Rumus Persamaan Gas Ideal

persamaan gas ideal :

PV = nRT

MY PRAY

YA ALLOH JADIKANLAH KAMI TERMASUK ORANG YANG SELALU BERADA DALAM KORIDORMU YA ALLOH.... AMIINNN

The Victory of the Romans

The Victory of the Romans and the Lowest Point on Earth A featured article Description: The Quran lays light on the lowest place of earth. By Sherif Alkassimi (© 2008 IslamReligion.com) Published on 23 Jun 2008 - Last modified on 09 Nov 2008 Viewed: 7721 (daily average: 18) - Rating: 4.8 out of 5 - Rated by: 29 Printed: 384 - Emailed: 36 - Commented on: 0 Category: Articles > Evidence Islam is Truth > The Scientific Miracles of the Holy Quran Category: Articles > The Holy Quran > The Scientific Miracles of the Holy Quran In the early 7th century, the two most powerful empires at the time were the Byzantine[1] and Persian Empires. In the years 613 - 614 C.E the two Empires went to war, with the Byzantines suffering a severe defeat at the hands of the Persians. Damascus and Jerusalem both fell to the Persian Empire. In the chapter, The Romans, in the Holy Quran, it is stated that the Byzantines had met with a great defeat but would soon gain victory: “The Romans have been defeated in the lowest land, but after their defeat they will soon be victorious. Within three to nine years. The decision of the matter, before and after, is with God.” (Quran 30:2-4) These verses, above, were revealed around 620 C.E, almost 7 years after the severe defeat of the Christian Byzantines at the hands of the idolater Persians in 613 – 614 C.E. Yet it was related in the verses that the Byzantines would shortly be victorious. In-fact, Byzantine had been so heavily defeated that it seemed impossible for the Empire to even maintain its very existence, let alone be victorious again. Not only the Persians, but also the Avars, Slavs and Lombards (located to the North and West of the Byzantine Empire) posed serious threats to the Byzantine Empire’s sovereignty. The Avars had come as far as the walls of Constantinople and had nearly captured the Emperor, himself. Many governors had revolted against Emperor Heraclius, and the Empire was on the point of collapse. Mesopotamia, Syria, Palestine, Egypt and Armenia, which had earlier belonged to the Byzantine Empire, were invaded by the Persians. In short, everyone was expecting the Byzantine Empire to be destroyed, but right at that moment the first verses of the chapter, The Romans, were revealed announcing that the Byzantines would regain triumph in a few years time. Shortly after this revelation, the Byzantine Emperor proceeded to order the gold and silver in churches to be melted and turned into money in order both to meet the demanding expenses of the army, and finance his drive to regain the lost territories. Around 7 years after the revelation of the first verses of The Romans, in December, 627 C.E, a decisive battle between The Byzantine Empire and the Persian Empire was fought in the area around the Dead Sea,[2] and this time it was the Byzantine army which surprisingly defeated the Persians. A few months later, the Persians had to make an agreement with the Byzantines which obliged them to return the territories they had taken from them. So, in the end, the victory of the Romans proclaimed by God in the Quran miraculously came through. Another miracle revealed in the mentioned verses is the announcement of a geographical fact that no-one would have been able to discover in that period. In the third verse of The Romans, it was mentioned that the Romans were defeated “in the lowest land” (Quran 30:3). Significantly, the places where the main battles took place (in Damascus and Jerusalem) lie in a vast area of low-lying land called the Great Rift Valley. The Great Rift Valley is a huge 5,000 km fault line in the earth’s crust that runs from northern Syria in the Middle-East of Asia to central Mozambique in East Africa. The northernmost extension runs through Syria, Lebanon, Palestine and Jordon. The rift then extends south to the Gulf of Aden, makes its way through East Africa, then finally ends at the lower Zambezi River valley in Mozambique. An interesting fact that has been discovered recently, with the help of satellite images, is that the area around the Dead Sea (located in the Great Rift Valley) has the lowest altitude on Earth. In fact, the lowest point on Earth is the shoreline of the Dead Sea, with an altitude of around 400 meters[3] below sea level. The fact that it lies at the lowest point means that water does not drain from the sea. No land point on earth has a lower altitude than the shoreline of the Dead Sea.[4] Dead Sea Rift Valley Dead Sea Rift Valley, Israel and Jordan October 1984. Seen from an altitude of 190 nautical miles (350 kilometers) in this near-vertical photograph, the Dead Sea Rift Valley slices south-north through the Middle East. The surface of the Dead Sea, 1292 feet (394 meters) below sea level, is the lowest point on Earth. (Courtesy: The Image Science & Analysis Laboratory, NASA Johnson Space Center, Photo #: STS41G-120-56, http://eol.jsc.nasa.gov) Therefore it becomes clear that the country or prefecture which occupies the rift valley in the vicinity of the Dead Sea is what is meant in the Quran by “the lowest land.” This is a true miracle of the Quran because no-one could have known or foreseen such a fact in the 7th century due to the fact that satellites and modern day technology were not available at the time. Once again, the only possible explanation is that Prophet Muhammad had truly received divine revelation from God, The Creator and Originator of the universe. Footnotes: [1] The Arabs also refer to the Byzantines as the Romans. [2] The History of Persia Part I: Ancient Persia by Scott Peoples [3] (http://hypertextbook.com/facts/2000/SanjeevMenon.shtml) [4] (http://www.elnaggarzr.com/index.php?l=ar&id=51&cat=6)

