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P7 Flashcards

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1
Q

How are object located in the sky?

A
  • sky is divided up into sections, names after constellations
  • Start pointing at the horizon due north
  • Turn westwards throughan angle until you are pointing at the horizon directly below the star

That gives the first angle

  • Now movw your arm upwards through an angle until you are pointing diectly at the star. That gives you the second angle
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2
Q

What is the equatorial coordinate system?

A
  • This is used to pin point the position of star at any time of the year and on any surface
  • uses a reference point in the sky called vernal equinox point
  • position defined by two angles
  • Right ascension and declination
  • Right ascension- measures an angle east of vernal equinox point, angle measured in hours and minutes and seconds
  • Declination- measures the angle of the star above the celestial equator
  • measured in degrees and minutes
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3
Q

What is retrograde motion and what causes it?

A
  • this is where planets seem to slow down and go in reverse for a short time
  • there reasons the planets seem to go backwards as planets orbit the Sun from West to East
  • The earth rotates in the opposite direction. But at one point in the earths rotation you can see the planets go from West to East, yet futher+photo

along the rotation we see the planets orbit from East to west again. This causes the strange orbits of planets

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4
Q

What youst to be considered the centre of the solar system in the 1600’s?

A
  • the earth
  • in 1543 astronomes only suggested That the earth orbited the Sun
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5
Q

What is a solar and lunar eclipse?

A
  • solar = the moon blocks the Sun’s light
  • lunar, the moon moves into thr Earth’s shadow
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6
Q

What is the umbra and penumbra?

A
  • umbra - is a region of the total darkness during an eclipse
  • the penumbra is a region of partial darkness
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7
Q

How does the Moon’ and the Earth’s umbra help us tell when an eclipse will occur?

A

When the Moon’ s umbra toches the surface of the Earth - a total solar eclipse will occur

  • When the Moon passes into the Earth’s umbra- a total lunar eclipse occurs
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8
Q

Why are eclipses so rare?

A
  • as the Moons orbit is tilted at about =photo a 5 degree angle relative to the palne of the earth
  • usually the Sun, moon and earth aren’t in a line, which means no eclipse will occur
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9
Q

What is special about a telescope compared to the human eye?

A
  • bigger aperture than the human eye, means radiation is collected, which allows it to see fainter objects
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10
Q

what are pulsars?

A
  • These are distant objects that send radio waves that vary with an extremely regular pulse
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11
Q

How does a pinhole camera work?

A
  • light is scattered, or given out by objects as it passes through the pinhole and makes an image on the paper
  • called a real image
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12
Q

What is a ray diagram?

A
  • shows how rays of light travel
  • eg. pinhole is very small, each point on an object produces tiny spotts on light sensitive paper
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13
Q

What can a ray diagram for a pinhole camera help explain?

A
  • why is the image upside down
  • what happens to the image if the screen is moved away from the pinhole
  • what happens if you enlarge the pinhole
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14
Q

What do converging lenses do?

A
  • cause light to refract and bend once in the lense and also wjen it leaves the lense
  • light is bent so it coverges at a point called the focus
  • the distance from the centre of the lens to the focus is called the focal length of the lens
  • longer focal length the bigger the image
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15
Q

How do the focal legth determine the shape of the lense?

A
  • a lens with a long focal length has surface that are not very srongly curved
  • a lens with a short focal length has a surface that are more strongly curved
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16
Q

What is the equation for the power of a lens?

A

power( in dioptres)= 1 divided by the focal length in meters

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17
Q

What do rays from infinity do when they reach a lens?

A
  • they all are parallel to eachother
  • converge at a focus on one side of the principal focus
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18
Q

What happens when you look through a converging and diverging lense?

A
  • when you look through a :
  • coverging lens nerby an object the object image is bigger that the object-lens magnifies it
  • the right way up
  • diverging lense
  • you see a vrtual image that appears smaller that the object and is the right way up
  • a diverging lense cannot make a real image on its own
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19
Q

What is refraction?

A
  • this is when light passes from one material to another and change direction slightly
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20
Q

When does refraction occur?

A
  • This is because light travels slower in different material
  • changes direction as one side of the ray slows down slower then the other causing it to turn
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21
Q

How was the first telescapoe made?

