Hubble Space Telescope

Text by
Göran Östlin
Professor in Astronomy, Stockholm University


 

Two inventions that have been important for our understanding of the universe are the telescope and the camera. With a telescope, images of celestial bodies can be magnified, and the amount of captured light is multiplied many times over, compared to the naked eye.

Photography – from the beginning analogue/chemical and nowadays digital/electronic – freezes time and creates a permanent image. Long exposure time also enables us to portray objects fainter than our eyes can perceive. The combination of telescope and photography offers astronomers powerful tools to study the secrets of the universe. The development of larger telescopes and more sensitive photographic methods conti- nues to push the boundaries of our know- ledge about the universe, and allows astro- nomers to see farther and farther away.

Since the speed of light isn’t infinite, astro- nomers are not seeing what’s happening now, but when the light was emitted: the light from the sun is eight minutes old when it reaches us, and the light from the Andromeda Galaxy (M31) a dizzying 2.5 million years old. It was towards M31, among others, that the American astronomer Edwin Hubble aimed the largest telescope at the time, at the Mount Wilson Observatory in California. He could show that the Andromeda Nebula in actuality was its own galaxy that, like our own Milky Way consists of hundreds of billions of stars.

One problem with astronomical observations is the Earth’s atmosphere. Not only do clouds and artificial light sources sometimes disturb the observations: turbulence – small air movements – makes the images slightly blurry (the same phenomenon makes the stars look like they are twinkling). On top of everything, the atmosphere only lets light of certain wavelength-intervals pass through. If we could place a telescope in space, orbi- ting the Earth, it would be possible to observe without the disturbances of the atmosphere. During the ‘60s and ‘70s, these ideas started to take form, and that eventually led to the construction of the Hubble Space Telescope.

Hubble was meant to be sent up by one of NASA’s space shuttles in 1986, but the Challenger accident happened that same year, which led to the space shuttles being stranded for several years while safety was improved. Finally, in 1990, Hubble was launched by the shuttle Discovery. The space shuttles also meant that Hubble could be upgraded and repaired when needed, and because of five separate visits – to change cameras and install spectrometers, among other things – Hubble has remained competi- tive despite its age. The shuttles were retired 2011, which makes new repairs impossible, and the space telescope is now living on borrowed time, until some vital part breaks.

The absence of an atmosphere means that Hubble, in theory, has about ten times better image-focus than the largest and best telescopes on Earth, but the first images trans- mitted down to Earth were far from success- ful, in fact they were all blurry. It turned out that the 2.4-meter primary mirror had the wrong cut, due to a faulty measuring instru- ment. Corrected optics were quickly constructed, and in December 1993, the astronauts of the Endeavour installed it, and since then Hubble has been serving science in a class of its own.

Hubble’s unique image definition makes it possible to study in detail how galaxies and nebulas are constructed, even seeing planets around other stars besides the Sun. Hubble also makes it possible for us to study what the universe looks like in the ultraviolet spectrum, which we can’t do from Earth. It’s fair to say that because of Hubble, a veil has been lifted between us and space, and it lets us see the universe in a new way. The most distant galaxies Hubble has captured emitted their light more than 13 billion years ago – a few hundred million years after the Big Bang, and long before the Sun and the Earth were formed. No other telescope has been able to study such distant celestial bodies. The young, bright blue stars in these distant galaxies, that make it possible for Hubble to capture them, have long since died.

What we register is essentially a light-memory traveling through space. Hubble teaches us that the universe, with its galaxies, is con- stantly changing: splendid spiral galaxies, like our own Milky Way for example, didn’t exist in the universe’s childhood, but have evolved over time from smaller galaxies colliding and combining.

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