Why the dog spins, and other things I said with total confidence

Thursday in August, 8:40 p.m., back porch. My nine-year-old pointed at a light sliding across the sky and asked what it was. I said "satellite" in the voice I save for things I'm sure about.

Then the six-year-old asked why it wasn't blinking. Then thunder rumbled somewhere west of us. Then the dog walked three slow circles and lay down on my foot, and both kids turned to me like I was the reference desk.

I have a deep, steady dad voice. It's done more damage to my children's education than any tablet ever has.

1. Why is the sky blue?

They think I know: Every color, every reason, probably invented a few.

What I actually know: "It reflects the ocean." I said this for years. My wife, who took physics, let me say it for years. That's love.

What you actually need to know: Sunlight hits air molecules, and those tiny molecules scatter short wavelengths (blue) much more than long ones (red). That's called Rayleigh scattering. The sky isn't violet, even though violet scatters more, because the sun puts out less violet and your eyes are less sensitive to it. Sunsets go orange because the light crosses more air and the blue gets scattered away before it reaches you.

2. How far away is that storm?

They think I know: To the mile.

What I actually know: I count like a launch commander, then announce a number that sounds about right.

What you actually need to know: Count the seconds from the flash to the thunder and divide by five. That's roughly the distance in miles, because sound covers a mile in about five seconds.

And this part isn't a joke. If you can hear thunder, you're close enough to be struck. Lightning can hit miles from the storm itself. Go inside a real building or a hard-topped car, and wait 30 minutes after the last thunder before going back out. The car is safe because of its metal shell, not its rubber tires.

3. Is that a star or a planet?

They think I know: The name of every light up there.

What I actually know: "That one's Mars." It's always Mars. I've called a passenger jet Mars.

What you actually need to know: Stars twinkle hard. Planets shine steadier, because they show up as tiny disks instead of single points. The brightest thing in the night sky after the moon is usually Venus, low in the west after sunset or low in the east before sunrise. Blinking red and green lights mean an airplane.

4. Which one's the North Star?

They think I know: "The brightest one." Obviously.

What I actually know: I pointed at the brightest one.

What you actually need to know: The North Star, Polaris, isn't the brightest star. That honor goes to Sirius. To find Polaris, locate the Big Dipper, take the two stars on the outer edge of the bowl, and follow the line they make about five times their own distance apart. You'll land on a moderately bright star sitting nearly still while everything else wheels around it. Face it and you're facing north.

5. Why does the moon follow the car?

They think I know: Something about gravity, said firmly.

What I actually know: I told my son it likes him best. He's still telling people.

What you actually need to know: The moon is about 239,000 miles away. Trees and mailboxes are close, so they rush past. The moon is so far off that a few miles of driving barely changes your angle to it, so it seems to hang in the window and keep pace. That's parallax, and you can demo it at the table: hold up a thumb, close one eye, then the other. Near things jump. Far things don't.

6. What does "40 percent chance of rain" mean?

They think I know: It'll rain 40 percent of the day.

What I actually know: I guessed that 40 percent of the town gets wet. Bring a jacket, maybe.

What you actually need to know: The National Weather Service defines it as the chance that any given spot in the forecast area gets at least a hundredth of an inch of rain during the forecast period. So a 40 percent forecast means your backyard has a 40 percent shot at measurable rain. It says nothing about how long it'll rain or how hard. Check the hourly forecast before you cancel the ball game.

7. Why does the dog spin before he lies down?

They think I know: Dog thoughts, fluently.

What I actually know: "He's winding up." Like a toy. I stand by the delivery, not the science.

What you actually need to know: Nobody knows for certain. The leading explanation is inherited instinct: flattening grass, checking the surroundings, settling in. A few circles is normal. If your dog suddenly circles far more than usual, struggles to lie down, or gets up and down restlessly, that can be a sign of pain like sore joints, and it's worth a call to your vet.

8. Can the dog have some of my chocolate?

They think I know: Yes, because I'm the fun one.

What I actually know: Nothing funny. This one I'm serious about.

What you actually need to know: No. Chocolate contains theobromine, which is toxic to dogs. Dark chocolate, baking chocolate and cocoa powder are the worst ounce for ounce. Also keep grapes and raisins, onions and garlic away from the dog, along with anything containing xylitol, a sweetener in some sugar-free gum and some peanut butters (check the label). If your dog eats something it shouldn't, call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435, which may charge a consultation fee. Don't try to make the dog vomit unless a vet tells you to.

9. How old is the dog in dog years?

They think I know: Multiply by seven. Every kid knows that.

What I actually know: I also multiplied by seven. Then I did it wrong in my head.

What you actually need to know: The times-seven rule is a myth. A common veterinary rule of thumb for a medium-sized dog: the first year is about 15 human years, the second adds about nine, and each year after adds roughly four or five. Big breeds age faster than small ones. Our four-year-old mutt is in his early thirties, which explains a lot about the couch.

The one I'm glad they asked

That light with no blinking? It wasn't a satellite in general. It was almost certainly the International Space Station, a steady white dot that crosses the sky in a few minutes. You usually see it around dusk or dawn, when it's still catching sunlight while you're standing in the dark.

So find it together, on purpose. Pull up NASA's Spot the Station site or app and get the next pass over your town. It gives the time, which direction it rises from, and how long it'll be visible. Most passes don't need a telescope or anything else. It's one of the best no-energy plans there's for nights when you've got nothing left.

Go out ten minutes early. Leave the phones inside once you've got the time, because a bright screen wrecks your night vision and your eyes need a good 20 minutes to adjust fully. A flashlight with red cellophane rubber-banded over it keeps you from tripping over the dog without ruining the view. If you need backup for that phone rule, these screen rules hold up.

When it shows up, let the kids spot it first. Then tell them the truth: there are people up there, right now, looking down at a planet with your porch on it.

Mine went quiet for a full minute. The dog spun three times and lay down on my foot.

I didn't explain that one. I've learned.