PHYS1160 Activity 4 Attempt review PDF

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PHYS1160-Introduction to Astronomy - T3 2021 Dashboard  My courses  PHYS1160-5219_01557  Module 1 (Weeks 1 & 2) — Introduction  PHYS Started on Wednesday, 3 November 2021, 12:56 AM State Finished Completed on Wednesday, 3 November 2021, 2:22 AM Time taken 1 hour 25 mins Marks 13.50/14.00 Grade 9.64 out of 10.00 (96%)

Question 1 Correct Mark 1.00 out of 1.00

First use of Astronomical Telescopes Telescopes are major tools for astronomical research. Galileo was the first to use a telescope to observe celestial bodies. His discoveries changed our ideas about our place in the Universe. An important feature of a telescope is its ability to collect much more light than our unaided eye can. Another advantage of telescopes is their resolving power, the ability to see more detail. These two features depends on the telescope's aperture (size of the primary lens or mirror).

Astrolabe - one of the instruments used for astronomical observations before telescopes were introduced. What information about the celestial objects could be accessed before telescopes were invented? (1 attempt) Select one or more: Brightness

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Spectrum Details of planetary surfaces Position

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Motion

Your answer is correct. Before telescopes were invented we could only observe the brightness, position and motions of the celestial objects. The correct answers are: Brightness, Position, Motion

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Question 2 Correct Mark 0.50 out of 1.00

Types of telescopes The two most basic types of telescope design are refracting and reflecting telescopes. A refractor uses a glass lens to collect light, while a reflector uses a mirror for this purpose. Reflectors are preferred designs, because they can be built larger as the mirror can be supported from its back. Large, heavy lenses are difficult to support and they tend to sag under the weight of glass. Check section 4.1 of Lesson 4 to recall how an image is formed in the telescope. As you will learn later, not all telescopes have eyepieces. In their place different instruments can be installed by measure properties of observed objects.

Two telescopes, A (left) and B (right). Which of two telescopes in the figure is a reflector? (2 attempts) Select one: A B

Your answer is correct. Reflectors have a mirror that is an aperture of the telescope, choice B. The correct answer is: B

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Question 3 Correct Mark 1.00 out of 1.00

Which is most important to ensure the largest light collecting power of a telescope? (2 attempts) Select one: Size of the primary mirror Size of the secondary mirror Size of the eyepiece lens

Your answer is correct. The aperture of the telescope needs to be large to collect as much light as possible. For the refractor this is its primary lens, for the reflector, this is its primary mirror. The correct answer is: Size of the primary mirror

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Question 4 Correct Mark 1.00 out of 1.00

Watch this review of some famous telescopes and the image of the planet you would see with them (ordered with increasing size of their apertures). Note that aperture is the diameter of a primary mirror or primary lens of the telescope.

You will notice that the image of planet Saturn observed through telescopes of different sizes appears less or more blurred. Decide what astronomers can do to see images of celestial objects sharper (choose three that apply): (2 attempts) Select one or more: They can use more powerful eyepieces. They can put telescopes on top of the mountains.

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They can record observations for longer times, using so called longer integration times. They can place telescopes outside of the Earth atmosphere in space.

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They can build telescopes with larger primary mirrors.

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Your answer is correct.  Resolution of the telescope depends on the size of its aperture (primary mirror or lens depending on the design). Also a presence of turbulent atmosphere makes images blurry and "twinkling". Therefore building telescopes high in the mountain is a good solution, otherwise astronomers can place telescopes in space like the Hubble Space Telescope. The correct answers are: They can put telescopes on top of the mountains., They can place telescopes outside of the Earth atmosphere in space., They can build telescopes with larger primary mirrors.

Question 5 Correct Mark 1.00 out of 1.00

Which telescope was used by Edwin Hubble for observations that led to discovery of the expansion of the Universe? (3 attempts) A:

B:

C:

D:

Select one: A B C

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D

Your answer is correct  It is the 100" telescope built on Mount Wilson in Los Angeles, California in 1917, which allowed Edwin Hubble to measure distances to galaxies. A. Cero Alto 1m Schmidt Telescope B. 100 inch Mount Wilson Telescope C. 200 inch Hale Telescope at Palomar D. Alvan Clark Telescope at Lowell Observatory The correct answer is: B

Question 6 Correct Mark 1.00 out of 1.00

Astro Imaging From drawing pictures of objects observed with the eyepiece, more reliable techniques of documenting observations followed. Photographic plates allowed the use of long exposures to collect more light to see faint stars and galaxies. CCD sensors developed in 1980s advanced astronomical imaging even further due to their superior sensitivity.