The Miraculous Quran (part 4 )

The Miraculous Quran (part 4 ) The Miraculous Quran (part 4): Various Aspects of the Law: Description: The comprehensiveness, completeness, balance and practicality of the law itself. By Jamaal al-Din Zarabozo (© 2007 IslamReligion.com) Published on 02 Apr 2007 - Last modified on 19 Feb 2008 Viewed: 7975 (daily average: 9) - Rating: 4 out of 5 - Rated by: 4 Printed: 553 - Emailed: 2 - Commented on: 0 Category: Articles > Evidence Islam is Truth > The Authenticity and Preservation of the Holy Quran Category: Articles > The Holy Quran > The Authenticity and Preservation of the Holy Quran I noticed almost immediately that the Quranic teachings are very comprehensive, complete, balanced and practical. For the sake of brevity, I will not go into this aspect in any detail but it was something that impressed me quite a bit. The range and flexibility of the laws of the Quran are impressive. It was clear to me that this book was not revealed just for a people at a specific time but was meant for people of very different times and places. The Quran is very comprehensive in that it touches upon and gives clear guidance concerning such diverse issues as ritual acts of worship, business transactions, marriage, divorce, the laws of warfare and so on. There is a definite balance that one feels when one reads the Quran. A human’s spiritual and mundane needs are met simultaneously in the same passage. Even the most detailed passages concerning law still contain admonition, remembrance of Allah and exhortation to behave in the best manner possible. The scope of the Quranic teachings is not just for the individual himself. It is not the case that Allah has given him some kind of spiritual guidance to, perhaps, only guide his morals and character. Instead, Allah has also revealed a law that is meant for society as a whole. Humans do not have to grope about trying to decide what is best for the community at large. It has been given by Allah to guide mankind to the best way of life. It covers the individual’s personal practice and piety as well as his relationship with his parents, spouse, children, neighbors, community and humanity as a whole. All of this with a proper balance and within the overall framework of making one’s life a true and complete form of worship of God alone. There is clearly one only goal for humans—the worship of God—and all of the deeds of this worldly life fall within the scope of that goal. There is no schizophrenia in a person’s life. He is not trying to please God and Caesar at the same time or even at different times. He does not even need to resort to chasing after vain desires and compromise his ethics to live a rewarding life in this world. He simply needs to live his life in this world in a wholesome manner under the shade of the comprehensive guidance of the Quran. One Particular Aspect of Islamic Law: Its Practicality The practicality of Islamic Law is one particular aspect that truly impressed me at that time, coming, again, from my Christian background. It is a great blessing that in Islam one finds detailed teachings that result in their desired goals while, at the same time, being extremely practical and consistent with human nature. The lack of such teachings is one of the greatest dilemmas faced by Christianity. For example, with respect to societal cohesion and interaction, the greatest teachings found in the New Testament are what are known as “the hard sayings” of Jesus. They are as follows: “Ye have heard that it hath been said, An eye for an eye, and a tooth for a tooth: But I say unto you, That ye resist not evil: but whosoever shall smite thee on thy right cheek, turn to him the other also. And if any man will sue thee at the law, and take away thy coat, let him have thy cloak also. And whosoever shall compel thee to go a mile, go with him twain. Give to him that asketh thee, and from him that would borrow of thee turn not thou away. Ye have heard that it hath been said, Thou shalt love thy neighbour, and hate thine enemy. But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you; That ye may be the children of your Father which is in heaven: for he maketh his sun to rise on the evil and on the good, and sendeth rain on the just and on the unjust. For if ye love them which love you, what reward have ye? do not even the publicans the same? And if ye salute your brethren only, what do ye more than others? do not even the publicans so? Be ye therefore perfect, even as your Father which is in heaven is perfect” (Matthew 5:38-48). Christian scholars themselves are perplexed. How are such obviously impossible or impractical teachings to be applied? Just one example of a discussion of these words will suffice to show how perplexing they are to those who staunchly believe in them: [For interpreting these words, t]he model proposed by Joachim Jeremias is simple, representative, and of continuing influence. According to this model, the Sermon usually is seen in one of three ways: (1) as a perfectionist code, fully in line with the legalism of rabbinic Judaism; (2) as an impossible ideal, meant to drive the believer first to desperation, and then to trust in God's mercy; or (3) as an ‘interim ethic’ meant for what was expected to be a brief period of waiting in the end time, and which is now obsolete. Jeremias adds his own fourth thesis: The Sermon is an indicative depiction of incipient life in the kingdom of God, which presupposes as its condition of possibility the experience of conversion. More complex or comprehensive schematizations have been offered, but most major interpreters can be understood in relation to the options posed by Jeremias.[1] In Islam, there are no such dilemmas. The teachings are easy, flexible, practical and completely suited to everyday life, even for a new Muslim living in a completely non-Islamic environment, such as I was. The famed author James A. Michener also noted and appreciated this aspect of Islam. In one of the earliest writings that I had read about Islam, entitled “Islam—the Misunderstood Religion,” Michener wrote, The Koran is remarkably down-to-earth in its discussion of the good life. In one memorable passage it directs: ‘When ye deal with each other in transactions involving future obligations reduce them to writing… and get two witnesses…’ It is this combination of dedication to one God, plus practical instruction, that makes the Koran unique.[2] Footnotes: [1] Lisa Sowle Cahill, Love Your Enemies: Discipleship, Pacifism, and Just War Theory (Minneapolis, MN: Fortress Press, 1994), p. 27. [2] Quoted in Islam—The First and Final Religion (Karachi, Pakistan: Begum Aisha Bawany Waqf, 1978), pp. 86-87.

