Hubble Space Telescope Diffraction Limit

In summary: Overall, the HST's angular resolution limit is determined by the diameter of the primary mirror, and the effects of the secondary mirror can be ignored. In summary, the diameter of the primary mirror is crucial for the HST's angular resolution limit, while the effects of the secondary mirror are negligible.
  • #1
Fightfish
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In the Hubble Space Telescope, light rays from a distant celestial object
(1) first passes through an aperture window of diameter 3m
(2) incident upon, and reflected by a primary mirror of diameter 2.4m
(3) reflected by a secondary mirror of diameter 0.3m to form the final image.

For the angular resolution limit of the HST (assuming diffraction limited), the diameter of the primary mirror is taken to be the diameter of the aperture. What I was wondering is why diffraction effects due to the secondary mirror are not taken into account? More generally, I think this concerns what happens to an Airy disk when I reflect it about, to which I'm not quite sure (does it just scale in size but retain the same angular resolution? - if so, does this not mean that there are no diffraction effects due to the secondary mirror?).

Would really appreciate input on this. Thanks in advance.
 
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  • #2
The diffraction effects due to the secondary mirror are not taken into account because its diameter is much smaller compared to that of the primary mirror, making its effect negligible. This is also why the diameter of the primary mirror is taken to be the diameter of the aperture. When an Airy disk is reflected, it does not retain the same angular resolution as it would in free space, since the beam is distorted by the reflection process. However, the effect is still small enough that it can be ignored in the case of the Hubble Space Telescope, since the secondary mirror is much smaller than the primary mirror.
 

1. What is the Hubble Space Telescope Diffraction Limit?

The Hubble Space Telescope Diffraction Limit is a measure of the smallest angular resolution that the telescope can achieve. In other words, it is the smallest details that the telescope can distinguish in an image.

2. Why is the Hubble Space Telescope Diffraction Limit important?

The Hubble Space Telescope Diffraction Limit is important because it determines the level of detail that can be observed in images taken by the telescope. This limit sets a boundary for the sharpness of images and helps scientists understand the capabilities and limitations of the telescope.

3. How is the Hubble Space Telescope Diffraction Limit calculated?

The Hubble Space Telescope Diffraction Limit is calculated using the formula λ/D, where λ is the wavelength of light being observed and D is the diameter of the telescope's primary mirror. This formula is known as the Rayleigh Criterion and is used to determine the theoretical limit of angular resolution for any optical system.

4. Can the Hubble Space Telescope Diffraction Limit be improved?

Yes, the Hubble Space Telescope Diffraction Limit can be improved by increasing the diameter of the telescope's primary mirror. This was actually done during a servicing mission in 1993 when the telescope's primary mirror was replaced with a larger one, improving the telescope's resolution and increasing the number of details that could be observed.

5. What has the Hubble Space Telescope Diffraction Limit allowed scientists to discover?

The Hubble Space Telescope Diffraction Limit has allowed scientists to discover many new and exciting things about our universe. It has captured stunning images of distant galaxies, observed the birth and death of stars, and provided evidence for the existence of black holes. The high resolution images taken by the Hubble Space Telescope have greatly advanced our understanding of the cosmos and continue to do so with each new observation.

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