Sun, Earth, and Moon
A Spin around the Solar System
Name _______________________________________
A solar system
is a sun (which is
a star) and
everything within
reach of its
gravity. Our solar
system is a part of
the Milky Way
galaxy.
In the solar system, nothing stands still, not even
you. You and everything else on earth are traveling
up to one thousand miles per hour right now! That’s
how fast the planet’s surface is spinning at the
equator. Other planets, moons, and even the Sun
itself spin, too.
While they spin, they circle. The Moon circles
Earth. Earth circles the Sun, so do other planets,
their moons, and asteroids.
Sometimes, these spinning, circling, moving objects
crash into one another. Comets plunge into planets.
Asteroids smash into moons. Spinning, circling,
crashing…why don’t all these planets and moons
and asteroids just stay put? The answer is…gravity.
All objects pull other objects toward them. The
more mass (or matter) an object has, the stronger
its pull.
The Sun has 99.9 percent of all the matter in the
solar system; everything else makes up just 0.1 percent.
So the Sun is, by far, the most massive thing in the
neighborhood. Its pull is so strong that it can even
“grab” comets millions of miles away. The Sun’s gravity
holds this solar system together. In fact, the Sun’s
gravity is why we even have a solar system.
The Sun
A planet
is a star. A star is like a
nuclear power plant. It’s a
giant ball of super-hot gas
that produces heat, light,
and other kinds of energy.
Orbits, or moves
in a path around
a star. There
are eight known
planets in our
solar system.
Pluto has been
demoted to a
dwarf planet.
A moon, or satellite,
orbits a planet. It can be
less than a mile wide or
as big as a small planet.
Comets
are balls of ice, dust, rocks, and gas
just a few miles across. Most
comets in the solar system have
long, stretched-out orbits. When
they pass very close to the Sun,
some of the ice evaporates (turns
to gas). The streams of gas and
dust often form a bright tail. Haley’s
Comet shows up every 76 years; its
next visit will be in 2062.
A meteor
is an asteroid
that has
plunged into the
atmosphere.
Most meteors
break up and
burn.
Sometimes,
pieces of
meteors make it
through the
atmosphere and
land on Earth.
They then get a
new name:
meteorites.
An asteroid
is a mini-planet.
The largest on
record-Cereswould stretch
from Washington,
D.C. to Louisville,
Kentucky.
Smaller asteroids
would easily fit
inside a house.
Why is Earth like Baby Bear’s porridge?
Earth is the perfect distance from the sun,
so it’s not too hot and not too cold; it’s just right.
Earth is the only planet where we know there is life.
Earth’s atmosphere, or the blanket of air that surrounds a planet,
contains oxygen for us to breathe, protects us from the Sun’s heat, and
keeps our planet warm. We haven’t found plant or animal life on any other planet in the solar system.
What am I?
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I’m the reason Earth is called the Blue Planet.
You can’t live without me.
You can swim in me.
I make up two thirds of your body.
I cover more than 2/3 of Earth’s surface.
I’m water! And the reason the sky looks blue is because the atmosphere scatters incoming blue light much more strongly
than red, orange, yellow, or green light. The sky would be blue even without oceans.
MERCURY
VENUS
MARS
About 60 days to rotate
88 days to orbit the Sun
243 days to rotate
225 days to orbit the Sun
24 ½ hours to rotate
687 days to orbit the Sun
Mercury is the closest
planet to the Sun. So it’s
the hottest, right? Not so.
Venus is as hot, or hotter.
On the side facing the Sun,
Mercury is a screaming hot
800F. The dark side is a
frigid -300F! That makes
Mercury one of the colder
planets! The reason:
atmosphere. Venus has a
super-thick one to hold in
heat. Mercury hardly has an
atmosphere at all. So heat
escapes into space very
quickly.
How hot is Venus?
 Lead, tin, and zinc
would easily melt.
 Mercury (the metal)
would boil.
 The rocky crust is
mushy, like a warm
chocolate bar.
After Earth, Mars is the
most likely planet to
support life.
 Need balmy weather?
On a summer day, it’s
72F on the equator.
Too bad nights plunge
to -94F. The poles are
even colder!
 Need liquid water?
Water may have run all
over Mars long ago.
But only dry channels
are left.
 Need oxygen? Too bad.
The thin atmosphere is
mostly carbon dioxide.
