Why Does a Solar Eclipse Move from West to East?

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Here’s why the path of a solar eclipse travels in the opposite direction of that of the sun

The sun rises and sets in the east. A glance at the map The April 2024 North American Solar Eclipse, however shows a direction from east to west. What’s going on?

The answer lies in the relationship that exists between rotation and EarthIt can be difficult to visualize the arrangement of the moon’s orbit.

First, let’s look at the total solar eclipse pathOn April 8, the moon’s shadow will fall on EarthThe sun will be blocked along a 100-mile-wide path that will cut across the U.S. continent, passing through Texas, central Mexico and Texas. It will then skim along the country’s border with Canada before it exits the U.S. near the northern tip of Maine and moves through parts of New Brunswick, Prince Edward Island, Newfoundland and Labrador.

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This path moves in the opposite direction of the sun’s apparent trek over Earth each day. But during an eclipse, the motion of the moon’s shadow—not the sun—is what matters. Michelle Nichols is the director of public observation at Adler Planetarium, Chicago. She says that Earth rotates from east to west. Imagine that your vantage point on Earth is moving from west to east every morning to welcome the sun.

A band running across a map of North America traces the April 8, 2024, solar eclipse’s path of totality. The moon’s shadow hits land in Sinaloa, Mexico, and tracks northeast to Labrador, Canada, crossing the continent in just an hour and 35 minutes.
Credit: Katie Peek; Source: NASA (Eclipse track data)

The following are some of the ways to get in touch with each other: Moon orbits EarthOn a path from west to east. Nichols explains that, if you were to look down from above the North Pole at the Earth, it would appear as if the Earth was rotating counterclockwise. However, the moon is moving in the same direction but much more slowly. Earth completes its rotation on its axis within 24 hours. The moon, however, takes about a month to complete a full orbital circle around the planet.

During a total solar eclipse, the moon comes between Earth and the sun, with all three bodies lined up in the same plane so that our natural satellite blocks the star’s light and casts a shadow on Earth’s surface. The west-to-east movement of the moon in our sky is now more apparent than usual. As the moon crosses the face of the Sun, it casts a shadow in the same directions as it moves, from west to eastern.

“It’s a rising and a setting concept,” says Jackie Faherty, an astronomer and senior education manager at the American Museum of Natural History. “It has everything to do with the way the moon is moving.”

The lunar shadow moves at more than 1,000 miles per hour across Earth’s face during an eclipse, Nichols says, which is why any given location experiences totality—the moment the moon completely blocks the sun—for only a few minutes. During the 2024 eclipse, the longest duration of totality will be four minutes and 28 seconds near Torreón, Mexico, EarthSky.

Solar eclipses have different paths depending on which side the Earth is facing when the moon passes in front of it. However, there are patterns to these paths. Known as saros cycles, these patterns are determined by the path of the moon’s orbit around Earth and its distance from our planet at the time of an eclipse, Nichols says. Every 18 years and 11 day, these patterns produce eclipse paths that repeat themselves (albeit in different locations). Every eclipse, no matter its exact path, travels from west towards east.

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