Astrophysics

What is the universe

Large collection of billions of galaxies

What is a galaxy

Large collection of billions of stars

Which galaxy is our solar system in

Milky Way

Why does gravitational field strength (g) vary

Greater mass of planet = greater grav field strength

How does grav field strength work

Attract object towards centre of planet

Why is g on moon different from earth g

Moon is smaller

Does mass change when u go to a diff planet

No

Does weight change when u go to a dif planet

Yes

What is weight

Force acting on mass due to gravitational attraction. W = mg

What causes things to orbit other bodies

Gravitational force

Similarities of shape of planet orbits around sun

All slightly elliptical ; same plane + direction

Differences of shape of planet orbits around sun

Different distances, speeds, time taken

How does distance from sun affect orbit

Orbital distance is longer, slower orbital speed, more time

Orbital shape of moons

Circular around planet

Orbital motion of comets

Very elliptical (hyperbolic); speed increases as approaches sun

Is orbital speed of comet constant

No, faster when closer to sun

What force causes artificial satellites to orbit earth

Gravitational force

Relationship between orbital speed, orbital radius and time period

v= 2pi r /t

What is star’s colour related to

Surface mperature

Evolution of stars similar mass to sun

Nebula → main sequence star → red giant → white dwarf

What can we classify stars by

Colour

How to classify stars according to colour

Hottest = blue (eg blue giants), yellow, Coolest = red (eg red giants)

What happens when stars expand

They cool

What happens when stars contract

They heat u

Describe how sun goes from nebula to star

Particles clump together then pressure and temp is high enough for nuclear fusion

Why do particles of nebula clump together

Experience weak attraction to each other due to gravitational force

Describe fusion in main sequence star

Hydrogen nuclei fuse to helium nuclei, releasing energy and creating pressure outwards

How come the star doesn’t just explode if the outwards pressure is so great from the fusion

Outwards pressure balances with inwards pressure due to gravity

Describe flop era of sun

Runs out of hydrogen; core collapses; expands to red giant, white dwarf, black dwarf.

Why does core collapses when star runs out of hydrogen to fuse

Not enough outward pressure from fusion so collapses under own weight, becomes unstable

What happens after star larger than sun runs out of hydrogen

Core collapses which restarts fusion in core of heavier elements

What happens after large star restarts fusion of heavier elements

Becomes red supergiant until fusion of heavier elements stops in core

What happens after fusion of heavier elements stops in core of red supergiant

explodes in supernova

What happens after star explodes in supernova

If super massive then black hole, otherwise neutron star

What is the end point for a star of similar mass to sun

Black dwarf

What is the end point for stars larger than sun

Black hole if mega massive otherwise neutron star