Transcript Planets, Moons & Stars

Planets, Moons & Stars
Gr 9 Science
Composition:
Terrestrial = Made of rock,
minerals
Gaseous = Made of gases
Stars are always gaseous.
Moons are always terrestrial.
Distances & Sizes
Stars look small, but are
huge.
They are the largest … just
very far.
Moons look large, because
they’re close to a planet.
They’re smallest.
The planets are different
sizes, but are all in between
the size of moons & stars.
Source of light
Luminous = makes light
Reflective = reflects light
Stars are luminous, making light
through nuclear fission. Seen from
Earth, they ‘twinkle’.
All planets & moons are reflective.
Seen from Earth, they ‘glow’.
Phases
Phases = an effect resulting from how light strikes a moon.
Lunar phases = Earth’s shadow on the moon.
Venus also appears to have phases, when seen from Earth.
Because they are luminous, stars do not have phases.
Phases
Here is an illustration of moon phases over one month
Motion & Orbital Period
Rotation = spinning around an axis
Revolution = orbiting around a star.
Orbital Period = time for 1 revolution.
All three rotate, but only planets &
moons revolve or orbit.
The orbital period of a planet is called its year.
The orbital period of a moon is called its month.
Position
Planets seem to change position when
observed from Earth. This is because we are
seeing them from Earth, which is also moving.
It’s like runners racing on a track
They look to their side and see:
the inside runners ahead of them
the outside runners behind them
Position
Because they orbit planets, moons change
position frequently. Earth’s moon changes
position every night.
Stars seem to stay in their position within
constellations, but shift during the night due to
Earth’s rotation
They also shift when observed from different angles on
Earth, due to parallax.
Parallax
This is an example of parallax you’ve experienced:
Parallax
An illustration of parallax in astronomy:
Atmospheres
Atmospheres = layers of gas
surrounding a planet, held in
place by gravity.
Stars don’t have atmospheres. Their
intense heat would burn off gases.
Moons are too small. They don’t have
enough gravity to hold onto an
atmosphere.
Some planets have atmospheres, but a
few don’t. Only Earth’s atmosphere
can support life.
Origins
Planets form when gravity pushes
together a mass of gases or other
particles.
Moons form out of pieces of debris
in space, trapped in a planet’s
atmosphere. Planets can have
many moons, if large enough.
Stars form when a cloud of gases &
dust called a Nebula condenses
enough to begin a nuclear reaction.