Robert Krulwich

Here's a question you probably didn't know was a question: Why is the sky dark at night?

My daughter asked me this about 10 years ago. We were looking up at the night sky, and she said, "There's lots of stars up there." And I said, "Yes."

Look at this map, and notice that deep, deep in the Republican South, there's a thin blue band stretching from the Carolinas through Georgia, Alabama and Mississippi. These are the counties that went for Obama in the last election. A blue crescent in a sea of red.

This is how we do it.

This is how they do it.

You are 200 miles directly above the Martian surface — looking down. This image was taken by the Mars Reconnaissance Orbiter on Jan. 27, 2010. (The color was added later.) What do we see? Well, sand, mostly. As you scroll down, there's a ridge crossing through the image, then a plain, then dunes, but keep looking. You will notice, when you get to the dunes, there are little black flecks dotting the ridges, mostly on the sunny side, like sunbathing spiders sitting in rows. Can you see them?

There was a time — and it wasn't that long ago — when kids would leave home on a summer morning and roam free. "I knew kids who were pushed out the door at eight in the morning," writes Bill Bryson of his childhood in the 1950s, "and not allowed back until five unless they were on fire or actively bleeding." That's what kids did. They went out. Parents let them, and everybody did it. "If you stood on any corner with a bike — any corner anywhere — more than a hundred children, many of whom you had never seen before, would appear and ask you where you were going," Bryson writes.

Before we go slow, let's go fast, so fast you can't go any faster. That would be light in a vacuum, traveling at 670 million miles per hour ...

Light, of course, can slow down. When light passes through water, it loses speed. A diamond is an even better speed bump. It can slow a beam of light by 40 percent.

But moving on, you and I are going pretty fast right now, though we don't notice. The planet we're on is zipping around the sun at 66,000-plus miles per hour ...

So you're minding your own business when all of a sudden, a nuclear bomb goes off, there's a shock wave, fires all around, general destruction and you, having somehow survived, need a drink. What can you do? There is no running water, not where you are. But there is a convenience store. It's been crushed by the shock wave, but there are still bottles of beer, Coke and diet soda intact on the floor.

So you wonder: Can I grab one of those beers and gulp it down? Or is it too radioactive? And what about taste? If I drink it, will it taste OK?

Here's an old, old, question, but this time with a surprise twist. The question is — and I bet you asked it when you were 8 years old and sitting on a beach: Which are there more of — grains of sand on the Earth or stars in the sky?

Obviously, grains and stars can't be counted, not literally. But you can guestimate.

What we have here is a moon — a small one (slightly wider than the state of Arizona) — circling Saturn.

If you look closely, you will see a small splay of light at its top, looking like a circular fountain.

That's because it is a fountain — of sorts. A bunch of volcano-like jets are sending fantastically high geysers of water vapor up into the sky, so high that you can see them in this remarkable print by Michael Benson, back lit by light bouncing off of Saturn.

Check out this graph of America's "Growing Season" — it measures the number of continuous days and nights when it never gets below 32 degrees. You could call this our "frost-free" time of year. In many places, the frost-free season begins in the spring and ends somewhere in October.

As you can see, over the 20th century, it's been staying frost-free longer...and longer...and longer...

On July 18, 1969, President Nixon's speechwriter Bill Safire drafted a statement — a just-in-case statement. The manned mission to the Moon was only days away. The White House was preparing for all contingencies. According to Safire, the chances of getting Neil Armstrong and Buzz Aldrin onto the moon were pretty good.

Why Mark Peters and his friends Jeremy, Dave and William had a torpedo onboard their fishing boat, I don't know.

These four guys were looking for tuna 20 miles off Santa Cruz, and not doing too badly. In the first minute of this video, shot last week on Aug. 6, they catch a nice fish. Then they take the torpedo, which Mark built to carry a GoPro high-definition camera, drop it in the water, and something crazy happens.

This is one of those fun-to-think-about questions. A brain isn't much to look at, after all. It's about the size of your two fists put together, three pounds to hold, but oh my, what it can do.

With our brains, we can think backwards, imagine forwards, conjure, create things that don't exist, leap vast distances. For example, suppose I say to you, close your eyes and imagine this:

Updated July 18, 2012: We have added an update to this post, which you can find below the original. Click here to read about what happened to the men.

They weren't crazy. They weren't being punished. All but one volunteered to do this (which makes it all the more astonishing).

He was old, but not ancient, the man next to us at the delicatessen. It was 1973. My then girlfriend (now wife) and I had ordered dinner and this old guy, sitting by himself, seemed lonely, so we got talking and he told us how he had grown up in St. Petersburg, Russia, and that when he was a boy, his next-door neighbor was a famous man, a really famous man.