Solar System
Solar system
The sun and the planets, the moon and the satellites of the other planets,
the comets, asterois, and meteoroids make up the solar system. The solar
system is located in the Milky Way Galaxy. Almost the whole galaxy is made
of stars. Astronomers believe there are at least 100 billion stars. If you
counted one star a second it would take you more than thirty thousand years
to count 100 billion. And each star has planets, like the sun.
Sun.
The big burning ball of gas that holds nine major planets in orbit is not
unlike many stars in the universe. The Sun makes up 99.86 percent of the
solar system's mass and provides the energy that both sustains and
endangers us. Scientists have lately begun calling its tremendous
outpouring of energy "space weather."
Massive energy
The Sun can be divided into three main layers: a core, a radiative zone,
and a convective zone. The Sun's energy comes from thermonuclear reactions
(converting hydrogen to helium) in the core, where the temperature is 15 to
25 million degrees. The energy radiates through the middle layer, then
bubbles and boils to the surface in a process called convection. Charged
particles, called the solar wind, stream out at a million miles an hour.
Sunspots
Magnetic fields within the sun slow down the radiation of heat in some
areas, causing sunspots, which are cool areas and appear as dark patches.
Sunspot activity peaks every 11 years. The next peak is due in 2000.
During this so-called solar maximum, the sun will bombard Earth's
atmosphere with extra doses of solar radiation. The last peak, in 1989,
caused power blackouts, knocked satellites out of orbit and disrupted radio
communications. (See our special report on Sunspots.)
Though NASA scientists aren't predicting any record-setting space weather
in 2000, the peak is expected to be above average. "It's like saying we're
going to have a mild or cold winter," says Dr. David Hathaway at NASA's
Marshall Space Flight Center. But as communications rely increasingly on
satellites, there are more targets in the sky and more significant
consequences to any disruptions.
And there may be more to sunspots than disrupted communications. An active
sun, known to heat the Earth's outer atmosphere, may also affect our
climate. Scientists say a small ice age from 1645 to 1715 corresponded to a
time of reduced solar activity, and current rises in temperatures might be
related to increased solar activity.
Solar flares
The Sun frequently spews plumes of energy, essentially bursts of solar
wind. These solar flares contain Gamma rays and X-rays, plus energized
particles (protons and electrons). Energy is equal to a billion megatons of
TNT is released in a matter of minutes. Flare activity picks up as sunspots
increase.
Effect on Earth
The Sun's charged, high-speed particles push and shape Earth's magnetic
field into a teardrop shape. The magnetic field protects Earth from most of
the harmful solar radiation, but extreme flares can disable satellites and
disrupt communication signals. The charged particles also excite oxygen and
nitrogen in the atmosphere to create the aurora borealis, or northern
lights. More solar radiation during the upcoming solar maximum means an
increase in the aurora.
Coronal mass ejections
Similar to a solar flare, a coronal mass ejection is a bubble of gas and
charged particles ejected over several hours. It can occur with or without
solar flares, and can also threaten Earth's atmosphere.
Final fact
If you stood on the Sun, its gravity would make you feel 38 times more
heavy than you do on Earth. But it's kind of hot, so please don't try it.
Mercury
The innermost planet is rarely seen because of the Sun's glare. With less
than half Earth's gravity, Mercury retains only a wisp of an atmosphere
(presumed to be helium). The lack of a significant atmosphere allows
temperatures to fluctuate from 750 degrees Fahrenheit during the day to
minus 320 Fahrenheit at night.
Like the other terrestrial planets -- Venus, Earth and Mars -- Mercury is
made mostly of rock and metal. This small world is scarred by craters and
looks somewhat like our Moon.
MERCURIUS: ROMAN WINGED MESSENGER OF THE GODS
Historical notes
Mercury has been known since ancient times. Its elusiveness generated the
name Hermes, given by the Greeks, later translated to Mercurius by the
Romans.
Venus.
The second planet from the sun bakes under twice as much solar radiation as
Earth and reaches temperatures of 895 degrees Fahrenheit (480 degrees
Celsius). Pressure from the dense atmosphere of sulfuric acid gas is about
95 times greater than Earth's and would crush a human.
