Introduction
S
olar System, the Sun and the celestial bodies orbiting the Sun, including the nine
planets and their satellites; the asteroids, comets, and meteoroids; and interplanetary
dust and gas. The term may also refer to a group of celestial bodies orbiting another
star. In this article, solar system refers to the system that includes Earth and the Sun.
The dimensions of this system are specified in terms of the mean distance from Earth
to the Sun, called the astronomical unit (AU).
One AU is 150 million km (about 93 million mi). The most distant known planet, Pluto,
has an orbit at 39.44 AU from the Sun. The boundary between the solar system and
interstellar space-called the heliopause-is estimated to occur near 100 AU.
The comets, however, achieve the greatest distance from the Sun; they have highly
eccentric orbits (see Orbit) ranging out to 50,000 AU or more.
This solar system was the only planetary system known to exist until 1995, when astronomers discovered a planet about 0.6 times the mass of Jupiter orbiting
the star 51 Pegasi. Soon after, astronomers found a planet about 8.1 times the mass of Jupiter orbiting the star 70 Virginis, and a planet about 3.5 times the mass of Jupiter orbiting the star 47 Ursa Majoris. Since then, astronomers have found planets and
disks of dust in the process of forming planets around many other stars.
Many astronomers think it likely that solar systems of some sort are numerous
throughout the universe.
Basic components
Our Solar System consists of five basic components 1-The star (The Sun):-
It dwarfs the other bodies, representing approximately 99.86%
percent of all the mass in the solar system; all of the planets
, moons, astroids, comets, dust and gas add up to only about
0.14% percent 2-The planets(from Mercury to pluto):-
The planets may be viewed as two categories
1-inner planets that are the most closest to the sun including
Mercury,
Venus, Earth, and Mars
2-Jovian Planets that are the planets beyond Mars that include
Jupiter,
Uranus, Saturn, Neptune, and Pluto 3-The Moons:-
They are the planets'followers, there are 61 natural satellites
around the
various planets in our solar system, ranging from bodies
larger than our
own Moon to small pieces of debris 4-The Astroids:-
They are rocky and metallic objects that are in orbit
around the the sun
but they are too small to be considered full-fledged planets,they may be
called minor planets.They are materials left over from
the formation of the
solar system 5-The Comets:-
They are icy debris left out from the beginig of the formation of the solar
system and can survive only far from the sun. Most comet nuclei reside
in the Oort
Cloud,a loose swarm of objects in a halo beyond the planets
and reaching perhaps halfway
to the nearest star
The Sun
Sun,closest star to Earth.The Sun is huge mass of hot,glowing gas. The strong gravitational
pull of the Sun holds Earth and the other planets in the solar system in orbit. The Sun's light
and heat influence all of the objects in the solar system and allow life to exist on Earth.
The sun is an average star-its size, age, and temperature fall in about the middle of the
ranges of these properties for all stars. Astronomers believe that the Sun is about 4.6
billion years old and will keep shining for about another 7 billion years.
For humans,the Sun is beautiful and useful, but also powerful and dangerous. As Earth turns,
the Sun rises over the eastern horizon in the morning, passes across the sky during the day,
and sets in the west in the evening.This movement of the Sun across the sky marks the passage
of time during the day (see Sundial). The Sun's movement can produce spectacular sunrises and
sunsets under the right atmospheric conditions. At night, reflected sunlight makes the Moon
and planets bright in the night sky.
The Sun provides Earth with vast amounts of energy every day. The oceans and seas store this
energy and help keep the temperature of Earth at a level that allows a wide variety of life
to exist.Plants use the Sun's energy to make food,and plants provide food for other organisms.
The Sun's energy also creates wind in Earth's atmosphere. This wind can be harnessed and used
to produce power.
in the solar system, the planet closest to the sun. Its
mean distance from the sun is approximately
58 million km (about 36 million mi); its diameter is 4875 km (3030 mi);
its volume and mass are
about x that of Earth;and its mean density is approximately equal to that of
Earth. Mercury revolves
about the sun in a period of 88 days. Radar observations of the planet show
that its period of
rotation is 58.7 days, or two-thirds of its period of revolution. The planet,
therefore, rotates one
and a half times during each revolution. Because its surface consists
of rough, porous, dark-colored
rock, Mercury is a poor reflector of sunlight.
one of the planets in the solar system, the second in distance from the sun. Except for the
sun and the moon,Venus is the brightest object in the sky.The planet is called the morning
star when it appears in the east at sunrise, and the evening star when it is in the west
at sunset. In ancient times the evening star was called Hesperus and the morning star
Phosphorus or Lucifer. Because of the distances of the orbits of Venus and earth from
the sun, Venus is never visible more than three hours before sunrise or three hours
after sunset.When viewed through a telescope, the planet exhibits phases like the moon.
Full Venus appears the smallest because it is on the far side of the sun from earth.
