It was the day of the winter science fair. Stella sat at a table with a jar of snow. There was a display with information about snowflakes behind her.
Her friend's mom came over to the table. "Hey, Stella. What's your project about?"
Stella smiled. "Hi, Mrs. Singer. I did some research on snow."
"That sounds interesting," Mrs. Singer said. "So, are you a snow expert now?"
Stella grinned. "I'm not sure yet. But I learned how snow forms."
By now a couple of other adults stood nearby.
"Let's hear about it," the man said.
"Okay," Stella said. "First the outdoor temperature must be 0 degrees Celsius or below. That freezes the water vapor in the air. The frozen vapor then attaches to specks of dust and pollen. When this happens, tiny ice crystals form. Like all crystals, these have flat sides and sharp corners.
"Some of the ice crystals stick together, forming clumps of crystals. They grow bigger and bigger. Eventually all these crystals fall to the ground as snow."
"Hmm." Mrs. Singer rubbed her chin. "So, snowflakes are just clumps of ice crystals that are stuck together?"
Stella nodded. "Some snowflakes have up to two hundred ice crystals."
"Whoa!" the woman said. "Can you tell us what makes the ice crystals fall out of the clouds?"
"Yes," Stella said. "But the ice crystals don't really fall out of the clouds. The ice crystals are the clouds. They are what clouds are made of. "
"Oh," the woman said.
"The bunches of ice crystals get heavy," Stella said. "That's when they fall to the ground as snow. It's the same thing with rain. Water vapor turns into water droplets. They join together. And when the droplets are heavy enough, they fall as rain."
Mrs. Singer pointed to the poster. "Tell us about those pretty snowflakes."
"Sure." Stella stood up so everyone could see the poster better. "My poster shows all the basic shapes of snowflakes. Some are shaped like stars, needles, or plates. Others have little branches. Most snowflakes have six sides or six points. But every snowflake is different. In fact, you'll probably never find two that are exactly the same."
"Huh," the man said. "Why are they all so different?"
"Because ice crystals stick together in lots of different ways," Stella said. "Other things affect their shape too—like the air's temperature and its moisture levels. When there's just a little moisture in the air, snowflakes are shaped like flat plates. They're shaped like stars when there's more moisture in the air."
"Very interesting!" the man said. "I never knew that."
"Oh!" Stella said suddenly. "I just remembered one other thing. You know how snow looks white? Well, that's only because of how light reflects off all the crystals. Snow is actually clear."
"Wow, Stella." Mrs. Singer smiled at her. "You are an expert on snow."
"I guess I am." Stella smiled too. "To me, snowflakes are amazing!"