As you may have read, our home planet will have a close call tomorrow, February 15, with a 180,000-ton asteroid called 2012 DA14. There is no chance of a collision, but the space rock will come within 17,200 miles, closer than many of our communication satellites.
You can follow the approach of the asteroid tomorrow from several of the Southern Stars apps for iOS. You won't be able to see the asteroid with the naked eye -- that will take a pretty large telescope with computerized tracking to get it into the correct position -- but SkySafari Plus and SkySafari Pro will do the job on your iOS device.
The math it takes to display the space rock is tricky, so Southern Stars founder Tim DeBenedictis consulted with experts at JPL and added a solar system orbit integrator into the app. That means the app is not just displaying a canned animation of the fly-by, but actually computing the asteroid position in real time. I watched the asteroid in my version of SkySafari Pro. It's easy to find it in the sky by typing in its name, but the best views were from a few miles away from the asteroid where you can watch it approach the Earth and graze by.