will trace across the earth. If you aren’t along that path, you’ll see only a portion of the sun covered by the moon in a partial eclipse.
Because most of the earth is covered with water, that path usually passes over an ocean or some other remote, inaccessible part of the earth.
Every once in a while, that shadow passes over the continental United States. The last time it happened was on February 26, 1972.
There have been partial eclipses including one that happened on Christmas Day in 2000 but total eclipses are far less common.
So here’s the first thing that has to happen for you to see a total solar eclipse:
YOU HAVE TO BE IN THE RIGHT PLACE
The sun is 400 times the diameter of the moon. But it’s also 400 times farther away. So, in the sky, they look to be the same size! That’s how the moon can cover the sun so well.
Sometimes, the moon is just a little further away from the earth because its orbit isn’t perfectly circular. When we have an eclipse at these times, we can see a ring of sun around the moon in what’s called an annular eclipse.
So that’s the second thing that has to happen for you to see a total solar eclipse:
THE MOON MUST BE THE CORRECT DISTANCE FROM THE EARTH
If we map the position of the sun against the background stars, it traces a path across the sky called the ecliptic.
If we map the position of the moon as it travels around the earth, we can see that its path is tilted compared to the ecliptic.
Now we have our third thing that has to happen for you see a total solar eclipse:
THE MOON MUST BE ON THE ECLIPTIC
Of course, if the moon isn’t on the same side of the earth as the sun, it’s not going to cast a shadow on the earth. When the moon and sun line up, we call this the new moon.
The last thing that has to happen for you to see a total solar eclipse:
THE MOON HAS TO BE ON THE RIGHT SIDE OF THE EARTH
As you can imagine, all four of these things don’t always happen at the same time. And that’s why total solar eclipses are fairly rare and not something you see all the time.
But it’s possible for all four of these things to happen for you on August 21, 2017… if you’re in the right place.
Part II – Where can I go to see the eclipse?
As mentioned earlier, the moon’s shadow is only about 70 miles across on the surface of the earth. But for this year’s eclipse, the path goes clear across the continental United States.
It starts on the west coast, near Lincoln City, Oregon. It will then sweep from west to east across Oregon, Idaho, Wyoming, Nebraska, Missouri, Illinois, Kentucky, Tennessee, North Carolina and South Carolina ending off the coast near Charleston, South Carolina. It also touches small corners of Montana, Kansas and Georgia. If you’re along the center of the path in one of these states, totality can last from 2 minutes to a maximum of 2 minutes and 41 seconds.
ECLIPSE FACT:
The longest duration for totality in this eclipse is 2 minutes and 41.6 seconds for folks southeast of Carbondale, Illinois.
Remember, if you aren’t along the path of totality, you’ll only see a partial eclipse.
Part III – What can I expect to see?
Any description of the experience of a total eclipse of the sun is going to fall short of actually experiencing it.
The partial phase of the eclipse starts when the moon first starts to cover the face of the sun. This is called “first contact.”
Over the next few hours, the moon will cover more and more of the sun’s face. This is the partial phase of the eclipse.
Just before totality is when things get interesting.
On the ground, you may see the shadow of the moon as it approaches your location.
When the last bit of the sun is still uncovered, there will be a bright spot along one edge of the moon. This is called the Diamond Ring effect.
At this time, the sky will darken to an eerie twilight. You may be able to see some of the brighter stars and planets.
When the entire face of the sun is covered, you may see small bits of sunlight as they peek between the mountains and valleys of the moon. These are called Bailey’s Beads.
If the sun is active, you may see reddish wisps of gas projected as prominences from the surface of the sun.
You’ll also be able to see the glow of the sun’s corona. This is the only time you’ll be able to see this.
You may notice the air becoming slightly cooler. Birds will roost and other animals will react to the eclipse as if nightfall has come early.
Before you know it (and long before you’re ready), the Diamond Ring will appear again and totality has ended.
But you’ll realize that you’ve just experienced one of the most amazing shows that nature has to offer.
Part IV – How can I view it safely?
The sun’s rays are very bright and you don’t want to look at it without proper protection.
Before learning what you should use, you should know what you absolutely should NOT use!
ECLIPSE FACT:
There is NOTHING that you can make at home that will allow you to safely look directly at the sun.
Do not use:
- Smoked glass
- Exposed photographic film
- Mylar wrappers from toaster pastries
- Sunglasses
- CDs/DVDs
Even if you have something that can block out the sun’s visible rays, it’s what you can’t see that can cause damage. The sun gives off heat in the form of infrared radiation. It also gives of ultraviolet light, the same kind of light that gives you sunburn. You’ll want something that can block out both of these as well as most of the visible light.
Fortunately, there are inexpensive options available.
Many companies make solar viewing glasses. These are usually solar filter material in cardboard frames and shouldn’t cost more than a dollar or two. If you’re going to buy some in time for the eclipse, order early because they’re going to sell out before the big event.
Make sure your glasses have the ISO (International Organization of Standards) rating #12312-2 printed clearly. Many companies have been selling glasses that don’t meet this standard and might actually be more harmful than not using them at all. The reason they could be more harmful is that your pupils will open wider allowing more ultraviolet light into your eyes.
You can also use Number 14 Welder’s glass if you have it handy. This will cut out the harmful UV and infrared light while also dimming the sun’s visible light to a safe level.
Another option is to turn your back towards the sun. Using a pinhole in a small piece of cardboard, project the image onto a piece of white cardstock or paper. Do NOT look directly at the sun through the pinhole. A larger pinhole will make a larger image but it won’t be as clear.
Any time you look at the sun when it’s not in totality, make sure you have your solar viewer covering both eyes.
But there is a time when you can take them off and view the sun safely: during totality. When the flash of the Diamond Ring ends, take your viewer off and enjoy the eclipse. But keep them handy! When the second Diamond Ring flash occurs, look away from the sun and put your viewer back on. Then you can safely watch the rest of the eclipse. You can even use binoculars at this time but do so briefly and make sure your binoculars are put away before the end of the eclipse.
Part V – What’s the big deal? Don’t these happen all the time?
Solar eclipses do happen somewhere on the earth about twice each year. But unless you want to take a flight to Antarctica, remote Siberia or some other place that’s hard to get to, you won’t see a total eclipse very often.
The next total solar eclipse that will touch anywhere in the continental United States will happen on April 8, 2024. Its path will pass across Texas, Oklahoma, Arkansas, Missouri, Illinois, Indiana, Ohio, Pennsylvania, New York, Vermont, New Hampshire and Maine.
As far as the difference between a partial solar eclipse and a total solar eclipse, an astronomer who has seen both made the following comparison: it’s the difference between sitting in the parking lot outside a concert hall listening to your favorite band play on an old AM radio and sitting in the front row knowing that you’ve got tickets for the meet and greet with the band after the show.
Because this eclipse cuts across such a wide swath of the country, those who experience it will be part of a phenomenal shared experience that they’ll remember the rest of their lives.
Be a part of that experience. Plan now to see
THE GREAT AMERICAN ECLIPSE!
