Physics EOYE 2nd Form

1st celestial object

the universe - the entire cosmos and everything within it; all of space and time.

2nd celestial object

galaxy - billions of stars, gravitationally bound, e.g. milky way/

3rd celestial object

nebula - cloud of gas and dust from which stars and planets are formed

4th celestial object

solar system - a star and all local bodies in orbit around it, e.g our Sun, 8 planets, dwarf planets etc.

5th celestial object

star - large mass of mainly hydrogen, undergoing nuclear fusion and emitting electromagnetic radiation

6th celestial object

planet - a spherical body (rocky/gaseous) in a cleared orbit around a star

7th celestial object

dwarf planet - a mostly spherical body in orbit around a star which has not cleared its orbit

8th celestial object

moon - a body in orbit around a planet; natural satellite

what does cleared orbit mean?

the planet is the most dominant mass in its orbital path, clearing away any other objects that could compete for that dominance. 

Which celestial bodies clear their orbit?

Only planets, not dwarf planets.

what are asteroids?

small, rocky objects in orbit around the Sun. They orbit closer in than Jupiter. There are millions of them ranging from the size of Ceres, to 10s of metres. They mostly orbit in the asteroid belt between Mars and Jupiter.

What is a meteoroid

dust and debris left behind from a comet or asteroid floating in space before it enters the atmosphere. Smaller than 10m. Asteroids are bigger.

Meteors?

Meteoroids that enter our atmosphere and burn up.

Meteorite?

A portion of a meteoroid that survives its passage through the atmosphere and impacts the ground without being destroyed. Oldest objects on Earth, and important for finding composition of other objects in the milky way.

comets?

lumps of frozen ice, md and rock travelling through the soalr system and between 1-10km. Have long tails as Sun blasts ice and dust off the comet - tails always point away from the sun as that is how sun radiation blasts them off.

Describe rocky planets?

Mercury, Venus, Earth, Mars. Small compared to gas giants, density = 5g/cm², made of rock.

Describe gas giants?

Jupiter, Saturn, Uranus, Neptune, larger than rocky planets, density = o.5-1.5g/cm², made of gases such as hydrogen, helium and methane.

Why are dwarf planets not planets?

They don't clear their orbits, and their orbits are a lot more elliptical than planets,

what is the centre of gravity?

a point where all the mass of an object appears to act.