Maximum brilliance (a stellar magnitude of -4.4, or 15 times the brightest star) is seen
in the crescent phase. The phases and positions of Venus in the sky repeat with the synodic
period of 1.6 years (see Time; Year). Transits across the face of the sun are rare, occurring in pairs at intervals of a little more than a century. The next two will be in 2004 and 2012.
Earth, one of the planets in the solar system,
the third in distance from the sun and the
fifth largest
of the planets in diameter. The mean distance of the earth
from the sun is
149,503,000 km (92,897,000 mi). It is the only
planet known to support life, although
some of the other planets
have atmospheres and contain water.
The earth is not a perfect
sphere but is slightly oblate, or
flattened at the poles. The diameter of the earth measured
around the North Pole and the South Pole is about 42 km (26 mi)
less than the diameter
of the earth measured at the equator.
Mars (planet), one of the planets in the solar system, it is the
fourth planet from the Sun
and orbits the Sun at a distance of about 228 million km (about 141 million mi). Mars is
named for the Roman god of war because it appears fiery red in Earth's night sky.
Mars is a relatively small planet, with about half the diameter of Earth and about
one-tenth Earth's mass. The force of gravity on the surface of Mars is about
one-third of that on Earth. Mars has twice the diameter and twice the surface gravity
of Earth Moon. The surface area of Mars is almost exactly the same as the surface area
of the dry land on Earth.
The Martian day, or the time it takes Mars to rotate once on its axis, is about a half
an hour longer than an Earth day. Its year, or the time it takes to revolve once around
the Sun, is about two Earth years long. Mars has two moons, Phobos and Deimos, which
are named after the dogs of the Roman god Mars. These tiny bodies are heavily cratered
dark chunks of rock and may be asteroids captured by the gravitational pull of Mars. Phobos orbits Mars once in less than one Martian day, so it appears to rise in the west and set in the east, usually twice each day. Deimos has the more ordinary habit of rising in the east and setting in the west.
Jupiter (planet), fifth planet from the Sun and the largest planet in Earth's solar system.
With the exception of the Sun, the Moon, and Venus, Jupiter is the brightest object in
Earth's sky-more than three times brighter than Sirius, the brightest star. Due to its
prominence in the sky, the ancient Romans named Jupiter for Jove, the chief god of
Roman mythology.
Jupiter orbits the Sun at an average distance of 780 million km (484 million mi), which is
about five times the distance from Earth to the Sun. Jupiter's year, or the time it takes
to complete an orbit about the Sun, is 11.9 Earth years, and its day, or the time it takes
to rotate on its axis, is about 9.9 hours, less than half an Earth day.
Unlike the rocky inner planets of the solar system (Mercury, Venus, Earth, and Mars), Jupiter is a dense ball of gas. It has a relatively small core of molten rock and iron, but Jupiter has no solid surfaces. Jupiter's mass is about 318 times the mass of Earth and its diameter is about 11.2 times the diameter of Earth. The force of gravity at the level of the highest clouds in Jupiter's atmosphere is about 2.5 times the force of gravity on Earth.
Because Jupiter has such a large diameter and high rate of rotation, material at the surface must travel quickly to circle the planet. This speed gives the material a great deal of momentum, or a strong tendency to fly away from the planet and continue traveling in a straight line through space. Material at the equator has the highest speed because, in a Jovian day, it must travel the greatest distance to circle the planet. Hence, material at the equator has the greatest momentum, and the strongest tendency to fly away from the planet. Because of Jupiter's weak, gaseous structure, the planet can not hold this material in as well as a more solid planet could, which results in Jupiter having the distorted shape of a flattened ball. The diameter of its equator is 143,000 km (89,000 mi), yet the diameter through its axis of rotation is only 133,700 km (83,000 mi).
Saturn (planet), sixth planet in order of distance from the sun, and the second largest in the
solar system. Saturn's most distinctive feature is its ring system, which was first seen in
1610 by Italian scientist Galileo, using one of the first telescopes. He did not understand
that the rings were separate from the body of the planet, so he described them as handles
(ansae).The Dutch astronomer Christiaan Huygens was the first to describe the rings
correctly.In 1655, desiring further time to verify his explanation without losing his claim
to priority, Huygens wrote a series of letters in code, which when properly arranged
formed a Latin sentence that read in translation, "It is girdled by a thin flat
ring, nowhere touching, inclined to the ecliptic." The rings are named in order of their
discovery, and from the planet outward they are known as the D, C, B, A, F, G, and E rings.
These rings are now known to comprise more than 100,000 individual ringlets, each of which
circles the planet.
Uranus (planet), major planet in the solar system, seventh planet from the Sun. Uranus
revolves outside the orbit of Saturn and inside the orbit of Neptune. The average
distance from Uranus to the Sun is 2.87 billion km (1.78 billion mi). Uranus has an inner
rocky core that is surrounded by a vast ocean of water mixed with rocky material.
