Radio, UV, Infrared and X-ray telescopes

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AQA A-level physics options - astrophysics chapter 1 telescopes.

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Draw a diagram of a single-dish radio telescope.

  • dish must be parabolic

  • dish reflects signal to the antenna, the signal is amplified and then computer-analyzed.

<ul><li><p>dish must be parabolic</p></li><li><p>dish reflects signal to the antenna, the signal is amplified and then computer-analyzed.</p></li></ul><p></p>
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Why must the dishes be large on single-dish radio telescopes?

  • Radio telescopes collect EM radiation with very large wavelengths (10-0.5mm)

  • When wavelength is large, angular resolution is also large, resulting in large airy disks

  • Therefore, the diameter of the dish must be large to reduce angular resolution.

  • Large dish increases the resolving power and collecting power of the telescope

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Advantages of radio telescopes

  • Can operate during the day as well as night

  • Many celestial objects active in the radio region (protostars, radio galaxies)

  • De-excitation produces radio radiation. Hydrogen gas is everywhere in the universe, therefore radio telescopes are useful in detecting hydrogen clouds

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Disadvantages of radio telescopes.

  • Poor angular resolution compared to optical telescopes

  • Ionosphere can absorb signals below 30MHz

  • Water vapour absorbs singals above 60GHz

  • Man-made interference at radio wavelengths (phones, radio, tv) forces telescopes to isolated areas.

  • Require large structures for support and steering.

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What are infrared telescopes?

  • telescopes that use the same design as optical telescopes (that detect visible light)

  • Detector is made from superconducting material

  • Used to observe cooler objects such as: cool stars, star formation regions, active galaxies, large-scale structures

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Benefits of IR telescopes?

  • Used to observe cooler objects such as: cool stars, star formation regions, active galaxies, large-scale structures. Which cannot be observed with visible light

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Disadvantages of IR telescopes?

  • detector material is sensitive and needs to be maintained just above 0K, and shielded from heat sources

  • Most only be used in space or above the atmosphere as the atmosphere absorbs infrared light

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What are UV telescopes?

  • use the same design as IR and optical telescopes

  • Detect wavelengths in the UV region

  • Most used to observe warmer objects such as: hot massive stars, new white dwarves, core regions of active galaxies.

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How do UV telescopes work?

They make use of the photoelectric effect to convert UV photons to electrons and convert the signal into a current.

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Disadvantages of UV telescopes?

  • UV radiation below 300nm is absorbed by the atmosphere and therefore the telescope must be placed in space (if observing within that region)

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What are X-ray telescopes

  • telescopes that detect in the X-ray region

  • X-ray are high energy so must be made from a combination of parabolic and hyperbolic mirrors to prevent them from passing through

  • Light rays are focused onto CCDs

  • Observe high-energy events such as active galaxies, black holes and neutron stars

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Disadavantages of X-ray telescopes

all X-ray is absorbed by the atmosphere, so can only be used in space.

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What are gamma-ray telescopes

  • telescopes that detect objects in the gamma region

  • gamma has such high-energy that it would pass straight through them, detector made of layers of pixels are used instead

  • gamma rays produce a signal in each pixel they come into contact with

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What are CCDs?

  • charged coupled devices

  • an array of light-sensitive pixels, which become charged

    when they are exposed to light by the photoelectric effect

  • convert light signals into electrical format

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CCD advantages compared to photographic film

  • Quantum efficiency is over 75% compared to 5% for photographic film.

  • The image produced is in digital format which can be processed by a computer immediately.

  • Can handle large differences in signal intensity, therefore faint objects can be captured next to bright objects

  • Can detect wavelengths in infrared, UV and visible

  • Pixel and spacial resolution is higher

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What is quantum efficiency?

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What is pixel resolution?

the total number of pixels used to form the image on a screen.

A lot of small pixels will be able to resolve an image more clearly than a small amount of

large pixels

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What is spatial resolution?

the minimum distance two objects must be apart in order to be

distinguishable. This is used to observe small details.