A
  • Dutch inventer Hans Lippershey, 1608
  • puts to converging lenses, together, which enlarged an image
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22
Q

How is a simple telescope made?

A
  • put the stronger of the two lenses near you eye
  • the weaker lense is further away
  • varying distance between the two lenses, allow the telescope to focus
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23
Q

What does a ray diagram of a telescope?

A
  1. objective lens collects light from a distant object
  2. Parallel rays of light enter the objective lens from a point on the distant object
  3. Each set of paralle rays is focused by the objective lense, so a real image is formed
  4. the eyepiece is magnifying glass, ehich is used for the eyepiece because it magnifies the image more .
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24
Q

How does magnification work in telescopes work?

A
  • the angle between the rays of light passing through the eyepiece and the principal axis is greater than the angle between the rays passing through the objective lens and the pricipal axis
  • makes the object seem bigger
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25
Q

What is the equation for magnification?

A

magnification= focal length of objective lense divided by focal length of eyepiece

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26
Q

What is used to measure the amount of radiation recieved at different frequencies?

A
  • spectrometer
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27
Q

What is dispersion?

A
  • this is where white lights passes through a prism and splits into different colours
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28
Q

What causes dispersion?

A
  • due to the colur depending on the frequnecy of light
  • red lowest frequency -violet highest frequency
  • colours travels through the light at different speeds . only small differences, but enough to split the colours apart
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29
Q

What are two different spectrometers?

A
  1. a spectrometer can be attached to a telescope so it produces a spectrum
  2. use agrating, which is set of very narrow evenly parallel liines on a very thin sheet of glass on ashiny surface
    - when the light shrines on the grating, different colours emerge at different angles to produce sveral spectra
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30
Q

Why aren’ t lense used in modern telescopes?

A
  • for large telescopes lenses have a disadvantage
    1. the largest objective lense possible is 1 meter in diameter
    2. it is very difficult to ensure that glass of a large diameter lense is uniform in composition all the awy through
    3. A large coverging lense is quite fat in the middle . some light is absorbed on its way through, making faint objects appear even fainter
    4. Glass lenses only focus visible ligth radiation in other parts of the electromagnetic spectrum is either completely absorbed eg. ultravioletor goes straight througheg radio
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31
Q

How do reflecting telescopes work?

A
  • mirror in the telescope is curved to focus ligth
  • in a parabola
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32
Q

What is the law of reflection?

A
  • angle of incidence=angle of reflection
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33
Q

What are the advantages of using a mirror over lenses on telescopes?

A
  1. a mirror reflects rays of all colours in exactly the same way
  2. it is possible to support a mirror several meters in diameter so that it does not sag. its weight can be supported from the bade as wellas the sides
  3. a mirror can be made to very smooth standards so that the image is not distorted

4, By choosing suitable materials, reflectors can be made to focus most types of electromagnetic radiation

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34
Q

What are the ides of where to place the observer in a reflector telescope?

A
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35
Q

What are proffessional telscopes very big?

A
  1. they need to collect a lot of radiation in order to detect faint images
  2. also the image is clearer so more detail can be seen
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36
Q

Why do radio telescopes need to be bigger that optica; ones?

A
  • as they need to get the same resolving power
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37
Q

What is diffraction?

A
  • there is where waves hit a barrier(apeture) and bend a little at the edge and then pass into the shadow region behind the barrier. the longer the wavelength of the wve, the more it diffracts
  • ata gap between two barriers, waves the width of the gap is similar to their wavelength, the waves beyond the gap were almost perfect semi- circles

i f the gap is really tiny, much laess than then the wavelength of the wave, the wab

ves do not go through at all

38
Q

What is the issue with light pollution?

A
  • it reduces visibility of star from urban locations
  • this is because ligth from the population enters the atmosphere where it is scattered, hiding stars
39
Q

Furthermore hoe can electrical equipment affect radio telescopes?

A
  • provides interference to telescopes, certain radionfrequencies must be left clear for astronomical observations
40
Q

What is parallax?

A
  • it is a way to measure the distance from earth to a star
  • compare the direction of the star at an interval of six months. the parallax angle is half the angle moved by the starin this time
41
Q

How is parallax measured?

