If you're a parent, your child has likely asked you a question that caught you off-guard. Whether it was about death or sex or why Grandpa smells funny, kids have a knack for making us think on our feet.

Then sometimes they ask more straight-forward questions that have a correct answer — we just don't know what it is. There's no shame in this, of course, but if you're like me, you want to look smart in front of your (know-it-all?) kids. You can Google answers, but you'll look way cooler having them at the ready on the tip of your tongue.

To that end, here are quick answers to nine common questions that kids ask. You may have to adjust to make the answers age-appropriate, and if you have a real smarty-pants on your hands, you may need to research beyond what's here. But study up, as there will be a quiz — from your kids.

1. Why is the sky blue?

Teddy-bear picnic A blue sky provides the perfect backdrop for a teddy-bear picnic. (Photo: Podlesnyak Nina/Shutterstock)

The light from the sun is made up of all colors of the rainbow, even if you can't see them in the sunlight. Light travels in waves; some waves, like red ones, are long and lazy. Other waves, like blue waves, are short and choppy. As NASA explains, all light travels in a straight line unless something gets in the way, and in that case the light either reflects it (like a mirror), bends it (like a prism) or scatters it. The latter is what happens when sunlight reaches the Earth's atmosphere. Blue is scattered more than other colors because it travels as smaller waves, and that's why we see the sky as blue.

2. Why do we need to sleep?

Child asleep in bed All animals need to sleep, and all parents need their kids to seriously just go to sleep already. (Photo: Ruslan Guzov/Shutterstock)

Ah yes, the age-old bedtime-delaying question. "I'm not tired. Why do I need to go to sleep anyway?" Because when you sleep, dear child, your brain does some serious work. Throughout the day, our brains take in an incredible amount of information, but that knowledge isn't automatically and permanently stored away in our minds. According to the National Sleep Foundation, while we sleep, our brain transfers the pieces of info from short-term memory to long-term memory in a process called "consolidation." This helps us retain information and perform better on memory tasks. In addition, our bodies need sleep to rest, repair and grow.

3. What are stars made of?

Future astronomer Future astronomer right here. (Photo: Khalchenko Alina/Shutterstock)

Stars are made of very hot gas (cue the giggles here), mostly hydrogen and helium. Stars shine by burning hydrogen into helium in their cores, according to the California Institute of Technology.

4. Where does water go when it goes down the drain?

Water down the drain If you're on a sewer system, this water is headed for a wastewater treatment plant via a series of pipes. (Photo: ML Harris/Shutterstock)

This one depends on whether you're connected to your town's sewer system or whether you have a septic tank. If you're on a sewer system, all the drains in your house are connected to one pipe that leads to the street, according to the city of Statesboro, Georgia. The pipe in the street collects the water from each house in your neighborhood and takes it a larger pipe that collects water from other streets. That process repeats with greater amounts of water flowing into larger pipes until it reaches a wastewater treatment plant, where it's treated, cleaned and put back into the environment.

If you have a septic tank, the water going down the drain goes into that, where most of the solids settle. Water goes into a leach field, or a group of pipes buried in the ground that have holes in the bottom from which the water seeps out and into the ground.

5. Why is Earth the only planet with life?

Child holding a snail Earth's temperature, atmosphere and liquid water make it possible for life — from tiny snails to tiny humans,to thrive here. (Photo: Purino/Shutterstock)

Hold on, sport. We don't know yet if that's true. Scientists have been trying to find life elsewhere in the universe for a long time, and they haven't so far.

As far as why Earth has life at all, this answer is courtesy of the University of California, Santa Barbara. Life as we know it can survive only where there's liquid water. Life also requires sun, moderate temperatures and certain chemical elements like carbon, oxygen and nitrogen. Besides Earth, no other planet has temperatures that are not too hot and not too cold, no other planet has liquid water (ice, but not water) and no other planet has the right mix of chemicals.

6. Why are there spots on the moon?

The moon Determining the age of the moon has proven to be a complicated endeavor. (Photo: SAENRIT KLINLUMDAUN/Shutterstock)

Spots or marks on the moon are one of two things: craters or maria. The moon has been hit thousands of times over its 4.5 billion-year existence by space debris, which left craters after the collisions,NASA says. Kids may be referring to craters if they ask about marks.

But they may also be referring to the dark spots on the moon, which are called maria — large volcanic plains that are made up basalt, similar in composition to the rocks found in Hawaii.

7. What are clouds made of?

Boy on a beach with clouds Nothing like a day at the beach to get a child's mind thinking about nature. (Photo: goodmoments/Shutterstock)

A cloud is a collection of tiny drops of water or ice crystals. The drops are so small that they can float on air. All air contains water, but most of the time you can't see it because the drops of water have turned into a gas called water vapor. As that vapor goes higher in the sky, the air gets cooler. The cooler air causes the water to stick to particles like dust, ice or sea salt. When billions of these particles come together, they form a cloud. (Scholastic has a great .pdf with cloud-related information and lessons for kids.)

8. Why do cows moo?

two cows Cows moo to talk to each other, and they even have regional accents. (Photo: thka/Shutterstock)

Why do chickens cluck? Why do lions roar? Why do people talk? Animals of all kinds make noises to communicate and express themselves. The languages and sounds we use to do this varies widely.

Cows moo to talk to other cows, like when they are scared or as a warning. (They even have regional dialects.) Calves moo to call their mothers and cows moo to attract a bull. Also, though in the U.S. we say that cows "moo," in France they "meuh" meuh" and in Thailand they "more-more" — an interesting tidbit that could segue into learning about other languages. (And if you want to know about more animal sounds in different languages, we've got plenty.)

9. Where do babies come from?

Baby asleep on its back without bedding This baby has it exactly right: asleep on the back, in his own bed, wearing warm clothes, but not using blankets, bedding or stuffed animals. (Photo: FamVeld/Shutterstock)

This one is all you, pal. Good luck.

What questions have your kids asked you where you had to look up the answer? Let us know in the comments section.

Angela Nelson ( @bostonangela ) is an exhausted mom of two young daughters and two old cats, and a Pulitzer Prize-winning digital editor with more than 15 years of experience delivering news and information to audiences worldwide.