Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Physics > Astrophysics > Flashcards

Astrophysics Flashcards

1
Q

How to calculate the length of a telescope

A

f0+fe

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How to calculate magnification

A

M=f0/fe

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How to calculate angular magnification

A

M= angle subtended by image / angle subtended by object

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How to reflecting/cassegrain telescopes work?

A

Reflecting telescopes use a parabolic mirror to focus incoming light into a point
A secondary mirror is placed before the focal point to reflect the rays back through a gap in the mirror
The rays cross over then pass into a lens
The rays emerge parallel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the structure of a CCD?

A

A series of silicon picture elements (pixels) which are very small
Beneath each is a potential well which traps electrons
Above each is a filter which only allows certain colour photons through

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How do CCDs work?

A

-The filter allows only certain wavelengths of photon to hit the pixels
-The photons will cause electrons in the pixels to be released into the potential wells
-Amount of electrons released is proportional to the intensity of the light incident (number of photons)
-The charge is then collected from each well
-The amount of charge and colour of filter tells the computer what colour and brightness needs to be displayed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is quantum efficiency?

A

When the number of photons incident on the surface causes a response

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What percentage of light does a CCD detect compared to the eye and photographic film?

A

CCD - 80%
Photographic film - 4%
Eye - 1%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the benefits of CCDs?

A

-Film can get saturated with the too much light ruining the image, CCDs don’t get saturated.
-CCDs detect a wider spectrum of light than human eye( infrared, visible and UV)
-Can have long exposures to capture faint images
-Capture finer detail as higher resolvable distance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is chromatic aberration?

A

Light reflects by different amounts depending on its wavelength
So different colours focus incoming light into different places after going through lens
short wavelengths like blue focus too close to lens
Red wavelengths focus too far away
This causes colour bleeding

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Problems with refracting telescopes

A

Chromatic aberration
Impurities
Lens distortion
Length of telescope

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Explain impurities on refracting telescopes

A

Any bubbles or impurities in the glass absorb and scatter light so faint objects can’t be seen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Explain lens distortion in refracting telescopes

A

Large lenses are heavy and can only be supported at the edge so the shape can become distorted

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Explain how the length of refracting telescopes is a problem

A

For large magnification long focal lengths are needed so telescopes are very long requiring big expensive buildings

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the advantages of reflecting telescopes?

A

Cost- mirrors are cheaper than large lenses
Support structure - less likely to distort due to light not passing through mirror, meaning they can be supported from the back
Collecting lower- telescope is large so more light can be collected - easier to make large
Resolving power

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the disadvantages of reflecting telescopes?

A

Spherical aberration
Second mirror

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is spherical aberration in reflecting telescopes?

A

Occurs when mirror isn’t shaped as a perfect parabola
Outer rays focus too close
Inner rays focus too far away
Causes blurry images

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Why is the second mirror a disadvantage in reflecting telescopes?

A

The secondary mirror may block and diffract some incoming light
Decreasing image clarity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the optical advantages of reflecting and refracting telescopes?

A

Refracting telescopes:
-No secondary mirror blocking light
Reflecting telescopes:
-Less chromatic aberration
-Better collecting and resolving power

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is the Rayleigh criterion?

A

Two light sources can be distinguished if the centre of the airy disc from one source is at least as far away as the first minimum of the other source

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How is resolving power calculated?

A

Smaller angle = more powerful
Theta= lambda / D
D = diameter of telescope

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the structure of visible, UV and infrared telescopes?

A

-A parabolic dish focuses electromagnetic radiation onto a point
-Visible, UV and infrared telescopes place a CCD at this point

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the structure of radio telescopes?

