On the morning of September 1, 2016, NASA witnessed something incredible. Through the use of their Solar Dynamics Observatory or SDO, NASA was able to catch 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, Earth briefly blocks SDO’s line of sight each day – a consequence of SDO’s geosynchronous orbit. However, on September 1, Earth completely eclipsed the sun from SDO’s perspective just as the moon began its journey across the sun.
In the SDO data, you can tell Earth and the moon’s shadows apart by their edges: Earth’s is fuzzy, while the moon’s is sharp and distinct. This is because Earth’s atmosphere absorbs some of the sun’s light, creating an ill-defined edge. On the other hand, the moon has no atmosphere, producing a crisp horizon.
The eclipse is known as the ring of fire, or annular, eclipse, which is quite similar to a total solar eclipse. However, the former takes place when the moon is at a point in its orbit farther from Earth than average.
