Solar Dynamics Observatory catches lunar freeze frame

March 7, 2019 by Sarah Frazier, NASA's Goddard Space Flight Center
The relative speeds and positions of the Moon, the Sun and NASA's Solar Dynamics Observatory resulted in this unusual lunar transit where the Moon appears to pause and reverse course. Credit: NASA/Goddard/SDO

On the evening of March 6, 2019, the Moon started to transit the Sun, then doubled back and retraced its steps in the other direction—at least, that's what it looked like from the perspective of NASA's Solar Dynamics Observatory, or SDO, in orbit around Earth.

SDO sees lunar transits regularly, when the Moon passes in front of its view of the Sun. The Moon's unusual apparent behavior during this particular transit is a phenomenon similar to retrograde motion: When a celestial object appears to move backwards because of the way that different objects move at different speeds at different points in their orbits. In this case, the first part of the transit—when the Moon moves left to right—appears to be "reverse" motion. SDO overtakes the Moon, moving at about 1.9 miles per second perpendicular to the Sun-Earth line compared to the Moon's 0.6 miles per second, making the Moon appear to move in the opposite you would see if you were standing still on Earth.

The second part of the transit—when the Moon appears to pause and rewind—happens as SDO enters the dusk part of its orbit and begins moving away from the Moon, nearly parallel to the shadow it's casting through space. At that point, the Moon once again moves faster than SDO—when compared to the Sun-Earth line—overtaking it. So the spacecraft now sees it move in the other direction—the same direction that a stationary observer on Earth would see.

NASA's Solar Dynamics Observatory spotted a lunar transit just as it began the transition to the dusk phase of its orbit, leading to the Moon's apparent pause and change of direction during the transit. This animation (with orbits to scale) illustrates the movement of the Moon, its shadow and SDO. Credit: NASA/SDO

This isn't the first time that SDO has seen the Moon seem to move in two different directions during a lunar transit. This time, the Moon just happened to remain in SDO's sight as it began the dusk part of its , leading to the freeze-frame effect.

This lunar lasted about four hours, from 5 p.m. to 9:07 p.m. EST, and, at peak, the Moon covered 82 percent of the Sun's face. The Moon's edge appears sharp because the Moon has no atmosphere. 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.

Explore further: SDO spots two lunar transits in space

Related Stories

SDO spots two lunar transits in space

September 10, 2018

On Sept. 9, 2018, NASA's Solar Dynamics Observatory, SDO, saw two lunar transits as the Moon passed in front of the Sun. A transit happens when a celestial body passes between a larger body and an observer. This first lunar ...

Image: NASA's SDO spots a lunar transit

October 23, 2017

On Oct. 19, 2017, the Moon photobombed NASA's Solar Dynamics Observatory, or SDO, when it crossed the spacecraft's view of the Sun, treating us to these shadowy images. The lunar transit lasted about 45 minutes, between 3:41 ...

SDO witnesses a double eclipse (w/ video)

September 2, 2016

Early in the morning of Sept. 1, 2016, NASA's Solar Dynamics Observatory, or SDO, caught both Earth and the moon crossing in front of the sun. SDO keeps a constant eye on the sun, but during SDO's semiannual eclipse seasons, ...

Recommended for you

Physicists discover new class of pentaquarks

March 26, 2019

Tomasz Skwarnicki, professor of physics in the College of Arts and Sciences at Syracuse University, has uncovered new information about a class of particles called pentaquarks. His findings could lead to a new understanding ...

Study finds people who feed birds impact conservation

March 26, 2019

People in many parts of the world feed birds in their backyards, often due to a desire to help wildlife or to connect with nature. In the United States alone, over 57 million households in the feed backyard birds, spending ...

Matter waves and quantum splinters

March 25, 2019

Physicists in the United States, Austria and Brazil have shown that shaking ultracold Bose-Einstein condensates (BECs) can cause them to either divide into uniform segments or shatter into unpredictable splinters, depending ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.