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النظام الشمسي (Solar System)
Solar System, the Sun and the celestial bodies orbiting the Sun, including the nine planets and their satellites; the asteroids and comets; and interplanetary dust and gas. The term may also refer to a group of celestial bodies orbiting another star. Solar system refers to the system that includes Earth and the Sun. The dimensions of the solar 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 miles). The most distant known planet, Pluto, orbits about 39 AU from the Sun. The boundary between the solar system and interstellar space—called the heliopause—is estimated to occur near 100 AU. Comets, however, achieve the greatest distance from the Sun; they have highly eccentric orbits ranging out to 50,000 AU or more.
The solar system was the only planetary system known to exist around a star similar to the Sun until 1995. Since then, astronomers have found planets and disks of dust in the process of forming planets around many other stars. Most astronomers think it likely that solar systems of some sort are numerous throughout the universe.
The Sun and the Solar Wind
The Sun is a typical star of intermediate size and luminosity. Sunlight and other radiation are produced by the conversion of hydrogen into helium in the Sun’s hot.
For all the Sun’s steadiness, it is an extremely active star. On its surface, dark sunspots bounded by intense magnetic fields come and go in 11-year cycles and sudden bursts of charged particles from solar flares can cause auroras and disturb radio signals on Earth. A continuous stream of protons, electrons, and ions also leaves the Sun and moves out through the solar system. This solar wind shapes the ion tails of comets and leaves its traces in the lunar soil.
The Major Planets
Nine major planets are currently known. They are commonly divided into two groups: the inner planets (Mercury, Venus, Earth, and Mars) and the outer planets (Jupiter, Saturn, Uranus, and Neptune). The inner planets are small and are composed primarily of rock and iron. The outer planets are much larger and consist mainly of hydrogen, helium, and ice. Pluto does not belong to either group, and there is an ongoing debate as to whether Pluto should be categorized as a major planet.
Mercury is surprisingly dense, apparently because it has an unusually large iron core. With only a transient atmosphere, Mercury has a surface that still bears the record of bombardment by asteroidal bodies early in its history. Venus has a carbon dioxide atmosphere 90 times thicker than that of Earth, causing an efficient greenhouse effect by which the Venusian atmosphere is heated. The resulting surface temperature is the hottest of any planet—about 477°C (about 890°F). Earth is the only planet with abundant liquid water and known life. Strong evidence exists that Mars once had liquid water on its surface, but now its carbon dioxide atmosphere is so thin that the planet is dry and cold, with polar caps of frozen water and solid carbon dioxide, or dry ice.
Jupiter is the largest of the planets. Its hydrogen and helium atmosphere contains pastel-colored clouds, and its immense magnetosphere rings, and satellites make it a planetary system unto itself.
At least four of Jupiter’s moons have atmospheres, and at least three show evidence that they contain liquid or partially-frozen water. Saturn rivals Jupiter, with a much more intricate ring structure and a similar number of satellites.
Uranus and Neptune are deficient in hydrogen compared with Jupiter and Saturn; Uranus, also ringed, has the distinction of rotating at 98° to the plane of its orbit. Pluto seems similar to the larger, icy satellites of Jupiter or Saturn. Pluto is so distant from the Sun and so cold that methane freezes on its surface.
Movements of the Planets and Their Satellites
If one could look down on the solar system from far above the North Pole of Earth, the planets would appear to move around the Sun in a counterclockwise direction. All of the planets except Venus and Uranus rotate on their axes in this same direction. The entire system is remarkably flat—only Mercury and Pluto have obviously inclined orbits. Pluto’s orbit is so elliptical that it is sometimes closer than Neptune to the Sun.
The satellite systems mimic the behavior of their parent planets and move in a counterclockwise direction, but many exceptions are found. Jupiter, Saturn, and Neptune each have at least one satellite that moves around the planet in a retrograde orbit (clockwise instead of counterclockwise), and several satellite orbits are highly elliptical. Jupiter, moreover, has trapped two clusters of asteroids (the so-called Trojan asteroids) leading and following the planet by 60° in its orbit around the Sun. (Some satellites of Saturn have done the same with smaller bodies.) The comets exhibit a roughly spherical distribution of orbits around 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.
