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Question: Why were the Apollo astronauts quarantined after they got back?

Answer: Let's say you're the person in charge of the moon program. (This is a "hypothetical" situation. We fully understand that in real life you were merely in charge of the Apollo guidance systems.) You have to make an important decision. What do you do with the astronauts when they get back?You know that, of all the dangers of the mission, the least and most far-fetched is that the astronauts might be exposed to, and bring back to Earth, a killer bacterium or virus. You know the moon has no atmosphere, no water, no sign of anything biological, and that the surface temperature of any given spot varies by hundreds of degrees from day to night. You are convinced the moon is sterile.

On the other hand, you know that it would be bad for your career if the astronauts came back infected by a Lunar Death Microbe that eventually wiped out life on Earth.

Your decision? Right. Quarantine. (Though you are tempted to let the astronauts shake hands first with President Nixon.)

"In retrospect we really didn't have to do this," says Richard S. Johnston, the former director of NASA's Lunar Receiving Lab where the Apollo 11 astronauts were sealed for 21 days. "Let's not go into the dollars. Tens of millions."

The astronauts were inside their spacesuits when they were plucked out of the ocean by the crew of an aircraft carrier. They were immediately placed in a pod called the Mobile Quarantine Facility. That was flown by plane to Houston and transferred on a flatbed truck to the Lunar Receiving Lab. The MQF had a portal that could be tightly sealed against the LRL (that's just FYI). The astronauts then went inside, where a staff of doctors, scientists, cooks and other NASA employees joined them in quarantine.

Another part of the lab was reserved for moon rocks. The rocks were kept in a vacuum and handled with special pressurized gloves. When one of the gloves came off, an alarm went off, the lab was evacuated and the "contaminated" worker and anyone else standing nearby were quarantined.

Lunar dust, meanwhile, was closely scrutinized and even injected into lab mice.

Hardly anyone at NASA actually thought there might be moon microbes, says Johnston, but people in the agriculture industry, as well as some university professors and disease specialists, said, "Something might be there and we might endanger the whole world."

The idea for this elaborate procedure came from a government panel, formed in 1963, called the Interagency Committee For Back Contamination. (That's right: as though people might get infections of the shoulder blades.)

"There are some really intelligent people who get off on some very deep ends," Johnston says.

It goes without saying that there wasn't any "back contamination" from the moon.

Though maybe the symptoms don't show up for 25 years.

Question: Why do meteorologists predict how many inches of snow will fall but never how many inches of rain?

Answer: Snow is forecast in inches, rain in percentage probabilities. This is because the two forms of precipitation usually come from completely different types of weather systems. For the sake of simplicity, and easy memorizing, let's just say that snow usually comes from stratiform precipitation and rain from convective precipitation.

Well, OK, so maybe that's hard to remember. How about this: Snow is wide. Rain is tall.

You see, in the winter, you have vast masses of air moving across the continent and driving the weather. Typically, there will be a relatively thin layer of warmer air moving across an area of cold air near the ground. Snow falls in a broad and fairly regular pattern across many hundreds of miles.

Rain usually comes from thunderstorms, which are localized and sometimes short-lived. They're vertical more than horizontal. They can boil up out of nowhere in a matter of hours. A thunderstorm is basically warm air rising up in a column. It's an air elevator. The air then cools and the moisture condenses and falls as rain. You might get 4 inches of rain in one county and nary a drop in the next.

You can see rain coming at you, yard by yard. You never see snow coming at you. (Almost never: There are thundersnows. A thunderstorm in spring will sometimes drop a load of snow.)

A thunderstorm "is simply too dynamic an entity and too small to allow for an accurate estimation of rainfall at a given point," says Patrick Michaels, the state climatologist for Virginia.

There's another factor: How many inches it rains doesn't really matter. But the amount of snow is crucial. For example, in Washington, anything more than about half an inch of snow will incite the government to announce a "liberal leave policy," which means workers don't have to show up. (So long as they're liberal, of course.)