Registration is now open for two Saturday-morning sessions of Science on Saturday, on April 28 at MIT’s Lincoln Laboratory (244 Wood Street in Lexington).   The topic will be The Science of Sight and Color, presented by Lincoln Laboratory’s Women’s Network. All children (5-17 years) must be escorted by an adult, and every adult must be escorted by a child or children.  Children under 5 are not admitted.  Admission is free but each person attending must be registered.  Space is limited, so register online soon for either Session 1 (9AM to 10:30AM) or Session 2: 10:45AM to 12:15PM). Register an adult first, then a child, then others. Adults must bring government photo identification.  See other rules on the registration pages. Due to construction, this event will be held in the cafeteria, accessed via the garage stairs instead of the main lobby.

The Newton Free Library will host the following STEM event(s) in April (not including the Girls Who Code club or the Crazy 8s Math club, for which registration has ended). For each, space is limited, and you should pick up tickets 15 minutes beforehand at the Children’s Desk.

• April 5:  Scratch Club, 7-8PM, Grades 3-4.
• April 19:  Rockets: There and Back Again, 3-4PM and 4-5PM, Ages 5+ (under 10 must be with an adult).
• April 28:  Solve a Mystery Like a Doctor, 10:30-11:30AM, Grades 2-5.

Boston Tech Mom (“a parent’s guide to raising a future techie”) is a great resource for all things STEM around Boston — including her monthly posts about free or low-cost STEM Events for Kids in Boston. Here’s her April list of STEM events.

Newton’s land trust, the Newton Conservators, will lead the following nature walks, free and open to the public:

• The Hidden Life of Vernal Pools: Forest and Vernal Pool Exploration at Webster Woods: March 31 and April 1, 1PM. Meet rain or shine at end of Warren Street, on the western edge of Webster Conservation Area.
• A Walk Around Hammond Pond and Nearby Plant Communities: April 21, 10:30AM. Meet at the Chestnut Hill Shopping Center parking lot at Hammond Pond by the informational kiosk. Canceled if raining at 9:30AM.

Framingham State University’s Christa McAuliffe Center will hold its fourth annual Science on State Street festival on April 21, 10AM-3PM, in the parking lot of FSU’s O’Connor Hall (map).  It’s free and open to all ages, with hands-on activities (in biology, chemistry, physics, food science, robotics and engineering), presentations by FSU faculty and invited scientists, conversations and performances that explore the interaction between science and the arts, over 30 exhibiting organizations, and planetarium programs. The keynote event, Exploring Mars’ Past, will be at noon. For more information, see these FAQs or email cmc@framingham.edu.

The Newton Free Library will host the Urban Search and Rescue Robotics Challenge on Thursday, March 22, 4-8PM. It’s a robotics challenge for Grades 11-12 presented by the Massachusetts Army National Guard and is based on real-life scenarios involving search-and-rescue robots. The event challenges competitors to engineer a robot that can navigate a unique obstacle course to locate and remove an object within a specified time, using heavy-duty, aircraft-grade aluminum elements, powerful drive motors, and wireless cameras. Online registration is required.

Besides the Museum of Science’s Pi Party on Boston’s City Hall Plaza, Boston will celebrate March 14 (3.14) with these other events:

• Museum of Science Sunrise Yoga: Pi Day Kickoff, 6-8AM at Museum of Science (for donation in the range of $31.41 to $314.15…)
• WPI Boston Seaport Open House, 11:30AM-1:30PM or 4:30-6:30PM at WPI Seaport, 303 Congress St, Boston (free)
• Pi Day Taste Test, 3-5PM, at Brookline Public Library (s0ld out)
• Pi Day with Boston Cream Pie, 4:30-6PM at Brookline Public Library (free)
• Pi Day sPIrographs, 5:30-7PM at Fab@CIC (free)

The LigerBots, Newton’s dual-high-school robotics team, has completed its six-week design-and-build season to create Chronos, the robot it will use in FIRST Power Up competitions. (See video introduction of Chronos here.) You can see Chronos and the LigerBots in action at the North Shore District Event, March 16-18 at Reading Memorial HS (62 Oakland Rd., Reading) or the Greater Boston District Event on April 6-8 at Revere HS (101 School St., Revere). Most of the action for public viewing will be on the last day of each event.

The Christa McAuliffe Center at Framingham State University opens its planetarium for free public presentations on the third Friday of each month (except April).  The presentation on March 16 will be Habitat Earth, full-dome film about the interconnected ecosystem of our planet and a live tour of the night sky. Registration is strongly recommended, and a few seats remain for both the 5:30 show and the 6:30 show.