The chromosphere is above the photosphere. Solar energy passes through this region on its way out from the center of the Sun. Faculae and flares arise in the chromosphere. Faculae are bright luminous hydrogen clouds which form above regions where sunspots are about to form. Flares are bright filaments of hot gas emerging from sunspot regions. Sunspots are dark depressions on the photosphere with a typical temperature of 4,000°C (7,000°F).
The corona is the outer part of the Sun's atmosphere. It is in this region that prominences appears. Prominences are immense clouds of glowing gas that erupt from the upper chromosp here. The outer region of the corona stretches far into space and consists of particles traveling slowly away from the Sun. The corona can only be seen during total solar eclipses.
The Sun appears to have been active for 4.6 billion years and has enough fuel to go on for another five billion years or so. At the end of its life, the Sun will start to fuse helium into heavier elements and begin to swell up, ultimately growing so large that it will swallow the Earth. After a billion years as a red giant, it will suddenly collapse into a white dwarf -- the final end product of a star like ours. It may take a trillion years to cool off completely.
Coronal loops, immense coils of hot gas on the surface of the Sun, vibrate wildly after the blast wave from a solar flare hits them. However, their dance is quickly squelched by resistance from the Sun's outer atmosphere (corona). The corona restricts motion due to internal friction hundreds of millions of times greater than expected, according to recent observations from NASA's Transition Region and Coronal Explorer (TRACE) spacecraft.
This friction, called viscosity, may help explain why the corona is more than 100 times hotter than the Sun's surface, a mystery that has occupied solar researchers for decades.
"Just as a guitar string vibrates when plucked, coronal loops move back and forth after being disturbed by a flare. The new TRACE observations show that, rather than vibrating like they are in thin air, the loops act as if they are trying to vibrate in something much thicker, like pudding," said Dr. Leon Ofman, chief scientist at Raytheon ITSS working at NASA's Goddard Space Flight Center, Greenbelt, Md. "This rapidly halts their swaying motion -- it stops after twelve minutes or so. If the original theories on coronal viscosity were correct, the loops would continue vibrating for more than a week."
"People have been studying the Sun for centuries. We expected progress, but few major surprises. To have a discovery like this is tremendously exciting," said Dr. Richard Fisher, mission scientist for TRACE.
Viscosity is a measure of the friction, or resistance to flow, in a fluid. Pudding is harder to stir than water because pudding has greater viscosity. High viscosity is responsible for the annoyingly slow flow of ketchup and molasses. The research will be published in the August 6 issue of Science. Dr. Valery Nakariakov, postdoctoral fellow at St. Andrews University, Scotland, is first author on the paper.
The greater than expected viscosity in the corona may help resolve a solar conundrum. The discovery that the Sun's atmosphere is much hotter than its surface seems contrary to the physical law that heat does not flow from a cooler object to a warmer one -- it is like discovering people heating their homes with ice cubes. Solar physicists suspect that magnetic energy produced by the roiling, electrically charged gases on the solar surface is somehow transferred to the corona, heating it.
"We thought magnetic energy could be used to heat the corona, but our old theory of a low viscosity corona made the process so inefficient that we could not see how it was done. Our new discovery reveals a high viscosity corona, which means it has a lot of friction. Brakes heat up when used to stop a wheel from turning because their high friction efficiently converts the wheel's motion to heat. If you put oil on the brake, you reduce its friction -- the wheel turns much longer, and the brake never gets very hot. Similarly, a high viscosity corona with a lot of friction can be used to transfer energy and generate heat much more efficiently," said Ofman.
"The discovery would not have been possible without the high resolution of the TRACE spacecraft," said Fisher. "We can see fine structure in the coronal loops, and the high rate at which TRACE takes images lets us see rapid changes."
"One of the goals of the TRACE mission was to make all of the data immediately available to the entire scientific community. This fundamental discovery was made by an independent scientist taking advantage of the open data policy," said Dr. Alan Title, principal investigator on TRACE.
