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عدد المساهمات : 6011 نقاط التميز : 24782 تاريخ التسجيل : 17/04/2009 العمر : 36 الموقع : العمارية المدية الجزائر 
solar system GENERALITY
الأربعاء 6 يناير - 9:44
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 medium. The Sun is the richest source of electromagnetic energy
(mostly in the form of heat and light) in the solar system. The Sun's nearest
known stellar neighbor is a red dwarf star called Proxima Centauri, at a distance
of 4.3 light years away. The whole solar system,
together with the local stars visible on a clear night, orbits the center of
our home galaxy, a spiral disk of 200 billion stars we call the Milky Way. The Milky Way has two small
galaxies orbiting it nearby, which are visible from the southern hemisphere.
They are called the Large Magellanic Cloud and the Small Magellanic Cloud. The
nearest large galaxy is the Andromeda Galaxy. It is a spiral
galaxy like the Milky Way but is 4 times as massive and is 2 million light
years away. Our galaxy, one of billions of galaxies known, is traveling through
intergalactic space.
Composition
Of The Solar System:
The Sun contains 99.85% of all the matter in the Solar System. The
planets, which condensed out of the same disk of material that formed the Sun,
contain only 0.135% of the mass of the solar system. Jupiter contains more than
twice the matter of all the other planets combined. Satellites of the planets,
comets, asteroids, meteoroids, and the interplanetary medium constitute the remaining
0.015%. The following table is a list of the mass distribution within our Solar
System.
DEFERENT PARTS FOR SOLAR SYSTEM:
The Sun:
The Sun is the
most prominent feature in our solar system. It is the largest object and
contains approximately 98% of the total solar system mass. One hundred and nine
Earths would be required to fit across the Sun's disk, and its interior could
hold over 1.3 million Earths. The Sun's outer visible layer is called the
photosphere and has a temperature of 6,000°C (11,000°F). This layer has
a mottled appearance due to the turbulent eruptions of energy at the surface.
Solar energy is created deep within the
core of the Sun. It is here that the temperature (15,000,000° C; 27,000,000° F)
and pressure (340 billion times Earth's air pressure at sea level) is so
intense that nuclear reactions take place. This reaction causes four protons or
hydrogen nuclei to fuse together to form one alpha particle or helium nucleus.
The alpha particle is about .7 percent less massive than the four protons. The
difference in mass is expelled as energy and is carried to the surface of the
Sun, through a process known as convection,
where it is released as light and heat. Energy generated in the Sun's core
takes a million years to reach its surface. Every second 700 million tons of
hydrogen are converted into helium ashes. In the process 5 million tons
of pure energy is released; therefore, as time goes on the Sun is becoming
lighter.
Mercury :
Mercury was named by the Romans after
the fleet-footed messenger of the gods because it seemed to move more quickly
than any other planet. It is the closest planet to the Sun, and second smallest
planet in the solar system. Its diameter is 40% smaller
than Earth and 40% larger than the Moon. It is even smaller
than Jupiter's moon Ganymede and Saturn's moon Titan.
If an explorer were to step onto the
surface of Mercury, he would discover a world resembling lunar terrain.
Mercury's rolling, dust-covered hills have been eroded from the constant
bombardment of meteorites. Fault-cliffs rise for several
kilometers in height and extend for hundreds of kilometers. Craters dot the
surface. The explorer would notice that the Sun appears two and a half times
larger than on Earth; however, the sky is always black because Mercury has
virtually no atmosphere to cause scattering of light. As the explorer gazes out
into space, he might see two bright stars. One appearing as cream colored Venus and the other as blue
colored Earth.
Venus :
Venus, the jewel of
the sky, was once know by ancient astronomers as the morning star
and evening star. Early astronomers once thought Venus to be two
separate bodies. Venus, which is named after the Roman goddess of love and
beauty, is veiled by thick swirling cloud cover.
