Planets, Moons & Stars Gr 9 Science

Composition : Terrestrial = Made of rock, minerals Gaseous = Made of gases Stars are always gaseous. Moons are always terrestrial.

Composition : Planets can be both Some planets are gaseous. Some planets are terrestrial.

Distances & Sizes Stars look small, but are huge. They are the largest … just very far.

Distances & Sizes 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. Some planets have phases. Venus has phases. 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. Planets, moons and stars all rotate, but only planets & moons revolve or orbit.

Motion & Orbital Period Orbital Period = time for 1 revolution. 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

Parallax Stars shift because change in angles, or Parallax

Parallax Here’s how Parallax works:

Atmospheres Atmospheres = layers of gas surrounding a planet, held in place by gravity. Moons & Stars don’t have atmospheres.. Some planets have atmospheres, but a few don’t. Only Earth’s atmosphere can support life.

Origins Planets form from gases, stone or metals pushed together by gravity Moons form from pieces of debris in space, trapped in a planets orbit. Planets can have many moons, if large enough..

Origins Stars form when a Nebula condenses. A Nebula is a kind of dust & gas cloud. When it condenses enough, a nuclear reaction begins.