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WATCH: Optical Illusion Video Shows The Moon Yo-Yo Across The Sun

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NASA captured strange images of the moon moving back and forth across the surface of the sun. This event called retrograde motion also happens when outer planets that move slower into their orbits are observed from Earth.  ( NASA/SDO )

NASA's Solar Dynamics Observatory (SDO) captured strange images of the moon behaving like a yo-yo while crossing the sun's surface.

Astronomers said it is not a cosmological anomaly. Instead, it is an optical illusion that is observed when the moon moves at varying speeds.

Weird Moon

When the moon moves from left to right across the sun's surface, it is considered a normal phenomenon. The event observed on March 6, where the moon paused momentarily and then moved in a reverse direction, is unusual.

This event is called retrograde motion. It is atypical for the moon to exhibit this kind of behavior because it is locked in a consistent and unidirectional orbit around the Earth.

Astronomer Christopher Crockett demonstrated how retrograde motion can be observed like when someone passes through a car that drives in the opposite direction.

"As you pull alongside and pass it, however, from your vantage point the car appears to move backwards for just a moment," Crockett explained.

Planets like Mars or Jupiter that have slower orbital speed will also appear to move in a reverse direction when they are observed from SDO.

(Photo : NASA | Goddard | SDO)

Earth, The Center Of The Universe

At the time of the image capture, the SDO was traveling at approximately 1.9 miles per second as opposed to the moon's 0.6 miles per second. The event lasted for about four hours from 5 p.m. to 9:07 p.m. EST. Approximately 82 percent of the sun's face was covered during the peak of the moon's movement.

The moon appeared to have sharp edges due to the absence of atmosphere. The Earth's eclipses of the sun would have blurry edges because most of the sun's light is blocked by gases.

"On the other hand, Earth eclipses of the Sun have a blurry edge when seen by SDO, because the gases in Earth's atmosphere let through only part of the Sun's light," Sarah Frazier from the NASA's Goddard Space Flight Center said.

Retrograde phenomena convinced early astronomers that the Earth was the center of the universe. They also theorized that the planets may be circling around a moving point in their orbits aside from their rotation around the Earth.

It was only until scholars accepted heliocentrism that they found a viable explanation for the back-and-forth movement of the outer planets.

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