2. Astronomy is a natural science that study of
celestial objects (such as stars, galaxies,
planets, moons, asteroids, comets and nebulae),
the physics, chemistry, and evolution of such
objects, and phenomena that originate outside the
Atmosphere of Earth, including supernovae
explosions, gamma ray bursts, and cosmic
microwave background radiation.
3. In sum, astronomy has been a cornerstone
of technological progress throughout
history, has much to contribute in the
future, and offers all humans a fundamental
sense of our place in an unimaginably vast
and exciting universe.
4. The earliest accounts of how the Sun, the Earth and the rest of the
Solar System were formed are to be found in early myths, legends
and religious texts. None of these can be considered a serious
5. The theory: Hydrogen and other gases
swirled around and condensed into our
sun and its planets.
The nebular hypothesis is the most widely
accepted model in the field of cosmogony to
explain the formation and evolution of the
Solar System. It suggests that the Solar
System formed from nebulous material.
6. The theory: One day our
sun burst open, and planets
and moons shot out at high
speeds and went to their
respective places, then
stopped, and started
orbiting the sun, as the
moons began orbiting the
7. Many of the moons surrounding other planets are
really captured asteroids and not objects
that formed in place with the mother planet, or
were ejected by the mother planet.
8. The theory: A pile of space dust and rock chunks
pushed together into our planet, and another pile
pushed itself into our moon. Then the moon got
close enough and began encircling the earth.
9. The theory: Our world collided with a small
planet, and the explosion threw off rocks
which became the moon, and then it began
10. The theory: Our planets, moons, and suns spun
off from the collision between stars.
11. The theory: Gas clouds were captured by our
sun. But instead of being drawn into it, they
began whirling and pushing themselves into
planets and moons.
12. Our Solar System consists of an average
star we call the Sun, the planets Mercury,
Venus, Earth, Mars, Jupiter, Saturn, Uranus,
Neptune, and Pluto. It includes: the satellites
of the planets; numerous comets, asteroids,
and meteoroids; and the interplanetary
14. Objects orbiting the Sun are divided into three classes:
Small Solar System bodies
A planet is any body in orbit around the Sun that:
Has enough mass to form itself into a spherical shape and
Has cleared its immediate neighborhood of all smaller objects
There are eight known planets:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
16. Mercury is the smallest and innermost
planet in the Solar System. Its orbital period
is less than any other planet in the Solar
System. Seen from Earth, it appears to move
around its orbit in about 116 days. It has no
known natural satellites.
17. Venus is the second planet from the
Sun, orbiting it every 224.7 Earth days.
It has the longest rotation period of any
planet in the Solar System and rotates
in the opposite direction to most other
planets. It has no natural satellite.
18. Earth is the third planet from the Sun, the
densest planet in the Solar System, the largest of
the Solar System's four terrestrial planets, and
the only astronomical object known to harbor
19. Mars is the fourth planet
from the Sun and the
second-smallest planet in
the Solar System, after
20. Jupiter is the fifth planet from
the Sun and the largest in the
Solar System. It is a giant
planet with a mass one-
thousandth that of the Sun,
but two and a half times that
of all the other planets in the
Solar System combined.
21. Saturn is the sixth planet from the Sun
and the second-largest in the Solar
System, after Jupiter. It is a gas giant
with an average radius about nine
times that of Earth.
22. Uranus is the seventh planet
from the Sun. It has the third-
largest planetary radius and
fourth-largest planetary mass
in the Solar System.
23. Neptune is the eighth and farthest
known planet from the Sun in the
Solar System. In the Solar System, it
is the fourth-largest planet by
diameter, the third-most-massive
planet, and the densest giant planet.