Astronomy Chapter 6

Front 1

what are the three basic components of an eye and or camera?

Back 1

pupil, lens, and a retna

Front 2

what does a pupil do?

Back 2

controls how much light enters they eye, it dilates in low light and constricts in bright light.

Front 3

What does the lense do?

Back 3

the lens bends light to form an image on the retina.

Front 4

what does the retina do?

Back 4

the retina contains light sensitive cells (cones and rods) that, when triggered by light, send signals to the brain via the optic nerve.

Front 5

how is light bended in the eye?

Back 5

th peaks and troughts of teh electric and magnetif fields are perpendicular to the light wave's direction of travel. the wave slows down when it hits glass or your eye becasue light travels more slowly through denser matter.

Front 6

what is refraction?

Back 6

for light travelling at an angle towards the eye slows and allows the side of the wave nearest the surface first, then the far side can catch up. the result is bending.

Front 7

what is the focus or focal point?

Back 7

where light from parallel rays converge to a point called the focus.

Front 8

what happens with lights that are not parrallel?

Back 8

they enter the lense from different directions and do not converge at the focus but still follow precise rules as they bend at the lens.

Front 9

what is an image?

Back 9

the result of bending light.

Front 10

what is the focal plane?

Back 10

the plave where the image appears in focus of the lense.

Front 11

In which direction is teh image formed by a lense recorded?

Back 11

it is formed upside down and then reinterpreted by our brain.

Front 12

What is a detector?

Back 12

makes a permanent record of the image. nearly always electronic but used to be photographic film. we can use a shutter to control exposure time and control how much light collects in the detector.

Front 13

what is a pixel

Back 13

modern detectors use electronic chips that are physically divided into gris of picture element. when a photon strikes a pixel it causes a bit of electric charge to accumulate. each subsequent phton striking the pixel adds to that charge. computers measure the total electric charge and determine how many photons have struck each onel

Front 14

what is image processing?

Back 14

alterations made to origionals by recording and manipulating them through techniqpues. often used to bring out details that might otherwise remain hidden.

Front 15

what are the two most fundamental properties of any telescope?

Back 15

light collecting area and angular resolution

Front 16

what is the light collecting area?

Back 16

tells us how much total light it can collect at one time. gnerally round. we usually characterize a telescope by the diameter of its light collecting area.

Front 17

What is angular resolution?

Back 17

the smallest angle over which we can tell that two dots or stars are distinct. if the human eye has an angular resolution of 1arc, two stars can appear distinct only if they have at least this much angular seperation in the sky. the resolution between objects of focus and telescope needs to be big enough for the telescope to be able to seperate the objects in interpretation.

Front 18

what is the diffraction limit?

Back 18

the resolution a telescope can achieve if it were limited only by the interference of light waves. depends on both the diameter of teh telescopes primary mirror and the wavelength of the light being observed.

Front 19

What is a refracting telescope?

Back 19

operates like an eye using transparent glass lenses to collect and focus light. representative of the earliest telescopes.

Front 20

what is a reflecting telescope

Back 20

uses a precisely curved primary mirror to gather light. the mirror reflects the gathered light in a secondary mirror that lies in front of it. this mirror reflects the light to a focus at a place where the eye or instraments can observe it. nearly all current telecopes are reflecting.

Front 21

Why are nearly all current telescopes reflecting?

Back 21

light passes through teh lense of a refracting telescope, lenses must be made from clear, high quality glass with precisely shaped surfaces on both sides. only the reflecting surface of a mirror must be precisely shaped and the quality of the underlying glass is not a factor.

second-- large glass lsenses are too heavy and can be held in place only by edges. it is difficult to prevent large lenses from warping.

chromatic abberation occurrs in refracting telescope brings different colors of light into focus at different ppaces.

Front 22

what is new technology that has improved reflecting telescopes?

Back 22

using many small mirrors to work together as one.

Front 23

what are three basic categories of telescopic observations?

Back 23

imiging-yeilds photographs of astronomical objects

spectroscopy- obtain and study the spectra

time monitoring- tracks how an object changes with time.

Front 24

Imiging

Back 24

at most basic is a camera. often use of filters allow only particualr colors or wavelengths of light to pass through.

these filters can be used to capture invisible light-- like an xray.

Front 25

how can images without natural light be captured?

Back 25

using color coding according to the intensity of the light or to physical properties of the objects in the image.

Front 26

spectral resolution

Back 26

the higher spectral resolution the more detail we can see. a telescope with high spectral resolution requires a longer exposure time than low res.

Front 27

time monitoring

Back 27

allows us to carefully study variations in stars brightness.

Front 28

light curves

Back 28

results of time monitoring in a graph that shows how an objects intensity varies with time

Front 29

how do most astronomers make observations?

Back 29

after identifying an unaswered question the astronomer proposes a set of observations to an organization that manages a large telescope. must make a clear, purposful, persuasive proposal. committees evaluate the proposals and decide which are worthy and which are not.

Front 30

how does earths atmosphere affect ground based observations?

Back 30

daylight, weather. prevents most forms of light from reaching the ground at all.

Front 31

What are three problems our atmosphere creates that affect observations?

