Planning the perfect party is all about finding the right chemistry.

Or paleontology. Or physics.

Experiment with them all at the Pacific Science Center. Every weekend, the museum opens its doors to birthday boys and girls by hosting parties with scientific themes (sunshine, dinosaurs, the planets, butterflies, weird science).

Hands-on demonstrations let your crew go one on one with the Van de Graaff generator (that lifts hair into the air) and discover how quickly liquid nitrogen turns milk into ice cream (twenty minutes). Plus, the museum takes care of the decorations, cake, and goodie bags — all of which are coordinated to match your theme.

In other words, they’ve got it down to a science.

Pacific Science Center, 200 Second Avenue North (206-443-2001 or pacsci.org).

LEARN
Super Salmon Sleuths
What: The program for preschoolers has a hatchery tour, slide show, salmon crafts, and stories.
Why: Something’s fishy.
When: Today, 9:30 a.m.
Where: Issaquah Salmon Hatchery, Watershed Science Center, 125 W. Sunset Way, Issaquah (425-392-8025).

REVEL
St. Patrick’s Day Parade
What: Join the floats and happy marchers to help kick-off the Irish Fest.
Why: We all need a little luck.
When: Sat., 12:20 p.m.
Where: Fourth Ave., from Jefferson St. to Westlake Park.

RIDE
Seattle International Bicycle Expo
What: Kids’ bike zone, cyclocross clinic, treasure hunt, crafts, and carnival games.
Why: It’s enough to make you pop a wheelie.
When: Sat., 9 a.m.-6 p.m.; Sun., 10 a.m.-4 p.m.
Where: Warren G. Magnuson Park, 7400 Sand Point Way NE, hangar 30 (206-522-3222).