Bad Astronomy

The Moon Swings in Front of the Sun. Then the Sun Belches.

The Moon takes a bite out of the Sun.

Photo by NASA/SDO/Helioviewer.org

The clockwork motion of the heavens has brought us another treat: The dark silhouetted Moon sliding across the fiery disk of the Sun, as seen from NASA’s Solar Dynamics Observatory just hours ago:

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SDO orbits the Earth, staring at the Sun 24/7. Every now and again the geometry lines up such that the Moon appears to move in front of the Sun, creating what astronomers call a transit (on Earth we’d call these solar eclipses). They usually last for a half hour or so, but this one lasted 2.5 hours! The video shows the Sun using SDO’s far-ultraviolet filter (30.4 nanometers, for those geeks keeping tabs), and was taken on Jan. 30, 2014, from 13:15 to 16:15 UTC (08:15 to 11:15 Eastern U.S. time). Note that the Moon’s path is an arc; that’s due to the combined orbital motions of the Moon and SDO around the Earth.

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SDO orbit geometry
The geometry of the orbits of SDO, showing how it can see a lunar transit while we on Earth completely miss it. Click to explicate.

Drawing by Phil Plait, used by permission

And we get a bonus: At 16:11 UTC, a sunspot erupted in a moderately strong M6.6 flare! This blasted material off the surface of the Sun, creating a lovely (if terrifying) prominence of ionized gas flowing along the magnetic field lines of the star.

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solar flare
Just minutes after the transit finished, a moderate flare erupted from the left side of the Sun.

Photo by NASA/SDO/helioviewer.org

This probably won’t cause aurorae tonight, but it may bring minor radio interference. Check SpaceWeather.com and the NOAA’s Space Weather Prediction Center for current info.

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