Lunar transit: SDO sees the Moon block the Sun.
The Moon Swings in Front of the Sun. Then the Sun Belches.
Bad Astronomy
The entire universe in blog form
Jan. 30 2014 12:34 PM

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/

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:

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.

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.

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

Photo by NASA/SDO/

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

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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