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PLANETS AND STARS A celestial body moving in an elliptical orbit round a star is
known an a planet. A star is a luminous sphere of plasma held together by its
own gravity.
SUN
EARTH MARS STARS
The planets in our Solar System are believed to have formed from
the same spinning disc of dust that formed the Sun. This disc, called the solar nebula, was composed mainly of hydrogen
and helium.
NEBULA
Particles in the spinning disc began to clump together as gravity attracted them to each other. Over a few million years many of these chunks had merged together and there were objects called planetesimals, with diameters of about 1000 m.
PLANETESIMALS
Over time the planetesimals continued to collide and join together, attracted by gravity. These larger objects, about the size and mass of our Moon, are called protoplanets. The accumulation of material to form planets in this way is called accretion.
MOON
ACCRETION PROTOPLANETS
Stars form inside relatively dense concentrations of interstellar gas and dust known as molecular clouds. These regions are extremely cold.At these temperatures, gases become molecular meaning that atoms bind together.
MOLECULAR CLOUDS
STARS FORMING
STARS
How many planets in the solar system have rings?
Four planets.Jupiter, Saturn, Uranus, and Neptune all have rings.