Section 8 - Astrophysics

Question 1

Universe

Answer 1

• large collection of billions of galaxies

Question 2

Galaxy

Answer 2

large collection of stars

Question 3

Sun

Answer 3

one of the billions of stars which form the Milky way Galaxy (about halfway long one of the spiral arms).

Question 4

Gravity astrophysics

Answer 4

Gravity - force keeping stars together in a galaxy (galaxies rotate slightly)

Question 5

universe made up of

Answer 5

Universe is mostly empty space. There is a great distance between stars, millions more than between neighbour plantes and an even greater distance between galaxies.

Question 6

our galaxy

Answer 6

We are part of the Milky Way Galaxy:

Question 7

Planets

Answer 7

Planets (large objects that orbit a star) Eight in our solar system (Mercury Venus Earth Mars Jupiter Saturn Uranus and Neptune) - my very easy method just speeds up nothin

Question 8

Dwarf Planets

Answer 8

Dwarf Planets: (pluto) planet-like objects not large enough to be considered planets

Question 9

Moons

Answer 9

Moons: Orbit planets with almost circular orbits. A natural satellite

Question 10

Artificial satellites:

Answer 10

man-made objets orbiting earth in almost circular orbits

Question 11

Asteroids

Answer 11

lumps of rock and metal that orbit sun, usually found in asteroid belt

Question 12

Comets

Answer 12

Comets: lumps of ice and dust that orbit Sun. Orbits usually highly elliptical.

Question 13

Centripetal Force -

Answer 13

acts towards the centre of a circle and causes the object to fall against whatever it is orbiting but as the object is already accelerating it just causes it to change direction. Object keeps accelerating towards what it is orbit ut the instantaneous velocity (right angle to acceleration) keeps it in a circle

Question 14

Gravitational force

Answer 14

Gravitational force - the gravitational attraction of the Sun keeps the planets and comets in their orbits around it

Question 15

satellites and orbit

Answer 15

Satellites kept in orbit by gravitational attraction of planet

Question 16

Gravitational field strength what affects it

Answer 16

distance/ mass

depends on mass of body creating the field. The larger the mass the stronger the field (earth> moon so object weigh more on earth than moon)
Also varies with distance (closer you get to object the stronger the field)

Question 17

Orbits of moons and planets

Answer 17

slightly elliptical

Question 18

Comets orbit

Answer 18

Comets orbit Sun but have very elliptical orbit with sun at one focus (near an end of the orbit). They have orbital periods for much longer than earth as they travel from the outer edges of our solar system. A comet travels much faster when its near a star due to the increased pul of gravity that makes it speed up

Question 19

Geostationary

Answer 19

Geostationary - Artificial earth satellites have an orbit period of exactly one day, useful in comunication because they are always over same part of planet

Question 20

Calculate Orbit Speeds

Answer 20

Orbital speed = 2π x orbital radius / time

Question 21

Nebula

Answer 21

Nebula - stars initially form a cloud of dust and gas

Question 22

Protostar

Answer 22

Protostar - force of gravity pulls the dust and gas together to for a prostar. The temp rises as the star gets denser and more particles collide. When the temp is high enough hydrogen nuclei undergo nuclear fusion to form helium nuclei. This gives out huge amounts of energy which keep star core hot. Star is born

Question 23

Main sequence stars-

Answer 23

Main sequence stars- star enters long stable period during which the outward pressure caused by thermal expansion (the energy produced by nuclear fusion tries to expand the star) balances force of gravity pulling everything inwards. This tyically lasts several billion years. The heavier the star the shorter time on the main sequence (sun is in middle of stable period).

Question 24

Red giant/supergiant

Answer 24

Red giant/supergiant - eventually the hydrogen in the core begins to run out and the force of gravity is larger than pressure of thermal expansion. The star is compressed until it is dense and hot enough that the energy (and pressure) makes outer layers of star expand. It becomes a red giant or supergiant depending on its size. Red = because surface cools-

Question 25

White dwarf

Answer 25

White dwarf a small to medium sized star (like sun) then becomes unstable and ejects its outer layer of dust and gas leaving behind a hot dense solid core called white dwarf

Question 26

Supernova

Answer 26

Supernova - big stars start to glow brightly again as they undergo more fusion to make heavier elements . They expand and contract several times as the balance shifts between gravity and thermal expansion. eventually they explode in supernova

Question 27

Neutron star/ black hole

Answer 27

Neutron star/ black hole - The exploding supernova throws outer layers of dust and gas into space leaving a very dense core called a neutron star. If the star is massive enough it will collapse and become a black hole - a super dense point in space not even light can escape

Question 28

Colour of a star

Answer 28

Colour of a star depends of the amount of visible light it emits, all stars emit visible light but how much and its frequency depends on its surface temperature Starts of similar colour will be of similar temperature Hotter = more light of higher frequencies it will emit Cool star - red, orange, yellow, white, blue - hottest - highest frequency light