Astronomers refer to
Venus as Earth's sister planet. Both are similar in size, mass, density and
volume. Both formed about the same time and condensed out of the same nebula. However, during the
last few years scientists have found that the kinship ends here. Venus is very
different from the Earth. It has no oceans and is surrounded by a heavy
atmosphere composed mainly of carbon dioxide with virtually no water vapor. Its
clouds are composed of sulfuric acid droplets. At the
surface, the atmospheric pressure is 92 times that of the Earth's at sea-level.
Venus is scorched with
a surface temperature of about 482° C (900° F). This high temperature is
primarily due to a runaway greenhouse effect caused by the heavy
atmosphere of carbon dioxide. Sunlight passes through the atmosphere to heat
the surface of the planet. Heat is radiated out, but is trapped by the dense
atmosphere and not allowed to escape into space. This makes Venus hotter than Mercury.
A Venusian day is 243
Earth days and is longer than its year of 225 days. Oddly, Venus rotates from
east to west. To an observer on Venus, the Sun would rise in the west and set
in the east.
Earth :
From the perspective we get
on Earth, our planet appears to be big and sturdy with an endless ocean of air.
From space, astronauts often get the impression that the Earth is small with a
thin, fragile layer of atmosphere. For a space traveler, the distinguishing
Earth features are the blue waters, brown and green land masses and white
clouds set against a black background.
Many dream of traveling in
space and viewing the wonders of the universe. In reality all of us are space
travelers. Our spaceship is the planet Earth, traveling at the speed of 108,000 kilometers
(67,000 miles)
an hour.
Earth is the 3rd planet
from the Sun at a distance of about 150 million kilometers (93.2 million
miles). It takes 365.256 days for the Earth to travel around the Sun and
23.9345 hours for the Earth rotate a complete revolution. It has a diameter of 12,756 kilometers
(7,973 miles),
only a few hundred kilometers larger than that of Venus. Our atmosphere is
composed of 78 percent nitrogen, 21 percent oxygen and 1 percent other
constituents.
Earth is the only planet in
the solar system known to harbor life. Our planet's rapid spin and molten
nickel-iron core give rise to an extensive magnetic field, which, along with
the atmosphere, shields us from nearly all of the harmful radiation coming from
the Sun and other stars. Earth's atmosphere protects us from meteors, most of
which burn up before they can strike the surface.
Mars :
Mars is the fourth planet from the Sun and is commonly referred to as
the Red Planet. The rocks, soil and sky have a red or pink hue. The distinct
red color was observed by stargazers throughout history. It was given its name
by the Romans in honor of their god of war. Other civilizations have had
similar names. The ancient Egyptians named the planet Her Descher
meaning the red one.
Before space
exploration, Mars was considered the best candidate for harboring
extraterrestrial life. Astronomers thought they saw straight lines crisscrossing
its surface. This led to the popular belief that irrigation canals on the
planet had been constructed by intelligent beings. In 1938, when Orson Welles
broadcasted a radio drama based on the science fiction classic War of the
Worlds by H.G. Wells, enough people believed in the tale of invading
Martians to cause a near panic.
Another reason for
scientists to expect life on Mars had to do with the apparent seasonal color
changes on the planet's surface. This phenomenon led to speculation that conditions
might support a bloom of Martian vegetation during the warmer months and cause
plant life to become dormant during colder periods.
Jupiter :
Jupiter is the fifth planet
from the Sun and is the largest one in the solar system. If Jupiter were hollow,
more than one thousand Earths could fit inside. It also contains more matter
than all of the other planets combined. It has a mass of 1.9 x 1027 kg and is 142,800 kilometers
(88,736 miles)
across the equator. Jupiter possesses 28 known satellites, four of which -
Callisto, Europa, Ganymede and Io - were observed by Galileo as long ago as 1610.
Another 12 satellites have been recently discovered and given provisional
designators until they are officially confirmed and named. There is a ring
system, but it is very faint and is totally invisible from the Earth.
