Science, Technology, and Society LET REVIEWER
General Education
Lesson 20: Planets
What is Astronomy?
Astronomy is the study of everything in the universe beyond Earth’s atmosphere. It includes planets, moons, stars, galaxies, and all other objects in space. Astronomers try to understand how these objects move, what they are made of, and how they formed.
- Astronomy is the science of outer space everything from our Sun and planets to faraway stars and galaxies.
Planetary
Motions - all planets in
our solar system move in orbits around the Sun.
These orbits are not perfect circles; they are elliptical, meaning
slightly oval-shaped.
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| Image from BYJU'S |
1. Revolution is the movement of a planet as
it travels around the Sun.
- All major planets revolve around
the Sun in the same direction.
- Direction keywords: revolves
eastward, from west to east, or counterclockwise when
viewed from above the Sun’s north pole.
- One revolution of
a planet around the Sun equals one year on that planet.
Revolution is
a planet going around the Sun along its orbit.
2. Rotation is the spinning of
a planet on its axis.
- Many planets rotate
eastward / from west to east / counterclockwise (same general
sense as their revolution).
- A complete rotation equals one
day on that planet.
- Exceptions: Venus and Uranus rotate
in unusual ways (they spin in a different direction or on a tilted axis).
Rotation is
a planet spinning like a top; revolution is a planet traveling around
the Sun.
Inner (Terrestrial) Planets
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| Image from Science | HowStuffWorks |
The inner
planets, also called terrestrial planets, are Mercury,
Venus, Earth, and Mars. They are small, rocky planets located closer
to the Sun.
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| Image from NBC News |
Mercury
- Closest planet to
the Sun.
- 1 revolution = 88 Earth days, so its year is very short.
- It is the fastest
orbiting planet because it is nearest to the Sun.
- Surface is covered with
craters and has almost no atmosphere.
Mercury races
around the Sun quickly, finishing its year in only 88 Earth days.
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| Image from NASA Science |
Venus
- Often called the “morning
star” or “evening star” because it is very
bright in our sky before sunrise or after sunset.
- The brightest planet in
our solar system as seen from Earth.
- Sometimes called Earth’s
“twin planet” because it is similar in size and mass.
- Has a thick atmosphere that
traps heat, making it the hottest planet.
- One of Earth’s closest
neighboring planets.
Venus looks
like a bright star in the sky and is Earth’s similar-sized neighbor, but it is
much hotter.
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| Image from NASA Science |
Earth
- Has one moon called Luna.
- The shape of Earth is an oblate
spheroid (slightly flattened at the poles and bulging at the
equator).
- Currently the only
known planet with life and liquid water on its surface.
- Has air, water, and a
protective atmosphere that makes life possible.
Earth is
our home planet, slightly squashed at the poles, with one moon and the
conditions needed for life.
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| Image from NASA Science |
Mars
- Known as the “Red
Planet” because of its reddish, iron-rich surface.
- Has two small moons: Phobos and Deimos.
- Has volcanoes, canyons, and
polar ice caps.
- Scientists are very interested
in Mars as a possible place where life might have existed.
Mars is
a cold, dusty red world with two tiny moons.
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| Image from Space |
Asteroid Belt
- The asteroid belt lies between
Mars and Jupiter.
- Contains many rocky objects
from grain-sized pieces up to objects hundreds of
kilometers in diameter.
- Asteroids are leftover
building blocks from the early solar system.
The asteroid
belt is a wide zone of rocks that orbits the Sun between Mars and Jupiter.
Outer (Jovian / Gas) Planets
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| Image from Science | HowStuffWorks |
The outer
planets are called gas giants or Jovian
planets: Jupiter, Saturn, Uranus, and Neptune. They are much
larger and mostly made of gases and ices.
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| Image from Britannica |
Jupiter
- Largest planet in our solar system.
- Has many moons (over
90 are known; different sources may show slightly different counts as new
moons are discovered).
- Four major moons are called
the Galilean moons: Io, Europa, Ganymede, and Callisto remembered
with the letters CIGE.
- These moons were discovered
by Galileo using one of the first telescopes.
- Jupiter has strong storms,
including the Great Red Spot.
Jupiter is
a giant planet with many moons; four large ones were first seen by Galileo.
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| Image from Lab Manager |
Saturn
- Famous as the ringed
planet.
- Has spectacular rings made
of ice, rocks, and dust.
- Has many moons (again, the
exact number changes as more are discovered; you may see counts like 82 or
more in different references).
- Saturn’s largest moon is Titan,
which has a thick atmosphere.
- The second largest
moon is Rhea.
Saturn is
known for its beautiful ring system and many moons, including big moons like
Titan and Rhea.
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| Image from BBC |
Uranus
- An ice giant with
a bluish color due to methane in its atmosphere.
- Rotates on a very tilted
axis, almost lying on its side.
- Has rings and many moons.
Uranus is
a blue-green planet that spins on its side because of its extreme tilt.
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| Image from Science Friday |
Neptune
- Another ice giant,
similar to Uranus, often called its twin.
- Appears deep blue and has
strong winds and storms.
- Has a system of rings and
moons.
Neptune is
Uranus’s cold, windy “twin” far out in the solar system.
Pluto
and Dwarf Planets
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| Image from Space |
Pluto
- Once considered the ninth
planet (1930–2006), now classified as a dwarf planet.
- Located in a region beyond
Neptune called the Kuiper Belt (part of the distant outer
solar system).
- Has five known moons: Charon,
Nix, Hydra, Kerberos, and Styx.
- Pluto was reclassified because
it lacks orbital dominance it does not clear other objects out
of its orbital path.
Pluto is
a small, icy world with five moons; it is now called a dwarf planet because it
shares its orbit with many other objects.
Memorize all the moons!
Planets Quiz: click here
