MILKY WAY GALAXY

                                                                                        MILKY WAY GALAXY                                                                                                                                                                                                               The Milky Way is the galaxy that contains our Solar System. Its name "milky" is derived from its appearance as a dim glowing band arching across the night sky in which the naked eye cannot distinguish individual stars. The term "Milky Way" is a translation of the Latin via lactea, from the Greek  (galaxías kýklos, "milky circle") From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Up until the early 1920s, most astronomers thought that all of the stars in the universe were contained inside of the Milky Way. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis,observations by Edwin Hubble definitively showed that the Milky Way is just one of many—now known to be billions—of galaxies.

The Milky Way is a barred spiral galaxy some 100,000–120,000 light-years in diameter, which contains 100–400 billion stars. It may contain at least as many planets as well. The Solar System is located within the disk, about 27,000 light-years away from the Galactic Center, on the inner edge of one of the spiral-shaped concentrations of gas and dust called the Orion Arm. The stars in the inner ≈10,000 light-years form a bulge and one or more bars that radiate from the bulge. The very center is marked by an intense radio source, named Sagittarius A*, which is likely to be a supermassive black hole.

Stars and gases at a wide range of distances from the Galactic Center orbit at approximately 220 kilometers per second. The constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much of the mass of the Milky Way does not emit or absorb electromagnetic radiation. This mass has been given the name "dark matter"The rotational period is about 240 million years at the position of the Sun. The Milky Way as a whole is moving at a velocity of approximately 600 km per second with respect to extragalactic frames of reference. The oldest known star in the Milky Way is at least 13.82 [26] billion years old and thus must have formed shortly after the Big Bang.

Surrounded by several smaller satellite galaxies, the Milky Way is part of the Local Group of galaxies, which forms a subcomponent of the Virgo Supercluster, which again forms a subcomponent of the Laniakea Supercluster.

When observing the night sky, the term "Milky Way" is limited to the hazy band of white light some 30 degrees wide arcing across the sky.[29] Although all of the individual stars that can be seen in the entire sky with the naked eye are part of the Milky Way Galaxy,[30] the light in this band originates from the accumulation of un-resolved stars and other material when viewed in the direction of the Galactic plane. Dark regions within the band, such as the Great Rift and the Coalsack, correspond to areas where light from distant stars is blocked by interstellar dust. The region where the Milky Way is self-obscuring is also known as the zone of avoidance.

The Milky Way has a relatively low surface brightness. Its visibility can be greatly reduced by background light such as light pollution or stray light from the Moon. It is readily visible when the limiting magnitude is +5.1 or better and shows a great deal of detail at +6.1. This makes the Milky Way difficult to see from any brightly lit urban or suburban location, but very prominent when viewed from a rural area when the Moon is below the horizon.

As viewed from Earth, the visible region of the Milky Way's Galactic plane occupies an area of the sky that includes 30 constellations. The center of the Milky Way lies in the direction of the constellation Sagittarius; it is here that the Milky Way is brightest. From Sagittarius, the hazy band of white light appears to pass westward to the Galactic anticenter in Auriga. The band then continues westward the rest of the way around the sky, back to Sagittarius. The band divides the night sky into two roughly equal hemispheres.

The Galactic plane is inclined by about 60 degrees to the ecliptic (the plane of Earth's orbit). Relative to the celestial equator, it passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth’s equatorial plane and the plane of the ecliptic, relative to the Galactic plane. The north Galactic pole is situated at right ascension 12h 49m, declination +27.4° (B1950) near β Comae Berenices, and the south Galactic pole is near α Sculptoris. Because of this high inclination, depending on the time of night and year, the arc of Milky Way may appear relatively low or relatively high in the sky. For observers from approximately 65 degrees north to 65 degrees south on Earth's surface, the Milky Way passes directly overhead twice a day.

ARYABHATA SATILITY

                                                                                             ARYABHATA SATILITY                                                                                                                                                                                                                                                           Aryabhata was India's first satellite, named after an Indian astronomer of the same name.

It was launched by the Soviet Union on 19 April 1975 from Kapustin Yar using a Kosmos-3M launch vehicle. It was built by the Indian Space Research Organisation (ISRO) to gain experience in building and operating a satellite in space.The launch came from an agreement between India and the Soviet Union directed by U.R. Rao and signed in 1972. It allowed the USSR to use India ports for tracking ships and launching vessels in return for launching India satellites.

On 19 April 1975 the satellite's 96.46-minute orbit had an apogee of 611 kilometres (380 mi) and a perigee of 568 kilometres (353 mi), at an inclination of 50.6 degrees. It was built to conduct experiments in X-ray astronomy, aeronomics, and solar physics. The spacecraft was a 26-sided polyhedron 1.4 metres (4.6 ft) in diameter. All faces (except the top and bottom) were covered with solar cells. A power failure halted experiments after four days and 60 orbits with all signals from the spacecraft lost after five days of operation. According the Soviet media reports, the satellite continued to function and transmit information for some time. The satellite reentered the Earth's atmosphere on 11 February 1992.
The satellite's image appeared on the reverse of Indian 2 rupee banknotes between 1976 and 1997 (Pick catalog and one rupee note number: P-79a-m).Aryabhata was named for the 5th century astronomer and mathematician from India by the same name.

