On August 21, for the first time in 38 years, a total solar eclipse will cut through the continental United States. It’s going to be awesome. If you’re in the bull’s eye center of the moon’s shadow known as the totality — the sky will go dark for a few minutes in the middle of the day, stars will appear, birds will become confused and start chirping their nighttime songs. And it’s all because of a cosmic coincidence: From the Earth, both the moon and sun appear to be roughly the same size.
Most of the country will see a partial eclipse, which is also cool. But for the complete show, you need to be in the 70-mile wide path of the totality. Luckily NASA has mapped the path of the totality to an absurd detail.
As NASA data visualizer Ernie Wright explains in the video below, normally people draw the path of an eclipse by assuming that the moon’s shape is perfectly round. But “we know that the moon isn't smooth,” he says. “Around the edge of the moon we have these sort of jagged peaks and valleys.” The resulting shadow’s shape is not a perfectly smooth oval. “It’s more like a polygon,” he says.
To make an absolutely precise map of the eclipse, you need to account for the geography of the moon, the geography of the Earth, and the angle of the sun’s light hitting the Earth. Put that all together and you get “the most accurate map of the eclipse path to date.”
Your elevation on Earth also matters. “In general, the shadow cone gets slightly larger at higher elevations,” Wright explains in an email. But because shadow is hitting the Earth at an angle “folks near the northern limit for this eclipse could be [shifted] outside the umbra [i.e. shadow], while folks near the southern limit could be [shifted] inside.”
Here’s a simple visualization of that effect.
All of this information was used to create these maps of the total eclipse path as it passes through each state:
Check out an interactive version of the map here. (Click on any spot in the US to get a time for when the eclipse will peak there.)
For those not traveling to the path of totality, my colleagues Casey Miller and Ryan Mark created an interactive to help visualize what you’ll see. It grabs your zip code and shows the exact path the moon will take across the sun for your area. You’ll also see when the eclipse will peak (i.e., reach maximum obscuration) in your area. Check it out. It’s very cool.
There’s a total solar eclipse somewhere in the world roughly every 18 months. (There’s even a whole underground of solar eclipse fanatics who chase them around the globe). But for residents of the United States, this year’s eclipse is special. It’s within day trip driving distance of millions of people. The next total solar eclipse over the United States will be in 2024. After that? 2045.
If you’re feeling really anxious about picking out the “perfect” spot to view, you’ll want to find a place with little cloud cover. That can be hard to predict. But, here, NOAA has crunched their data on the average cloud cover that typically occurs August 21st. The darker the dot, the greater chance of clouds. “The chance for clearer skies appears greatest across the Intermountain West,” NOAA explains.
If we’re lucky, and August 21st is a clear day for most, we’ll see something like this — a show that's captivated people on this planet for as long as we've been on Earth: