The April 8 total solar eclipse will cut a 2,000-mile path across the United States in just over an hour, casting near darkness over a region of more than 200,000 square miles from Texas to Maine. The rest of the continental United States — plus Hawaii and a spot of southern Alaska — will enjoy a consolation prize of partial occlusion. The following interactive simulates what this will look like from any location in the U.S., no special glasses needed.
[time-brightcove not-tgx=”true”]Monday’s eclipse is the second time in seven years that such an astronomical rarity has favored a large part of the nation. The August 2017 total solar eclipse — for which TIME rented a private four-seat plane to document the phenomenon — cut a mirroring path from Oregon to South Carolina.
This means there is 9,286 square-mile quadrangle centered on southern Illinois that the cosmos has favored with two complete solar eclipses in less than a decade. As astrophysical odds go, one envies the residents of this anointed parallelogram.
TIME’s solar eclipse simulation uses coordinates for the sun, Earth, and moon from NASA’s industrial-grade SPICE toolkit, which we calculated in the J2000 reference frame centered on the Earth. (Many modern calculations use this pre-Copernican view of the cosmos as a matter of convenience.)
Rather than calculating the exact moment that the eclipse begins and ends for thousands of locations, our simulation uses these coordinates to create a realtime 3D simulation with the same type of computer programming that is common in video games. This includes rotating the viewer’s camera in accordance with the Earth’s rotation over the course of the eclipse, which accounts for why the moon appears to cut a curved path across the sky.
We took a few small artistic liberties in moderately exaggerating the degree of darkness one witnesses in a partial eclipse by adding a faint ambient light to see the surface of the moon in better detail.
Where the times you see in this simulation differ from other sources of eclipse data by a minute or two, the discrepancy is most likely a small difference in the precise location of the calculation or a slightly different way of accounting for the time it takes the speed of light to travel from the sun to the Earth.
