It is a man-made object orbiting a planet or the Su the Earth's first
artificial satellite, Sputnik 1. was. launched by the USSR on Oct. 4, 1957. The
first U.S satellite was Explorer I launched on January 31, 1958. Artificial
satellites have also been launched to move round the Moon, Mars, Venus and the
Sun.
It is a satellite that relays E.Mail, Fa,x, Internet. telephone, telex
and T.V. transmission between ground stations on Earth. The first active
communications satellite was Telstar launched in 1962. These satellites
eliminate the need for expensive cables or chains of radio relay stations.
These are more flexible than long distance can ventional communication links
because a satellite can link any two points on Earth that are visible from the
satellite. Each communications satellite or comsat) is placed in orbit above
Earth's equator at the height of 35680 km. and takes 24 hours to circle the
Earth - the same time as is taken by the Earth to spin round its own axis once.
Therefore in relation to the Earth it seems stationary and is called
synchronous orbit orgeostationary, They receive transmission from ground stations, amplify them and
rebroadcast them back to Earth.
These are a series of Russian unmanned
Earth satellite. which were successors to the sputniks. used for scientific
tests. The first was launched on March 16, 1962.
These
were an early series of U.S satellites, launched between 1959 and 1962. These
showed that manned spacecraft could safely return from orbit. These satellites
were also used to test a prototype of modern rnilitam `spysatellites', which
eject capsules containing film for recovery on Earth.
Ecliptic is the Earth's path round the Sun. On the celestial
sphere. the Sun appears to move along the ecliptic during the year, this is the
effect of the Earth moving in orbit round the Sun.
Escape Velocity is the speed
that an object like rocket. must reach to escape permanently from the body of a
planet. The escape velocity from the surface of the Earth is nearly 11 km., per
second or 40.000 km, per hour.
Explorer Satellites A series of U.S scientific satellites designed
to study the Earth, its surroundings in space, and astronomical objects such as
the Sun and Stars. The first Explorer was launched on January 31, 1958.
Satellites Natural satellites, also termed moons, are small
planets which revolve round the larger once. In the solar system, moons orbit
six of the nine known planets.
Skylab was a U.S space station in which astronauts set up
duration records for living and working in space. The skylab space station was
launched in May 1973. Three separate three — men crews boarded the station for
periods of up to three months each; fell back to Earth near Australia about two
years back.
Weightlessness is the condition encountered in space in which the
,astronaut, his craft. and object inside it seem to hang without weight. The
term Zero gravity is incorrect because the craft is still within the
gravitational pull of the Earth and Sun,
Zodiac is a band of 12 constellations through which the
Sun passes Zodiac do not coincide \Nri th the constellations named after the
each .ear- These signs of Zodiac used by the astrologers.
Pulsars are fast
rotating neutron stars. They send out radio Pulsars - gaff frequency, at the
remarkably short radio period of 0.033 Waves in re second.
Quasars or Quasi
Stellar Radio sources are part star and part radio objects. They combine the
characteristics of stars and radio galaxies. Many of the Quasars are radio
quiet. These are compact blue objects that emitted radiation strongly in the
ultra – violet as well as the radio portion of the spectrum. They exhibit many
peculiarities like fluctuating brightness and large red shifts. Quasars are
small objects compared to galaxies but all of them emit radiation for in excess
of their size or brightness. Some are believed to emit energy which is greater
than the combined energy emitted by a hundred galaxies like the Milky way. They
fluctuate in brightness at intervals. Since they emit enormous energy, their
life times are son. Many of them die out in less than a billion years. All of
them are removed from Earth by distances of billions of light years.
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