Planets, View the planets up close

The Eight Planets
Enjoy

A view of the third planet from the sun . Earth as seen from the moon.

ASTRONOMY

Here's a little of what I know about the universe and planets.

The planets can be divided into two principal groups--terrestrial and Jovian. The terrestrial group is made up of the four innermost planets: Mercury, Venus, Earth, and Mars. The Jovian planets are the outer gaseous giants: Jupiter, Saturn, Uranus, and Neptune. The outermost planet of the solar system, Pluto, is distinct from the members of either group, having a makeup more characteristic of an icy satellite than a planet proper.

The terrestrial planets lie between 0.39 and 1.52 astronomical units (AU) from the Sun. (One astronomical unit equals 149,598,000 km, or 92,955,800 miles, and represents the mean distance between the Earth and the Sun.) All four planets are small (less than 13,000 km in diameter), rocky, and have thin or negligible atmospheres. It is thought that the heat from the young Sun prevented the abundant gases in the original solar nebula from condensing in these planets. These bodies thus were not able to retain extensive gassy envelopes, and so they remained bare, rocky cores whose atmospheres (if any) resulted from internal degassing.

Between 5.2 and 30.4 AU, the gas in the solar nebula was cool enough for several abundant gases to condense, enabling the embryonic outer planets to grow very massive and retain huge atmospheres of light gases, predominantly hydrogen and helium. Jupiter, Saturn, Uranus, and Neptune all appear to be similar in structure, and none of them has an accessible surface. Of the four gaseous giants, Jupiter is the largest, with a diameter of nearly 143,000 km. Except for Neptune, each of these planets is surrounded by at least one full ring and by a complex satellite system.

The inner and outer planets are separated by a gap between the orbits of Mars and Jupiter that is filled by tens of thousands of minor planets, known as asteroids. Although some of them, such as Ceres and Pallas, are several hundred kilometres in diameter and spherical in shape, the majority are irregular chunks of rock or metal only a few metres across. The asteroids are probably fragments of a number of slightly larger bodies that failed to accrete into a single planet because of the influence of Jupiter's strong gravitational pull. Some asteroids have very elongated orbits that take them well outside the asteroid belt and close to the other planets. Asteroids or asteroidal fragments can thus collide with the Earth (as well as with various other planetary bodies), and excessive bombardment by large objects of this type in the past has given rise to extensive cratering on the surfaces of the inner planets and their satellites. By now, however, most of the larger asteroidal bodies have disappeared; some of the smaller fragments enter the Earth's atmosphere to become bright meteors. If such an asteroidal fragment survives the fiery entry and reaches the surface, it is called a meteorite.

Most meteoroids are much smaller than those originating in the asteroid belt. They are fragile, low-density dust particles that come from comets worn down by repeated passes through the inner solar system. Comets are thought to originate in a huge swarm of cosmic debris known as the Oort cloud, the outer boundary of which is estimated to be 50,000 AU or more from the Sun. When the orbit of one of these comet nuclei is disturbed by the gravity of a nearby star, the nucleus may travel out of the Oort cloud and into the inner solar system in an elongated orbit. As the incipient comet approaches the Sun, its outer layer of icy matter melts and vaporizes, releasing gases and dust that form a spherical, diffuse cloud (the coma) around the nucleus. Eventually, some of the gas molecules and dust particles are ejected from the coma, forming one or two tails millions of kilometres in length.

With a diameter of only about 2,300 km, Pluto is by far the smallest major planet. I strongly believe ( I have no proof )that there may be planets beyond Pluto. The existence of such bodies may be responsible for the still-unexplained deviations in the orbits of Uranus and Neptune. ( Something to think about)

Feel free to email your thoughts on this matter.I can be reached at basic_astronomy@yahoo.com

Mercury: This is the closest planet to the Sun.Its year is 88 days.At times during the year you can't see it, being so close to the Sun.Mercury is 3 times smaller than Earth.Its day is about 59 Earth days.

Venus: This is the 2nd planet from the Sun.At its closest its about 26 million miles away from Earth.The year on Venus is about 225 Earth days.Its day is 243 Earth days( turns very slowly).Its called both "the evening star and "the morning star.The reason being that its the first to appear in the evening and the last to disappear in the morning.

Earth: This is the third planet from the Sun,our home.So far its the only planet with liquid water.Earth is over 4 billion years old.Its young compared to the rest of the universe.Earth is about 93 million miles away from the Sun.Our year is about 365 days.Our day is 24 hours.Earth has no rings but it does have 1 moon,that was first visited by humans in July of 1969.

Mars: Mars is the fourth planet from our Sun.Its about half the size of Earth.Its year is a little less than 2 Earth years.(687 days) Its day is about the same as ours( Earth that is) Mars has two moons,Deimos and Phobos.One of the many pictures taken from the Carl Sagan Memorial Station (re Mars Pathfinder).

Jupiter: Jupiter is fifth planet from the Sun.After Venus its the next brightest object in the night sky.Its year is almost 12 Earth years.Its days are close to 10 hours,(it spins fast) the shortest of all the planets. Jupiter is about 11 times bigger than Earth.The planet is made of gas,which has no solid surface.Theres a red spot on Jupiter,thought to be a storm that is larger than all of Earth.

