Billions and billions are expected to participate. Bryan & Dave say,
The Carl Sagan Blog-A-Thon commemorates the 10th anniversary of Dr. Sagan's death (December 20): Link. In conjunction with the blog-a-thon, we created celebratingsagan.com as a place for people who don't have their own blogs, but would like to participate. Aside from testimonial we have received original art and songs from worldwide Sagan fans who range from students to professors and pilots to musicians.
Also: Novelist and screenwriter Nick Sagan is one of Carl Sagan's sons, and he has a blog: Link.
Update: Nick Sagan tells BoingBoing,
For more information on the subject, here's Cornell University's Chronicle Online on the blog-a-thon. Here's what I've said on my blog.
Nick is a grown-up now, but here's what he sounded like as a kid:
At age six, Nick Sagan's greeting, "Hello from the children of planet Earth," was recorded and placed aboard the NASA Voyager Interstellar Record. Launched with a selection of terrestrial greetings, sights, sounds and music, the Voyager I and Voyager II spacecraft have since left the solar system; they are now the most distant human-made objects in the universe.
Apart from being a great scientist and educator, Carl Sagan appears to have been the Coolest Dad Ever.