Back 31

the scattering of human made light, the blurring of images by atmospheric motion, the fact that most forms of light cannot reach the ground at all.

Front 32

Light pollution

Back 32

scattered bright lights of cities at night.

Front 33

Twinkling and atmospheric turbulence

Back 33

the air in our atmosphere is continually moving and mixing around resulting in turbulance. this changes the light bending properties of light. as a result our view of things outside earths atmosphere appear to jiggle around.

Front 34

What is adaptive optics?

Back 34

can eliminate much of the blurring caused by atmospheric turbulence and allows telescopes to achieve angular resolution close to their diffraction limit.

Front 35

how does adaptive optics work?

Back 35

makes the mirrors do the opposite dance of turbulence to cancel out the atmospheric distortions. shapes of mirrors are changed slightly many times each second to compensate for the rapidly changing distortions. Computers calulate the necessary changes.

if there is no star to serve as a focal point the telescope will shine a laser into the sky to create an artificial star that can monitor for distortions.

Front 36

What is an ideal site for ground base observations?

Back 36

a site that mitigates the effects of weather, light pollution, atmospheric distortion. dark, dry, calm, high.

Front 37

where are the threeimportant sites for telescopes?

Back 37

mauna kea on hawaii

lapalma in spains canary islands, paranal observatory in chile.

Front 38

what types of light can be observed from the ground?

Back 38

radio waves, visible light, longest wavelengths of ultraviolet light, and small parts of the infrared spectrum.

Front 39

Why put telescopes in space?

Back 39

to allow us to observe the rest of teh electromagnetic spectrum that doesnt reach earth.

Front 40

Radio telescopes

Back 40

a specialized kind of telescope now most common in the world. i.e. sattallite. it is shaped to bring radio waves to a focus in front of the dish. the reciever collects the radiowaves reflected by teh primary mirror and reflects them to the television.

Front 41

what are geostationary orbits?

Back 41

orbit above earths equator in exactly the same amount of time earth takes to rotatate. a dish aimed at a particular satellite can always point to the same spot in the local sky.

Front 42

what are cosmic radio sources?

Back 42

rise and set with the earths rotaition.

Front 43

Why are radio telescopes so large?

Back 43

The long wavelengths of radio waves mean that larger telescopes are necessary to achieve reasonable angular resolution.

Front 44

What is radio wave poultion?

Back 44

seruiys unoedunebt ti radui asrtibint use of many portions of the radio spectrum that signals from cosmic sources are almost completly drowned out.

putting radio telescopes on teh far side of the moon would drown out the interference from earth and because radio telescopes can work together , putting them into space in principal can allow them to spread out over a greater distance

Front 45

Infared telescopes

Back 45

look much the same as visible light telescopes. most infrared wavelengths do not reach teh ground. Putting this telescope into space would allow the telescope to cool so that they emit less infrared light.

Front 46

Ultraviolet telescope

Back 46

earths atmosphere almost compleatly absorbs ultraviolet light making observations impossible from the ground. the hubble space telescope is ultraviolet.

Front 47

Xray telescope and grazing incidence mirrors

Back 47

needs to be in space. have sufficient energy to penetrate many materials including living tissue. poses a challenge because it is liek trying to focus bullets.

mirrors can deflect x rays so that they do not damage the image. Chandra is an example of this.

Front 48

Gamma Ray Telescope

Back 48

can penetrate even grazing incidenice mirros and therefore cannot be focused in any traditional sense. these rays are emitted from a number of different astronomical objects but most mysterious sources produce short bursts of gamma rays that quickly fade away.

Front 49

What are three other types of information, aside from light, that we can observe/?

Back 49

known as cosmic messengers

subatomic particle known as neutrino-- produced by nuclear reactions including fusion.

can catch and study cosmic rays with sattelites

gravitational waves

Front 50

1) An optometrist finds that the focal plane of your eye does not coincide with your
retina when you look at objects that are far away from you. What problem would
you notice with your eyesight?
a) everything you see is upside down.
b) everything you see is stretched out.
c) everything you see is blurry.
d) you could not see anything.

Back 50

The focal plane is the distance from a lens in which all of the light rays will form a
clear image of their source. If the focal plane does not coincide with the retina, a blurry
image will result, as light rays from many parts of the object will end up on the same
spot on the retina. When the retina is in the focal plane, each point on the object will
be resolved to a point on the retina.
As an interesting aside, your eye does in fact invert the light that it receives from the
outside world, meaning the image that is formed on your retina is upside-down. Your
brain, however, is used to this happening, and re-inverts the image that you see. If you
were to put on special glasses that flip the image again, everything would appear
upside-down for a few days as your brain adjusted to the new signals being sent to it.
Eventually, it will re-invert and seem normal to you once more, until you take off the
glasses.

Front 51

2) A motorcycle and a car are driving side by side on a highway at night. The
motorcycle’s headlight is twice as bright as each car headlight, so that the total light
coming from each vehicle is the same. You are standing far enough from the vehicles
that the angular separation of the car’s headlights is much lower than the angular
resolution of your eye. Can you tell which vehicle is which?
a) Yes, the car will appear brighter as there are two light sources instead of one.
b) Yes, the car will appear as two point sources of light, the motorcycle as one.
c) No, each will appear as a point source of equally bright light.
d) Yes, the motorcycle will make motorcycle noises, the car will make car noises.

