8 Astrophysics

Question 1

what does N/Kg measure

Answer 1

gravitational field strength

Question 2

what is the universe

Answer 2

a large collection of billions of galaxies

Question 3

what is a galaxy

Answer 3

large collection of billions of stars

Question 4

what galaxy is our solar system in

Answer 4

Milky way

Question 5

why does gravitational field strength vary from planet to planet and moon to earth

Answer 5

the different masses and radiuses

Question 6

what does gravitational force cause

Answer 6

causes moons to orbit planets
causes the planets to orbit the Sun
causes artificial satellites to orbit the Earth causes comets to orbit the Sun

Question 7

what are the differences in the orbits of comets, moons and planets

Answer 7

planets have a slightly elliptical orbit around the sun

moons orbit planets in circles

comits orbit the sun in a very elliptical orbit

Question 8

what is the orbital speed formula

Answer 8

(2 x pi x orbital radius) / time period

Question 9

how can stars be classifed by colour

Answer 9

Warm objects emit infrared and extremely hot objects emit visible light as well
Therefore, the colour they emit depends on how hot they are
A star’s colour is related to its surface temperature
A red star is the coolest (at around 3000 K)
A blue star is the hottest (at around 30 000 K)

Question 10

what does the stars color relate to

Answer 10

surface temperature

Question 11

evolution of stars of similar mass to the sun

Answer 11

stellar nebula (cloud of gas + dust)
gravity pulls the cloud inwards, causing it to shrink and heat up forming a protostar
protostar
eventually the core of the protostar gets hot enough for fusion to start becoming a main sequence
main sequence star (fuses hydrogen into helium in its core)
eventually the star runs out of fuel in the core for fusion and the core shrinks as fusion stops pushing outwards
as the core shrinks, fusion begins in a layer around the core and the star swells up to become a red giant
red giant star
planetary nebula
once the helium fusion has finished, the star collapses and becomes a white dwarf which cools over time
white dwarf

Question 12

evolution of stars with a larger mass than the sun

Answer 12

stellar nebula (cloud of gas + dust)
gravity pulls the cloud inwards, causing it to shrink and heat up forming a protostar
protostar
eventually the core of the protostar gets hot enough for fusion to start becoming a main sequence
main sequence star (fuses hydrogen into helium in its core)
eventually the star runs out of fuel in the core for fusion and the core shrinks as fusion stops pushing outwards
as the core shrinks, fusion begins in a layer around the core and the star swells up to become a red super giant
red super giant star (the larger stars become a red super giant quicker than the smaller ones)
once the helium fusion has finished the core of the star will suddenly collapse which is a supernova
supernova
at the center of the explosion, a dense body called a neutron star will form
the outer remnants of the star are ejected into space forming new nebulas
neutron star
in the most massive stars, the neutron star that forms at the centre will continue to collapse under the force of gravity until it forms a black hole

Question 13

how can the brightness of a star at a standard distance be represented using absolute magnitude

Answer 13

as stars exist at very different distances from the earth so their brightness is represented on a standard scale (absolute magnitude)
absolute magnitude compares stars as if they were all 10 parsecs (32.6 light years (3.1x10 ^ 17m) ) from earth
the scale is centered at zero with bright stars having negative absolute magnitude and dimmer stars having positive absolute magnitudes

Question 14

what is apparent magnitude

Answer 14

The perceived brightness of a star as seen from Earth

The apparent magnitude scale runs back to front:
the brighter the star, the lower the magnitude
the dimmer the star, the higher the magnitude

Question 15

how to draw a Hertzsprung-Russell diagra

Answer 15

luminosity (compared to the sun) goes on the y-axis and temperature (kelvin) on the x-axis

luminosity increases in brightness as the y value increases
temperature decreases is heat as x value increases (so starts at the hottest value)

stars can also be displayed with colour where the hottest stars are blue and the coolest stars are red

The key areas of the H-R diagram are:
The brightest stars (high luminosity) are found near the top
The dimmest stars (low luminosity) are found near the bottom
The hottest stars (high temperature) are found towards the left
The coolest stars (low temperature) are found towards the right

Question 16

where are stars found on H-R diagrams

Answer 16

The life cycle of a star can be shown on a Hertzsprung-Russell diagram

The main features of the Hertzsprung-Russell diagram are:
Most stars are found to lie on the main sequence. This is the band of stars going from top left to bottom right
Below the main sequence (and slightly to the left) are the white dwarfs
Above the main sequence on the right-hand side are the red giants
Directly above the red giants are the red supergiants

This means that
The hottest, brightest stars are the largest main sequence stars, also called supergiant stars
The coolest, brightest stars are red supergiants
The hottest, dimmest stars are white dwarfs
the coolest, dimmest stars are the smallest main sequence stars, also called red dwarfs

Question 17

equation with change in wavelength, velocity of a galaxy, speed of light and reference wavelength

Answer 17

reference wavelength = speed of light

Question 18

evidence for the big bang - expanding universe

Answer 18

the universe is constantly expanding - everywhere we look the galaxies are moving away from us and each other faster
the fact that everything is moving away from each other and further away objects are moving faster, shows that the universe is expanding and so if you reverse that then everything gets closer and closer together until it all converges at one point, the big bang

Question 19

evidence for the big bang - red shift

Answer 19

when observing light spectrums from supernovas in other galaxies we see that the light has been redshifted showing that the galaxies are moving away from us as the wavelengths are increasing which shifts the colour to red.
The further away galaxies are even more redshifted showing that the further away galaxies are moving even faster
this shows the universe is expanding and started from an explosion as the universe is now moving out in all directions getting further and further from the source of the explosion

Question 20

evidence for the big bang - cosmic microwave background radiation

Answer 20

380,000 years after big bang protons and electrons combined to form neutral hydrogen atoms which radiated light.
As the universe expanded and cooled, the wavelength of the visible light increased and shifted to microwaves.
the CMBR has stretched during the expansion and cooling so the universe must have been smaller and hotter in the past.
The CMBR is the same everywhere we look is evidence that all the points were touching during the big bang

Question 21

what is the doppler effect

Answer 21

when a source emitting waves is moving towards an observer, the waves are released closer together so the observer perceives the wavelength and frequency to have changed (wavelength decreases + frequency increases if the source if moving closer to the observer)