(The rings were discovered in 1979 by Voyager
1.) The atmosphere is very deep, perhaps comprising the whole planet, and is
somewhat like the Sun. It is composed mainly of hydrogen and helium, with small
amounts of methane, ammonia, water vapor and other compounds. At great depths
within Jupiter, the pressure is so great that the hydrogen atoms are broken up
and the electrons are freed so that the resulting atoms consist of bare
protons. This produces a state in which the hydrogen becomes metallic.
Saturn :
Saturn is the sixth planet from the Sun and is the second largest in the
solar system with an equatorial diameter of 119,300 kilometers
(74,130 miles).
Much of what is known about the planet is due to the Voyager explorations in
1980-81. Saturn is visibly flattened at the poles, a result of the very fast
rotation of the planet on its axis. Its day is 10 hours, 39 minutes long, and
it takes 29.5 Earth years to revolve about the Sun. The atmosphere is primarily
composed of hydrogen with small amounts of helium and methane. Saturn is the
only planet less dense than water (about 30 percent less). In the unlikely
event that a large enough ocean could be found, Saturn would float in it.
Saturn's hazy yellow hue is marked by broad atmospheric banding similar to, but
fainter than, that found on Jupiter.
The wind blows at high
speeds on Saturn. Near the equator, it reaches velocities of 500 meters a second (1,100 miles an hour).
The wind blows mostly in an easterly direction. The strongest winds are found
near the equator and velocity falls off uniformly at higher latitudes. At
latitudes greater than 35 degrees, winds alternate east and west as latitude
increases.
Uranus:
Uranus is the seventh planet from the Sun and is the
third largest in the solar system. It was discovered by William Herschel in 1781. It has an
equatorial diameter of 51,800 kilometers (32,190 miles) and
orbits the Sun once every 84.01 Earth years. It has a mean distance from the
Sun of 2.87 billion kilometers (1.78 billion miles). The length of a day on
Uranus is 17 hours 14 minutes. Uranus has at least 22 moons. The two largest
moons, Titania and Oberon, were discovered by
William Herschel in 1787.
The atmosphere of
Uranus is composed of 83% hydrogen, 15% helium, 2% methane and small amounts of
acetylene and other hydrocarbons. Methane in the upper atmosphere absorbs red
light, giving Uranus its blue-green color. The atmosphere is arranged into
clouds running at constant latitudes, similar to the orientation of the more
vivid latitudinal bands seen on Jupiter and Saturn. Winds at mid-latitudes on
Uranus blow in the direction of the planet's rotation. These winds blow at
velocities of 40 to 160
meters per second (90 to 360 miles per hour).
Radio science experiments found winds of about 100 meters per second
blowing in the opposite direction at the equator.
Neptune :
Neptune is the outermost planet of the
gas giants. It has an equatorial diameter of 49,500 kilometers
(30,760 miles).
If Neptune were hollow, it could contain
nearly 60 Earths. Neptune orbits the Sun every
165 years. It has eight moons, six of which were found by Voyager. A day on Neptune is 16 hours and 6.7 minutes. Neptune
was discovered on September 23, 1846 by Johann Gottfried Galle, of the Berlin
Observatory, and Louis d'Arrest, an astronomy student, through mathematical
predictions made by Urbain Jean Joseph Le Verrier.
The first two thirds
of Neptune is composed of a mixture of molten
rock, water, liquid ammonia and methane. The outer third is a mixture of heated
gases comprised of hydrogen, helium, water and methane. Methane gives Neptune its blue cloud color.
Neptune is a dynamic planet
with several large, dark spots reminiscent of Jupiter's hurricane-like storms. The
largest spot, known as the Great Dark Spot, is about the size of
the earth and is similar to the Great Red Spot on Jupiter. Voyager
revealed a small, irregularly shaped, eastward-moving cloud scooting
around Neptune every 16 hours or so. This scooter
as it has been dubbed could be a plume rising above a deeper cloud deck.
