Astrophysics

Question 1

What is the universe?

Answer 1

The universe is a large collection of billions of galaxies that is always expanding.

Question 2

What is a galaxy?

Answer 2

A galaxy is a large collection of billions of stars.

Question 3

In which galaxy is the solar system located?

Answer 3

The solar system is in the Milky Way galaxy.

Question 4

What does gravitational field strength depend on?

Answer 4

Gravitational field strength depends on the mass of the body creating the field and the distance to it.

Question 5

How does gravitational field strength vary with distance?

Answer 5

he closer you are to a star or planet, the stronger the gravitational force.

Question 6

Why does an object weigh more on Earth than on the Moon?

Answer 6

An object weighs more on Earth than on the Moon because the gravitational field on Earth is stronger.

Question 7

What is an orbit?

Answer 7

An orbit is the path of a planet around a star or a satellite around a planet.

Question 8

What causes an object to remain in orbit?

Answer 8

An object remains in orbit due to the gravitational field of the more massive body it is orbiting.

Question 9

How does the strength of gravitational force affect velocity in orbit?

Answer 9

The stronger the gravitational force, the larger the velocity needed to balance it; so the closer to a star or planet you are, the faster velocity required to remain in orbit.

Question 10

What type of orbits do natural and artificial satellites typically have?

Answer 10

Natural and artificial satellites typically have fairly circular orbits with a constant velocity.

Question 11

Describe the orbit of a comet.

Answer 11

A comet has a highly elliptical orbit with a star closer to one end, speeding up as it approaches the star and slowing down at the opposite end.

Question 12

What happens to a comet’s gravitational force as it approaches a star?

Answer 12

As the comet gets closer to the star, the gravitational force increases, causing it to speed up.

Question 13

What makes a comet return to the star if the gravitational field strength is so weak at its furthest point?

Answer 13

At its furthest point, there is a lot of gravitational potential energy (GPE), which is transformed into kinetic energy (KE) as it returns.

Question 14

What is the formula for orbital speed?

Answer 14

orbital speed = 2π x orbital radius / time period

Question 15

How is the orbital radius measured?

Answer 15

The distance from the center of the larger body to the center of the orbiting body

Question 16

What does the colour of a star depend on?

Answer 16

Surface temperature

Question 17

List the colours used to classify stars in ascending order of heat

Answer 17

• Red
• Orange
• Yellow
• White
• Blue

Question 18

How does the temperature of a star affect its emitted light frequency?

Answer 18

The hotter the star, more light of a higher frequency is emitted, making it appear more blue.

Question 19

What factors determine a star’s brightness?

Answer 19

• Size
• Temperature

Question 20

What factors determine a star’s apparent magnitude?

Answer 20

• Size
• Temperature
• Distance from Earth

Question 21

What is absolute magnitude?

Answer 21

A measure of how bright a star would be at a fixed distance from Earth.

Question 22

What is the relationship between absolute magnitude and brightness?

Answer 22

The lower the absolute magnitude, the brighter the star.

Question 23

What does the Hertzsprung-Russel diagram graph?

Answer 23

Absolute magnitude against temperature for many stars

Question 24

What type of stars are represented as red supergiants on the H-R diagram?

Answer 24

Very large and bright stars that are cooler in temperature

Question 25

What is the typical temperature and size characteristics of red giants?

Answer 25

Cool but very large

Question 26

What defines white dwarfs in terms of temperature and size?

Answer 26

Very hot but small and dim

Question 27

How do main sequence stars compare in size and brightness?

Answer 27

Roughly the same size, but brighter stars have higher temperatures

Question 28

What is a nebula?

Answer 28

A huge gas cloud, mainly of hydrogen.

Question 29

What process initiates the formation of a protostar?

Answer 29

Gravitational attraction pulls the gas cloud into its center of mass.

Question 30

What happens to the gravitational potential energy (GPE) of gas and dust as it forms a protostar?

Answer 30

It is transformed into kinetic energy (KE) and thermal energy, which creates enough heat and pressure for fusion of hydrogen to begin

Question 31

What are the conditions for hydrogen to undergo fusion?

Answer 31

The temperature and pressure must be high enough.

Question 32

What stabilizes a main sequence star?

Answer 32

The pressure outwards from fusion is balanced by the gravitational pressure pushing inwards.

Question 33

What happens when hydrogen runs out in a medium mass star?

Answer 33

The core contracts and gets hotter while the surface expands and cools, forming a red giant. The outer layers then drift off, leaving a white dwarf.

Question 34

What type of stars are classified as medium mass stars?

Answer 34

Stars like the sun.

Question 35

What occurs in the core of a medium mass star as it becomes a red giant?

Answer 35

Increased pressure allows helium to be fused.

Question 36

What is the fate of high mass stars after they evolve into red supergiants?

Answer 36

They explode, forming a supernova.

Question 37

What happens to the core of a high mass star after a supernova?

Answer 37

It contracts to form a neutron star.

Question 38

What happens to the core of a huge mass star after a supernova?

Answer 38

It contracts to form a black hole.

Question 39

Describe the life cycle of a star

Answer 39

Stars begin their life as a nebula, a cloud of gas and dust pulled together by gravity, forming a protostar, which heats up until nuclear fusion starts. Hydrogen is fused into helium, releasing energy so the star is a main sequence star. The pressure outwards from fusion and the pressure inwards from its gravitational field keeps the star stable. When the hydrogen runs out, the star’s life depends on its mass. Low-mass stars like the Sun expand into red giants, then their outer layers drift off as a planetary nebula, leaving behind a hot white dwarf. High-mass stars become red supergiants, fusing heavier elements until they explode in a supernova. What remains after the explosion is either a dense neutron star or, if the core is massive enough, a black hole.

Question 40

What occurs when a source of waves is moving relative to an observer?

Answer 40

The waves undergo a change in frequency and wavelength, known as the Doppler effect.

Question 41

What happens to light emitted by a source moving away from an observer?

Answer 41

The waves reach the observer at a lower frequency, so the light observed is shifted towards the red end of the spectrum (red-shift)

Question 42

What evidence suggests that most galaxies are moving away from each other?

Answer 42

The absorption spectrum shows dark lines at frequencies absorbed by different elements, which appear at lower wavelengths in light from distant galaxies, indicating red-shift.

Question 43

What is the significance of dark lines in an absorption spectrum?

Answer 43

Dark lines indicate the specific wavelengths of light that different elements have absorbed.

Question 44

What does red-shift indicate?

Answer 44

It indicates that all galaxies are moving away from us, suggesting that the universe is expanding.

Question 45

What does the measurement of red-shift suggest about distant galaxies?

Answer 45

All distant galaxies are moving away from us very quickly

Question 46

How does the red-shift vary with distance of galaxies?

Answer 46

More distant galaxies have greater red-shifts, suggesting they are moving away faster than nearer ones

Question 47

What type of radiation can scientists detect coming from all directions?

Answer 47

Low frequency Cosmic Microwave Background Radiation (CMBR)

Question 48

What happens to the frequency of background radiation as the universe expands?

Answer 48

This background radiation drops in frequency as the universe cools

Question 49

What does the evidence of galaxies getting further from each other suggest about the universe's origin?

Answer 49

The universe started at a single point, and an 'explosion' got all the galaxies going, and they are still moving away.

Question 50

According to the Big Bang model, what is CMBR?

Answer 50

The leftover energy from the initial explosion

Question 51

What was the state of all matter in the universe before the Big Bang?

Answer 51

All matter occupied a single point that was very dense and hot

Question 52

What formula is used to calculate the red-shift of a galaxy?

Answer 52

Change in wavelength . galaxy's velocity ------------------------------ = ----------------------- reference wavelength . speed of light