A

A parabolic dish focuses EM radiation onto a point
A combination of amplifiers to boost weak signals and a tuner to focus on specific frequencies

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Perfection of non optical telescopes

A

An imperfection cannot be greater than 1/20 th of the wavelength
UV telescopes has to be the most perfect making them more expensive
Radio can be the least perfect so they are cheaper and much large
Radio dishes often not solid but made of mesh

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Resolving power of non optical telescopes
UV and Xray telescopes have a much higher resolving power Radio have the worst However resolving pier is inversely proportional to the diameter A bigger telescope means better resolving power This is easier with cheap radio telescopes than expensive UV
26
Collecting power of non optical telescopes
Radio telescopes have the best collecting power Because large telescope area can collect more photons So can see the dimmest stars UV and Xray telescopes tend to be small as expansive to make, so worst collecting power
27
Where are radio and visible telescopes placed?
Can be on the ground because visible and radio waves can pass through atmosphere Some visible light is blocked so more effective in space
28
Where are IR UV and Xray telescopes placed?
Atmosphere blocks most infrared ultraviolet and Xray waves so must be put in space Although can put infrared telescopes on top of mountains or on planes
29
How to do the parallax method?
Use trig with the angle of parallax and one astronomic unit for the radius
30
What is an arc second?
1/3600 of a degree
31
What is a light year?
The distance that light travels in one year
32
How to calculate intensity?
I=power/area I=p/4pi r^2
33
What is apparent magnitude?
The brightness as viewed from earth
34
What is the brightness ratio equation?
I2/I1 = (2.51)^(m1-m2) 5th root of 100≈2.51
35
What is absolute magnitude?
How bright a star appears from 10 parsecs away
36
What is the distance and magnitude equation?
m-M=5log(d/10) Remember d is measured in parsecs
37
Why are type 1A supernovae unique?
When they expose and rapidly increase in brightness they all have the same peak in absolute magnitude So combined with apparent magnitude from earth we can calculate the distance to them Peak at -19.3 Called standard candles
38
What is the definition of a black body?
A body which emits and absorbs all types of EM radiation
39
What is stefans law?
P= sigma A T^4
40
What are hydrogen balmer lines?
The absorption lines created by electrons in hydrogen at level 2 or above
41
What are the stellar spectral classes?
OBAFGKM
42
What are the temperatures of the stellar spectral classes?
O 50000-25000 B 25000-11000 A 11000-7500 F 7500-6000 G 6000-5000 K 5000-3500 M >3500
43
What are the colours of the stellar spectral classes?
O Blue B Blue A Blue-White F White G Yellow-White K Orange M Red
44
What are the absorption lined of the stellar spectral classes?
O Strong He and He+ , weak H B Strong He and H A Strongest H lines, ionized metals F Strong ionized metal lines G Strong neutrals metal and ionized metal lines K strong neutral metal lines M strong neutral atom and molecular compound lines
45
What is the scale for Hertzsprung Russell diagrams?
Y axis - absolute magnitude +15 at bottom to -15 going down in 5s X axis - temperature 50000-2500 K
46
Where does the sun go on a HR diagram?
6000K +5
47
Where are red giants and white dwarfs on a HR diagram?
Red giants - top right White dwarfs - bottom left
48
How is a star born?
Stars are born in clouds of dust and has known as stellar nebula Usually left from previous supernovae The denser clumps contract slowly due to gravity
49
How does a protostar form?
The clumps from a stellar nebula get dense enough to form protostars These continue to contract and heat up.
50
What is core hydrogen burning?
The protostar becomes hot and dense enough to fuse hydrogen into helium. Pressure produced by this balanced out gravitational collapse
51
When does a star become a red giant?
The hydrogen from core hydrogen burning runs out so fusion stops Core contracts and heats up Outer layers expand and cool
52
What is shell hydrogen burning?
After core contacts and heats up, Material around core contains hydrogen Due to contracting the shell around core is hot enough to fuse hydrogen into helium
53
What is core helium burning occur?
Core continues to contract until it’s hot and dense enough to fuse helium into carbon and oxygen. This releases oxygen which pushes outer layers outwards
54
What is shell helium burning?
Eventually the helium in the core runs out and fusion stops Forces unbalanced so core contracts again This heats shell around core so it’s hot enough for helium into carbon it to fuse
55
How do electrons prevent stars from contracting more?
They exert enough pressure to stop it collapsing further