A
  • fractions of a second of an arc
  • 360 degrees in a full circle
  • 60 minutes of arc in 1 degree
  • 60 seconds od an arc in 1 min
  • so seconds of an arc is 1 divided 3600 of a degree
42
Q

What is the unit distance used by astronomers?

A
  • a parsec9pc)
  • an object whose parallax angle is 1 second od arc is a distance of 1 parsec
  • Distance(parses)=1 divided by the parallax angle
  • smaller angles means a bigger distance
  • a 0.5 parsec=3.1 times10(13)km.
43
Q

How can relative brightness used to calculate the distanec far away a star is?

A
  • Juggens
  • studied star Sirus
  • next day placed a screen between himself and the sun, he made asucesssion os smaller and smaller holes in the screen until he felt that the light was the same as Sirus
  • calculated1 divided by 30000 of Sun’s brightness= Sirus
  • estimated the distance to Sirus was 27664 times as distant as the Sun
44
Q

What were some problems with Huggens method?

A
  • all the measurments were subjectice
  • his method assumed Sirus and the Sun were identical star
  • he had to assume that no light was absorbed between Sirus and his screen
45
Q

What is luminosityof a star and what does it depend on?

A

-is the power output of a star

factors dependent on it are

    1. its temperature- a hotter star radiatesmore energy per second from each square metre of its surface
      1. its size- a bigger star has a greater suface radiating energy
      2. distance away from earth
46
Q

Why are Cepheids variable stars?

A
  • stars with luminosity that variates regulary
  • it is thougth these star are expanding and contarcting, which makes its temperature and luminosity vary
47
Q

What were the two parts to Henrietta leavitts’s method to measure the distance to star clusters in theMilky Way and other galaxies?

A
    1. find some nearby Cepheids whose distance have been measured using other methods
  • measure their brigthness and work out their luminosities
  • plot graph of luminosities against period
    2. look for a cepheid in a star cluster or galaxy of interest
  • measure its observed brigthness and period of variation
  • from the period , read its luminosity off the graph
  • use the luminosity and observed brightness to work out the distance
48
Q

How did William Herschel try to measure the shape of the Milky Way and what did he assume?

A
  • 1785
  • took his telescope and counted stars,rotated a little bit, until he completed full circle
  • assumed 1. he could see all the stars in the direction he was looking wrong as more powerful telescope can see more stars
    2. could see to the far end od the galaxy - wrong Dust clouds dide stars in the centre of the galaxy
49
Q

What did Shapley discover around about globular clusters?

A
  • they were at maxium about 100,000 light year away and seemed to lie in a sphere around the Milky Way
50
Q

What did Hubble discover in 1923?

A
  • that spiral nebulae were seperate galaxies
  • Hubble found at first Andromeda
51
Q

What else is studied in the Universe apart from stars and planets?

A
  • comets
  • rocky,icy rockes that orbit the Sun elliptically
  • asteriod
  • large jagged rocks- orbit the Sumn in between Mars and Jupiter
  • planetary nebulae
  • formed by dying stars

Supernovas

  • remains of dying star that exploded
  • quasar
  • galaxies containing giant blade holes
52
Q

What can we learn from supernova’s?

A
  • how a star dies
  • can be used to measure the distance to far away galxies like Cepheids
53
Q

What did Hubble discover ?

A
  • he discovered galaxies were moving away from the earth
  • redshift
  • turned out the more distant the galaxy its speed of recession
54
Q

What is the Hubble constant?

A

speed of recession= Hubble constant times distance

  • first valu was 500km/s per megaparsec
  • but other astronomers realised Hubbles constant was too hight
  • 2010 accepted value is 70.6 plus or minus 3.1km/s per megaparsec
55
Q

What did Hubble discover about the Universe?

A
  • it was expanding from the point of the big bang
56
Q

How is the colour of a star linked to temperature?

A
  • red 4.2 times 10(14) Hz
  • violet 7.5 times 10(14) hz
  • can be measured by a spectrometer
57
Q

How do hot stars appear on graphs?

A
  1. for a hotter star, the area under the graph is greater, it shows that the luminosity of the star is greater
  2. For a hotter star , the peak frequency is greater, it produces a greater proportion of radiation of higher frequencies
58
Q

How canwe know the composition of the Sun?

