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A black hole is a region of space from which nothing, including light, can escape. It is the result of the deformation of space-time caused by a very compact mass. Around a black hole there is an undetectable surface which marks the point of no return, called an event horizon. It is called "black" because it absorbs all the light that hits it, reflecting nothing.



Despite its invisible interior, a black hole can be observed through its interaction with other matter. A black hole can be inferred by tracking the movement of a group of stars that orbit a region in space.


Astronomers have found compelling evidence that a super massive black hole of more than 2 million solar masses is located near the Sagittarius A region in the center of the Milky Way galaxy.

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A galaxy is a massive, gravitationally bound system, consists an important but poorly understood component tentatively dubbed dark matter. Typical galaxies range from dwarfs with as few as ten million (107) stars up to giants with hundred trillion (1014) stars, all orbiting the galaxy's center of mass. 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.

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A nebula is an interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases. Originally nebula was a general name for any extended astronomical object, including galaxies beyond the Milky Way 3. Nebulae often form star-forming regions. This nebula is depicted in one of NASA's most famous images, the "Pillars of Creation". In these regions the formations of gas, dust and other materials "clump" together to form larger masses, which attract further matter, and eventually will become big enough to form stars. The remaining materials are then believed to form planets, and other planetary system objects.

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The Big Bang is the prevailing cosmological theory of the early development of the universe. Cosmologists use the term Big Bang to refer to the idea that the universe was originally extremely hot and dense at some finite time in the past and has since cooled by expanding to the present diluted state and continues to expand today.



If the distance between galaxy clusters is increasing today, everything must have been closer together in the past. This idea has been considered in detail back in time to extreme densities and temperatures, and large particle accelerators have been built to experiment on and test such conditions, resulting in significant confirmation of the theory, but these accelerators have limited capabilities to probe into such high energy regimes.

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In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. Dark energy is the most popular way to explain recent observations and experiments that the universe appears to be expanding at an accelerating rate. In the standard model of cosmology, dark energy currently accounts for 74% of the total mass-energy of the universe.



Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space homogeneously,

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In astronomy and cosmology, dark matter is matter that is inferred to exist from gravitational effects on visible matter and background radiation, but is undetectable by emitted or scattered electromagnetic radiation. Its existence was hypothesized to account for discrepancies between measurements of the mass of galaxies, clusters of galaxies and the entire universe made through dynamical and general relativistic means, and measurements based on the mass of the visible "luminous" matter these objects contain: stars and the gas and dust of the interstellar and intergalactic media. Dark matter accounts for 23% of the mass-energy density of the observable universe, while the ordinary matter accounts for only 4.6%.



Dark matter was postulated by Fritz Zwicky in 1934 to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters. Subsequently, other observations have indicated the presence of dark matter in the universe, including the rotational speeds of galaxies, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster.

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Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, especially in the inner Solar System; they are smaller than planets but larger than meteoroids. The term "asteroid" has historically been applied primarily to minor planets of the inner Solar System, as the outer Solar System was poorly known when it came into common usage. The distinction between asteroids and comets is made on visual appearance: Comets show a perceptible coma while asteroids do not.

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The current official definition of a meteoroid from the International Astronomical Union is "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom". The NEO definition includes larger objects, up to 50 m in diameter, in this category. Very small meteoroids are known as micrometeoroids.



The composition of meteoroids can be determined as they pass through Earth's atmosphere from their trajectories and the light spectra of the resulting meteor. Their effects on radio signals also give information, especially useful for daytime meteors which are otherwise very difficult to observe. From these trajectory measurements, meteoroids have been found to have many different orbits.

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A meteor is the visible streak of light that occurs when a meteoroid enters the Earth's atmosphere. Meteors typically occur in the mesosphere, and most range in altitude from 75 km to 100 km. Millions of meteors occurs in the Earth's atmosphere every day. Most meteoroids that cause meteors are about the size of a pebble. They become visible between about 40 and 75 miles above the earth.

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A meteorite is a portion of a meteoroid or asteroid that survives its passage through the atmosphere and impact with the ground without being destroyed. Meteorites are sometimes, but not always, found in association with hypervelocity impact craters.

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A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma, and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet. Comets nuclei are themselves loose collections of ice, dust, and small rocky particles, ranging from a few hundred meters to tens of kilometers across.
Comets have a wide range of orbital periods, ranging from a few years to hundreds of thousands of years.

Some Famous Comets

 Halley’s comet

The comet was named for the English Astronomer Edmond Halley. It reappears after every 78 years. It was last seen in 1986.

***MeRcUrY***

It is 58 million km (36 million miles) away from the sun. It has no moons and revolves around the sun in every 88 earth days. The side facing the sun can have a temperature of 430 C. It is only 4,830 km across at the equator.

