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What is geocentric model of the UNIVERSE?

The earth is stationary and all celestial objects revolve round it. Each planet goes round in a small circle ( epicycle ), the centre of which follows a circular path round the earth. Suggested by greek astronomer Ptolemy in the first century A.D.

What is heliocentric model of the UNIVERSE?

The sun is at rest and the planets revolve round it, proposed by Copernicus in the fifteenth century A.D.

What are the atmosphere’s details around various planets?

Venus and Mars – carbon dioxide. ( CO2 )

Jupiter and Saturn – H2, He, CH4, NH3

Uranus and Neptune – H2, He, CH4

Mercury – NIL

Pluto – not known properly.

Earth – Air

Name the terrestrial planets:

Mercury, Venus, Earth and Mars ( Pluto is also sometime included ). these are relatively small, dense and are probably made of rocks and metallic material.

Name the Jovian planets:

These are Jupiter, Saturn, Uranus and Neptune. These are comparatively large, low in density and are predominantly composed of H2 and He.

What are the comets?

These are composed of frozen gases with nuclei of solid particles. they move around the sun in highly elongated elliptical orbits, spending most of the time far away from the sun. Heads of comets are 10000 – 20000 km in size, the tails can stretch to millions of kilometers. the mass of a comet is exceedingly small, about a billionth that of the earth. comets’ that is always oriented away from the sun due to radiation pressure and solar wind.

What are asteroids?

These are minute planets most of whom are only a few kilometers across. Most of them are cofined to the space between the orbits of Mars and Jupiter.

What are meteoroids?

Minute objects orbiting the sun, meteoroids are too small to be observed even with telescopes, when they enter earth’s atmosphere, they become visible due to burning & then they are known as ‘ meteors’ or shooting stars.’ Sometime they land on the earth’s surface and then they are known as ‘ meteorites.’

Who is zero ‘magnitude’ star?

‘VEGA’ star is of zero magnitude and its brightness is lb = 2.52´10-8 Wm-2 brighter stars than VEGA have negative magnitudes.

What are the magnitudes of brightness of various stars? and also limits of minimum brightness to be observed by various instruments?

Sun -26.5

Full moon -12.5

Venus -4.0

Jupiter, mars -2.0

Sirius -1.5

Aldebaran, Altair 1.0

Naked-eye limit 6.5

Binocular limit 9.0

20 cm telescope limit 14.0

5 meter telescope 20.0

5 meter telescope ( visual )

5 metre telescope ( photo ) 24.

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