For the fourth year, the Cambridge Science Festival is returning with a nine-day run, kicking off in spectacular fashion at noon on April 24 with a carnival featuring over 80 booths and demonstrations outside the city's main library at 449 Broadway and a laser show commemorating the 50th anniversary of the invention of the laser.

The festival is the first of its kind in the nation, now being followed in places such as New York, Philadelphia and San Diego, with more than 30,000 visitors last year and this year slated to have over 200 events in 30 different locations around the city, almost all of them free.

Like the Red Sox? There will be a program on the science of baseball (and the science of cheese for gourmets). Like Music? Among the artistic presentations, the North Cambridge Family Opera will perform "Looking Up," celebrating the 400th anniversary of Galileo's observation of the moons of Jupiter. Want to meet a Nobel laureate? You can, during weekday brown bag luncheons at the MIT Museum.

In addition, there will be science fairs at the city's public schools, treasure hunts, a chance to meet the producers of the popular WGBH science program NOVA,
a "technology night" when companies at the Cambridge Innovation Center in Kendall Square will open their doors to visitors, a trivia challenge and much more.

The science festival is a collaboration of MIT, the city of Cambridge, Harvard University and the Museum of Science and underwritten through donations from a number of corporate and non-profit organizations.

For more information and a complete schedule of events (brochures are available at the MIT museum, located at 265 Massachusetts Ave., and the Cambridge main library) go to: www.cambridgesciencefestival.org.