ASTRONOMERS DISCOVER 11 MORE SMALL MOONS OF JUPITER

The discovery of 11 small moons orbiting Jupiter leapfrogs the number of that
planet's moons to 39, nine more than the record of the previous champ, Saturn.

A team led by astronomers from the University of Hawaii, Honolulu, made the
discovery based on images taken in December 2001 and later follow-up observations.
Orbits were determined by collaborators at NASA's Jet Propulsion Laboratory, in
Pasadena, Calif., and the Harvard-Smithsonian Center for Astrophysics, Cambridge,
Mass.

Researchers estimate the new-found natural satellites are each about two to four
kilometers (one to two miles) in diameter, and were probably passing rocks captured by
Jupiter's gravity long ago.

The discovery-team leaders, Scott Sheppard and Dr. David Jewitt of the
University of Hawaii, also discovered 11 other small satellites of Jupiter in 2000.

The new moons were discovered by Sheppard, Jewitt and Jan Kleyna of
Cambridge University, England. They used the Canada-France-Hawaii 3.6-meter (142-
inch) telescope with one of the largest digital imaging cameras in the world to obtain
sensitive images of a wide area around Jupiter.

The digital images were processed and searched using computers. Candidate
satellites were monitored in the succeeding months at the University of Hawaii's 2.2-
meter (88-inch) telescope to confirm their orbits and to reject asteroids masquerading as
satellites.

JPL's Dr. Robert Jacobson and Harvard-Smithsonian's Dr. Brian Marsden
determined the satellites' irregular -- highly elongated and tilted -- orbits. All 11 objects
orbit in the direction opposite to the rotation of the planet.

The orbits of the irregular satellites strongly suggest an origin by capture. Since
no efficient contemporary capture mechanisms are known, it is likely that the irregular
satellites were acquired when Jupiter was young, possibly still in the process of
condensing down to its equilibrium size. As yet, nothing is known about their surface
properties, compositions or densities, but they are presumed to be rocky objects like the
asteroids.

The new discoveries bring the known total of Jovian satellites to 39, of which 31
are irregulars. The eight regular satellites include four large moons discovered by the
astronomer Galileo Galilei and four smaller moons on circular orbits closer to Jupiter.
Jupiter's nearest rival for having the largest number of known satellites is Saturn, with 30,
of which 13 are irregular.

The satellites were formally announced by the International Astronomical Union
on Circular No. 7900 (May 16, 2002).

Saturn: Saturn is the sixth planet from the Sun.Its year is about 30 Earth years.Its day is about 10 hours,a little longer than Jupiter's day.Its close to an all gas planet,the least dense in our universe.Saturn is famous for its rings,rocky material in orbit around its planet.Saturn is about 9 times bigger than Earth.One of its moons,Titan has its own atmosphere.

Uranus: Uranus is the seventh planet from the Sun.Its year is about 84 Earth years.Its day is about 18 hours.It is composed of gases,rock,and ices.Uranus also has rings like Saturn.The rings were first viewed in 1977.Uranus can only be viewed by telescope. Its also a gas planet.

Neptune: Neptune is the eighth planet from the Sun at times!Right now its the ninth ,because of Pluto's ellipitical and not circular orbit. Actually none of the planets have circular orbits!Its year is about 165 Earth years.Its day is about 19 hours.It has a rock core and is surrounded by gases.Neptune has 8 moons and 4 rings.

Pluto: Pluto is no longer our ninth planet from the sun.Its year is about 250 Earth years.Its day is slightly more than 6 Earth days.Pluto is mostly composed of rock,and being so far from the Sun,its also the coldest.It has a moon,Charon that is almost as big as Pluto. Pluto is a dwarf planet.

PLUTO DECLARED A DWARF PLANET: Today August 24 2006 at the International Astronomical Union (IAU) General Assembly in Prague, astronomers decided that the Solar System has eight planets, and Pluto is not one of them. Instead, Pluto is a "dwarf planet."

To be a planet, the assembly ruled, a world must meet three criteria:

(1) It must have enough mass and gravity to gather itself into a ball.

(2) It must orbit the sun.

(3) It must reign supreme in its own orbit, having "cleared the neighborhood" of other competing bodies.

So, e.g., mighty Jupiter, which circles the sun supreme in its own orbit, is a planet--no adjective required. Pluto, on the other hand, shares the outer solar system with thousands of Pluto-like objects. Because it has not "cleared its own neighborhood," it is a dwarf planet.

This decision clarifies the vocabulary of planetary astronomy while simultaneously upturning 76 years of "Pluto is a planet" pop-culture. Will non-specialists heed Pluto's demotion? That remains to be seen. Meanwhile, according to the IAU, the Solar System has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune; and three dwarf planets: Ceres, Pluto and 2003 UB313

The Sun is a star at the center of our solar system.The Sun is 93 million miles away from Earth.It takes under 8 and a half minutes for its light to reach us.Scientists can only estimate that the temperature at the center is about 25 million degrees Fahrenheit.Just how big is it,well you can fit more than a million planets the size of Earth in it.

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