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Why is the Hubble Telescope in space?

Do we get enhanced clarity and range by placing it in space?

What can it achieve from space that it could not achieve from Earth?

hubble telscope in space

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2 Answers

up vote 19 down vote accepted

As @astromax observed, one of the primary factors that makes a space based telescope better than an equivalent telescope of the same size is scattering.

Along with scattering, there is also refraction which can be especially problematic when combined with atmospheric turbulence. In the modern era, this problem can be remedied to a certain extent using adaptive optics, but since the Hubble was designed, built, and launched before AO became practical in the 1990's, a space telescope represented the pinnacle of optical clarity for that time.

However, there is another important optical property of the atmosphere, absorption. Although the Hubble is primarily a visible light telescope, it does have instruments that cover both the near UV and near IR, both of which are absorbed by the atmosphere more than visible light.

Furthermore, there are practical advantages of space based telescopes. There is neither weather, nor light pollution in space.

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There are a number of things which are important for a telescope. The first is the light collecting power of the telescope, which is simply a measure of how many photons the telescope can collect from an object. This, not surprisingly, is affected by the size of the primary mirror/lens of the telescope. The second issue is the telescope's angular resolution, which is a measure of the level of detail which can be seen within an image. Telescopes on the surface of the Earth have to worry about the atmosphere, which due to its non-uniformity causes blurring and smearing of images (this contributes significantly to what's known as the point spread function). The HST is in space to avoid atmospheric effects, and thus, it achieves higher angular resolution by doing so.

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