Pluto :
Although Pluto was
discovered in 1930, limited information on the distant planet delayed a
realistic understanding of its characteristics. Today Pluto remains the only
planet that has not been visited by a spacecraft, yet an increasing amount of
information is unfolding about this peculiar planet. The uniqueness of Pluto's
orbit, rotational relationship with its satellite, spin axis, and light
variations all give the planet a certain appeal.
Pluto is usually farther from the Sun than any of the nine
planets; however, due to the eccentricity of its orbit, it is closer than Neptune for 20 years out of
its 249 year orbit. Pluto crossed Neptune's orbit January 21, 1979, made its
closest approach September 5, 1989, and will remain within the orbit of Neptune until February 11, 1999. This will not occur
again until September 2226.
As Pluto approaches perihelion it reaches its maximum distance
from the ecliptic due to its 17-degree
inclination. Thus, it is far above or below the plane of Neptune's
orbit. Under these conditions, Pluto and Neptune will not collide and do not
approach closer than 18 A.U.
to one another.
Pluto's rotation period is 6.387 days, the
same as its satellite Charon. Although it is common for a satellite to travel
in a synchronous orbit with its planet,
Pluto is the only planet to rotate synchronously with the orbit of its
satellite. Thus being tidally locked, Pluto and Charon continuously face each
other as they travel through space.
Solar
system history:
From our small world we have gazed upon the cosmic ocean for untold
thousands of years. Ancient astronomers observed points of light that appeared
to move among the stars. They called these objects planets, meaning wanderers,
and named them after Roman deities -- Jupiter, king of the gods; Mars, the god of war; Mercury, messenger of the gods; Venus, the god of love and beauty, and Saturn, father of Jupiter and god of agriculture. The
stargazers also observed comets with sparkling tails, and meteors or shooting
stars apparently falling from the sky.
Future historians will likely
view these pioneering flights through the solar system as some of the most
remarkable achievements of the 20th century
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 medium. The Sun is the richest source of electromagnetic energy
(mostly in the form of heat and light) in the solar system. The Sun's nearest
known stellar neighbor is a red dwarf star called Proxima Centauri, at a distance
of 4.3 light years away. The whole solar system,
together with the local stars visible on a clear night, orbits the center of
our home galaxy, a spiral disk of 200 billion stars we call the Milky Way. The Milky Way has two small
galaxies orbiting it nearby, which are visible from the southern hemisphere.
They are called the Large Magellanic Cloud and the Small Magellanic Cloud. The
nearest large galaxy is the Andromeda Galaxy. It is a spiral
galaxy like the Milky Way but is 4 times as massive and is 2 million light
years away. Our galaxy, one of billions of galaxies known, is traveling through
intergalactic space.
Composition
Of The Solar System:
The Sun contains 99.85% of all the matter in the Solar System. The
planets, which condensed out of the same disk of material that formed the Sun,
contain only 0.135% of the mass of the solar system. Jupiter contains more than
twice the matter of all the other planets combined. Satellites of the planets,
comets, asteroids, meteoroids, and the interplanetary medium constitute the remaining
0.015%. The following table is a list of the mass distribution within our Solar
System.
- Sun: 99.85%
- Planets: 0.135%
- Comets: 0.01% ?
- Satellites: 0.00005%
- Minor Planets:
0.0000002% ? - Meteoroids: 0.0000001%
? - Interplanetary Medium:
0.0000001% ?
DEFERENT PARTS FOR SOLAR SYSTEM:
The Sun:
The Sun is the
most prominent feature in our solar system. It is the largest object and
contains approximately 98% of the total solar system mass. One hundred and nine
Earths would be required to fit across the Sun's disk, and its interior could
hold over 1.3 million Earths. The Sun's outer visible layer is called the
photosphere and has a temperature of 6,000°C (11,000°F). This layer has
a mottled appearance due to the turbulent eruptions of energy at the surface.
