We’ve all seen photos of Earth: the blue parts are water, the green and brown parts are land, and clouds show up as white swirls. What’s amazing is that NASA, America’s space agency, made a picture of Earth out of people’s photos of themselves. As the bottom half of this photo shows, it’s a collection of 36,000 tiny photos, all taken 5 years ago on Earth Day 2014, with each photo pasted on the spot where it was taken. People had either blue sky or white clouds above their heads, or dusty desert or green grass behind them. So each photo gives that place the right color! And since everyone took the photos during daylight, Earth gets to look sunny everywhere at once.
Wee ones: If all the photos are green, blue, white or brown, how many background colors does the giant selfie have?
Little kids: If you take your picture of yourself at 1:00 pm, and your friend takes a selfie 2 hours later, at what time does your friend take a selfie? Bonus: If you want to send in 20 selfies from your town, including yours, how many friends have to take selfies along with yours?
Big kids: The U.S. is about 3,000 miles wide, and has about 30 photos stretching across it. About how many miles of real land does each photo cover? Bonus: Earth is about 25,000 miles around at the equator. If each photo covers 100 miles, how many photos were needed to wrap around Earth?
Wee ones: 4 colors.
Little kids: 3:00 pm. Bonus: 19 friends.
Big kids: About 100 miles. Bonus: 250 photos.
Laura Bilodeau Overdeck is founder and president of Bedtime Math Foundation. Her goal is to make math as playful for kids as it was for her when she was a child. Her mom had Laura baking before she could walk, and her dad had her using power tools at a very unsafe age, measuring lengths, widths and angles in the process. Armed with this early love of numbers, Laura went on to get a BA in astrophysics from Princeton University, and an MBA from the Wharton School of Business; she continues to star-gaze today. Laura’s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.