A rare solar eclipse will occur on August 21, when the moon will completely cover the sun for more than two minutes. The Great American Eclipse can be seen mainly from North America, where millions will be in the path of totality.
Monday's solar eclipse will be the first total eclipse seen in the United States in nearly 40-years.
"We're just really lucky. Lucky because the moon's apparent diameter in the sky is the same as the sun so it can completely block it but it's not too big," says Jason Craig with the NASA Jet Propulsion Lab.
The rare celestial event happens when the moon passes between the sun and Earth. It's a moment of perfect orbit and timing, when the sun's light is blocked from reaching our planet. The sun is "eclipsed" by the moon's shadow.
"And the whole thing is under an hour an a half. That's how fast the moon crosses over and the shadow hits," explained Craig.
The shadow will streak across 14 states in the U.S. on a path from Oregon to South Carolina.
Those who aren't on that 70-mile-wide line will see a partial eclipse.
NASA Jet Propulsion Laboratory spent a year developing an internet application called NASA's Eyes. The app shows what the eclipse will look like from anywhere in the country. "Any city you want to check out you just click on it"
When the sun's bright surface is covered for more than two minutes, the only light visible in the sky will be the sun's outer atmosphere ring known as the corona.
But before you look up on Monday...
"The number one rule for safe eclipse viewing is don't improvise. If you don't know, don't chance it. It's not worth it. You really can damage your eyes," reminds Dr. Laura Danly with the Griffith Observatory in California.
Make sure you have glasses that meet safety standards.