Stardust and eternity – 3.5.3

Space-based telescopes

Space-based telescopes are located beyond the Earth, in outer space, in orbit around the planet or in deep space. Space telescopes have several advantages over ground-based telescopes. Astronomy performed from ground-based observatories on Earth is limited by the filtering and distortion of light (scintillation or twinkling) due to the atmosphere. A telescope orbiting the Earth, outside the atmosphere, is subject neither to twinkling nor to light pollution from artificial light sources on Earth. The angular resolution of space telescopes is therefore often much higher than that of ground-based telescopes with similar aperture, although nowadays many large ground-based telescopes can reduce atmospheric effects with adaptive optics. Indeed, space-based astronomy is most important for frequency ranges outside the optical window and the radio window, the only two wavelength ranges of the electromagnetic spectrum that are not severely attenuated by the atmosphere. For instance, astronomy of UV and X-rays is almost impossible when carried out from Earth, as these short-wavelength radiations are almost totally blocked by the Earth’s atmosphere and never reach the surface. Another important advantage is that telescopes in space are able to operate 24 hours a day, free from Earth’s day-night cycle, clouds and other limiting weather conditions.

Space telescopes also have some disadvantages. Their most obvious one is that they are much more expensive than ground-based telescopes, not to mention the high launch costs, and they are also extremely difficult to maintain, since they operate fully automatically, without humans on site to fix faulty equipment or deal with other problems. There are also major limitations on the size and mass of telescopes that can be launched, as well as the need to use special materials and designs that can withstand the extreme environment of space.

The rush to build space telescopes began in the 1960s, when astronomers started attaching balloons to telescopes as a means of taking them above the Earth’s atmosphere to obtain a sharper view of astronomical objects. The Hubble Space Telescope – launched by the space shuttle Discovery in 1990 and still operative today – is the most famous of the space observatories; however, it is just one of many that have provided astronomers with new insights into the universe. The James Webb Space Telescope (JWST), launched in 2021 by the European Space Agency (ESA), is the most powerful telescope ever launched into space, with a 6.5 m primary mirror and designed mainly for infrared astronomy. The JWST can also detect orange and red light; its improved resolution and sensitivity will allow it observe objects that are too old, distant or faint for the Hubble Space Telescope, allowing it provide detailed atmospheric characterisation of potentially habitable exoplanets.

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The James Webb Space Telescope – Credit: ESA/ATG medialab

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Images

Transparency of the atmosphere (ESA/Hubble, F. Granato)