The thick cloud cover around Venus rotates much faster than the planet
itself -- once every four days. After the moon, Venus is the brightest
object in the sky.
The surface of Venus is mostly a rocky desert (this computer-generated view
shows lava flows around Sif Mons). Like Mercury, Earth and Mars, Venus is
composed of mostly rock and metal.
VENUS: ROMAN GODDESS OF LOVE AND BEAUTY
Historical notes
The Greeks believed Venus was two separate objects -- one in the morning
sky and another in the evening. Because it is often brighter than any other
object in the sky -- except for the sun and moon -- Venus has generated
many UFO reports.
Final facts
While all of the planets orbit in an ellipse, Venus' orbit is the closest
to a perfect circle. It is the only planet in the solar system whose day
(241 Earth days) is longer than its year (225 Earth days).
Earth
The third planet from the sun is, in scientific terms, quite similar to the
first two. In fact, the four planets of the inner solar system (Mercury,
Venus, Earth and Mars) all share rock and metal as their primary
ingredients. Each of these so-called terrestrial planets has a solid
surface, unlike the gaseous planets of the outer solar system.
Perhaps Earth's most distinguishing factor, at least from our point of
view, is the presence of water, which contributed to the formation of life
some 3,000 million years ago. Most of us ought also to be fond of Earth's
unique atmosphere, rich in life-sustaining nitrogen and oxygen.
Final fact
The Earth's surface is rotates about its axis at 1,532 feet per second --
slightly over 1,000 miles per hour -- at the equator, and the planet zips
around the sun at more than 18 miles per second.
The Moon
Though a satellite of Earth, the Moon is bigger than Pluto. Some scientists
think of it as a planet (four other moons in our solar system are even
bigger). There are various theories about how the Moon was created, but
recent evidence indicates it formed when a huge collision tore a chunk of
the Earth away.
How the Moon's phases change
Because it takes 27.3 days both to rotate on its axis and to orbit Earth,
the Moon always shows us the same face. We see the Moon because of
reflected sunlight. How much of it we see depends on its position in
relation to Earth and the Sun.
The 27.3-day number is what scientists call a sidereal month, and it is how
long it takes the Moon to orbit the Earth in relation to a fixed star.
Another measurement, called a synodic month, is measured between in
relation to the Sun and equals 29.5 days. Full moons and new moon are
measured by the synodic month.
Earth's gravity keeps the Moon in orbit, while the Moon's gravity creates
tides on our oceans
On the moon
Like the four inner planets, the Moon is rocky. It's pockmarked with
craters formed by asteroid impacts millions of years ago. Because there is
no weather, the craters have not eroded.
The Moon has almost no atmosphere, so a layer of dust -- or a footprint --
can sit undisturbed for centuries. And without an atmosphere, heat is not
held near the planet, so temperatures vary wildly. Daytime temperatures on
the sunny side of the Moon reach 273 degrees F; on the dark side it gets as
cold as -243.
In June of 1999, reserchers discovered by accident that a huge cloud of
sodium gas trails behind the Moon.
The Lunar Prospector in 1998 provided evidence of ice near the Moon's
poles, perhaps as much as 6 billion tons of it.
Final fact
The Moon travels around the Earth at a little more than half a mile per
second; its speed is slowing and the satellite is gradually moving away
from Earth.
Mars
The fourth planet from the sun has always captivated our imagination, and
while scientists haven't proven there's any life, not even the microscopic
variety, the dusty red planet still commands our attention (and a lot of
space missions).
On the planet
The surface of Mars is more interesting than most planets. Like Mercury,
Venus and Earth, Mars is mostly rock and metal. Mountains and craters scar
the rugged terrain. The dust, an iron oxide, gives the planet its reddish
cast. A thin atmosphere and an elliptical orbit combine to create
temperature fluctuations ranging from minus 207 degrees Fahrenheit to a
comfortable 80 degrees Fahrenheit on summer days (if you are at the
equator). Researchers have recently monitored huge storms swirling on Mars.
The storms are very similar to hurricanes on Earth.
Mars has two moons, Phobos and Deimos.
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