A
  • by analysing Spectrums
  • an emission spectrum is looking at the light emitted by a chemical
  • each chemical has its own unique spectra
59
Q

What do the black lines represent in the Sub’s spectrum?

A
  • wavelength that are aborsorbed by the atomosphere
  • eg. the absorbtion spectrum
  • allows astronomers to identify all the elements in the Sun and other stars
60
Q

How is light emitted?

A
  1. the electrons in an atom can only have certain values of energy Scientists think of them as ocuppying points on a ladder of energy levels
  2. When an elctron drops from one energy level to another, it loses energy
  3. As it does so, it emits a single photon of light - that is, apacket of energy. then the energy of the photon is equal to the difference between the two energy levels
    - the greater the energy the energy gap
    - the greater the photon, the higher energy photond correspond to high frequncy colours
61
Q

How is light absorbed?

A
  1. white light consists of photons with all possible values of energy
  2. An electron in a low energy level can only absorb aphoton whose energy is just right to lift it upto a higher energy level. when it absorbs such a photn, it jumps to a higher level

the white light is now missing photons that have been absorbed because their energies correspond to rung on the ladder of energy levels

the ‘missing’ photons correspond to the dark lines in an absorbtion spectrum

62
Q

How does nuclear fusion occur in the Sun?

A

-fusion occurs when two atomic nuclei het close together, that the strong nuclear force

makes them react

  • originally nuclei repel eachother, because of electrostatic forces
  • can only get close enough, with very high ebergy
  • so very hot, so nuclei are enrgetic enough to fuse
63
Q

What is the process for fusion in the Sun?

A
  1. two nuclei make a deuterium nuclei photo
    - in the process as protons decay a to become neutrons it realeses a positron
    - small positive particle like an electron
    - the whole process is
64
Q

How can the energy released be described?

A

E=mc(2)

energy released= loss of mass times the speed of light in a vacuum (2)

fusion of hydrogen to helium involves a moss loss of 0.7%

65
Q

What is the H-R diagram?

A

it shows stars being plotted on a grapg looking at luminosity and temperature to see if there is a connection

  • published by Ejnar Hertzsprung

1911

66
Q

How the H-r diagram interpreted?

A
  • 1924 200,000 stars catalogued
  • stars fell into three groups
  • 90% of star =sun fell across a diagonal line called the main sequence
  • 10% of star were white dwarfs small and hot

1% of satrs were red gianst and supergiants - more luminosous that the main sequence starts with same temperature

67
Q

What does the H-R diagram reveal?

A
  • astronomers believe stars chnge grops during thier lifetime
  • they spend most of thier time in the main sequence, than less time as a giant or white dwarf
  • only exceptions- supernova explosions
68
Q

What is between stars?

A

interstellar medium(ISM)- a gas

  • mostly hydrogen, helium and small amounts of other elements
  • can form new stars under the right conditions
  • ISM includes clouds

planetary nebulae, supernova remments and other hot nebulae

  • dense clouds
  • cold and more dense then ISM
  • only seen because they block light

between dense cloud and glowing nebulae more ISM

69
Q

How can you describe a gas?

A
  • volume
  • mass the amount of matter in kg.
  • pressure- the force the gas exerts per unit area on the walls of its container
  • temperature-in celcius and kelvin
70
Q

What is the relation between volume and pressure?

A
  • as volume decreases pressure increases
  • pressure inverly proportional to volume
  • this occurs because there is less space for the gas so there is more collisions with the wall
71
Q

How does temperature affect pressure and volume?

A
  • gas is cooled- pressure and volume decresae
72
Q

What is the difference between the Kelvin scale and Celcius scale of temperature?

A
  • Celcius starts at ) celcius- melting point of ice
  • Kelvins start at absolute zero
  • 273
  • gas between each degree the same
  • conversion

k=c+273

c=k-273

73
Q

Why does low temperature affect pressure and volume?

A
  • the particles lose energy
  • less colisions with the containers- pressure down
  • if pressure not constant volume decreses to compenste
  • there is no pressure at absolut zero
74
Q

What are some gas equations?

A
75
Q

How does a star form?

