How to watch NASA's James Webb Space Telescope launch on Christmas Day

NASA and its international partners are counting down to a Christmas Day launch of the most expensive science probe ever built, a $10 billion telescope designed to capture starlight from the first galaxies born in the fiery crucible of the Big Bang.

Billions over budget and years behind schedule, the James Webb Space Telescope is targeted for blastoff from the European Space Agency's Kourou, French Guiana, launch site at 7:20 a.m. EST Saturday atop an Ariane 5 rocket, weather permitting.

Equipped with two solid-fuel strap-on boosters, the workhorse rocket will propel Webb away from the northeast coast of South America on an easterly trajectory, releasing the telescope to fly on its own about 27 minutes after liftoff.