Ask Marilyn

I was surprised when my face got sunburned when I went skiing recently. I wasn't on the slopes long, and I know the sun is at a much lower angle in the winter. How can this happen?

— S.G., Paso Robles, Calif.

Sunlight reflects strongly off snow, the way it reflects off sand at the beach. So in addition to the UV rays striking your face directly (from above), you're exposed to the rays that are redirected from below. Some people call this phenomenon "snowburn." And then there's the fact that the sun's UV rays are much stronger at higher altitudes, so mountain activities bring even greater risk. Skiing calls for heavy-duty sunblock.

Why are manhole covers round versus any other geometrical shape?

— James Arndt, Garden Grove, Calif.

It's time to clear up this longstanding misconception. The standard answer is, "A round shape is the only one that will prevent the cover from falling through the opening." This is not correct. A round cover will fall through a matching round opening no matter which way you turn it. This is not the case with other shapes. For example, a square cover will not fall through a matching square opening when simply rotated on a horizontal plane in any way where the corners don't match with the hole.

The correct answer is more complicated. A round manhole cover will not fall through a round opening only when the opening is made smaller than the cover. This is also the case for other geometric shapes, but the difference in the size of the cover and the size of the opening needs to be greater to prevent the cover from slipping through when it's rotated in various planes. So the round shape is more practical, assuming you want the cover shape and opening shape to be the same. (It's easy to make a square cover that won't it through a round hole.)

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