[P8] Space

What objects are in our solar system?

• one star (the Sun) • eight planets • some dwarf planets • moons • comets and asteroids

What is the name of our galaxy?

the Milky Way galaxy

What do planets orbit?

the central star

What do dwarf planets orbit?

the central star

What do moons orbit?

planets

What was our Sun formed from?

a cloud of dust and gas (nebula) pulled together by gravitational attraction

How does a nebula reach the stage where fusion can occur?

• the nebula is pulled together by gravitational attraction • work is done by gravity, so the temperature increases • more particles are in a smaller volume, so the pressure increases • eventually the temperature and pressure are high enough for fusion to begin

Why does a main sequence star have a constant size?

there is an equilibrium between the gravitational collapse of a star and the expansion of a star due to energy from fusion

Describe the lifecycle of a star which is a simliar size to our Sun

• nebula • protostar • main sequence star • red giant • white dwarf • black dwarf

Describe the lifecycle of a star which is much more massive than our Sun

• nebula • protostar • main sequence star • red supergiant • supernova • neutron star or black hole

What is a main sequence star?

a star that is mainly fusing hydrogen into helium

What is a black hole?

an object with such a strong gravitational field that no light can escape

What change causes protostars to become main sequence stars?

the centre is hot and dense enough for nuclear fusion to begin

What change causes main sequence stars to become red giants or supergiants?

the proportion of hydrogen falls below 50%, so the star is no longer mainly fusing hydrogen into helium

What causes a white dwarf star to become black dwarf star?

it cools down by emitting radiation (this takes so long that no white dwarf stars have yet become black dwarfs)

What causes a red supergiant to become a supernova?

it begins to fuse elements beyond iron, which causes a massive core collapse

How are elements produced?

by fusion in stars

How are all naturally occurring elements beyond iron produced?

by fusion in a supernova

How are elements distributed throughout the Universe?

by the explosion of massive stars (supernovae)

What does the colour of a star indicate?

its surface temperature

What force allows planets and satellites to maintain their circular orbits?

gravity

What are natural satellites?

planets, moons, asteroids, comets (things that orbit something else but are 𝗻𝗼𝘁 made by humans)

What are artificial satellites?

the ISS, weather satellites, GPS satellites (things that orbit something else and are made by humans)

What are some similarities and differences between planets and moons?

• they are both natural satellites • planets orbit a star, whereas moons orbit planets

What are some similarities and differences between moons and artificial satellites?

• they both orbit planets • artificial satellites are made by humans, whereas moons are not • moons are much bigger than any artificial satellite

Describe the speed and velocity of an object in an unchanging circular orbit

• their speed is constant • their velocity is changing

What will happen to the radius of an orbit if the speed increases?

decreases

What is red-shift?

an observed increase in the wavelength of light from a light source moving away from the detector

What trend do we see between the distance of a galaxy from Earth and its red-shift?

The further away the galaxies, the faster they are moving and the bigger the red-shift (the observed increase in wavelength)

What does red-shift suggest about the Universe?

it provides evidence that space itself (the universe) is expanding and supports the Big Bang theory.

What does the Big Bang theory suggest?

that the universe began from a very small region that was extremely hot and dense

What evidence do we have that the universe is expanding at an accelerating rate?

Since 1998 onwards, observations of supernovae suggest that distant galaxies are receding (moving away) ever faster

What is dark matter(/mass)?

matter which has a gravitational field but does not interact with electromagnetic radiation