On Aug. 21, the first total solar eclipse in 38 years will cross over the continental United States. The 70-mile-wide shadow created by the moon will cross from Oregon to South Carolina. Those in that path will be able to see a total eclipse of the sun for 2 minutes. Although Massachusetts is not in this shadow, people will still see a partial eclipse that will partially block the sun and change the ambient light for a few minutes.

According to NASA, while total solar eclipses are not particularly rare, occurring roughly every 18 months, the United States will not experience a total solar eclipse until October 2023. That one will travel between Northern California and Florida and this also will result in a partial eclipse for the Northeast. In 2024 there will be a total eclipse with a path over Massachusetts. For a total eclipse to take place, the sun, moon and Earth must be in a direct line. Eclipses occur due to the special coincidence of the moon and the sun being the same angular size. The sun is 400 times wider than the moon, but it is also 400 times farther away, so they coincidentally appear to be the same size in the sky.

“During a solar eclipse, the moon casts two shadows on Earth,” NASA says. “The first shadow is called the umbra (UM bruh). This shadow gets smaller as it reaches Earth. It is the dark center of the moon’s shadow. The second shadow is called the penumbra (pe NUM bruh). The penumbra gets larger as it reaches Earth. People standing in the penumbra will see a partial eclipse. People standing in the umbra will see a total eclipse.”

Read more articles from the 08/04/17 Hotline issue.