Exposure is a time that telescope spends on a given field of view during single observation. In other words this is the time when the shutter is open and photons that are falling on a CCD or photographic plate are being detected or counted.Image reproduced from Bubbles, Voids and Bumps in Time: The New Cosmology by James Cornell Above you can see two images of the same region of sky taken with two different telescopes and different detectors: photographic plate and CCD chip. What can you deduce about these two detectors? Tick correct answers. (3 attempts)

Select one or more: It is always better to observe with a smaller telescope when the CCD detector is used. The CCD detector has a superior sensitivity compared with photographic plates or films.

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Sensitivity on the photographic plate does not depend on exposure time of observation. Equivalent observations done with the CCD detector can be done much faster than with the photographic plates.

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Your answer is correct. Correct options are B and D. The advantage of CCDs is their superior sensitivity, therefore comparable observations with the CCD detector can be done faster than with the photographic plates. The correct answers are: The CCD detector has a superior sensitivity compared with photographic plates or films., Equivalent observations done with the CCD detector can be done much faster than with the photographic plates.

Question 7 Correct Mark 1.00 out of 1.00

Spectra A spectrum is seen when light is decomposed into its constituent wavelengths. An example of a spectrum is a rainbow formed when the light from the Sun reflects from the droplets of water in the air.

The rainbow can only form if light reflects at the special angle of 42 degrees inside the droplets of water. 

Another way of forming a spectrum (dispersing light) is passing light through a glass prism. 

 Currently in astronomy large spectrographs use diffraction gratings, which disperse light to form a spectrum. In the image above, what is the function of the mirror at the bottom left that reflects light from the slit to the diffraction grating? (2 attempts) Select one: It disperses the light into its different colours It is the collimator that makes the light rays parallel

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It focuses light onto the detector

Your answer is correct. This is a collimator mirror that makes all the light rays parallel (or collimated). The diffraction grating works best with collimated light and a second mirror (the camera mirror) then focuses the dispersed light onto the detector. The correct answer is: It is the collimator that makes the light rays parallel

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Spectroscopy Why are we interested in observing spectra from stars and other celestial objects? All atoms and molecules leave a unique signature in form of lines in spectrum at wavelengths where they can absorb or emit light. By observing these lines we can learn about composition of different objects. Three types of spectra that you can see below, arise in different situations as described in Lesson 4.

In the puzzle above match necessary elements to produce different types of spectra.

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Doppler effect Spectroscopy can be used to measure movement of objects by observation of the Doppler effect. Review the section 3.18 in Lesson 3 and recall that light source that is moving away from the observer appears redder, redshifted towards longer wavelengths, and light source that is moving toward observer is blueshifted towards shorter wavelengths as shown on the cartoon below.

In the simulation the observer is located on Earth. You can control the movement of the star in any direction. Wavy lines represent the wavelength of light moving towards the Earth and in the perpendicular direction. Observers can measure velocities only along the line of sight. Explore all options in the above simulation and watch the spectral line changing its position compared with the stationary spectrum. The total speed of the object is given together with its component (x-speed) in the direction of the line of sight. Speed is given as a multiple of the

speed of light c = 299,792 km/s. You should notice that the shift of the line depends on the object's velocity. Now, answer Questions 8 and 9.

Question 8 Correct Mark 1.00 out of 1.00

If a star moves in direction perpendicular to the line of sight to the observer, they will see its light 

. (2 attempts)

Your answer is correct. If the star moves in direction perpendicular to the line of sight, the wavelength of light emitted is not changed. The correct answer is: If a star moves in direction perpendicular to the line of sight to the observer, they will see its light [unchanged]. (2 attempts)

Question 9 Correct Mark 1.00 out of 1.00

Can you figure out how high the speed of star has to be in direction of the Earth in order to blueshift the line in the blue part of the spectrum by 10 nanometers? (2 attempts) 600 km/s 

One possible correct answer is: 5996

Your answer is correct. The x-speed corresponding to 10nm was 0.02c (0.02 of speed of light). After multiplying 0.02 by c = 299 792 km/s the result is 5996 km/s. You were allowed 5% deviation from this result.