The Miraculous Quran (part 3)

The Miraculous Quran (part 3): From Savages to Saints

Description: The Quran’s Effect on the Generation of the Prophet and Afterwards.

By Jamaal al-Din Zarabozo (© 2007 IslamReligion.com)

Published on 09 Apr 2007 - Last modified on 01 Apr 2008 Viewed: 7873 (daily average: 9) - Rating: 3.7 out of 5 - Rated by: 3 Printed: 528 - Emailed: 3 - Commented on: 0 Category: Articles > Evidence Islam is Truth > The Authenticity and Preservation of the Holy Quran Category: Articles > The Holy Quran > The Authenticity and Preservation of the Holy Quran

The next aspect that caught me eye—and this again was something that non-Muslims were mentioning in their works—was the effect that the Quran had on the generation of the Prophet. May the mercy and blessings of God be upon him, and afterwards.

It is clear that the Arabs at the time of the Prophet were wont to drink, make merry and engage in tribal battles. They were known to sometimes kill their female babies. However, one finds that in a short span of close to twenty years a movement that started with just one man was able, due to the grace of God and the miraculous effect of the Quran, to change almost all of the Arabs and non-Arabs in the Arabian peninsula and bind them together into a brotherhood of faith and mercy which was so strong that if any one part of this brotherhood was in anguish, the whole brotherhood would be affected negatively. At that time, one could find two people who were from previously antagonistic tribes sharing their wealth and willing to give up their lives for each other. Indeed, one was willing to split half of his wealth and divorce one of his wives for the sake of his new brother who was from a “foreign” tribe. Perhaps one of the best descriptions of the change that took place among the Muslims can be seen in the famous statement of the Companion Jafar ibn Abu Talib who was asked by the Negus of Abyssinia about the mission of the Messenger. He told him, O king, we were an ignorant people, worshipping idols, eating carrion and indulging in sexual pleasures. We ridiculed our neighbors, a brother oppressed his brother, and the strong devoured the weak. At this time a man rose among us, who had already been known to be truthful, noble and honest. This man called us to Islam. And he taught us to give up worshipping stones, to speak the truth, to refrain from bloodshed, and not to defraud the orphans of their property. He taught us to provide comfort to our neighbors and not to bring a slander against chaste women. He enjoined upon us to offer prayers, observe fasts and give alms. We followed him, gave up polytheism and idolatry and refrained from all evil deeds. It is for this new way that our people have become hostile to us and compel us to return to our old misguided life.[1] That generation, in turn, took the message to the rest of the world. They were clearly a people who were taken from darkness into light and to the straight path of God. When asked by the Emperor of Persia what brought the Muslims to their lands, two different Companions answered in similar terms: “God has sent us to take whoever wishes from the servitude of mankind to the servitude of God and from the tightness of this world to its expanse and from the injustice of the ways of life [in this world] to the justice of Islam.”[2] During the lifetime of the Prophet, may the mercy and blessings of God be upon him, one can see how these people were turned into a pious generation, fearing God and hoping for God’s reward. Even when they, as humans, slipped and committed sins, they eagerly repented and turned to God for His forgiveness. They would much rather face a severe penalty in this life, such as death, than face God with their sins on their hands. This can be seen in the cases of Maaiz ibn Maalik al-Aslami and the woman called al-Ghaamidiyah. Both of them came to the Prophet to admit that they had committed adultery and each asked the Prophet for the worldly retribution to erase their sins. In the case of al-Ghaamidiyah, the Prophet asked her to go back after her confession and to return to the Prophet after she had given birth. She came back with her child in her arms and asked the Prophet to purify her from her sins. The Prophet then asked her to return after she had weaned the child. Then she returned after some time and told the Prophet that the child was no longer in need of her breastfeeding. She once again asked for her expiation from her sin. Then, finally, the Prophet implemented the legal retribution as an expiation for her sin of adultery. The Prophet then praised her act of repentance.