Back 51

c If the angular separation was comparable to your angular resolution, you may see
that one object has a peanut-shaped single light, while the other has a circular single
light, in which case you could reason correctly that the car is the peanut-shaped one.
However, if the angular separation is much lower than your angular resolution, you

Front 52

3) What is the main benefit of using CCD cameras over standard film cameras?
a) CCDs detect a higher fraction of photons.
b) CCD cameras allow for longer exposures, up to hours in length.
c) CCD cameras allow for the colour of an object to be determined.
d) Modern telescopes are designed in a way that makes it impossible to use film

Back 52

CCDs have a much better efficiency than film or your eyes. This means that, for a given
number of incident photons, you will detect many more with a CCD than the other
methods. The more signal, the shorter your exposures need to be to get the same
results, which is very desirable.

Front 53

4) If you have a camera (but not a spectrometer) hooked up to your telescope, which
of the following experiments can you not perform?
a) Measure the period of a variable star (how long it takes to brighten and dim)
b) Determine the colour of a star
c) Measure the brightness of a star
d) Find out how fast a star is rotating

Back 53

Measuring the period of a variable star is as easy as taking a long series of pictures,
finding the brightness in the star of each, and making a graph of brightness versus
time (what astronomers call a “light curve”). The colour can be pinned down by
looking at the star through two or more filters and comparing its brightness in each.
The rotation speed normally requires you to take the spectrum of the star, and look at
how much the emission lines are broadened by the star’s rotation (the light is
redshifted from the part of the star that’s spinning away from you, and blueshifted
from the part of the light that’s spinning towards you, making the line a lot broader).

Front 54

5) If you have a spectrometer attached to your telescope, and are not capable of
direct imaging, which of the following experiments can you not perform?
a) Determine the radial speed of a star.
b) Determine the colour of a star.
c) Determine the rotational speed of a star.
d) Determine the size of a galaxy.

Back 54

The radial speed of the star is found from an offset of the emission line positions from
where you find them in a non-moving source. The colour can be found by looking at the
blackbody continuum of the spectrum. The rotational speed can be found as it is
described in the last question. However, since you only get a graph of intensity versus
wavelength out of a spectroscopic measurement, you cannot measure the physical size
of an object like a galaxy

Front 55

6) Which of the following experiments is least likely to yield useful results?
a) A sea-level visual imaging telescope.
b) A space-based infrared imaging telescope.
c) A sea-level X-ray imaging telescope.
d) A mountaintop visual telescope.

Back 55

Visible light penetrates the atmosphere quite well, so a sea level or mountaintop
imaging telescope would be fine. It’s better to put it into space where there is no such
thing as weather or nighttime, but that’s expensive. Infrared doesn’t penetrate the
Earth’s atmosphere very well, so any infrared telescope would have to be elevated
quite high (ideally into space). X-rays are awful at penetrating the atmosphere, so a
sea-level based X-ray telescope would not work very well at all. In fact, the first
astronomical X-ray observation had to wait until satellite technology allowed for a
space-based observatory.

Front 56

7) Which of the following is not a good reason to launch a telescope into space?
a) It can detect X-ray radiation.
b) There is no atmospheric interference.
c) It is closer to the objects it is measuring.
d) It is able to take data 24/7.

Back 56

Putting a telescope into space puts it a few hundred kilometers above the Earth. This
distance is peanuts compared to even the distance of the nearest star (4 light years or
38,000,000,000,000 km)

Front 57

8) Why must you cool an extreme infrared space-based telescope down to observe
faint objects?
a) Infrared photons will not interact with a warm CCD.
b) A warm telescope will emit its own infrared spectrum.
c) Electronic equipment will work much better at lower temperatures.
d) Detecting infrared radiation will heat up and eventually melt your optics.

Back 57

A warm object emits blackbody radiation. For a spaceborne telescope, this blackbody
curve peaks near the extreme infrared, meaning the detector will pick up a lot of
photons coming from the body of the telescope. This is very bad. If the telescope is
cooled down, it will not emit as many photons in the energy range it is meant to detect,
which means less background noise in the spectra and images.

Front 58

9) Which of the following is not an advantage of reflection (mirror) telescopes over
refraction (lens) telescopes?
a) Reflectors collect more light than a refractor of the same size.b) Reflector optics are easier to manufacture.
c) Lenses on refractors must be held from the edges, and are very heavy.
d) Lenses cause chromatic aberration of the images.

Back 58

Reflectors and refractors collect the same amount of light per unit area. The problem
with refractors is that they are tough to make, have to be very long (reflecting allows
you to make the tube more compact and the light still travels a long distance) and they
degrade much faster (glass warps over time). That is why the majority of scientific
telescopes are reflectors.
Chromatic aberration occurs because different colours of light refract different
amounts through glass (why a prism works). This means that photons of different
wavelengths will focus at different lengths, blurring the object different amounts for
each colour