A view from here to eternity

Naked eye

The most basic way to study the universe is simply to look at it. Even with just the naked eye it is possible to make all kinds of observations. While some astronomical objects are easy to see, such as the meteors, comets and distant stars, it is also possible to spot several of the planets including Venus, Jupiter, Saturn and Mars, all without a telescope. If the night is clear enough it should also be possible to detect different coloured stars. Danish astronomer Tycho Brahe, who lived in the late 16th century, before the invention of the telescope by Galileo in 1609, was able to measure the angular movement of planets to an accuracy of one 60th of a degree.

Radio telescopes

Using large parabolic dishes, radio telescopes are able to detect a range of different kinds of astronomical phenomena such as pulsars and the remains of supernovae. Celestial objects do not just emit electromagnetic radiation in the form of light: they also act as radiowave sources - for example through the movement of charged particles within their magnetic fields. Radio telescopes function just like regular radios but using directional antennae. They simultaneously detect a wide range of radio frequencies because the precise frequencies given off by celestial objects can be used to help determine their chemical makeup. The largest earth-bound radio telescope, the Arecibo Observatory in Puerto Rico, has a 305m dish, which in the past has been used to provide the first solid evidence that neutron stars exist and to reveal Mercury's correct orbit.

Refractive telescopes

Even with a relatively cheap telescope it's possible to see much more of our universe, or at least our solar system, than would be possible with the naked eye. For example, with a 50mm lens the rings around Saturn become visible. Spend a bit more on a 70mm lens and the Cassini Division of Saturn's ring (usually seen as a dark ring) and Titan, its largest moon, should take shape. Meanwhile a more expensive 114mm telescope will push the resolution further and reveal more of Saturn's rings as well as features on the planet's gaseous surface. Such telescopes usually all work by using lenses to bend light on to a light detector, camera or your eye. Loosely speaking the larger the lens, the further it can see.

Reflective telescopes

Telescopes that use mirrors to focus light instead of refractive lenses have a distinct advantage of allowing much larger lenses to be created. The larger traditional glass lenses are, the greater they suffer from chromatic aberrations - essentially bumps that distort the image. Its weight also becomes impractical. But using mirrors avoids these problems. The Hubble Space Telescope uses this reflective method. Placing telescopes like the Hubble in space, although costly, has the advantage of capturing clearer images that are not blurred by the atmosphere or obscured by weather.

Infrared

Studying infrared light, which exists just beyond the far end of the visible spectrum, can be extremely useful for detecting heat radiated by objects and dust in space that may not show up in the visible light spectrum. Infrared telescopes, such as the Large Binocular Telescope in Arizona, have been used to detect protostars, collections of gas that will eventually form stars, and extrasolar planets. Although too small and cool to see directly, the latter can be spotted by detecting changes in infrared given off by a star as the planet passes by it.

X-ray

Although only useful for detecting celestial objects or gases with temperatures in excess of millions of degrees celsius, such as stars, x-ray emissions do have the advantage of sometimes being greater than the energy given off as visible light. Most of these x-rays are absorbed by the Earth's atmosphere so they are best detected from space, for instance from Nasa's Chandra X-ray Observatory, or from high-altitude, balloon-mounted telescopes. They work by using oblique ring-shaped reflectors made of heavy metals to deflect and focus the x-rays. To date Chandra has been used to observe supernovae and brown dwarfs, and has provided strong evidence that dark matter exists.

Gamma ray 

Some of the first cosmic gamma-ray bursts to be detected were picked up fortuitously by a series of US military satellites equipped with sensors originally intended to spot flashes of the rays given off by terrestrial nuclear bomb blasts. Like x-rays, cosmic gamma rays are mostly absorbed by our atmosphere and hard to detect unless at high altitude or from a space telescope. Being the highest energy form of radiation, detecting gamma rays from the cosmos is a good way to record some of the most violent events taking place in the universe, such as those caused by neutron stars and black holes. Before being decommissioned in 2000, Nasa's Compton Gamma-ray Observatory was able to detect 200 gamma-ray sources that are believed to be highly energetic cores of galaxies beyond our own. Since then, the European Space Agency's International Gamma Ray Astrophysics Laboratory, or Integral, has taken up the mantle and has been used to help detect some of the furthest known objects from Earth.

Ultraviolet

By measuring ultraviolet light given off by stars it is possible to infer a lot about their chemical composition, temperature and even their density. It can also tell us a lot about how the universe evolved. Stars that we can see, giving off visible light, tend to be relatively cool compared with those in their infancy or towards the end of their life cycles. In contrast, hotter stars give off a lot more energy in the ultraviolet part of the electromagnetic spectrum. So, by observing the cosmos in this waveband, it is possible to look at stars at different phases of their so-called evolution. The Hubble Space Telescope has a UV detector that has been used to take some of the deepest images of space - events that took place 13bn years ago.

Neutrino

Another, relatively new, way to observe the universe is to look for neutrinos given off by nuclear reactions taking place in stars and supernovae. These are elementary particles that have a minuscule mass and no charge. The fact that they can pass through ordinary matter makes their detection extremely difficult. But by building neutrino detectors, scientists hope to observe processes that they can't with other types of detector, such as those that take place at the sun's core. Because their signals are extremely weak, detectors such as the IceCube Neutrino Observatory, currently being built at the south pole, have to be built deep underground where other background noise sources are filtered out.