[3] The effect of this change in the Companions continued long after the death of the Prophet. Note the following accounts of the Companions as they sought to spread the message of Islam to the rest of the world: The sterling character and qualities of the Muslim soldiers were once praised by a Roman officer in these words: “At night you will find them prayerful; during the day you will find them fasting. They keep their promises, order good deeds, suppress evil and maintain complete equality among themselves.” Another testified thus: “They are horsemen by day and ascetics by night. They pay for what they eat in territories under their occupation. They are first to salute when they arrive at a place and are valiant fighters who just wipe out the enemy.” A third said: “During the night it seems that they do not belong to this world and have no other business than to pray, and during the day, when one sees them mounted on their horses, one feels that they have been doing nothing else all their lives. They are great archers and great lancers, yet they are so devoutly religious and remember God so much and so often that one can hardly hear talk about anything else in their company.”[4] The benefits of the civilization developed upon the teachings of the Quran went well beyond the Muslim lands. Many are familiar with the Muslims’ influence on Europe and how Islamic influences eventually led to the Renaissance. The author of A History of the Intellectual Development of Europe, John Draper wrote, “Four years after the death of Justinian, A.D. 569, was born at Mecca, in Arabia, the man who, of all men, has exercised the greatest influence upon the human race.”[5] This work was quite an eye opener for me at the time of my conversion to Islam. Draper, writing in the 19th century, was very disappointed and seemingly angered that Muslims continually failed to receive their proper accolades for all that they contributed to European society and civilization. For instance, he writes "To these Saracens we are indebted for many of our personal comforts. Religiously cleanly, it was not possible for them to clothe, according to the fashion of the natives of Europe, in a garment unchanged till it dropped to pieces of itself, a loathsome mass of vermin, stench and rags... They taught us the use of the oft-changed and oft-washed under-garment of linen and cotton, which still passes among ladies under its old Arabic name...”[6] Many scholars have recognized the importance of Islam and the Quran’s teachings for the betterment of humanity. The famous intellect George Bernard Shaw once stated, “I have always held the religion of Muhammad in high estimation because of its wonderful vitality… I have prophecied about the faith of Muhammad that it would be acceptable tomorrow as it is beginning to be acceptable to the Europe of today. Mediaeval ecclesiastics, either through ignorance or bigotry, painted Muhammadanism in the darkest colours. They were, in fact, trained to hate both the man Muhammad and his religion. To them Muhammad was anti-Christ. I have studied him, the wonderful man, and in my opinion far from being an anti-Christ he must be called the saviour of Humanity.[7] Footnotes: [1]The translation of this statement was taken from Allama Shibli Numani, Sirat-un-Nabi (Lahore, Pakistan: Kazi Publications, 1979), p. 211. The incident was recorded by ibn Ishaq in al-Maghazi and Ahmad. And its chain is sahih according to al-Albaani. See al-Albaani's footnotes to Muhammad al-Ghazaali, Fiqh al-Seera (Qatar: Idaarah Ihyaa al-Turaath al-Islaami, n.d.), p. 126. [2]Ismaaeel ibn Katheer, Al-Bidaayah wa al-Nihaayah (Beirut: Dar al-Kutub al-Ilmiyya, n.d.), vol. 7, pp. 39-40. [3]The story of both Maaiz and al-Ghaamidiyyah are recorded by Muslim. [4]Quoted from Abul Hasan Ali Nadwi, Islam and the World (International Islamic Federation of Student Organizations, 1983), p. 81. Also see ibn Katheer, al-Bidaayah, vol. 7, p. 53. [5] Quoted in Islam—The First and Final Religion, p. 39. Of course, more recently, Michael H. Hart’s The 100: A Ranking of the Most Influential Persons in History put the Prophet Muhammad r number one among all the world’s influential leaders. [6] Draper’s work is not available to me at the current time. Therefore, this quote was taken from Aslam Munjee, The Crusades: Then and Now (Arlington, VA: First Amendment Publishers, 2004), p. 3. [7] “A Collection of Writings of Some of the Eminent Scholars,” published by the Woking Muslim Mission, 1935 edition, p. 77. Quoted in Islam: The First & Final Religion (Karachi, Pakistan: Begum Aisha Bawany Waqf, 1978), p. 57. In reality, many non-Muslim, Western thinkers have had words of great praise for the religion of Islam, the Prophet Muhammad (peace and blessings of God be upon him) or the Quran. The work just cited compiles numerous such quotes and is interesting reading.