Solar energy is created deep within the
core of the Sun. It is here that the temperature (15,000,000° C; 27,000,000° F)
and pressure (340 billion times Earth's air pressure at sea level) is so
intense that nuclear reactions take place. This reaction causes four protons or
hydrogen nuclei to fuse together to form one alpha particle or helium nucleus.
The alpha particle is about .7 percent less massive than the four protons. The
difference in mass is expelled as energy and is carried to the surface of the
Sun, through a process known as convection,
where it is released as light and heat. Energy generated in the Sun's core
takes a million years to reach its surface. Every second 700 million tons of
hydrogen are converted into helium ashes. In the process 5 million tons
of pure energy is released; therefore, as time goes on the Sun is becoming
lighter.
Mercury :
Mercury was named by the Romans after
the fleet-footed messenger of the gods because it seemed to move more quickly
than any other planet. It is the closest planet to the Sun, and second smallest
planet in the solar system. Its diameter is 40% smaller
than Earth and 40% larger than the Moon. It is even smaller
than Jupiter's moon Ganymede and Saturn's moon Titan.
If an explorer were to step onto the
surface of Mercury, he would discover a world resembling lunar terrain.
Mercury's rolling, dust-covered hills have been eroded from the constant
bombardment of meteorites. Fault-cliffs rise for several
kilometers in height and extend for hundreds of kilometers. Craters dot the
surface. The explorer would notice that the Sun appears two and a half times
larger than on Earth; however, the sky is always black because Mercury has
virtually no atmosphere to cause scattering of light. As the explorer gazes out
into space, he might see two bright stars. One appearing as cream colored Venus and the other as blue
colored Earth.
Venus :
Venus, the jewel of
the sky, was once know by ancient astronomers as the morning star
and evening star. Early astronomers once thought Venus to be two
separate bodies. Venus, which is named after the Roman goddess of love and
beauty, is veiled by thick swirling cloud cover.
Astronomers refer to
Venus as Earth's sister planet. Both are similar in size, mass, density and
volume. Both formed about the same time and condensed out of the same nebula. However, during the
last few years scientists have found that the kinship ends here. Venus is very
different from the Earth. It has no oceans and is surrounded by a heavy
atmosphere composed mainly of carbon dioxide with virtually no water vapor. Its
clouds are composed of sulfuric acid droplets. At the
surface, the atmospheric pressure is 92 times that of the Earth's at sea-level.
Venus is scorched with
a surface temperature of about 482° C (900° F). This high temperature is
primarily due to a runaway greenhouse effect caused by the heavy
atmosphere of carbon dioxide. Sunlight passes through the atmosphere to heat
the surface of the planet. Heat is radiated out, but is trapped by the dense
atmosphere and not allowed to escape into space. This makes Venus hotter than Mercury.
A Venusian day is 243
Earth days and is longer than its year of 225 days. Oddly, Venus rotates from
east to west. To an observer on Venus, the Sun would rise in the west and set
in the east.
Earth :
From the perspective we get
on Earth, our planet appears to be big and sturdy with an endless ocean of air.
From space, astronauts often get the impression that the Earth is small with a
thin, fragile layer of atmosphere. For a space traveler, the distinguishing
Earth features are the blue waters, brown and green land masses and white
clouds set against a black background.
Many dream of traveling in
space and viewing the wonders of the universe. In reality all of us are space
travelers. Our spaceship is the planet Earth, traveling at the speed of 108,000 kilometers
(67,000 miles)
an hour.
Earth is the 3rd planet
from the Sun at a distance of about 150 million kilometers (93.2 million
miles). It takes 365.256 days for the Earth to travel around the Sun and
23.9345 hours for the Earth rotate a complete revolution. It has a diameter of 12,756 kilometers
(7,973 miles),
only a few hundred kilometers larger than that of Venus. Our atmosphere is
composed of 78 percent nitrogen, 21 percent oxygen and 1 percent other
constituents.