56
How is a planetary nebula and white dwarf formed?
After shell helium burning the star pulsates and throws off outer layers into a planetary layer. This leaves behind a very hot and dense core known as a white dwarf No more fusion occurs
57
Overview of stellar evolution
Stellar nebula Protostar Core hydrogen burning Red giant Shell hydrogen burning Core helium burning Shell helium burning Planetary nebula/white dwarf
58
What happens when a star is less than 1.4 solar masses?
Fusion stops and core collapses Gravitational force < electromagnetic repulsion (between electrons in atoms) This is called **electron degeneracy pressure** Results in a **white dwarf**
59
What happens when a star is between 1.4 and 3 solar masses?
Gravitational force > electrostatic repulsion between electrons Electrons are forced into protons creating neutrons However the gravitational force is not greater than repulsion between the neutrons (SNF) Results in **neutron star **
60
What happens if a star is greater than 3 solar masses?
Gravitational force > electrostatic repulsion Gravitational force > SNF after neutrons formed Results in **black hole**
61
What are the features of neutron stars
-Primarily made up of neutrons -20km diameter -Same density as a nucleus: very high -Rotate 600 times per second -Emit radio waves as they rotate
62
What is the accretion disc?
A flat disc of matter that is spiralling into the black hole Pieces of planets and stars that are being shredded Hot and bright
63
What is the schwarzchild radius?
Where gravity is so strong that Escape velocity = speed of light
64
What is the singularity?
The original stars code Infinitely dense point
65
How to derive shwarzchild radius equation?
Escape velocity = c Sqrt(2GM/r)=c Etc
66
What’s a quasar?
The accretion disc around a supermassive black hole Produced intense radio signals Absorption lines did not match known elements Known as active galactic nuclei
67
Define the Doppler effect
The apparent change in the frequency of a wave caused by relative motion between the source and the observer
68
Define red shift
The increase in the wavelength of EM radiation due to a relative recessive velocity between the source and observer
69
What is cosmological red shift?
Red shift caused by the fact to e universe is expanding Distant galaxies appear red shifted due to them moving away as the space between expands
70
When calculating change in lambda over lambda what do you put on the bottom of the fraction?
The lab/normal source
71
What are the two key principles of the cosmological principle?
The universe is homogenous (every part is the same) The universe is isotropic ( everything looks the same in every direction)
72
How to start the calculation of the age of the universe?
v=d/t v=Hd d/v=1/H So t=1/H
73
How to use Hubbles law?
V=Hd Velocity is kms^-1 Distance is Mpc
74
Evidence for the Big Bang
Increasing red shift of distant galaxies Cosmic background radiation Abundance of hydrogen and helium
75
How is large abundance of hydrogen and helium evidence for the Big Bang?
Early universe just have been hot and dense enough for hydrogen fusion to occur This can’t have lasted long Hydrogen would have formed first as it is the simplest element Presence of helium due to fusion So universe previously much hotter
76
How is cosmic background radiation evidence for the Big Bang?
The EM radiation produced by the Big Bang cannot have escaped the universe As the universe expanded the EM radiation got stretched out resulting in microwaves
77
Why is dark energy controversial?
Cannot be seen
78
What does dark energy cause?
Causes universe to accelerate
79
Why can’t we see binary stars through direct observation?
No telescopes have a high enough resolving power
80
What’s an exoplanet?
Planet outside our solar system
81
What is the transit method?
Where the light received from a star system as the stars and planets orbit in front of each other
82
What is the radial velocity method?
An exoplanet orbiting a star causes the star to wobble This causes red and blue shift So we can use this to estimate time period and mass
83
Why is transit method hard?
Only works if the star or exoplanet passes between the star and the Earth
84
Why is the radial velocity method difficult?
The mass at the planet barely moves the star so red shift must be found
85
Define the Hubble constant
Gives the ratio of the recessional velocity of galaxies to distance from earth
86
What is the assumption used when using Hubbes law to estimate age of universe?
The universe is expanding at a constant rate
87
When comparing apparent magnitude what does a lower apparent magnitude mean?
Brighter
88
Define a supernova
An object which produced a rapid increase in brightness
89
Explain what is meant by a parsec
The distance at which 1Au subtends an angle of 1 arc second

Physics (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions