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Astrophysics

Advantages of large diameter telescopes

  • 4 things to know
  • Paper 3, section B

Overview

Collecting power, the Rayleigh criterion, minimum angular resolution and quantum efficiency.

What you need to know

Answer each one before you reveal it.

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Numbers

What does the Rayleigh criterion state, and in what units is angular resolution given?

Numbers

What is a radian, and how do wavelength and diameter affect a telescope's performance?

Numbers

What is quantum efficiency, and how do a CCD and the human eye compare?

Process

In terms of wavelength sensitivity, how do CCDs differ from the human eye?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is meant by the minimum angular resolution of a telescope?

    Model answer

    The smallest angular separation at which two point sources can be distinguished as separate objects.

  2. 2

    State the Rayleigh criterion for resolving two point sources.

    Model answer

    Two point sources are just resolved when the central maximum of one diffraction pattern coincides with the first minimum of the other.

  3. 3

    Write the Rayleigh criterion formula for minimum angular resolution and define each symbol.

    Model answer

    θ ≈ λ/D, where θ is the angular resolution in radians, λ is the wavelength of light, and D is the diameter of the objective lens or mirror.

  4. 4

    In what units must the angular resolution θ be expressed when using the Rayleigh criterion formula?

    Model answer

    Radians.

  5. 5

    Calculate the minimum angular resolution when wavelength = 1 m, diameter = 1.44 m.

    Model answer

    Minimum angular resolution = 1 ÷ 1.44 = 0.694 rad.

  6. 6

    Does a smaller or larger value of angular resolution θ indicate better resolving power?

    Model answer

    A smaller value of θ indicates better resolving power, meaning the telescope can distinguish finer details.

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