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Photometry The simulation below shows two stars orbiting each other. This is what is called an eclipsing binary. And we are looking at the brightness of the binary system over time - this is called a lightcurve. We see dips in the brightness of the system each time one star passes in front of the other. Binary Stars

© University of New South Wales, Sydney, Australia

Watch changes in the observed intensity of light from two stars orbiting each other, or the radial velocity of each star as a function of their orbital period. Toggle between displays with the button below. Use the sliders to adjust the temperature of each star and the inclination of the orbit. Select presets with different ratios of stellar sizes (for lightcurves) or masses (for radial velocities).

System type:

Stars of identical radius show radial velocity reset pause

Orbital Inclination:

90°

Temperature of Red Star:

3000 K

Blue Star:

3000 K

In the simulation you can change the inclination of the orbit of both stars (from edge-on to faceon, see below), their temperatures and see how this affects the dips in the lightcurves recorded by the photometer. You can also select a range of different mass ratios (size ratios) for both stars. face on orbit inclination near 0 degrees

edge on orbit inclination near 90 degrees

 You can also observe radial velocity of each star, but we will learn more about it later in the course. The simulation starts with two stars of equal temperature and mass that move around each other in the edge-on orbit. Observe the dips in the brightness over duration of one orbital period. How many dips can you see within one period? Do they look different? Now change the inclination of the orbit and observe what happened to the dips. Now answer questions 10 and 11.

Question 10 Correct Mark 1.00 out of 1.00

Select inclination to be 90 degrees and answer this questions. Why are there two dips in the lightcurve in each period? (2 attempts) 

Your answer is correct. When the orbit is edge-on or close to it, two stars can either eclipse or transit in front of each other, partially or entirely covering one star. When the orbit is face-on, there is no transits and eclipses that can be seen and the amount of light seen by observer is always constant. At 90 degrees the maximum area can be covered by another star and the effect is strongest. In each orbital period two dips are observed, because the first one corresponds to one star transiting in front of the other, and the second dip is due to that star moving behind the other (being eclipsed). The correct answer is: Select inclination to be 90 degrees and answer this questions. Why are there two dips in the lightcurve in each period? (2 attempts) [Every time one star eclipses the other, there is a dip in brightness]

Question 11 Correct Mark 1.00 out of 1.00

Increase the temperature of the red star. Choose a correct statement.(2 attempts) 

Your answer is correct. Depending on the temperatures of stars the dips will be different, if the stars have exactly the same size. Imagine that a hotter star is covered by the cooler star, this will result with a bigger decease in total brightness, than if the cooler star is covered by the hotter star in the orbital motion. The correct answer is: Increase the temperature of the red star. Choose a correct statement.(2 attempts) [The size of both dips is different]

Information

Radio Telescopes In Section 4.5 we talked about radio telescopes, which are made of an antenna that can pick up radio wavelengths that are brought to a receiver and recorded on the computer. Radio sources in space are rather weak, therefore receivers have amplifiers that help to detect such radio waves. Antennas can be similar to your TV aerial, but most often they look like a dish to increase a collecting area (collecting ability) of radio emission. The Parkes telescope is an example of such a design.

Parkes "The Dish" Radio Telescope

Question 12 Correct Mark 1.00 out of 1.00

What is the size of the Parkes telescope aperture?(2 attempts) Select one: 15 m 25 m 64 m 84 m

Your answer is correct. The size of Parkes Telescope's dish is 64m. The correct answer is: 64 m

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Question 13 Correct Mark 1.00 out of 1.00

What is the purpose of the dish in a telescope like this?(2 attempts) Select one: It is a framework carrying a grid of receiving antennas spread over its surface It acts like the mirror of an optical telescope, reflecting radio waves to the receiver at the top

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It is designed to select the exact radio wavelength to be observed

Your answer is correct. The dish acts as a mirror to reflect radio waves to the receiver. The correct answer is: It acts like the mirror of an optical telescope, reflecting radio waves to the receiver at the top

Question 14 Correct Mark 1.00 out of 1.00

Interferometry The Australia Telescope Compact Array at Narrabri in NSW is an example of a radio interferometer. It consists of six radio dishes (five can be seen in the picture below) spaced along a distance of up to 6 km.

Which of the following statements about such an interferometer is correct? (2 attempts) Select one: The interferometer can provide the same resolution as a single telescope 6 km across.

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The interferometer can provide the same sensitivity as a telescope 6 km across. The telescope is designed to observe six different radio sources at the same time.

Your answer is correct  The interferometer can provide the resolution of a telescope 6 km across. However, it does not provide the same sensitivity as a telescope of this size. The sensitivity is just determined by the combined collecting area of the dishes.

The correct answer is: The interferometer can provide the same resolution as a single telescope 6 km across....