November 12, 1998 transcript # 259-4
Subject(s): brainstorm, barometer
Title: Brainstorm Answer: Similar Triangles

Hi, I’m Dave Thurlow from the Mount Washington Observatory, and this is the Weather Notebook. On a recent Brainstorm I asked what weather instrument, among an anemometer, a barometer, or thermometer, could be used to measure the height of the Seattle Space Needle. Here’s one of our more creative suggestions

"This is Virginia Reed in Potsdam, New York and I listen to The Weather Notebook on WSLU. I believe that the instrument you’d use to measure the height of the Seattle Space Needle would be the barometer."

Yeah, that’s right—but how?

Virginia: "You could take it out, stand it up a distance from the building along the side where the shadow is and you can use the law of similar triangles…"

Hear that? The Law of Similar Triangles. Not bad.

Virginia: "…and figure out, knowing the height of the barometer and the length of the shadow, you could figure out the height of the building."

You see, if you stand up a three-foot tall mercury barometer—that’s about how tall they are—on a sunny day, it will, of course, cast a shadow. As will the Space Needle. Both of these vertical objects can make up one side of a triangle, with the other sides represented by the shadow along the ground, and the hypotenuse.

Now, if the shadows are measures at the same time, and you know the height of the barometer, then it’s only a little trigonometry between you and a successful measurement of the 605-foot Seattle Space Needle.

Now you can check out the details of this and all other listener suggestions at our website: weathernotebook.org. Weather Notebook music is composed and performed by George Brandl, and our engineer is Sean Doucette. Our show is underwritten by Subaru, with major support provided by the National Science Foundation.

Glossary description of Barometer