Aryabhata, first unmanned Earth satellite built by India. It was named for a prominent Indian astronomer and mathematician of the 5th century ce. The satellite was assembled at Peenya, near Bangalore, but was launched from within the Soviet Union by a Russian-made rocket on April 19, 1975. Aryabhata weighed 794 pounds (360 kilograms) and was instrumented to explore conditions in the Earth’s ionosphere, measure neutrons and gamma rays from the Sun, and perform investigations in X-ray astronomy. The scientific instruments had to be switched off during the fifth day in orbit because of a failure in the satellite’s electrical power system. Useful information, nevertheless, was collected during the five days of operation.
Aryabhatta was the first satellite launched by India. It was named after the great Indian astronomer of the same name. Aryabhatta weighed 360kg and was launched by the Soviet Union on April 19, 1975 from Kapustin Yar using a Cosmos-3M launch vehicle. 
First Satellite Launched by India

                                                                                                                                           .The satellite had following objectives:.To indigenously design and fabricate a space-worthy satellite system and evaluate its perfromance in orbit..To evolve the methodology of conducting a series of complex operations on the satellite in its orbital phase..To set up ground-based receiving, transmitting and tracking systems..To establish infrastructure for the fabrication of spacecraft systems.
.Aryabhatta carried experiments related to X-Ray Astronomy, Solar Physics and Aeronomy. The satellite re-entered the Earth's atmosphere on 11 February 1992.

SATILITY

                                                                                                                                                                                                                                  SATILITY                                                                                                                                                                                                                                                                 In the context of spaceflight, a satellite is an artificial object which has been intentionally placed into orbit. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon.

The world's first artificial satellite, the Sputnik 1, was launched by the Soviet Union in 1957. Since then, thousands of satellites have been launched into orbit around the Earth. Some satellites, notably space stations, have been launched in parts and assembled in orbit. Artificial satellites originate from more than 40 countries and have used the satellite launching capabilities of ten nations. A few hundred satellites are currently operational, whereas thousands of unused satellites and satellite fragments orbit the Earth as space debris. A few space probes have been placed into orbit around other bodies and become artificial satellites to the Moon, Mercury, Venus, Mars, Jupiter, Saturn, Vesta, Eros, and the Sun.

Satellites are used for a large number of purposes. Common types include military and civilian Earth observation satellites, communications satellites, navigation satellites, weather satellites, and research satellites. Space stations and human spacecraft in orbit are also satellites. Satellite orbits vary greatly, depending on the purpose of the satellite, and are classified in a number of ways. Well-known (overlapping) classes include low Earth orbit, polar orbit, and geostationary orbit.

About 6,600 satellites have been launched. The latest estimates are that 3,600 remain in orbit.Of those, about 1,000 are operational;[2][3] the rest have lived out their useful lives and are part of the space debris. Approximately 500 operational satellites are in low-Earth orbit, 50 are in medium-Earth orbit (at 20,000 km), the rest are in geostationary orbit (at 36,000 km).

Satellites are propelled by rockets to their orbits. Usually the launch vehicle itself is a rocket lifting off from a launch pad on land. In a minority of cases satellites are launched at sea (from a submarine or a mobile maritime platform) or aboard a plane (see air launch to orbit).

Satellites are usually semi-independent computer-controlled systems. Satellite subsystems attend many tasks, such as power generation, thermal control, telemetry, attitude control and orbit control.

The first fictional depiction of a satellite being launched into orbit is a short story by Edward Everett Hale, The Brick Moon. The story is serialized in The Atlantic Monthly, starting in 1869.The idea surfaces again in Jules Verne's The Begum's Fortune (1879).

Konstantin Tsiolkovsky

In 1903, Konstantin Tsiolkovsky (1857–1935) published Exploring Space Using Jet Propulsion Devices (in Russian: Исследование мировых пространств реактивными приборами), which is the first academic treatise on the use of rocketry to launch spacecraft. He calculated the orbital speed required for a minimal orbit around the Earth at 8 km/s, and that a multi-stage rocket fuelled by liquid propellants could be used to achieve this. He proposed the use of liquid hydrogen and liquid oxygen, though other combinations can be used.

In 1928, Slovenian Herman Potočnik (1892–1929) published his sole book, The Problem of Space Travel — The Rocket Motor (German: Das Problem der Befahrung des Weltraums — der Raketen-Motor), a plan for a breakthrough into space and a permanent human presence there. He conceived of a space station in detail and calculated its geostationary orbit. He described the use of orbiting spacecraft for detailed peaceful and military observation of the ground and described how the special conditions of space could be useful for scientific experiments. The book described geostationary satellites (first put forward by Tsiolkovsky) and discussed communication between them and the ground using radio, but fell short of the idea of using satellites for mass broadcasting and as telecommunications relays.

In a 1945 Wireless World article, the English science fiction writer Arthur C. Clarke (1917–2008) described in detail the possible use of communications satellites for mass communications.Clarke examined the logistics of satellite launch, possible orbits and other aspects of the creation of a network of world-circling satellites, pointing to the benefits of high-speed global communications. He also suggested that three geostationary satellites would provide coverage over the entire planet.

The US military studied the idea of what was referred to as the earth satellite vehicle when Secretary of Defense James Forrestal made a public announcement on December 29, 1948, that his office was coordinating that project between the various services.

The first satellite, Sputnik 1, was put into orbit around Earth and was therefore in geocentric orbit. By far this is the most common type of orbit with approximately 2,456 artificial satellites orbiting the Earth. Geocentric orbits may be further classified by their altitude, inclination and eccentricity.