The Hubble Space Telescope has for the past 27 years powered NASA’s dream of putting people into space.
Launched on 24 April 1990, aboard Space Shuttle Discovery, it was designed to be looked after by flesh-and-blood astronauts, and repairs and maintenance have run up a bill that would have paid for several new telescopes.
Hubble has been the training ground for a generation of spacefarers. Servicing it has taught NASA everything it knows about building and maintaining the International Space Station. It is also a very fine instrument indeed. For the past 27 years, Hubble has given us new perspectives on planets across the solar system and jaw-dropping views of locations across the universe. Here are some of the space telescope’s greatest hits.
Many revolutions in astronomy have been tied to specific telescopes and their uers, from the tiny telescope with which Galileo proved that the Earth revolved around the Sun and discovered the moons of Jupiter; the Leviathan of Parsonstown, used to by the 3rd Earl of Rosse to discover the spiral structure of what are now known as galaxies, and the 2.5-meter Hooker Telescope used by Edwin Hubble during the 1920s to measure the expansion of the Universe itself. And over the last 27 years, the Hubble Space Telescopes has kept up this noble tradition.
Although the Hubble’s mirror, with a diameter of 2.4 meters, is smaller than the mirror of even the Hooker telescope, it’s location in orbit above the Earth’s distorting atmosphere and the use of state-of-the-art CCD image sensors has helped to pin down the age of the Universe, determine the existence and distribution of dark matter and dark energy, and probe the atmosphere of planets in distant star systems.
The Age of the Universe
Astronomers measure the distance of galaxies by observing cepheids, a type of variable stars in which the brightness is related to the period of their brightness variations. Because of its sensitivity, the Hubble is able to observe cepheids in very distant galaxies, millions of light years away. By calculating how long these galaxies have taken to reach the measured distances, starting from the Big Bang, they helped establish the age of the Universe, 13.7 billion years.
Besides cepheids, supernovae can also serve as distance indicators, and because they are much brighter than cepheids, they can be observed over enormous distances. Images of supernovae in very distant galaxies provided by Hubble showed that their apparent brightness was too low to be at the distance of these galaxies inferred by the red shift alone. So their distance showed that the expansion of the universe is speeding up. Why this happens is still an open question. It has to be caused by a yet unknown force, called dark energy.
Dark matter is not visible by itself, but its effects can be identified in images taken by the Hubble and other ground-based telescopes: the dark matter in galactic clusters deforms the apparant shape of distant galaxies behind it by bending the light coming from them into arcs. Known as gravitational lensing, this allows the location of dark matter clouds to be established.
The discovery of numerous exoplanets, planets that circle stars other than the Sun, has given rise to the speculation that many planets with atmospheres and temperatures to Earth’s might exist and would harbor life. That one could actually analyze the composition of the atmospheres of such planets was one of the unexpected achievements of the telescope. In 2013 the Hubble succeeded in detecting small amounts of water in the infrared spectra of five planets while they were passing in front of the stars they are circling.
NASA hopes to keep Hubble operating through 2020 to overlap with its successor, the James Webb Space Telescope, due to launch in October 2018.