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The Solar System and The Planets
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Science
Astronomy
Solar
: Asteroids, Comets, Extrasolar, Jupiter, Mars, Mercury, Neptune, Orbits, Pictures, Planets, Pluto, Saturn, Sun, Uranus, Venus • Books, Posters
The solar system consists of the Sun; the nine planets,
sixty eight (68) satellites of the planets,
a large number of small bodies (the comets and asteroids),
and the interplanetary medium.
A planet is any of the nine major celestial bodies
(Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune,
Pluto) that orbit the sun and shine by reflecting its light.
Smaller bodies that also have the sun as their primary (that is,
are not satellites of a planet) are called asteroids or planetoids.
The inner solar system contains the Sun, Mercury, Venus,
Earth and Mars;
The planets of the outer solar system are Jupiter, Saturn, Uranus,
Neptune and Pluto.
The orbits of the planets are ellipses with the Sun at one focus,
though all except Mercury and Pluto are very nearly circular.
The orbits of the planets are all more or less in the same plane
(called the ecliptic and defined by the plane of the Earth's orbit).
The ecliptic is inclined only 7 degrees from the plane of the Sun's
equator.
Pluto's orbit deviates the most from the plane of the ecliptic with
an inclination of 17 degrees. They all orbit in the same direction
(counter-clockwise looking down from above the Sun's north pole);
all but Venus, Uranus and Pluto also rotate in that same sense.
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The night sky is full of stars, so distant they are mere points of
light. The Sun is a star that, by the gravitational effects of its
mass, dominates the planetary system that includes the Earth, and we
are much closer to it than to any other star. Along with the other
planets, the Earth orbits the Sun. The Sun is a ball of glowing gases,
three quarters hydrogen and one quarter helium, with traces of other
elements.
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An asteroid, also called a minor planet or planetoid, is a member of
a group of small, planet-like bodies that are part of our solar system.
They are believed to be remnants of the interstellar clouds, nebula,
that were not incorporated into planets during the formation of the
solar system.
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A comet is a small body from the outer reaches of the solar system
similar to an asteroid but composed of ice. Often described as "dirty
snowballs," they are composed largely of carbon dioxide ice, methane
ice, and water ice with a mixture of dust and small stony aggregates
mixed in. Comets are thought to be small pieces of debris left over
from the formation of the solar system, representing a sample of the
original composition of the nebula that condensed to form the Sun and
all of its planets.
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Our Earth is one of 9 planets orbiting the Sun. The planets are
vast balls of rock, metals, and gases that orbit a star.
Other stars may have planets too. A planet is a celestial object which
revolves around a star and reflects that star's light.
The planets are vast balls of rock, metals, and gases that orbit a star,
and reflects that star's light.
Nine planets are known in our solar system.
Mercury, Venus, Earth, and Mars are the planets closest to the Sun.
They are called the inner planets.
The inner planets are made up mostly of rock.
The outer planets are Jupiter, Saturn, Uranus, Neptune, and Pluto.
Jupiter, Saturn, Uranus,
and Neptune are large balls of gases with rings around them.
Pluto is the farthest planet from the Sun. It is coated with ice.
More...
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Earth is the third closest planet to the Sun.
It has an atmosphere made up of many different gases, mainly nitrogen and oxygen. Earth is the only planet in the solar system that can have eclipses of the Sun. It takes one year to go completely around the Sun. The Earth also rotates, or spins, on its axis once per day. The Earth's axis is not straight up and down relative to the orbit, but is tilted a little bit. This tilt is responsible for the seasons. Otherwise, the temperature would be pretty much the same all year long. It has one natural satellite, the Moon.
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An extrasolar planet is a planet orbiting around a star other than the Sun. Extrasolar planets were first discovered in the 1990s as a result of improved telescope technology, CCD and computer-based image processing which allowed far more accurate measurements of stellar motions.
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Jupiter is the fifth planet from the Sun, and is by far the largest planet in our solar system. It could hold all the other planets put together, or over 1300 Earths!
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Mars is much smaller than Earth, but recent research shows that it once had flowing rivers. Mars also has a canyon that stretches over 2000 miles. Mars has many craters which were formed by meteorites or asteroids hitting it. Mars also has some of the tallest volcanoes and some of the deepest valleys in our solar system. Mars has two moons, Phobos and Deimos which have unusual shapes. Scientists think these potato-shaped moons were once asteroids captured by Mars' gravitational pull.
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Mercury is the closest planet to the Sun. It is in a highly eccentric orbit around the Sun. At its closest (perihelion), it is only 46 million km from the Sun. At its most distant (aphelion), it is 70 million km. Its orbit perihelion moves backward (precesses) around the Sun at a very slow rate.
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Neptune has two thick and two thin rings which surround it. Neptune also has eight moons. Four of these moons orbit the planet within the rings. One of these moons, Triton, orbits the planet in a direction opposite that of the seven other moons. The ground breaking Voyager spacecraft found "geysers" on Triton.
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The inner planets (Mercury, Venus, Earth, and Mars), are relatively
small and made primarily of rock and iron. The asteroids orbit the sun
in a belt beyond the orbit of Mars, tumbling and sometimes colliding
with one another.
The outer planets, with the exception of Pluto, are much larger and made
mainly of hydrogen, helium, and ice.
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Pluto is so far away that the Sun is not much bigger or brighter than most of the other stars in its sky. It is only about two-thirds the size of our Moon and is a cold, dark, frozen place. Its composition is presumed to be rock and ice, with a thin atmosphere of nitrogen, carbon monoxide and methane. The Hubble Space Telescope has produced only fuzzy images of Pluto.
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Saturn is a very large gas planet which spins very rapidly on its axis. It spins so fast that it flattens out the top and the bottom of the planet and bulges at its equator. Saturn's atmosphere has winds which can blow at over 1800 kilometers per hour! The white spots on Saturn are believed to be powerful storms.
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Perhaps because of a collision with a large object long ago,
Uranus orbits at an extreme tilt of 98 degrees, sort of on its side.
The planet is the only one in our solar system that lays on its side
instead of standing straight up. This causes one pole to point toward
the sun for decades, giving the planet strange seasons.
Uranus has 18 known satellites (the most recent was found in May, 1998)
and a faint set of rings.
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Venus has very thick, rapidly spinning clouds which cover its surface.
These clouds hold heat in which is why Venus gets so hot.
These clouds also reflect sunlight, so Venus appears very bright to us
here on Earth. There are constant thunderstorms in these clouds.
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