I’m retiring as director of Perkins Observatory on July 31. During the last three weeks in July, we have 13 programs scheduled. Most of them are for school-aged children attending outside day camps.

Each one is to me more precious than platinum. Of all the joys attendant to our public programs, the most sustained, week after week and year after year, are the question and answer periods, especially the ones for children.

Boys tend to ask fact-based questions, and they are the most difficult to answer. The difficulty lies not in my ignorance. If I really don’t know, I can always look up the answer on the computerized star map I have projected on the screen.

The problem is that astronomical numbers are, well, astronomical. Our brains evolved to understand the world on a human scale of single and double digits. They are not designed to understand thousands, let alone millions and billions.

And so I make comparisons to illustrate sizes and distances. How big is Jupiter? “89,000 miles wide.” Quizzical expression. “Earth is only 8,000 miles wide.” More quizzical expression, but we’re getting there. “You could fit 482 Earths inside of Jupiter.” Light is beginning to dawn. ”If Earth at 8,000 miles wide were the size of this pinhead, Jupiter would be the size of this walnut. Revelation! It pays to have pinheads and walnuts handy, just in case.

The inevitable follow-up question is, “How many Earth’s will fit into the sun?” That one I have memorized: “1.3 million very crispy Earths.” That number is, of course, totally meaningless to the boy and, quite frankly, to me. So I grab my pin and a volleyball I keep handy and say, “Remember, Earth is the size of this pinhead. The sun would be the size of this volleyball.”

If I’m lucky, a given child is satisfied at that point. Occasionally, other quantity-based questions will open. How many Earths will fit into Neptune? How many Neptunes will fit into Jupiter? As I hem and haw, trying desperately to remember the formula for the volume of a sphere, I find myself instead remembering the sage advice my mother once gave me. “Take up plumbing as a career,” she said. “You’ll be paid well, and people are always happy when you arrive.”

Distance questions are just as difficult. “How far is it from the sun to the Earth?” someone asks. Many students know the answer already. They had it on some test. Now they are testing me. “About 93 million miles or 150 million kilometers for those of you who are into kilometers,” I reply. “But that number is so big that I don’t really know how far away the sun is.”

I can feel the respect draining away. Kids tend to think of answers to questions as numbers and facts, and I want their understanding to be far deeper than that.

So, I grab my trusty volleyball and pin and take them outside. We start at the sun and create a scale model. With the sun the size of a soccer ball, Earth is about 37 of my paces away.

We march off the distance, and I have them turn and face the now-tiny volleyball. I ask them to stretch out their arms all the way and put their little fingernails next to the volleyball. For most people, young or old, they match.

“Now put your little fingernail in the sky!” I say. “The sun is a million-mile wide hydrogen bomb, and yet it is no bigger in the sky than your pinky fingernail held at arm’s length. That’s how far away 93 million miles really is.”

If I’m lucky, a few of them will get it. When I see the look of revelation on their faces, I say, “Now you know, not just in your head, but in your heart, where it counts.”

When boys ask value-based questions, it is often about looking through a telescope. They ask, “What is your favorite planet?” I answer, “Earth is my favorite because it gave me life and a place to stand to look up at Saturn, my second favorite planet because of its weird rings.”

Boys will always ask about black holes because they think they are gateways to alternate universes. “They’re just big stars that died and became very dense, tiny stars that have so much gravity that even light cannot shine from their surface.”

“What would happen if I got sucked into a black hole?” (They always say, “sucked” as if a black hole’s gravity were some kind of cosmic vacuum cleaner.)

I say, “The gravity would tear you into tiny pieces (“subatomic particles” for the older kids), and you would become part of the black hole. Splatto. You’d be dead.”

This, of course, is not the trip to an alternative universe the kid was looking for, but he usually gets a kick out of the “splatto.” Besides, boys have a cavalier attitude toward death. I suspect that all those superhero movies have something to do with it. “Dead,” they often say, “Cool!”

Many questions are unanswerable. Some well-read child will always ask, “What is the largest star in the universe. He has read the answer on the internet and has memorized its catalog number: UY Scuti or (incorrectly) NML Cygni, depending on how old his source is.

He is always surprised when I say, “I dunno. We haven’t looked at all the stars in the universe.”

It’s important to realize that “UY Scuti” is just some catalog number to the questioner. At that stage in his life, he probably doesn’t even know the location of the constellation Scutum. Also, UY Scutum is very faint, even in a telescope, and visually indistinguishable from the stars around it.

If he is to remember the enormous volume of supergiant stars, he needs to associate the number with some kind of experience. Therefore, I say, “The largest star that you can see is probably Betelgeuse in the constellation Orion.” I show him the star on my computerized star map. “It’s so big that if we took the sun out of our solar system and put Betelgeuse in it, our Earth would no longer be orbiting around the star. It would be orbiting inside it. Big enough for you?” And it always is.

My favorite question, which is also the favorite of girls and boys alike is, “How many stars are there in the universe?”

The question is, of course, unanswerable with any level of exactness, but exactness is what most kids expect. So I pretend to try.

If they know what a galaxy is, I start by saying, Hmm. Well, let’s see … The number of stars in the average galaxy is, let’s say, 200 billion. That’s a two with eleven zeros after it. The last time I looked, astronomers estimate that there are about 2 trillion galaxies in the universe. That’s a two with 12 zeros. Two times two equals … “Four!” They yell. “Now we have to multiply the zeros. Did you know that to multiply the zeros, all you have to do is add the zeroes together, so that’s 23 zeros. How many stars are there in the universe? A four with 23 zeros after it, give or take a zero, and that’s a whole lot of stars. It’ll make your arm tired just writing the 23 zeros.”

Neither they nor I can imagine the meaning of a number that big, but at least a few of them will now know how to multiply zeros.

I must confess that I like the girls’ questions better. They generally want to know whether I believe in aliens or how it feels to look at the stars, or what I like most about working at Perkins Observatory. We’ll tackle those values-based questions next week.