Update, Oct. 28 at 23:30 UTC: Not much is known at this time, but there is video of the explosion, and I have links to more information in a new post.
Update, Oct. 28 at 22:30 UTC: The Antares rocket was launched on time today, but exploded a few seconds after takeoff. It’s not clear what happened - I have not seen a replay yet, but a lot of people on Twitter say they saw flames above the bottom of the rocket. This was an uncrewed flight; no humans were on board and so far there are no reports of injuries on the ground. I don’t know what this means for the astronauts on the ISS, but I’ll have more information as I get it.
Update, Oct. 28 at 01:30 UTC: The launch was scrubbed Monday night when a boat was seen in the ocean off the coast of Virginia under the rocket’s flight path. Another launch will be attempted Tuesday, Oct. 28, at 18:22 Eastern (22:22 UTC).
An Antares rocket sits on the launch pad in Virginia and is go for launch tonight at 6:45 p.m. Eastern time (22:45 UTC).
The rocket will boost a Cygnus spacecraft—named the SS Deke Slayton, after the original Mercury astronaut—filled with supplies for the astronauts on board the International Space Station. This is the third resupply mission for Orbital Sciences Corporation, which, along with SpaceX, is contracted by NASA to send rockets up to ISS.
And if you live on the East Coast, you might be able to see the launch for yourself! As it gets higher, it will be visible to more people on the ground, from South Carolina up to New Hampshire. Universe Today has the details, including a visibility map.
Correction, Oct. 27, 2014 at 18:50 UTC: I originally wrote that the launch was in Florida, not Virginia.