What Is a Shadow?

Luz woke up on Saturday morning with a very important question stuck in her brain.

It had gotten stuck there the night before, right when Papá turned off her bedroom light. One second, her shadow was on the wall — big and wiggly, waving when she waved. The next second... click... it was gone.

"Where did it go?" Luz whispered into the dark.

She couldn't sleep for a long time after that.

But now it was morning, and the sun was pouring through her window like warm honey, and there it was again — her shadow — stretched out long and skinny on the bedroom floor.

"There you are," said Luz. She wiggled her fingers. The shadow wiggled its fingers back. She jumped. It jumped. She stuck out her tongue, but she couldn't really tell if the shadow stuck out its tongue too, because shadow-tongues are very hard to see.

Luz grabbed the little notebook she used for important investigations. So far, the notebook had entries like:

How many raisins fit in my nose? (Answer: 2, do NOT try 3)

Can fish hear me talking? (Still testing)

She opened to a fresh page and wrote in her very best handwriting:

INVESTIGATION: What Is a Shadow?

Theory: A shadow is a COPY of me that lives on the ground.

Luz drew a little picture of herself and a little picture of her shadow and connected them with a dotted line. Then she put on her rain boots — even though it wasn't raining, because they were her investigation boots — and marched outside.

The morning sun was low and golden, and Luz's shadow was enormous. It stretched all the way from her feet to the fence. She looked like a giant.

"Okay, Shadow," she said, putting her hands on her hips. Her shadow put its hands on its hips too. "If you're a copy of me, then you should be the same size as me. But you're not. You're way bigger."

She wrote in her notebook: Shadow is NOT the same size. Shadow is a GIANT right now. Very suspicious.

Luz decided to keep watching.

She ate breakfast on the back porch — a banana and two pieces of toast with strawberry jam. She tried to share with her shadow, but when she held out the banana, the shadow just held out a shadow-banana. "You already have your own," said Luz. "Never mind."

After breakfast, Luz rode her bike up and down the sidewalk. Her shadow rode alongside her, rippling over the grass and sliding up the neighbor's fence and stretching over a fire hydrant in a way that made it look all lumpy and weird.

She stopped and wrote: Shadow does NOT stay the same shape. It got all lumpy on the fire hydrant. I did NOT get lumpy. This is important.

By mid-morning, Luz was standing in the driveway, staring down. The sun was higher now, and her shadow had gotten shorter. Much shorter. It was almost right underneath her feet, like it was hiding.

"Hey!" said Luz. "You were huge this morning. Now you're tiny! What happened?"

The shadow did not answer, because shadows are not great conversationalists.

Luz's older brother, Marco, came outside bouncing a basketball. "Why are you yelling at the ground?"

"I'm not yelling at the ground. I'm yelling at my shadow. It keeps changing size."

Marco shrugged. "Shadows do that."

"But WHY do they do that? That's the whole point, Marco. That's the investigation."

Marco bounced his basketball three times and went back inside. He was not a lot of help.

At lunchtime, Luz sat under the big oak tree in the backyard to eat her sandwich. It was shady and cool, and when she looked down —

Her shadow was gone.

Luz gasped. She looked left. She looked right. She spun in a circle.

"Shadow? SHADOW!"

She ran out from under the tree into the sunny yard, and — whoosh — there it was again, right at her feet.

She ran back under the tree. Gone.

Out in the sun. There.

Under the tree. Gone.

Luz stood very still in the sunlight, breathing hard, thinking harder. She looked up at the sun, then quickly looked away because that was way too bright. She looked at the tree's shadow spread across the grass like a big dark blanket. She looked at her own shadow.

And then something clicked — like a little light turning on inside her head. Which was funny, because this was all about light turning off.

Luz opened her notebook.

The shadow is NOT a copy of me, she wrote slowly. The shadow is what happens when I BLOCK the light. I am in the way of the sun, and the ground behind me stays dark.

She drew a picture of the sun with lines coming down, and a stick figure of herself in the middle, and a dark shape behind the stick figure where the light couldn't reach.

Under the tree, the TREE is already blocking the light. So there is no extra dark spot for me. That is why my shadow disappears in the shade.

She tapped her pencil on the page.

In the morning, the sun is low, so I block a LONG stretch of light and my shadow is big. When the sun is high, I only block a little bit, so my shadow is small.

On the fire hydrant, the shadow looked lumpy because the dark part went OVER the lumpy shape. The shadow is not flat like a copy. It is just the light that is missing.

Luz sat back on her heels and read her notes again. She felt a fizzy, sparkly feeling in her chest — the kind she got when she finally found the last puzzle piece under the couch.

She ran inside. "Papá! Papá!"

Papá was washing dishes and listening to his music. "¿Qué pasó, mija?"

"I figured out what a shadow is! It's not a copy of me. It's the light that's MISSING. I block the sun, and wherever my body blocks it, the ground stays dark, and THAT'S the shadow!"

Papá turned off the water and looked at her with his eyebrows raised. "You figured that out by yourself?"

"I did experiments ALL DAY."

Papá dried his hands and knelt down to look at her notebook. He studied her drawings — the sun with the lines, the stick figure, the dark shape. He smiled a slow, warm smile.

"Luz," he said, "do you know what your name means?"

"It means light," said Luz. She'd known that since forever.

Papá tapped the drawing of the sun in her notebook. "A girl named Light figured out how shadows work. I think that makes perfect sense."

That night, Luz stood in her bedroom with the lamp on. Her shadow was on the wall again — big and wiggly. She waved at it. It waved back.

"You're not a copy of me," she told it. "You're just where I stop the light from going."

She moved closer to the lamp, and her shadow got HUGE. She moved further away, and it got smaller. She held up her hand and made a duck shape, and a shadow-duck appeared on the wall, quacking silently.

She made a rabbit. A dog. Something that was either a butterfly or a very confused spider.

Luz laughed.

Then Papá came in and said it was bedtime. He tucked her in, kissed her forehead, and turned off the light.

Click.

The shadow disappeared. And this time, Luz knew exactly where it went.

It didn't go anywhere. Without any light, everything was a shadow.

She smiled in the dark, pulled up her blanket, and opened her notebook to a fresh page — in her mind:

Next investigation: Where does the sun go at night?

But that one could wait until tomorrow.