We had some time to kill today, so Tom Wolf and I made a little video to explain today’s launch postponement. Since making this video, we learned that launch is GO for tomorrow, so yay! My full post is below, but in the meantime…
I woke up this morning in my hotel to a beautiful, albeit cold, morning on Chincoteague Island, VA. I glanced at my email only to discover that today’s launch had been postponed. It wasn’t a problem with the Cygnus spacecraft, nor the Antares rocket, nor (thankfully) a new problem on board the International Space Station. Everything was perfect down here on earth.
But in space, the weather was absolutely horrible. Here’s why:

Holy mother of all sunspots, Batman, those are HUGE! To give you an idea of just how large we’re talking about, let’s make a little comparison for scale:

Those sunspots are the reason for today’s postponement. Sunspots are regions of angelic magnetic instability on the “surface” of the Sun. They mark the locations of magnetic field lines that rupture, unleashing a storm of charged particles into space at speeds of up to 2 million miles per hour. Those particles strike Earth’s magnetic field, giving us aurorae at the north and south poles:

Unfortunately, that means a lot more radiation in the near-Earth environment, and this poses a problem for launch. The Cygnus spacecraft is “hardened” against radiation, but the Antares rocket isn’t, and the launch team were concerned that it might play havoc with the rocket’s avionics, hence the postponement.
Damn the protons, full speed ahead!
This afternoon, the launch team met to review the data and have decided to go ahead with tomorrow’s launch! Launch is set for 1:07pm EST.
That’s a good thing, because the astronauts are still waiting for their Christmas presents.