Tomorrow afternoon, Venus will be visible from Earth for several hours as it transits the Sun.
Venus' orbit differs from Earth's a mere 3.4 degrees, which is enough to usually keep the planet out of sight. The event is a once-in-a-lifetime event -- as the next transits are slated for December 2117, December 2125, June 2247 and June 2255.
According to NASA, the transit will begin around 6:04 p.m. Eastern, 5:04 p.m. Central, 4:05 p.m. Mountain, and 3:06 p.m. Pacific Time. Astronauts expect that over the course of several hours, Venus will be a small dot that will move slowly across the backdrop of the Sun.
(Note: To see Venus, astraunauts recommend using a pinhole-type camera or observing it through reflection. Even the Hubble space craft cannot point directly at the sun, so astronomers will use a telescope pointed at the moon, which will act as a mirror to capture reflected sunlight. The small amount of light that passes through that passes through Venus' atmosphere will be observed and documented in this way so that scientists can learn more about the planet's atmospheric makeup.)
If you'd rather skip staring at a mole on the Sun in 113 degrees, you can watch the whole thing live on NASA's website from the comfort of your air-conditioned environment. If you plan to take pictures, you can upload them to NASA's flickr page, and if you pack the car now, you might be able to watch the whole thing from the nearest viewing station at Mount Wilson in California.