TRACE is equipped with a special telescope that can see extreme ultraviolet radiation emitted by the hot gasses in the solar corona. This radiation is absorbed by the Earth's atmosphere and is not visible from the ground.
TRACE is a Small Explorer mission and the science instrument was developed by teams at the Stanford Lockheed Institute for Space Research, Smithsonian Astrophysical Observatory, Montana State University, and Goddard.
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.
From our journeys into space, we have learned much about our home planet. The first American satellite, Explorer 1, discovered an intense radiation zone, now called the Van Allen radiation belts. This layer is formed from rapidly moving charged particles that are trapped by the Earth's magnetic field in a doughnut-shaped region surrounding the equator. Other findings from satellites show that our planet's magnetic field is distorted into a tear-drop shape by the solar wind. We also now know that our wispy upper atmosphere, once believed calm and uneventful, seethes with activity -- swelling by day and contracting by night. Affected by changes in solar activity, the upper atmosphere contributes to weather and climate on Earth.
Besides affecting Earth's weather, solar activity gives rise to a dramatic visual phenomenon in our atmosphere. When charged particles from the solar wind become trapped in Earth's magnetic field, they collide with air molecules above our planet's magnetic poles. These air molecules then begin to glow and are known as the auroras or the northern and southern lights
Mass (kg) 5.976e+24
Mass (Earth = 1) 1.0000e+00
Equatorial radius (km) 6,378.14
Equatorial radius (Earth = 1) 1.0000e+00
Mean density (gm/cm^3) 5.515
Mean distance from the Sun (km) 149,600,000
Mean distance from the Sun (Earth = 1) 1.0000
Rotational period (days) 0.99727
Rotational period (hours) 23.9345
Orbital period (days) 365.256
Mean orbital velocity (km/sec) 29.79
Orbital eccentricity 0.0167
Tilt of axis (degrees) 23.45
Orbital inclination (degrees) 0.000
Equatorial escape velocity (km/sec) 11.18
Equatorial surface gravity (m/sec^2) 9.78
Visual geometric albedo 0.37
Mean surface temperature 15°C
Atmospheric pressure (bars) 1.013
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.
The planets, most of the satellites of the planets and the asteroids revolve around the Sun in the same direction, in nearly circular orbits. When looking down from above the Sun's north pole, the planets orbit in a counter-clockwise direction. The planets orbit the Sun in or near the same plane, called the ecliptic. Pluto is a special case in that its orbit is the most highly inclined (18 degrees) and the most highly elliptical of all the planets. Because of this, for part of its orbit, Pluto is closer to the Sun than is Neptune. The axis of rotation for most of the planets is nearly perpendicular to the ecliptic. The exceptions are Uranus and Pluto, which are tipped on their sides.
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% ?
Nearly all the solar system by volume appears to be an empty void. Far from being nothingness, this vacuum of "space" comprises the interplanetary medium. It includes various forms of energy and at least two material components: interplanetary dust and interplanetary gas. Interplanetary dust consists of microscopic solid particles. Interplanetary gas is a tenuous flow of gas and charged particles, mostly protons and electrons -- plasma -- which stream from the Sun, called the solar wind.
The solar wind can be measured by spacecraft, and it has a large effect on comet tails. It also has a measurable effect on the motion of spacecraft. The speed of the solar wind is about 400 kilometers (250 miles) per second in the vicinity of Earth's orbit. The point at which the solar wind meets the interstellar medium, which is the "solar" wind from other stars, is called the heliopause. It is a boundary theorized to be roughly circular or teardrop-shaped, marking the edge of the Sun's influence perhaps 100 AU from the Sun. The space within the boundary of the heliopause, containing the Sun and solar system, is referred to as the heliosphere.
The solar magnetic field extends outward into interplanetary space; it can be measured on Earth and by spacecraft. The solar magnetic field is the dominating magnetic field throughout the interplanetary regions of the solar system, except in the immediate environment of planets which have their own magnetic fields.
