On March 2, 2013, NASA’s Solar Dynamics Observatory (SDO) entered its semiannual eclipse season, a period of three weeks when Earth blocks the orbiting observatory’s view of the sun for a period of time each day. On March 11, though, SDO was treated to two transits across the sun’s face of two big objects: our Earth and moon. Earth blocked SDO’s view of the sun from about 2:15 to 3:45 a.m. EDT on March 2. Later in the same day, from around 7:30 to 8:45 a.m. EDT, the moon moved in front of the sun for a partial eclipse as seen by SDO.
When Earth blocks the sun as seen by the orbiting observatory, the boundaries of Earth’s shadow appear fuzzy. That’s because SDO can see some light from the sun coming through Earth’s atmosphere. The line of Earth appears almost straight, since Earth — from SDO’s point of view — is so large compared to the sun.
The eclipse of the caused by the moon looked very different to SDO. Since the moon doesn’t have an atmosphere, its curved shape can be seen clearly, and the line of its shadow is crisp and clean. Any spacecraft observing the sun from an orbit around Earth has to contend with such eclipses, but SDO’s orbit is designed to minimize them as much as possible, with only two three-week eclipse seasons each year. The 2013 spring eclipse season continues until March 26. The fall season will begin on September 2, 2013.
Bottom line: As seen by an observatory in space – NASA’s Solar Dynamics Observatory – two large objects passed in front of the sun on a single day, March 11, 2013. First, Earth passed in front of the sun as seen from the orbiting observatory. Then the moon passed in front of the sun, later that same day. Cool photos here.