The Weight Of Sunlight |
 Dave Thurlow, Host |
It's a sunny spring day, and you're lying outside soaking up the rays. You're totally relaxed. You may not even realize that you're under pressure . . . from the sun. Hi, I'm Dave Thurlow from the Mount Washington Observatory and this is The Weather Notebook.
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Believe it or not, sunlight exerts a tiny but measurable pressure on humans and everything around us. We've all heard of air pressure, which is simply the weight of the atmosphere bearing down on us. The equivalent for sunlight is called radiation pressure. It's the impact of all those little photons banging against us, especially during the late spring and early summer when sunlight is at its peak concentration.
You won't feel much pain due to solar pressure, because it's a mere drop in the bucket compared to the 14.7 pounds per square inch of air pressure. Solar pressure is only 30 millionths of a pound, per square inch.
Where can you see the effects of solar radiation pressure? In space, on the tail end of a comet. As I'm sure you've seen, in pictures anyway, the tail on a comet always points away from the sun. That's because the force of solar pressure as tiny as it is, is still enough to push space dust and the like from the surface of the comet away from the sun.
So, back here on earth, where can you see or feel the effects of air pressure, billions of times more powerful than solar pressure? Think about it.
Thanks to contributing writer Bob Henson. The Weather Notebook is underwritten by Subaru and the National Science Foundation.