Quasar

one of a number of star-like heavenly bodies which are very distant from Earth and which give out light. They are extremely compact and give out light even though they are vast distances away, up to 10¹⁰ light years.

Taken from Dictionary of Science

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A quasi-stellar radio source (quasar) is a very energetic and distant galaxy with an active galactic nucleus. Quasars were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than extended sources similar to galaxies.

While there was initially some controversy over the nature of these objects—as recently as the early 1980s, there was no clear consensus as to their nature—there is now a scientific consensus that a quasar is a compact region in the centre of a massive galaxy surrounding the central supermassive black hole. Its size is 10-10,000 times the Schwarzschild radius of the black hole. The quasar is powered by an accretion disc around the black hole.

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Oceans

technically, those bodies of water that occupy the ocean basins, which begin at the edge of the continental shelf. Marginal seas such as the Mediterranean, Carribean and Baltic are not classed as oceans. A more general definition is all the water on the Earth's surface, excluding lakes and inland seas. The oceans are the North and South Atlantic; North and South Pacific; Indian and Arctic. Together with all the seas the salt water covers almost 71% of the Earth's surface.

From the shore the land dips away gently in most cases--the continental shelf--after which the gradient increases on the continental slope leading to the deep sea platform (at about 4 km depth). There are many areas of shallow seas on the continental shelf (epicontinental seas) e.g. North Sea, Baltic and Hudson Bay. In the ice age, much of the shelf would have been land and conversely should much ice melt, the continents would be submerged further. The floors of the oceans display both mountains, in the form of the mid-oceanic ridges, and deep trenches. The ridges rise 2-3 km from the floor and extend for thousands of kilometres while the trenches reach over 11 km below sea level, at their deepest (Mariana Trench, south-east of Japan).

The oceans contain currents, i.e. faster-moving large-scale flows (the slower movements are called drifts). Several factors contribute to the formation of currents, including the rotation of the Earth, prevailing winds, differences in temperature and sea water densities. Major currents move clockwise in the northern hemisphere and anticlockwise in the southern hemisphere. Well-known currents include the Gulf Stream and the Humboldt current.

Taken from Dictionary of Science

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An ocean (from Greek Ωκεανός, Okeanos (Oceanus)) is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface (~3.61 X 10¹⁴ m²) is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.

More than half of this area is over 3,000 metres (9,800 ft) deep. Average oceanic salinity is around 35 parts per thousand (ppt) (3.5%), and nearly all seawater has a salinity in the range of 30 to 38 ppt. Scientists estimate that 230,000 marine life forms of all types are currently known, but the total could be up to 10 times that number.

Taken from Wikipedia

Radio Astronomy

the recording and study of radio waves given out by many bodies in space including the Sun, stars and QUASARS.

Taken from Dictionary of Science

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Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. It differs from radar astronomy in that the latter utilizes artificial, rather than natural, radio sources. The initial detection of radio waves from an astronomical object (the Milky Way) was made in the 1930s, but subsequent advances (especially post-World War II) have identified a number of different sources of radio emission. These include stars and galaxies as well as entirely new classes of objects, such as Radio Galaxies, Pulsars and Masers. The discovery of the Cosmic Microwave Background Radiation was a particularly significant event. Radio astronomy is conducted using large radio antenna referred to as radio telescopes, that are either used singularly, or with multiple linked telescopes utilizing the techniques of radio interferometry and aperture synthesis. The latter has allowed radio sources to be imaged with unprecedented angular resolution.

Taken from Wikipedia

Galaxy

(plural galaxies) specifically, the name given to the band of stars, numbering one hundred thousand million bodies, which includes the Sun, and is alternatively called the Milky Way. The galaxy has a spiral structure and is approximately one hundred thousand LIGHT YEARS across. In general usage it refers to a collection of stars held together by gravitational forces. They form different shapes including spiral, elliptical and irregular galaxies and range from dwarf galaxies with 100 000 stars to massive galaxies such as the giant elliptical M 87 which has three thousand billion stars.

Taken from Dictionary of Science

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A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The name is from the Greek root galaxias [γαλαξίας], meaning "milky," a reference to the Milky Way galaxy. Typical galaxies range from dwarfs with as few as ten million (10⁷) stars up to giants with one trillion (10¹²) stars, all orbiting the galaxy's center of mass. Galaxies can also contain many multiple star systems, star clusters, and various interstellar clouds. The Sun is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun.

Historically, galaxies have been categorized according to their apparent shape (usually referred to as their visual morphology). A common form is the elliptical galaxy, which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped assemblages with dusty, curving arms. Galaxies with irregular or unusual shapes are known as peculiar galaxies, and typically result from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in galaxies merging, may induce episodes of significantly increased star formation, producing what is called a starburst galaxy. Small galaxies that lack a coherent structure could also be referred to as irregular galaxies.

There are probably more than 100 billion (10¹¹) galaxies in the observable universe. Most galaxies are 1,000 to 100,000^[4] parsecs in diameter and are usually separated by distances on the order of millions of parsecs (or megaparsecs). Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter. The majority of galaxies are organized into a hierarchy of associations called clusters, which, in turn, can form larger groups called superclusters. These larger structures are generally arranged into sheets and filaments, which surround immense voids in the universe.

Although it is not yet well understood, dark matter appears to account for around 90% of the mass of most galaxies. Observational data suggests that supermassive black holes may exist at the center of many, if not all, galaxies. They are proposed to be the primary cause of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy appears to harbor at least one such object within its nucleus.

Taken from Wikipedia