The photosphere is the layer of
the Sun that emits the visible light we see. Below the photosphere are the
Sun's interior layers. Above the photosphere are other atmospheric layers.
All layers of the Sun are made of gases.
Most of the planets have
Earth has one moon, Mars has two moons, and each of the
outer planets has several moons. Mercury and Venus are the only two
planets that do not have moons.
A meteor is a sudden streak of
light caused by friction between the Earth's atmosphere and an incoming
piece of solar system debris. The incoming debris could be an asteroid, a
comet, or a meteoroid. Most meteors are caused by very small meteoroids
entering the atmosphere.
The inner planets are also known as
the terrestrial planets because they are solid, rocky planets.
The gas giants is another name for the outer planets. As the name
implies, these planets are very large and made mostly of gas.
All eight planets in the solar system
orbit a star, which is the Sun.
The Earth is the only planet
known to have liquid water or organisms on it. Also, the planets have many
different sizes. The smallest planet, Mercury, has a diameter of 4,880 km.
The largest planet, Jupiter, has a diameter of about 143,000 km.
Prominences are huge loops or
sheets of gas erupting from active regions around sunspots. These features
arch into the Sun's atmosphere and connect pairs of sunspots.
prominences can last from hours to weeks, and their frequency and
magnitudes are affected by sunspot cycles.
The planets of the solar system can be
divided evenly into a group of four inner planets and a group of
four outer planets.
Group 1 in the table describes the outer
planets, which are larger, made mostly of gases, have rings, and have
several moons per planet.
Group 2 in the table describes the inner
planets, which are smaller, made of solid materials, have no rings, and
have between 0 and 2 moons per planet.
The planet Jupiter is large and made
mostly of gases.
The inner planets have no rings and are small,
near the Sun, made mostly of rock, and have 0-2 moons each. The outer
planets have rings and are larger, farther from the Sun, made mostly of
gases, and have several moons each.
During a total solar eclipse, when the
Sun's photosphere is blocked by the Moon, the Sun's corona
can be seen as a white halo. Most other times, the light from the
photosphere is so bright that the corona cannot be seen.
The corona is the outermost layer of
the Sun's atmosphere. This layer has an extremely low density and
usually cannot be seen due to the brightness of the photosphere.
Impact craters are depressions on
the surface of a solar system body that form from impacts with other solar
system bodies, such as asteroids and meteoroids. All of the inner planets
and many of the solar system's moons have impact craters.
Sunspots are located on the Sun's
photosphere. These dark spots are caused by concentrations of the
Sun's magnetic field.
The majority of the asteroids in our
solar system are found in the region known as the asteroid belt,
which exists in the space between Mars and Jupiter.
A comet has a tail that is visible only
when light reflects off of vaporizing ice and dust streaming from
the comet's body.
Picture modified from
under GNU FDL.
A moon revolves around its
A moon is kept in orbit around a planet by the
gravitational force between the two bodies.
Asteroids vary greatly in size,
the smallest being the size of pebbles and the largest having a diameter
of approximately 1000 kilometers. Asteroids are mostly made up of
stone, iron and nickel.
Comets are mostly made up of dust
particles, frozen water and frozen gases. While in the far reaches of
their orbits, which is where they spend most of their time, they reflect
little sunlight and are difficult to see. However, as they get closer to
the Sun, the water and gas unfreeze and begin reflecting sunlight much
better, making them very easy to see.
Sunspots are darker and cooler
than the gases surrounding them. These spots form where concentrations in
the Sun's magnetic field cause temperatures to decrease on the
photosphere. Although these cooler spots still shine brightly, they appear
dark because the surrounding gases are hotter and shine more
Sunspots are temporary features. They typically last for
a few weeks and tend to occur in cycles.
Solar flares are violent
explosions from sunspots in which gas and tremendous amounts of energy are
blasted into space away from the Sun.
Solar flares are usually more
violent and shorter lived than prominences. Because of their association
with sunspots, the frequencies and magnitudes of flares and prominences
are affected by sunspot cycles.
A piece of solar system debris that
passes through Earth's atmosphere and strikes the ground is a
meteorite. Most meteorites are meteoroid-size when they enter the
atmosphere, and some of their mass burns up as they speed toward the
Larger bodies—asteroids and comets—do collide with Earth on
rare occasions and can devastate the planet. Earth's geologic record
preserves evidence that suggests one such collision may have occurred at
the end of the Mesozoic era. Many scientists theorize that this impact
killed the dinosaurs and many other groups of organisms in a mass