Friday

Rocket lies flat on the Sky Deck grass and stares up. "Gravity is holding me down right now," he says.

"It is holding the air down too," Raven says. "And pulling on the ocean. What do you notice when you think bigger?"

"The Moon orbits Earth. Earth orbits the Sun." Rocket pauses. "Does the Sun orbit anything?"

Nova rises a little higher. "The Sun is one star among hundreds of billions in the Milky Way," she says.

"And every one of them has mass," Raven says slowly. "So every one of them pulls."

Rocket sits up. "The whole galaxy is held together by gravity. Just like my marble in the bowl." Nova glows. "Now you are thinking in scale."

A NASA page lists what gravity does for us. We could not live on Earth without it.

The Sun's gravity keeps Earth in orbit at a comfortable distance for light and warmth.

Earth's gravity holds down our atmosphere, the air we need to breathe. It gives you weight and makes things fall.

The Moon's gravitational pull draws the seas toward it, causing the ocean tides.

Gravity even builds stars and planets by pulling together the material they are made from. You will see that next week.

The standards say Earth and its solar system are part of the Milky Way galaxy, one of many galaxies in the universe.

NASA describes the Milky Way as a spiral galaxy with a disk of stars more than 100,000 light-years across.

Earth sits along one of the spiral arms, about halfway from the center. Our solar system takes about 240 million years to orbit the Milky Way once.

OpenStax Astronomy says the Sun is one of hundreds of billions of stars in the Galaxy.

The Sun's pull joins with the pull of billions of other stars to make the gravity of the whole Milky Way. That pull holds the galaxy together.

Strong week. Tomorrow is Sky Night: a Moon check and a gravity game with your family.