Rocky planets are mostly core and mantle. They have a very, very thin crust and a very, very thin
atmosphere. Gas giants are mostly atmosphere with a very, very tiny core compared to their size.
Jupiter, Saturn, Uranus, and Neptune are big, swirling clouds of gas.
A cloudy atmosphere makes gas giants tough to get to know. It’s like studying an egg, but seeing
only the shell. Scientists can only guess what’s under all those clouds.
JUPITER 12 Earth years to orbit the Sun once
Why is Jupiter the king of planets? Jupiter is the largest planet and is heavier than all the other eight
planets put together. Jupiter is so big that more than 1,300 Earths could fit inside it! Could you stand
on Jupiter? No, because there’d be nothing to stand on, Jupiter’s gravity is more than twice as much
as Earth’s. That means you’d feel as if you had barbells attached to your hands and feet. Jupiter has
a cloudy atmosphere with raging storms and lightning. Its atmosphere is hydrogen (88%) and helium
(11%), two invisible gases. So why is Jupiter colorful: pink, yellow, blue, green, brown, white, red, and
more shades? The colors may be chemicals in the gases. Ammonia is white, for example. And the
Great Red Spot? Maybe red sulfur. Jupiter’s ferocious winds blow its thick clouds around, always
changing the way the planet appears. The winds also move Jupiter’s Great Red Spot, a huge storm
that’s almost three times the size of the Earth! It grows, shrinks, darkens, and lightens. But it just doesn’t
quit. Earthlings have watched the storm since 1655. Who knows how long it existed before then?
SATURN 29 ½ Earth years to orbit the Sun
Why does Saturn belong in a jewelry store? Because of all its beautiful rings! Jupiter, Uranus, and
Neptune have rings. But Saturn’s rings are the most stunning. They’re less than a mile thick. The rings’
sparkly bits of ice and metal chunks come in all sizes too: from the size of your thumb to the size of a
house.
URANUS 84 Earth years to orbit the Sun
How is Uranus like a carnival ride? Compared to the other planets, Uranus is lying on its side – so its
eleven rings go around the planet up and down, like a Ferris wheel. Some astronomers believe a
planet-sized object came and knocked Uranus onto its side long ago. Sometimes the poles (not the
equator) face the Sun. each pole gets 42 years of light and then 42 years of darkness. How did
Uranus make the solar system bigger? When Uranus was discovered, the solar system got twice as
big. That’s because Uranus is twice as far away from the Sun as its neighbor, Saturn. Uranus is so far
away that, even through a telescope, the icy planet looks like a tiny greenish-blue disk.
NEPTUNE 165 Earth years to orbit the Sun
What’s the weather report for Neptune? The forecast calls for storms, storms, and more storms, raging
into the next several days and possible into the coming weeks and months. Expect super cold winds
to whip around at more than 1,250 miles per hour. Hold on to your hats!
PLUTO 248 Earth years to orbit the Sun (Diameter 1,437 miles)
Why do you think Pluto is:
 Colder than all the other planets;
 Very hard to see, even with a telescope
 Dark all the time, even during the day;
 Downgraded as an official planet to a dwarf planet because it did not clear the area around its orbital
neighborhood.
Answer: because Pluto is so far away from the Sun. Once known as the smallest, coldest, and most distant planet from
the Sun, Pluto has a dual identity, not to mention being enshrouded in controversy since its discovery in 1930. Faraway
Pluto is named for the Roman god who ruled the dark and mysterious underworld.
Write true if the statement is true. Write false if it is not true
and then write the word to make it true.
1. Earth is the largest object in the solar system. ____
2. Earth’s crust is the thinnest layer. ____
3. Earth formed about 4.5 billion years ago. ____
4. Most of Earth’s land is in the Southern Hemisphere. ____
5. The Sun is one of hundreds stars in the Milky Way galaxy. ____
6. The greenhouse effect keeps Earth’s temperatures moderate. ____
7. The “changing shapes” of the moon are called phases. ____
8. It takes the Earth 24 hours to complete one revolution. ____
9. We have seasons because of Earth’s rotation. ____
10. We can see the entire lighted half of the Moon during a Full moon. ____
11. The Moon gets its light from Earth. ____
12. The blanket of gases that surrounds Earth is called the lithosphere. ____
13. The Earth’s gravity keeps all the planets orbiting the Sun. ____