Section 8 - Astrophysics P1

Question 1

What is the universe a collection of?

Answer 1

billions of galaxies

Question 2

What is a galaxy?

Answer 2

a large collection of stars

Question 3

What galaxy is earth part of?

Answer 3

the milky way galaxy

Question 4

What is our sun within the milky way galaxy?

Answer 4

• our sun is just one of many billions of stars which form the milky way galaxy
• its about halfway along one of the spiral arms of the milky way

Question 5

What is the force which keeps stars together within a galaxy?

Answer 5

gravity

-galaxies also rotate within the universe

Question 6

What is most of the universe?

Answer 6

empty space

Question 7

What makes up our solar system?

Answer 7

Our solar system has one star, the sun, and everything that orbits it makes up the solar system

• planets
• dwarf-planets
• moons
• artificial satellites
• asteroids
• comets

Question 8

What is a satellite?

Answer 8

A satellite is an object that orbits a second, more massive object

Question 9

What is a planet?

Answer 9

Large objects that orbit a star

Question 10

How many planets do we have in our solar system and what are they called? (order from the sun outwards)

Answer 10

eight planets

• Mercury
• Venus
• Earth
• Mars
• Jupiter
• Saturn
• Uranus
• Neptune

Question 11

What is a dwarf-planet?

Answer 11

They are planet-like object that aren’t big enough to be planets (e.g. Pluto)

Question 12

What is a moon?

Answer 12

They orbit planets with almost circular orbit

-they’re a type of natural satellite

Question 13

What is an artificial satellite?

Answer 13

man-made that usually orbit Earth in a fairly circular orbit

Question 14

What is an asteroid?

Answer 14

Lumps of rock and metal that orbit the sun

-usually found in an asteroid belt

Question 15

What is a comet?

Answer 15

Lumps of ice and dust that orbit the sun

-their orbits are often highly elliptical(stretched circle)

Question 16

What is the orbit of planets around the sun described as?

Answer 16

Almost circular

Question 17

What does a circular orbit mean?

Answer 17

-it is constantly changing direction (and so constantly accelerating), which means there must be a force acting on it

Question 18

What the force which causes a circular orbit called?

Answer 18

Centripetal force

-it acts toward the centre of a circle

Question 19

If the centripetal force acts towards the centre of a circle, how come planets remain in orbit?

Answer 19

-since the object is already moving, this force towards the centre of a circle just causes it to change its direction instead of just falling towards the centre of a circle

Question 20

How do orbits occur circular?

Answer 20

it keeps accelerating towards what it’s orbiting but the instantaneous velocity keeps it travelling in circle

• the gravitational force makes this happen
• the gravitational attraction of the sun keeps planets in orbit, satellites are kept in orbit by a planet in the same way

Question 21

What does gravitational field strength depend on?

Answer 21

• the mass of the body creating the field
• the larger the mass of the body, the stronger the gravitational field (e.g. earth’s GFS is greater than the moons)
• the distance you are from a planet or star, the closer you are the greater the force

Question 22

What are orbits of moons and planets normally?

Answer 22

slightly elliptical

Question 23

What are the orbits of comets around the sun?

Answer 23

very elliptical

• orbit with Sun at one focus (near one end of the orbit)
• have very long orbital periods because of the distance they travel
• comet travels quicker closer to the Sun than further away (because of the gravitational pull)

Question 24

What are geostationary satellites?

Answer 24

artificial Earth satellites that have an orbital period of exactly one day
-useful in communications

Question 25

What is the equation linking orbital radius, time period and orbital speed?

Answer 25

orbital speed = (2π x orbital radius) / time period

Question 26

What is the path of stellar evolution?

Answer 26

Nebula - Protostar - Main Sequence Star - Red Giant - White Dwarf

OR

Nebula - Protostar - Main Sequence Star - Red Supergiant - Supernova - Neutron Star OR Black Hole

Question 27

What is the Nebula stage of stellar evolution?

Answer 27

Stars initially form from a cloud of dust and gas called a Nebula

Question 28

What is the Protostar stage of stellar evolution?

Answer 28

Force of gravity pulls the dust and gas together to form a Protostar
the temperature rises as the star becomes more dense and their are more collisions
when the temperature is high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei
this gives out lost of energy keeping the core of the star hot (a star is born)

Question 29

What is the Main Sequence Star stage of stellar evolution?

Answer 29

star enters a long, stable period
outward pressure from thermal expansion(the energy produced from nuclear fusion tries to expand the star) balances the force of gravity pulling everything in
-lasts for several billion years (the heavier the star the shorter the time)

Question 30

What is the Red Giant stage of stellar evolution?

Answer 30

the hydrogen in the core of the star begins to run out, the force due to gravity is larger than the pressure of thermal expansion
the star is compressed until it is dense and hot enough that the energy created causes the outer layers of the star to expand
small stars become red giants (red because the surface cools)

Question 31

What is the White Dwarf stage of stellar evolution?

Answer 31

the red giant then becomes unstable and ejects its outer layer of dust and gas
leaving behind a hot, dense solid core

Question 32

What is the Red Supergiant stage of stellar evolution?

Answer 32

the hydrogen in the core of the star begins to run out, the force due to gravity is larger than the pressure of thermal expansion
the star is compressed until it is dense and hot enough that the energy created causes the outer layers of the star to expand
small stars become red supergiants (red because the surface cools)

Question 33

What is the Supernova stage of stellar evolution?

Answer 33

The Red Supergiant then begins to glow brightly again, as it undergoes more fusion to make heavier elements
they expand and contract several times as the balance shifts between thermal expansion and gravity
they eventually explode in a supernova

Question 34

What is the Neutron Star OR Black Hole stage of stellar evolution?

Answer 34

the exploding supernova, throws outer layers of dust and gas into space, leaving a dense care called a Neutron Star
-if the star is big enough it will collapse and become a black hole

Question 35

What is a black hole?

Answer 35

A super dense point in space that not even light can escape from

Question 36

What can stars be classified by?

Answer 36

Their colours

Question 37

What does the colour of a star depend on?

Answer 37

The visible light it emits

• all stars emit visible light, how much it emits of each frequency depends on the surface temperature
• stars of a similar colour will have a similar surface temperature

Question 38

What colours do we use to classify stars?

Answer 38

red
orange
yellow
white
blue

Question 39

What visible light will a cooler star emit?

Answer 39

-visible light at the lowest frequency of visible light, so red

Question 40

What visible light will a hotter star emit?

Answer 40

The hotter a star is, the more light of higher frequencies it will emit
-they appear blue

Question 41

What is the order of visible light according to the surface temperature of stars? (starting from the coolest)

Answer 41

Red
Orange
Yellow
White
Blue