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NOTE: LACK OF DATA UPDATES. SOHO went into "Emergency Sun Reacquisition" mode on Friday May 4, 2012, caused by a false trigger of the Coarse Sun Pointing Attitude Anomaly Dector. We are working on the recovery of the spacecraft to normal mode. Nominal science operations should be re-established in the next couple of days.
Anyway, I just think this is neat. Jupiter is roughly one-billionth as bright as the Sun, yet there it is in the picture! And even though SOHO is designed to look at the Sun, Jupiter is so bright it’s overexposed. Imagine if the spacecraft moved a bit and the Sun were to peek out from behind the occulter… which can happen. SOHO goes into "safe mode" when that happens, shutting down systems that might get damaged. Every astronomical satellite has contingency plans like that, since it’s hard to send a repair service to most of ‘em. Generally it’s fixable by sending software commands to the spacecraft once the underlying problem has been ascertained.
Coronal holes are the Old Faithfuls of the sun’s surface. Though solar flares produce good auroras, scientists’ only chance to predict their effects come in the three days between their occurrence and their arrival at Earth’s ionosphere. Coronal holes can exist for one year or more, and holes such as the one now affecting Earth’s magnetism tend to come back with every rotation of the sun. If the electrical circuit between Earth and sun is oriented in a favorable way for aurora production—as it has been during the life of this coronal hole—an aurora forecaster’s job becomes easier, and a bit more fun.