From the core, this ocean extends upward until it meets an atmosphere of hydrogen,
helium, and methane.Uranus has 10 known rings and 18 moons. The mass of Uranus is
14.5 times greater than the mass of Earth, and its volume is 67 times greater than that
of Earth. The force of gravity at the surface of Uranus is 1.17 times the force of
gravity on Earth. Because of its size and mass,
scientists classify Uranus as one of the giant or Jovian (like Jupiter) planets-along with Jupiter, Saturn, and Neptune.
Uranus was the first planet that people discovered by using a telescope. Sir William Herschel, a German-born British musician and astronomer, discovered the planet in 1781. Herschel accidentally discovered it while measuring shifts in the positions of stars in the constellation Gemini. He observed that Uranus is a moving object, so he first reported his discovery to the British Royal Society as a comet. However, people had observed and plotted Uranus on star charts dating back to 1690 (believing it was a star). Astronomers used these earlier observations to identify the object as a planet and to establish its orbit. Herschel originally named the planet Georgium Sidus (Star of George) in honor of King George III of Great Britain. Later, astronomers named the planet after Uranus, a figure who embodied the heavens and was the father of Saturn and the grandfather of Jupiter in Greek and Roman mythology.
Neptune (planet), major planet in the solar system, eighth planet from the Sun,and fourth
largest in diameter. Neptune maintains an almost constant distance, about 4.5 billion km
(about 2.8 billion mi), from the Sun. Neptune revolves outside the orbit of Uranus and
for most of its orbit, moves inside the elliptical path of the outermost planet Pluto.
Every 248 years, Pluto's elliptical orbit brings the planet inside Neptune's nearly
circular orbit for about 20 years, temporarily making Neptune the farthest planet from the
Sun. The last time Pluto's orbit brought it inside Neptune's orbit was in 1979. In 1999,
Pluto's orbit brought it back outside Neptune's orbit.
Astronomers believe Neptune has an inner rocky core that is surrounded by a vast ocean of water mixed with rocky material. From the inner core, this ocean extends upward until it meets a gaseous atmosphere of hydrogen, helium, and trace amounts of methane. Neptune has four rings and eight known moons. Even though Neptune's volume is 72 times that of Earth's volume, its mass is only 17 times Earth's mass. Because of its size, scientists classify Neptune-along with Jupiter, Saturn, and Uranus-as one of the giant or Jovian planets (so-called because they resemble Jupiter).
Mathematical theories of astronomy led to the discovery of Neptune. To account for wobbles in the orbit of the planet Uranus, British astronomer John Couch Adams and French astronomer Urbain Jean Joseph Leverrier independently calculated the existence and position of a new planet in 1845 and 1846, respectively. They theorized that the gravitational attraction of this planet for Uranus was causing the wobbles in Uranus's orbit. Using information from Leverrier, German astronomer Johann Gottfried Galle first observed the planet in 1846.
After its discovery, Leverrier proposed that the new planet be named after the sea god Neptune from Greek and Roman mythology. The appropriateness of this name was confirmed in the 20th century when astronomers learned about Neptune's watery interior.
Pluto (planet), ninth planet from the Sun and outermost known member of the solar system.
Pluto was discovered as the result of a telescopic search inaugurated in 1905 by the
American astronomer Percival Lowell, who postulated the existence of a distant planet
beyond Neptune as the cause of slight perturbations (see Orbit) in the motions of Uranus.
Continued by members of the Lowell Observatory staff, the search ended successfully in
1930, when the American astronomer Clyde William Tombaugh found Pluto near the
position Lowell had predicted.Pluto revolves about the Sun once in 247.7 Earth
years at an average distance of 5.9 billion km (3.67 billion mi) from the Sun. The orbit is so eccentric that at certain points along its path Pluto is closer to the Sun than is Neptune. No possibility of collision exists, however, because Pluto's orbit is inclined more than 17.2° to the plane of the ecliptic and never actually crosses Neptune's path.
Visible only through large telescopes, Pluto appears to have a yellowish color. For many years very little was known about the planet, but in 1978 astronomers discovered a relatively large moon orbiting Pluto at a distance of only about 19,000 km (about 12,000 mi) and named it Charon. The orbits of Pluto and Charon caused them to pass repeatedly in front of one another from 1985 through 1990, enabling astronomers to determine their sizes fairly accurately. The Hubble Space Telescope allowed astronomers to determine the sizes of Pluto and Charon even more accurately in 1994. Pluto is about 2,320 km (1,440 mi) in diameter, about two-thirds the size of Earth's moon. Charon is about 1,270 km (790 mi) in diameter, making Pluto and Charon the planet-satellite pair closest in size in the solar system. Pluto was also found to have a thin atmosphere, probably of methane, exerting a pressure on the planet's surface that is about 100,000 times weaker than Earth's atmospheric pressure at sea level.
Introduction
Our Solar System consists of five basic components