A
  1. cold gas cloud and dust starts to cpntarct

pulled together by gravity

  1. break up into several smaller clouds, which contract
  2. in clouds- each particle attracts each other, cloud collapses into its centre, forms a rotating disc
  3. gas particles attracted to the centre

move faster and get hotter

  1. hot enough for fusion- star is born
  2. material further out in the disc clump released and forms planets
    - at the begining as prostar
    - multiple stars formed- cluster
    - planets formed also
76
Q

What are the two ways that explain how fusion occurs in a star?

A
  • gas compressed -temperature rises gravity compresses the gas
    2. each particle in the cloud attracting every other particle fall(inwards) particles collide with each other sharing energy .Fastest particles in the centre(hotest there(particles that have fallen further have more kinectic energy)
77
Q

How is the Sun believed to be made up internally of Sun?

A
  • 1 core hottest part with a temperture of about 14 million Kelvin
    2. Radiation travels outwards through radioactive zone(photons)
    3. close to the surface, only 1 million Kelvin, matter can flow quite readliy, and convections current are set up, carrying haet of convective cells that cause thr granter appearence of the Sun’s surface
    4. Electromagnetic radiation is emitted by the photosphere and radiates outwards through the solar atmosphere
  • this can be applied to other

main sequence stars

+table

78
Q

How did the Sun became a red giant?

A
  1. fusion slow down, causing core to cool down- less pressure are collapsed
  2. Star’s outer layerscountaining hydrogen, fall inwards, becoming hot
  3. new fusion reaction, shell expands
  4. suface temperature falls yellow= red
79
Q

What is happening inside a red giant?

A
  • outer layers expand, core contracts and heating up to 100 million Kelvin
  • Helium nuclei have bigger positive charge, requires more energy to fuse with hydrogen
  • form heavier elements carbon, nitrogen and oxygen
  • out layers cool and drift off
  • collapsed inner core remain white dwarf. No fusion occurs in white dwarf, so cools
80
Q

What can massive star become?

A
  • become supergiants
  • core 3 billion K
  • can form more complex elements
  • heavier elements
81
Q

What happens when elementsbeyond iron are made in a star’s core?

A
  • fusion of nuclei to make iron
  • increase in mass
  • no energy output
82
Q

What happens to supergiants?

A
  • once start making iron
  • outer layer no held up by the pressure of the core, collapse inwards
  • core becomes very hot
  • outer material collides with the core and is flung outwards
  • huge explosion- supernove
  • temperatures rise to 10 billion K
  • can form elements up to uranium
83
Q

What happens to Supernova rement?

A
  • become part of contarcting dust clouds
84
Q

What happens to the core of a supernova?

A
  • if mass is lower than 25 solar masses- becomes a netron star
  • made up only of neutrons that are compressed
  • bigger core collapses into a black hole
85
Q

How does can neturon stars be the origin for pulsars?

A
  • core collapses
  • spins faster
  • magnetic field becomes concentrated
  • results in beam of radio waves coming out of its magnetic poles
  • as netron stars spin round become swept across space
86
Q

Is there life on other planets?

A
  • 100 thousand million stars in the Milky Way
  • may be life there
  • may be organisms with intelligence
  • maybe can communicate with them
87
Q

What are exoplanets?

A
  • planets orbitting stars
  • all exoplanets have been bigger than earth
88
Q

What is SETI?

A

search for extra- Terestrial Intelligence

  • began n 1950’s when first satellites were launches
  • eg. 50,000 people around the worl, allow use of their computers to procees data for radio telescopes to see weather it conrains any sign of inteeligence signals
89
Q

What is the difference between the Sun and the Moon’s path through the sky?

A

The Sun appears every 24 hours

  • the Moon moves acroos the sky every 24 hours and 49 minutes

sun doesn’t go through the sky the earth spins on its axis

  • earth spins east the west

moon slowly moves from west to east

explains movements of the Sun and moon

90
Q

What are the moon’s phases?

A
  • Moon is lit up by the Sun’s rays
  • when moon is on the opposite side of the earth to the Sun- full
  • when the moon is in the diection of the Sun- -new moon
91
Q

Why are the constellations diferent at different times of year?

A
  • Earth orbits halfway round the Sun every six months can see starsin the opposite direction to the Sun
92
Q

whta is the difference between a solar and sideral day?

A
  • solar day is 24 hours
  • sideral day is 23 hours 56 minutes

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