Earth is the only planet in
the solar system known to harbor life. Our planet's rapid spin and molten
nickel-iron core give rise to an extensive magnetic field, which, along with
the atmosphere, shields us from nearly all of the harmful radiation coming from
the Sun and other stars. Earth's atmosphere protects us from meteors, most of
which burn up before they can strike the surface.
Mars :
Mars is the fourth planet from the Sun and is commonly referred to as
the Red Planet. The rocks, soil and sky have a red or pink hue. The distinct
red color was observed by stargazers throughout history. It was given its name
by the Romans in honor of their god of war. Other civilizations have had
similar names. The ancient Egyptians named the planet Her Descher
meaning the red one.
Before space
exploration, Mars was considered the best candidate for harboring
extraterrestrial life. Astronomers thought they saw straight lines crisscrossing
its surface. This led to the popular belief that irrigation canals on the
planet had been constructed by intelligent beings. In 1938, when Orson Welles
broadcasted a radio drama based on the science fiction classic War of the
Worlds by H.G. Wells, enough people believed in the tale of invading
Martians to cause a near panic.
Another reason for
scientists to expect life on Mars had to do with the apparent seasonal color
changes on the planet's surface. This phenomenon led to speculation that conditions
might support a bloom of Martian vegetation during the warmer months and cause
plant life to become dormant during colder periods.
Jupiter :
Jupiter is the fifth planet
from the Sun and is the largest one in the solar system. If Jupiter were hollow,
more than one thousand Earths could fit inside. It also contains more matter
than all of the other planets combined. It has a mass of 1.9 x 1027 kg and is 142,800 kilometers
(88,736 miles)
across the equator. Jupiter possesses 28 known satellites, four of which -
Callisto, Europa, Ganymede and Io - were observed by Galileo as long ago as 1610.
Another 12 satellites have been recently discovered and given provisional
designators until they are officially confirmed and named. There is a ring
system, but it is very faint and is totally invisible from the Earth.
(The rings were discovered in 1979 by Voyager
1.) The atmosphere is very deep, perhaps comprising the whole planet, and is
somewhat like the Sun. It is composed mainly of hydrogen and helium, with small
amounts of methane, ammonia, water vapor and other compounds. At great depths
within Jupiter, the pressure is so great that the hydrogen atoms are broken up
and the electrons are freed so that the resulting atoms consist of bare
protons. This produces a state in which the hydrogen becomes metallic.
Saturn :
Saturn is the sixth planet from the Sun and is the second largest in the
solar system with an equatorial diameter of 119,300 kilometers
(74,130 miles).
Much of what is known about the planet is due to the Voyager explorations in
1980-81. Saturn is visibly flattened at the poles, a result of the very fast
rotation of the planet on its axis. Its day is 10 hours, 39 minutes long, and
it takes 29.5 Earth years to revolve about the Sun. The atmosphere is primarily
composed of hydrogen with small amounts of helium and methane. Saturn is the
only planet less dense than water (about 30 percent less). In the unlikely
event that a large enough ocean could be found, Saturn would float in it.
Saturn's hazy yellow hue is marked by broad atmospheric banding similar to, but
fainter than, that found on Jupiter.
The wind blows at high
speeds on Saturn. Near the equator, it reaches velocities of 500 meters a second (1,100 miles an hour).
The wind blows mostly in an easterly direction. The strongest winds are found
near the equator and velocity falls off uniformly at higher latitudes. At
latitudes greater than 35 degrees, winds alternate east and west as latitude
increases.
Uranus:
Uranus is the seventh planet from the Sun and is the
third largest in the solar system. It was discovered by William Herschel in 1781. It has an
equatorial diameter of 51,800 kilometers (32,190 miles) and
orbits the Sun once every 84.01 Earth years. It has a mean distance from the
Sun of 2.87 billion kilometers (1.78 billion miles). The length of a day on
Uranus is 17 hours 14 minutes. Uranus has at least 22 moons. The two largest
moons, Titania and Oberon, were discovered by
William Herschel in 1787.
