Astro Flashcards
When is the Doppler effect observed?
when there is relative motion between two objects that are in a wave pair. there is an emitter and a receiver. eg. a car passing a person stood still.
What happens when an object moves further away from the other in Doppler effect?
wavelength gets longer
frequency decreases
light would get redder
sound would get lower
What happens when an object moves closer to the other object in Doppler effect?
wavelength gets shorter
frequency increases
light would get bluer
sound would get higher
When is required for Doppler shift to occur?
v is much greater than c. (non-relativistic)
What is meant by a ‘nearby’ galaxy?
it is not receding significantly by universala expansion. ie. ignore redshift of galaxy as a whole away from us
Why does the Doppler effect on a rotational galaxy increase the further from the centre?
If a galaxy spins with constant angular velocity, ω, then velocity, v, will increase the further from the centre, causing a greater doppler effect.
v = ωr
Why is Doppler shift harder to measure on galaxies than planets?
Galaxies are more complex as they are not solid so don’t spin with constant angular velocity, like planets do
What is Hubble’s law?
v ∝ r so v=Hd
What evidence is there to support Hubble’s law?
light from all galaxies is red shifted so they must be moving away from us with recessional velocity, v.
the further away a galaxy is, d in megaparsecs, the greater the recessional velocity
What is the current value of Hubble’s constant?
65km/s/MPc
Describe the universe at t=0.
a singularity
infinitely hot and dense
four fundamental forces combined into a super force
How and when did matter and antimatter form in the timeline of the universe?
t = 1x10^-27s
ratio of matter to antimatter is M : AM, 10^9 +1 : 10^9
so majority annihilates leaving a small amount of matter which goes on to create everything
When did quarks form?
t = 1x10^-12s to 1x10^-6s
When did hadrons form?
t = 1x10^-6s - 1s
What happened between the times of 1s and 20mins in the timeline of the universe?
Nucleosynthesis
What was the ratio of elements in the universe before stars as seen today?
H : He : Li
75 : 24 : 1
What are the advantages of refracting telescopes?
robust
sealed - low maintenance
air doesn’t circulate so sharper image
What are the disadvantages of refracting telescopes?
chromatic aberration
not all wavelengths of EM spectrum pass through glass
larger lenses sag under their own weight
What are the advantages of reflecting telescopes?
no chromatic aberration
long focal length for size so high magnification
less sag in both body and mirror
What are the disadvantages of reflecting telescopes?
Open so air circulates causing turbulence (twinkles)
diffraction as light passes secondary reflectors
spherical aberration unless mirror is parabolic
What is collecting power proportional to?
the area (and so diameter) of the lens
What are the features of the objective lens in a refracting telescope?
convex
large diameter
long focal length
What are the features of the eyepiece lens in a refracting telescope?
convex
smaller diameter
short focal length
What type of mirrors are used in a Newtonian reflector?
convex and flat
What type of mirrors are used in a Cassegrain telescope?
convex and concave
What is resolving power?
the smallest angle of separation at which two points can be distinguished
What is an airy disc?
when EM waves diffract through a circular gap or aperture they produce rings rather than fringes. This circular diffraction pattern is known as an airy disc.
What is the Rayleigh criterion?
when the 1st minimum of object A falls under the maximum of object B, the two objects are just resolvable.
𝜃 = 𝜆 / D
