The transit of Venus, which occurs when the planet's orbit brings it between Earth and the sun, takes place roughly twice a century.
Skywatchers across the world, including Antarctica, will be able to see all or part of the transit using a telescope with solar filters.
During the pass -- one of the rarest astronomical events -- Venus appears as a small, dark round spot moving across the face of the sun.
The marathon event, which will last nearly seven hours, last occurred on June 8, 2004 -- and won't come again until 2117.
The Venus show will begin around 6 p.m. EDT and end at roughly 12:50 a.m. EDT for skywatchers in the United States.
Even astronauts aboard the International Space Station are joining in.
I've been planning this for a while, space station flight engineer Don Pettit said in a NASA interview. I knew the transit of Venus would occur during my rotation, so I brought a solar filter with me.
As in a solar eclipse, do not look directly at the sun.
Video streaming by Ustream But there are plenty of opportunities to watch the event online. NASA's EDGE program is featuring a live feed from the top of Mauna Kea in Hawaii, starting at 5:45 p.m. PDT.
The NASA page also links to other live feeds around the world.