Week 08 · How Big: Sizes and Properties

Friday

Where the numbers come from

// Reading the planets as a data table

⏱ about 20 min

Friday: Where the Numbers Come From

Rocket taps the fact sheet. "Who measured Saturn's rings? Nobody has stood on Saturn."

"Three kinds of eyes," Raven says. "Telescopes on the ground. Telescopes in space. And spacecraft that go there."

"What do you notice about stars at night?" she adds. "They twinkle." Rocket nods. "Air wobbles the light."

Nova rises a little. "A telescope above the air sees steady light," she says. "And a spacecraft needs no telescope at all."

"It just looks out the window," Rocket says. "Or lands and picks up a rock."

Raven writes three columns in her Sky Log. "Ground, space, spacecraft. Each one adds to the table." Nova glows. "Review time."

Telescopes on the ground

NASA says Jupiter's four largest moons were first observed by Galileo Galilei in 1610, using an early version of the telescope.

Ground telescopes gather light and show distant objects larger and brighter. Much of what we know began with them.

But NASA explains a limit. Shifting pockets of air in Earth's atmosphere make stars twinkle, and that motion blurs pictures taken from the ground.

Telescopes in space

NASA placed the Hubble Space Telescope in orbit above the atmosphere to avoid that blur. It has orbited about 483 kilometers up since 1990.

Above the air, it sees steady light and sharper detail. It also sees some ultraviolet and infrared light that the atmosphere blocks.

NASA says Hubble charts changes in the atmospheres of the outer planets in our solar system.

Spacecraft that go there

OpenStax Astronomy says spacecraft have flown past, orbited or landed on every planet, returning images and data.

Probes have entered Jupiter's atmosphere and landed on Venus, Mars, our Moon, Saturn's moon Titan, several asteroids and a comet.

OpenStax adds that the most precise planet masses come from tracking how a planet's gravity bends the path of a passing spacecraft.

NASA says Jupiter's rings were discovered in 1979 by a passing spacecraft. They are dark and hard to see from Earth.

Tool	What it adds	A limit
Ground telescope	Moons, rings, surface markings seen from Earth	Air blurs the view
Space telescope	Sharper images; light the air blocks; changes in planet atmospheres	Still far from the planets
Spacecraft	Close images, landings, samples, precise masses	A long, slow trip

THREE KINDS OF EYES

Read the question.
Tap your answer.

Why do pictures from ground telescopes come out blurry?

Why was Hubble placed above the atmosphere?

How are the most precise planet masses measured?

Week review	True or false?
Jupiter is about 11 times wider than Earth.	?
The four inner planets are small and rocky with solid surfaces.	?
The giant planets have hard surfaces you could land on.	?
Venus is hotter than Mercury because its thick atmosphere keeps heat in.	?
Spacecraft have never visited the outer planets.	?

WHY THIS EXERCISEThese five ideas are the similarities and differences the standard asks you to find in solar system data.

OUR WEEK, IN ORDER

?We read six property rows on the NASA fact sheet.
?We sorted the planets into terrestrial and giant families.
?We learned how ground telescopes, space telescopes and spacecraft each add data.
?We compared the diameters of Earth, Jupiter and the Sun.
?We cut paper planets to scale and laid out a string Sun.

WHY THIS EXERCISEThe week moved from one number to two families to a whole table and its sources.

In what year did Galileo first observe Jupiter's four largest moons? Type the number.

WHY THIS EXERCISEThe planet table began with a small telescope on the ground more than 400 years ago.

Try it

On a clear evening with a grown-up, notice whether any bright point of light twinkles. That wobble is the air at work.
Write why a telescope above the air would not see that wobble.

Safety first

Night observation only with a grown-up, from the yard, a porch or a window. Never look at the Sun.

Draw three panels. First, a telescope on a hill with wavy air above it. Second, a telescope in orbit above the air. Third, a spacecraft beside a ringed planet.

Explain to a younger child why we send spacecraft when we already have telescopes.Which of the three tools would you most like to work with, and what would you measure?Next week turns to rocks and how they change. Write a guess about where a rock in your yard came from.

Strong week. Tomorrow is Sky Night: a Moon check and a size guessing game for the family.

Grown-up checked my answers

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