Tuesday, August 25, 2015

Welcome to the Fall 2015 Eclipse Season

Today is the beginning of SDO's Fall 2015 eclipse season. From today until September 17, 2015, the Earth will pass between SDO and the Sun once each day. SDO orbits at about the longitude of Boulder, Colorado, so the eclipse is at midnight solar time there. This corresponds to roughly 0700 UTC. Here is the first eclipse, right on schedule at 0710 UTC (1:10 a.m. MDT).

This picture shows the edge of the Earth against the Sun in AIA 193. You can see the edge of the Earth is rough, where the absorption of the Earth's atmosphere dims but does not block the light. This is different from the lunar transits, such as the one coming up on September 13, where the Moon's edge is very crisp. That transit occurs near the end of that day's eclipse and coincides with a solar eclipse in the far southern parts of the Earth.

Eclipse season is a result of our geosynchronous orbit. We don't like missing the Sun for up to 72 minutes each day. But the constant contact with SDO allows the high speed data downlink we use to bring the Sun to everyone.