Posted by DrJeff on June 6th, 2009
Copyright 2009 | About this blog
“Daddy, how long would it take to drive around the Sun?”
So there we were on the Washington, DC, beltway heading for his elementary school. We were cruising at 60 mph—yes, on the beltway, I know!! (© Craig Ferguson, CBS). Jordi said, “daddy, how far has this car gone since you and mommy got it?” I looked down at the odometer and read 249,000 and some odd miles. Cool! The ’95 Camry was doing just fine. Besides getting close to the 250,000-mile mark, the space guy in me knew that the Earth’s circumference is about 24,900 miles. “Jordi! This car could just have gone around the entire planet Earth 10 times!” He wasn’t expecting that answer. He thought that was … way cool. Cars aren’t supposed to be able to go around an entire planet are they?
But before we get to the rest of the story, first a detour at a Jeffism—
Science Education is about conceptual understanding
at an emotional level.
The learning wasn’t about the 249,000 miles. It was about relating that distance to something familiar or concrete or impressive—which caused an emotional reaction
in … both of us. The trick is to build a bridge to the familiar. (Want more on this? Read my Power of Models page.)
Then the discussion really took off. “You know, it took mommy and daddy 14 YEARS to drive that far. We’re not on the road all day as part of our jobs, but we’re still driving 18,000 miles a year.” (For you cross-country U.S. drivers, that’s 7 New York to California trips a year.)
That’s when he hit me with the question. “Daddy, how long would it take to drive around the Sun?” “Uuugh, you mean drive along the path the Earth takes around the Sun?” “No daddy, if the Sun were a solid ball and we were driving on it, how long would it take to drive around it once?” I’m not kidding, that’s what my first grader asked. So I started figuring it out aloud so he could follow along, and even do the math with me.
The Sun is about 100 times the diameter of the Earth (actually 109, but 100 is a nice round number and close enough), so its circumference is about 100 times that of Earth. Our little-Camry-that-could made it 10 times around the Earth, which is only ONE TENTH THE WAY AROUND THE SUN. “Jordi, to drive around the Sun just once, we’d need to have ten Camrys, each with 249,000 miles on them. Or … drive this Camry for 140 years! He said woooaah! We got to school. He told his friends.
Isn’t science an adventure? So is life with Jordi. Hope you can share this with your kids.
Teachers and parents:
1. How long it takes for a trip is a good way to get a feel for a distance, as long as your audience is familiar with the vehicle you’re using, and they’ve got a good feel for its typical speed.
The magic equation: trip time = total distance / speed
A more concrete approach to this Driving with Jordi is to have your kids figure out how long it would take to drive the distance in a car at a speed of 60 mph (97 km/hr) IF YOU DRIVE NON-STOP.
So we also need: circumference = diameter x pi where pi = 3.14
equatorial diameter: 7,926 miles (12,756 km)
so circumference is: 24,888 miles (40,054 km)
time to drive around once at 60 mph (97 km/hr): 415 hours = 17.3 days
That’s living in your car—not stopping—for 17.3 days!
Sun diameter: 865,000 miles (1,392,000 km)
so circumference is: 2,716,000 (4,371,000 km)
time to drive around once at 60 mph (97 km/hr): 45,270 hours = 5.2 YEARS!
Now try the drive between Earth and the Moon:
average Earth-Moon distance: 238,900 miles (384,400 km)
time to drive at 60 mph (97 km/hr): 3,980 hours = 166 DAYS!
How long did it take the Apollo spacecraft?
Can’t finish without a drive to the Sun:
average Earth-Sun distance: 93,000,000 miles (149,600,000 km)
time to drive at 60 mph (97 km/hr): 1,550,000 hours = 64,580 days = 176 YEARS!!
2. If you want to use this Driving with Jordi to introduce your kids (and you) to the scale of the Solar System, you can download one of the many lessons we developed for the Voyage scale model Solar System in Washington, DC, and are now installing around the nation. This particular lesson allows you to lay out a one to 10-billion scale model Solar System in your local park. It includes the relative sizes of Sun, Earth, and Moon, and the distances between them—on the same scale.
Parents, here’s the family version of the lesson: Voyage! (PDF, 500 KB)
Teachers, here’s the lesson (written for grades 5-8): Voyage of Discovery (PDF, 870 KB). You might want to do the lesson Our Solar System (PDF, 900 KB) first, which develops a concrete understanding of what we mean by the Solar System.
I think you’ll be blown away.
Photo credit: Courtesy of SOHO/[instrument] consortium. SOHO is a project of international cooperation between ESA and NASA.
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