Our sun is one of around 200 thousand million stars in the Milky Way galaxy, which itself is one of 140 thousand million or so other galaxies … The average distance between stars is greater than 30 thousand million kilometres, and the nearest star to ours is Proxima Centauri, 4.3 light years away. There is a lot of space.
An enormous amount of information about the stars, both in our own galaxy and others, and even discovery of exoplanets orbiting around some, has been gleaned using terrestrial telescopes. But however powerful, Earth-based instruments suffer from a major drawback – they are Earth-based. Techniques for identifying far-distant stars from the ground rely not on ‘seeing’ them (via the visible light they give out) but on observing and analysing the radiation they emit, and the Earth’s atmosphere blocks out a large proportion of the electromagnetic spectrum (ultraviolet, gamma and x-rays) and distorts images and measurements. Thus a star-gazing observatory operating from beyond the atmosphere is able to acquire data of a much broader spectrum of frequencies, and also has the advantage of being free from gravitational pull which can cause mechanical deformation.
Mapping the cosmos
The first space ‘astrometry’ telescope was the HIgh Precision PARallex COllecting Satellite Hipparcos (neatly named after the ancient Greek astronomer Hipparchos), launched in 1989. The Hipparcos mission produced a catalogue of around 2.5 million stars which was up to 100 times more accurate than those compiled using ground instruments. It was followed by the celebrated Hubble telescope, launched in 1990, which took some of the most stunning images humans have ever seen, giving glimpses of unsuspected cosmic splendours.
Spaceflight has truly broadened the horizons of astronomy – the vast XMM-Newton space telescope, launched in 1999, can analyse powerful X-ray sources far more distant than before, allowing us to look into the mists of time, and upcoming missions such as Herschel/Planck will take us even further, investigating the origin of the very first stars and galaxies.
