On April 16, an M-class flare erupted on the limb of the sun, triggering a coronal mass ejection (CME). The CME - a magnetized bubble of superheated plasma - wasn't thrown in the direction of Earth, but toward Mars and Venus, both of which may experience a glancing blow according to Spaceweather.com.
Additional analysis by NASA's Space Weather Laboratory at Goddard Space Flight Center has shown that the CME will likely wash over the Mars Science Laboratory (currently en route to the Red Planet), the STEREO-B spacecraft and the Spitzer space telescope. (The Lab produced a nifty animation showing the predicted trajectory of the CME.)
We may be getting used to the headline-grabbing "X-class" solar flares as the sun continues to amp-up its activity toward solar maximum (predicted to occur in 2013), but there's nothing tame or "medium" about M-class flares.
As demonstrated in June 2011, an M2 flare triggered a stunning CME that caused a cascade of plasma to shroud the solar surface. Solar physicists were stunned, to put it mildly.
As shown in a series of photographs from NASA's Solar Dynamics Observatory (SDO) - pictured top and edited by our favorite SDO mascot, Camilla Corona - Monday's M1.7 flare and CME was another one for the photo album.
Before we continue, it's worth emphasizing the difference between a solar flare and CME.
Often, the two phenomena will be bundled into the one "solar flare" category, but this isn't entirely correct. Although flares and CMEs are both caused by magnetic eruptions deep inside the sun's atmosphere (or corona) and are associated with increased solar activity, they don't always occur at the same time. Flares can erupt without a resulting CME and vice versa. However, as this example shows, some magnetic instability caused an eruption, blasting extreme-ultraviolet electromagnetic radiation into space (a solar flare), followed quickly by the ejection of a huge bubble of plasma wrapped in magnetism (a CME).
As demonstrated in the SDO video below, shortly after the CME had been released from the sun, plasma was pulled back, following previously invisible magnetic field lines, raining down to the sun's chromosphere (the layer of the sun that separates the photosphere - the sun's "surface" - from the corona), generating little flashes of light as the blobs of plasma made impact.
So it goes to show, no matter how big or "medium" a solar eruption is, the result is often of stellar beauty. But when flares and CMEs are aimed at Earth, they can also be dangerous.
Image: A series of images from the April 16 eruption in the lower corona as seen by the SDO in extreme-ultraviolet light (171A). Credit: SDO/AIA edited by Camilla Corona SDO