Calendar: June 29-July 5

Today
MATH-MAGICAL
If equations make you queasy, this is the lecture for you. Tonight at the Boston Public Library, Edward Burger, a math professor from Williams College, will present a magic show full of illusions -- each of which can be unraveled with a simple mathematical concept. The show is geared for people of all ages who love, fear, or hate math. And it's great for a date, according to Burger. Audience members will leave with a new perspective on math and a free mathematical memento. "Magic with Mathematics: Is the Formula Faster than the Eye," Rabb Lecture Hall at the Boston Public Library, 700 Boylston St., Boston. Call 617-536-5400, ext. 2270, for more information. At 7:30 p.m. Free.

THE DARK SIDE
It's a small universe after all. Astronomers and physicists say that the stuff we can see -- stars, planets, people, even dust -- makes up a mere 4 percent of our universe. The most of the rest of what's out there is invisible, and is called "dark matter" or "dark energy" by the scientists who hunt for new ways to study it. Tonight, the PBS show, "Scientific American Frontiers," will take a look at the evolution of the unseen part of our universe -- from the Big Bang (or the "Infinite Taffy Pull," as host Alan Alda puts it) until the present. "The Dark Side of the Universe," WGBH-TV (Ch. 2), at 9 p.m.

Wednesday, June 30
KEEP COOL
Don't let the heat get you down. The summer brings increased risk of heat exposure, heat exhaustion and dehydration -- especially for the very young or old. Dehydration can cause mild headaches or may, in severe cases, become a life-threatening illness. The Woburn Senior Center teaches seniors and others how to play safe this summer. "Dehydration and Hot Weather Survival," Woburn Senior Center, 144 School St., Woburn. Call 781-937-7899 for more information. At 10:30 a.m. Free.

Thursday, July 1
SKY HIGH
Get into your harness! Cross narrow bridges suspended between treetops, 40-feet above the forest floor in Worcester's EcoTarium. Take one of the daily Eco-Expeditions to learn how forests keep the environment healthy by fighting air pollution; or look for owls, bats, hawks -- and, of course, bugs on an evening adventure. Learn what it means to be a treetop scientist by conducting your own experiments among the branches and leaves, or just come for the bird's-eye view. Tree Canopy Walks. "Sky-High Safari" and "Eco-Expeditions" offered most days, "Creatures of the Night" offered Wednesdays in July. Worcester Ecotarium, 222 Harrington Way, Worcester. Registration required. Call 508-929-2703. Ages 7 and up; $12 plus admission ($8 for adults, $6 for children, seniors and college students).

ALL WEEK
UNDER THE SEA
Before you go to the beach, see what it really means to explore the ocean. Starting this week, get a peek behind the scenes at the Woods Hole Oceanographic Institution. Daily, hourlong walking tours bring visitors out to the dock where scientists launch their marine explorations. Learn about work being done at the frontier of ocean science. Videos, a life-size model of the deep sea submersible, Alvin, and interactive exhibits help visitors imagine what life is like on the ocean floor. Woods Hole Oceanographic Institution, 93 Water St., Woods Hole (Falmouth). Parking is limited; call 1-800-526-8532 for the WHOOSH trolley schedule. Tours at 10:30 a.m. and 1:30 p.m. Monday through Friday. Reservations required; call 508-289-2252. Free.

Calendar was compiled by Globe correspondent Carolyn Johnson.Event notices may be sent to healthscience@globe.com.