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Earth and Space 6-8 / Week 06 / Sky Night
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Week 06 · A Disk of Dust and Gas

Sky Night

Sky Night: The family disk
// How a spinning cloud became a solar system
⏱ about 20 min

Sky Night: The Family Disk

The crew gathers at the Sky Deck window at dusk with a grown-up. Clouds hide most of the sky tonight.

"Backup plan," Rocket says, pulling out the big bowl and the sand. "The family gets to see the disk."

Raven sets the Moon log on the sill. "What do you notice? A gap in the clouds. There, the Moon is almost full."

Everyone sketches the shape quickly before the gap closes.

Then Rocket stirs the bowl, and a younger cousin watches the grains all swirl the same way. "Like the planets!"

Nova hovers above with her light on the water, never in anyone's eyes. "One spin, one direction," she says. "The family found the pattern."

  1. The solar system appears to have formed 4.6 billion years ago from a disk of dust and gas pulled together by gravity.
  2. As the cloud shrank it spun faster and flattened into a disk. The Sun formed at the hot center and took in more than 99 percent of the material.
  3. Because the planets formed in one spinning disk, they orbit the Sun in the same direction and in nearly one plane.
  4. Rocky planets formed near the hot Sun. Gas and ice giants formed farther out where it was cooler.
  5. The NASA fact sheet shows all eight planets within 7 degrees of Earth's orbit. Pluto, a dwarf planet, tilts 17.2 degrees.
  6. Asteroids and comets are leftovers that never joined a planet. They help scientists read the first page of the story.
◇ SKY NIGHT: MOON CHECK AND THE FAMILY DISK
With a grown-up, go to your usual Sky Deck spot after dark. If the sky is clear, find the Moon and sketch its shape with the date.
Indoors, set the clear bowl of water on a tray. Let a family member sprinkle the sand and stir.
Ask everyone to point which way the grains go. Then ask them to guess which way the planets go around the Sun.
Have someone turn slowly with arms out and then pull them in. Ask the family what the spinning cloud did.
Cloudy night backup: the bowl and the spin are the whole show. Sketch the Moon from your last clear night instead.
For a grown-up
Please go outside together. Use a flashlight for the path and point it at the ground, never at anyone's eyes.
Stay in a known spot in the yard, on the porch or at a window. No one crosses a road or climbs for a better view.
The bowl stays on a tray over a towel. Please wipe spills right away, and have everyone wash hands after touching sand.
Safety first
Night observation only with a grown-up, from the yard, a porch or a window.
Spin slowly in an open space and stop if dizzy. Sand stays away from eyes and mouths.
SKY NIGHT CHECK
  • Read the question.
  • Tap your answer.
Which way did the grains move in the stirred bowl?
What does that pattern explain about the real planets?
Draw the Moon as you saw it tonight, or as you expect it from your log. Beside it, draw the family bowl from above with arrows.

Well done, crew. Next week you walk out the distances between the planets, one step at a time.

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