The atmosphere of
Uranus is composed of 83% hydrogen, 15% helium, 2% methane and small amounts of
acetylene and other hydrocarbons. Methane in the upper atmosphere absorbs red
light, giving Uranus its blue-green color. The atmosphere is arranged into
clouds running at constant latitudes, similar to the orientation of the more
vivid latitudinal bands seen on Jupiter and Saturn. Winds at mid-latitudes on
Uranus blow in the direction of the planet's rotation. These winds blow at
velocities of 40 to 160
meters per second (90 to 360 miles per hour).
Radio science experiments found winds of about 100 meters per second
blowing in the opposite direction at the equator.
Neptune :
Neptune is the outermost planet of the
gas giants. It has an equatorial diameter of 49,500 kilometers
(30,760 miles).
If Neptune were hollow, it could contain
nearly 60 Earths. Neptune orbits the Sun every
165 years. It has eight moons, six of which were found by Voyager. A day on Neptune is 16 hours and 6.7 minutes. Neptune
was discovered on September 23, 1846 by Johann Gottfried Galle, of the Berlin
Observatory, and Louis d'Arrest, an astronomy student, through mathematical
predictions made by Urbain Jean Joseph Le Verrier.
The first two thirds
of Neptune is composed of a mixture of molten
rock, water, liquid ammonia and methane. The outer third is a mixture of heated
gases comprised of hydrogen, helium, water and methane. Methane gives Neptune its blue cloud color.
Neptune is a dynamic planet
with several large, dark spots reminiscent of Jupiter's hurricane-like storms. The
largest spot, known as the Great Dark Spot, is about the size of
the earth and is similar to the Great Red Spot on Jupiter. Voyager
revealed a small, irregularly shaped, eastward-moving cloud scooting
around Neptune every 16 hours or so. This scooter
as it has been dubbed could be a plume rising above a deeper cloud deck.
Pluto :
Although Pluto was
discovered in 1930, limited information on the distant planet delayed a
realistic understanding of its characteristics. Today Pluto remains the only
planet that has not been visited by a spacecraft, yet an increasing amount of
information is unfolding about this peculiar planet. The uniqueness of Pluto's
orbit, rotational relationship with its satellite, spin axis, and light
variations all give the planet a certain appeal.
Pluto is usually farther from the Sun than any of the nine
planets; however, due to the eccentricity of its orbit, it is closer than Neptune for 20 years out of
its 249 year orbit. Pluto crossed Neptune's orbit January 21, 1979, made its
closest approach September 5, 1989, and will remain within the orbit of Neptune until February 11, 1999. This will not occur
again until September 2226.
As Pluto approaches perihelion it reaches its maximum distance
from the ecliptic due to its 17-degree
inclination. Thus, it is far above or below the plane of Neptune's
orbit. Under these conditions, Pluto and Neptune will not collide and do not
approach closer than 18 A.U.
to one another.
Pluto's rotation period is 6.387 days, the
same as its satellite Charon. Although it is common for a satellite to travel
in a synchronous orbit with its planet,
Pluto is the only planet to rotate synchronously with the orbit of its
satellite. Thus being tidally locked, Pluto and Charon continuously face each
other as they travel through space.
Solar
system history:
From our small world we have gazed upon the cosmic ocean for untold
thousands of years. Ancient astronomers observed points of light that appeared
to move among the stars. They called these objects planets, meaning wanderers,
and named them after Roman deities -- Jupiter, king of the gods; Mars, the god of war; Mercury, messenger of the gods; Venus, the god of love and beauty, and Saturn, father of Jupiter and god of agriculture. The
stargazers also observed comets with sparkling tails, and meteors or shooting
stars apparently falling from the sky.
Future historians will likely
view these pioneering flights through the solar system as some of the most
remarkable achievements of the 20th century
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