***VeNuS***

It is 108 million km (67 million miles) away from the sun. It has no moons and revolves around the sun in every 225 earth days. It is 12,070 km across at the equator. It is so hot that even some metals would melt on the surface. The weird thing about Venus is that is rotates clockwise different from all other planet. Another thing is that Venus takes 243 earth days to rotate on its axis but it takes only 225 earth days for it to orbit the sun.

***EaRtH***

It is 150 million km (142 million miles) away from the sun. It has 1 moon and revolves around the sun in every 365 earth days. The weight of earth is 6,000 million, million, million tones. The distance around the earth along the equator is 40,000 km (24,856 miles).It is also believed to be the only planet in the universe having some form of life.

***MaRs***

It is 228 million km (201 million miles) away from the sun. It has 2 moons and revolves around the sun in every 687 earth days. It is 6,760 km across at the equator. The highest mountain on mars is Mount Olympus and it more than 27 km high and is 3 times taller than Mount Everest. It is said once Mars used to have water as well as some form of life.

***JuPiTeR***

It is 778 million km (480 million miles) away from the sun. It has 16 moons and revolves around the sun in every 12 earth days. It is 12,800 km across at the equator. One of the great things at the Jupiter is the Great Red Spot. The Red Spot is actually a giant storm and it is greater than our planet earth. Also there is no solid surface on Jupiter.

***SaTuRn***

It is 1472 million km (886 million miles) away from the sun. It is having 17 moons and revolves around the sun in every 29.5 earth years. It is about 119,300 km across and the sun rays take 8 ½ minutes to reach Saturn.

***UrAnUs***

It is 2870 million km (1,783 million miles) away from the sun and is mostly made up of gas. It is having 15 moons and revolves around the sun in every 84 earth years. The weird thing about Uranus is that its axis is tilted 98 degrees. Another thing is that it too has rings.

***NePtUnE***

It is 4500 million km (3,700 million miles) away from the sun. It is having 3 moons and revolves around the sun in every 165 earth years.

***StAr***

A star is a massive, luminous ball of plasma held together by gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun.



For most of its life, a star shines due to thermonuclear fusion in its core releasing energy that traverses the star's interior and then radiates into outer space. Almost all naturally occurring elements heavier than helium were created by stars. Astronomers can determine the mass, age, chemical composition and many other properties of a star by observing its spectrum, luminosity and motion through space. The total mass of a star is the principal determinant in its evolution and eventual fate.

***BiNaRy sTaR***

Each binary star is actually 2 stars. Because they are so close together, the gravity field of each star pulls them together and causes them to spin around a central point in space.

***SuPeRnOvA***

A supernova is a stellar explosion that is more energetic than a nova. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months. During this short interval a supernova can radiate as much energy as the Sun is expected to emit over its entire life span. The explosion expels much or all of a star's material at a velocity of up to 30,000 km/s, driving a shock wave into the surrounding interstellar medium.



On average, supernovae occur about once every 50 years in a galaxy the size of the Milky Way. The expanding shock waves from supernova explosions can trigger the formation of new stars.

***PuLsAr***

So.metimes the leftover of the star after explosion becomes a neutron star and begins to rotate rapidly. This spinning neutron star is called pulsar

***ThE SuN***

The sun is a yellow- white star. It is a ball of hot hydrogen and helium gas. At the core of the sun the hydrogen is changed into helium gas by nuclear fusion. The fusion produces enormous energy. The surface is very active with sunspots, flares and prominences. The sun turns on its axis once in every 27 days. Its diameter is 100 times bigger than that of earth. At the core of the sun the temperature is 15,000,000 C and it is 5,500 C on the surface.

***WoRmHoLe***

In physics and fiction, a wormhole is a hypothetical topological feature of space-time that would be, fundamentally, a "shortcut" through space-time. A wormhole is, in theory, much like a tunnel with two ends each in separate points in space-time.



There is no observational evidence for wormholes, but on a theoretical level there are valid solutions to the equations of the theory of general relativity which contain wormholes. The first type of wormhole solution discovered was the Schwarzschild wormhole which would be present in the Schwarzschild metric describing an eternal black hole, but it was found that this type of wormhole would collapse too quickly for anything to cross from one end to the other. Wormholes which could actually be crossed, known as traversable wormholes, would only be possible if exotic matter with negative energy density could be used to stabilize them.


The American theoretical physicist John Archibald Wheeler coined the term wormhole in 1957; however, in 1921, the German mathematician Hermann Weyl already had proposed the wormhole theory, in connection with mass analysis of electromagnetic field energy.