Astronomy is the science dealing with all the celestial objects in the universe, including the planets and their satellites (e.g. our Earth and the moon), comets and meteors, the stars (including our sun), and interstellar matter, the star systems known as galaxies, and clusters of galaxies.
Ancient peoples watched the stars and memorised their positions relative to each other by visualising constellations - shapes which suggested to them mythical figures. If a new star appeared its position was noted on a star map. The first comet was recorded this way, over 2,000 years ago.
Today, astronomers use telescopes (optical, radio, and others) to study stars, planets, and galaxies. Astronomers are scientists who study all the objects in the universe, such as stars, planets, and Galaxies. They use ground-based telescopes of many kinds, launch space probes that visit the other planets in the solar system, and send satellites into space to study the universe from high above the Earth's atmosphere.
Astronomy analyses the radiation received on Earth or its vicinity, from the constituent parts of the Universe. For most of man's history, the visible part of the electromagnetic spectrum was the sole medium used for astronomical observation, and the human eye was the only receiver. The invention of the optical telescope greatly enhanced our view of the night sky, revealing spectacular details of the Moon and planets, and masses of previously unseen stars and nebulae.
Instruments such as photometers (which measure light intensity) and spectrometers (which split light into its spectrum, or constituent colors), have made the physical study of stars possible, leading to knowledge of their nature, structure, and evolution. These instruments, and photographic plates and electronic imaging devices (e.g. charge-coupled detectors, or CCDs - now used in the consumer market such as in digital cameras) have made possible the field known as astrophysics - the aplication of physics to astronomy, and have extended the range of the accessible spectrum outside the visible portion.
Astronomers are no longer limited to the visible or near-visible spectrum. Radio telescopes, invented in the 1930s, and the discoveries they made have revolutionised astronomy, and thanks to space technology, we now have access to the whole electromagnetic spectrum, as well as particles from the Sun and other objects. Spacecraft carry telescopes and other astronomical instruments above the Earth's atmosphere, and to other planets in our solar system. This has created whole new branches of astronomy such as X-ray and Gamma-ray astronomy.
- Radio telescopes
- can detect radio objects that are extremely far away and are hard or impossible to see optically. Pulsars, quasars, and radio galaxies were discovered this way. The 'mirror' of a radio telescope is typically a dish of metal or wire mesh. Some radio telescopes are simply rows of wire antennae in a field. Signals from radio telescopes are analysed by computers; and if the data from several telescopes are properly combined, the results can be equivalent to a single telescope much larger than the individual ones involved.
- Infrared (IR)
- is the part of the near-optical spectrum we perceive as heat rays, and these are emitted by stellar objects such as the Sun. IR is detected by satellites and ground telescopes, revealing the centers of galaxies, and gas clouds ('nebulae') where stars are being born.
- Ultraviolet (UV)
- is at the other end of the optical spectrum from IR, and can be used to learn the composition of stars.
- can be received by satellites carrying special detectors. These satellites have observed supernovae, and black holes which emit X-rays as they suck in gases from nearby stars.
- Gamma rays
- have very high energy, and come from many objects, e.g. galaxies, and pulsars - the remnants of novae.
- are elementary particles with no rest mass and no electric charge; they pass through virtually everything, unimpeded. Neutrino detectors placed deep underground can intercept a few of them, and the data used to analyse the Sun and novae.
- Visible light
Theoretical Astrophysics is the discipline that seeks to explain the phenomena observed by astronomers in physical terms. With this purpose, theoretical astrophysicists create and evaluate models to reproduce and predict the observations. Theoretical astrophysicists use a wide variety of tools which include analytical models (for example, polytropes to approximate the behaviors of a star) and computational numerical simulations. Each has some advantages. Analytical models of a process are generally better for giving you insight into the heart of what is going on. Numerical models can reveal the existence of phenomenon and effects that you would not otherwise see.
A comet is a small body from the outer reaches of the solar system similar to an asteroid but composed of ice. Often described as "dirty snowballs," they are composed largely of carbon dioxide ice, methane ice, and water ice with a mixture of dust and small stony aggregates mixed in. Comets are thought to be small pieces of debris left over from the formation of the solar system, representing a sample of the original composition of the nebula that condensed to form the Sun and all of its planets.
Questions concerning the nature of the Universe as a whole were until recently, the province of philosophy and superstition only. There was no way to examine the fabric of the heavens to see what it was made of - until the invention of spectroscopy and the construction of powerful telescopes in the past century. The data collected have been analysed with sophisticated mathematical techniques, and models have been developed which help us to understand how this Universe may have come to be how it is. Cosmology draws on the physical sciences - especially mathematics, physics, and astronomy.
The planets are vast balls of rock, metals, and gases that orbit a star, and reflects that star's light. Nine planets are known in our solar system. Mercury, Venus, Earth, and Mars are the planets closest to the Sun. They are called the inner planets. The inner planets are made up mostly of rock. The outer planets are Jupiter, Saturn, Uranus, Neptune, and Pluto. Jupiter, Saturn, Uranus, and Neptune are large balls of gases with rings around them. Pluto is the farthest planet from the Sun. It is coated with ice. More...
Radio Astronomy is the study of the Universe and astrophysical phenomena, by examining their emission of electromagnetic radiation in the radio portion of the spectrum. Radio astronomy has greatly improved our understanding of the evolution of stars, the structure of galaxies, and the origin of the universe.
The solar system consists of the Sun; the nine planets, sixty eight (68) satellites of the planets, a large number of small bodies (the comets and asteroids), and the interplanetary medium.
Stars and Constellations
On a really dark night, you can see about 1000 to 1500 stars. Trying to tell which is which is hard. The constellations help by breaking up the sky into more managable bits. They are used as mnemonics, or memory aids. For example, if you spot three bright stars in a row in the winter evening, you might realize that you are seeing "Orion's Belt". Then you begin to recognise the rest of Orion: There's Betelgeuse in Orion's left shoulder and Rigel is his foot. And once you recognize Orion, you can remember that Orion's Hunting Dogs are always nearby.
A telescope is an instrument composed of one or more lenses or mirrors to gather and focus electromagnetic radiation. Telescopes increase the observed angular size of objects, as well as their apparent brightness. The largest telescopes are used in astronomy. A telescope was first turned on the sky by Galileo Galilei, the Italian scientist. (Telescopes used for non-astronomical purposes may be called "transits," "monoculars," "binoculars," "camera lenses," or "spyglasses".)
The universe is everything there is that can be detected by physical effects, from the Earth beneath our feet, to the Sun in our sky, to other worlds in the farthest reaches of Space. It contains billions of 'island universes' called Galaxies, which are huge clusters of stars. The galaxies are all moving away from each other, because the universe is expanding as a result of the Big Bang - a kind of 'explosion' which happened some 15 billion years ago. This singular event created space, time, and matter/energy. There are at least 100 billion galaxies, each with approximately 1 billion stars.