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Ask Dr. Universe Physics
University Communications Network > Ask Dr. Universe > Academic Subjects > Physics

Why do glow-in-the-dark things light up when it’s dark? – Haygarth, 5, United Kingdom

Dear Haygarth,

I love glow-in-the-dark stickers. I leave them next to a sunny window for a little while. Then turn off the lights and watch them glow.

I asked my friend Hergen Eilers how those stickers work. He’s a physicist at Washington State University.

He told me that glow-in-the-dark things use a type of phosphorescence. That means they absorb energy—like light—and then glow. A material that can do that is called a phosphor.

Glowing in the dark works because of electrons.

Everything in the universe is made of atoms. That includes you, me, whatever you’re reading this note on—and glow-in-the-dark stickers.

All those … » More …

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What are protons made of? – Dean, 11, Utah

Dear Dean,

There’s a pencil lying on my desk right now. It’s not much to look at, but what if I could zoom way in and see the protons and other itty-bitty stuff inside it?

My friend Ryan Corbin told me it would be like looking at a bubbling soup of fundamental particles. He’s a quantum physicist at Washington State University.

He told me that protons—along with neutrons—form the nucleus in the middle of an atom.

“Atoms make up all the stuff that we see,” Corbin said. “An atom has neutrons and protons in its nucleus. Protons have a positive electric charge. Neutrons … » More …

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How many atoms are in a leaf? – Lily, 8, Georgia

Dear Lily,

I love thinking about things I can’t see with just my eyes. Like the atoms that make up everything.

I asked my friend Fred Gittes how to figure out the number of atoms in a leaf. He’s a physicist at Washington State University.

He showed me a worksheet he gives his students. It included a question exactly like yours!

“It’s a question I assign college students for fun,” Gittes said.

So, you’re in great company when you ponder big questions like this.

We decided to use stoichiometry to find the answer. That’s a kind of math that scientists do to understand chemical reactions.

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Dr. Universe: Why does the sky turn darker in winter? - Alex, 6, Cincinnati

Dear Alex,

As winter gets underway here in North America, you may notice we don’t feel the sun’s rays for quite as many hours as we did in fall and summer.

To find out why this happens, I talked with my friend Vivienne Baldassare, an astronomer at Washington State University.

She said the reason we get fewer hours of daylight in the winter has to do with how Earth rotates. As our planet goes around the sun, it is always rotating. This rotation is also why we have day and night.

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Dr. Universe: Can a shadow make a shadow? – Aven, 7, Palouse, WA

Dear Aven, When we look around our world, we can find all kinds of shadows. One way we can explore the answer to your shadow question is with a little experiment. My friend Anya Rasmussen, a physics professor at Washington State University, told me all about it. First, you will need to cast your shadow on a wall. Rasmussen reminded me shadows form when an object—such as your body— blocks light and keeps the rays from reaching a surface—like a wall. Read More ...

Dr. Universe: Why do we have seasons? -Bella, 9, North Carolina

Dear Bella,

It turns out seasons can be quite different depending on where you live. But no matter where you live, the reason for the seasons has to do with the way the Earth rotates.

To find out exactly why we have seasons, I talked to my friend Vivienne Baldassare, a physics and astronomy professor at Washington State University.

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Dr. Universe: What are shooting stars made of? – Erin, 11, Arkansas

If you are anything like me, you probably like watching for shooting stars in the night sky. A shooting star, or a meteor, is usually a small rock that falls into Earth’s atmosphere. When I went to visit my friend Michael Allen, a senior instructor of astronomy and physics at Washington State University, he told me a lot of shooting stars are no bigger than a pencil eraser. Read More ...