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In between the stars in a galaxy, there are
clouds of hydrogen gas and dust called
nebula
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Our Sun and solar system were probably
formed from one of these Nebula.
The two most accepted theories of how this
occurred are:
 Stellar Collision Theory
 Nebular Hypothesis
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Our Sun and the planets were spun off from
collisions between stars
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believed to be more likely,
from our observations of
other star systems
that the Sun and planets
formed when a large
nebula condensed and
collected together by
gravity
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Distances to most stars from Earth are in the
millions of A.U.s
Light Year It is the distance that light, which
moves at 300 000 km/s, travels in a year. It is
equal to about 9.5 trillion km.
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Moon takes about 1.3 s
The Sun takes 8 min
Jupiter takes 41 min
Alpha Centauri light takes 4.3 years
Polaris 430 years
Andromeda galaxy of 2.5 million light-years
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227,939,100 km ÷ 300,000 km/sec
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= 75.997 sec = 1.27 min
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(i)nebula
(ii)spiral and elliptical galaxies
(iii)giant stars
(iv)dwarf stars
(v)quasars
(vi)black holes