The Terrestrial Planets
The terrestrial planets are the four innermost planets in the solar system, Mercury, Venus, Earth and Mars. They are called terrestrial because they have a compact, rocky surface like the Earth's. The planets, Venus, Earth, and Mars have significant atmospheres while Mercury has almost none. The following diagram shows the approximate distance of the terrestrial planets to the Sun.
The Jovian Planets
Jupiter, Saturn, Uranus, and Neptune are known as the Jovian (Jupiter-like) planets, because they are all gigantic compared with Earth, and they have a gaseous nature like Jupiter's. The Jovian planets are also referred to as the gas giants, although some or all of them might have small solid cores. The following diagram shows the approximate distance of the Jovian planets to the Sun.
Why is Mars red?
Why is Mars red?
Mars is red because that is where men are from. Men like red, so Mars must be red. Men get red when they are angry or embarrassed or trying to hold back a fart in mixed company. Mars is red because it has such a thin atmosphere, which cannot hold the blue like the earth's atmosphere can. Mars is also red because of all of the rusted iron dust surrounding the planet and all the rusted iron on the planet
Mars used to be a big iron rock and over time it has rusted. Rust never sleeps and it is better to burn out than it is to rust. Into the Mars and into the dust.
No, really, why is Mars red?
Mars is red because it is made up of thousands or even hundreds of Mars bars. The light traveling through the galaxy gets reflected and refracted and by the time it gets to earth it is red. Mars, when you are close to it, actually looks like spumoni.
Seriously, why is Mars red?
The ancient Roman god, Mars was a great hunter (and resident of Georgia) who was smeared with red blood. Mars had a gun rack on the back of his truck, drank lots of beer and liked to shoot off his guns on New Year's Eve. Mars was originally called the Redneck god, but over time, people just started saying, "Mars is red."
Why Can Sun Be Harmful For Your Health?
Sun rays can heal and destroy; they can be the kiss of life or death, depending on the way we use them or how much time we spend being exposed to them.
Sunlight is known to kill microbes, strengthen the immune and cardiovascular system, improve mood, insomnia and liver functioning, to help the synthesis of vitamin D, the
elimination of toxins, to fight cancer of colon, breast, leukemia and lymphomas. Sun rays can help one lose weight by stimulating the thyroid, and ease symptoms of premenstrual syndrome; they also heal swollen joints during peaks of inflammation in cases of arthritis.
Nevertheless, excessive exposure to the sun represents one of the major risk factors in the appearance of skin cancer, especially in the case of light-skinned persons and those with a fat rich diet. All the negative effects of the sunlight on the skin are induced by the ultraviolet (UV) light.
It is also worth knowing that sun burns at skin level are nothing but a harmful process for everyone. Each burning destroys a part of a healthy and live tissue. Repeated burnings can induce irreversible changes that can, in turn, represent the foundation for skin cancer. Various researches showed a clear link between prolonged exposure to sun and skin cancer.
Melanoma, an extremely aggressive skin cancer that is deadly in 20 % of the cases, has been strongly connected to repeated burnings of the skin. Sun radiations seem to have an accumulative effect, manifested through malign tumors which appear after the age of 50.
Moreover, repeated burnings and even intensive tanning gradually destroy the elastic proteins of the skin and its fatty glands, leading to the appearance of wrinkles and premature skin aging.
Solar protection creams must be applied 30 minutes before sun exposure and this operation must be repeated at each 3-4 hours after going into the water or if there is abundant sweating. Light-skinned persons need a solar protection factor with a filter of a power of 30-40, while darker-skinned persons need a protection factor 15-30.
Light-skinned, light-haired persons should starts sun exposure with 5 minutes per day; darker-skinned persons with 15 minutes daily. The maximum should be 30 minutes of daily exposure for the largest body surface. Avoid exposure to sun during the summer months between 10:00-15:00, when the sun is extremely powerful.
Even so, the creams do not ensure a complete protection, and tanning lotions can aggravate the problem, producing more profound burnings. The false protection feeling conferred by the creams can make people stay for longer periods in the sun, thus increasing the risks.
Small children must never be exposed to direct sun, as their skin defense system against radiations is still not well developed