MIRACLE OF QURAN PART. 1

<div dir="ltr" style="text-align: left;" trbidi="on">
<br />
<blockquote></blockquote>The Story of the Quran (part 1 of 2)<blockquote></blockquote>
<blockquote></blockquote>God’s Final Revelation In the top 20 of viewed articles A new article (Published within the last 30 days)<blockquote></blockquote>
<blockquote></blockquote>Description: What is the Quran?<blockquote></blockquote>
By Aisha Stacey (© 2009 IslamReligion.com)
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<blockquote></blockquote>Category: Articles &gt; The Holy Quran &gt; The Authenticity and Preservation of the Holy Quran<blockquote></blockquote>

Muslims believe the Quran to be God’s final revelation. They believe it is the literal word of God, revealed over many years, to His final prophet, Muhammad. The Quran is full of wisdom. It is full of the wonder and glory of God, and a testament to His mercy and justice. It is not a history book, a storybook, or a scientific textbook, although it contains all of those genres. The Quran is God's greatest gift to humanity – it is a book like no other. In the second verse of the second chapter of the Quran, God describes the Quran by calling it a book whereof there is no doubt, a guidance to those who are pious, righteous, and fear God. (Quran 2:2)

The Quran is core to Islam. Believing in it is a requirement. One who does not believe in the Quran, in its entirety, cannot claim to be a Muslim.

"The Messenger (Muhammad) believes in what has been sent down to him from his Lord, and (so do) the believers. Each one believes in God, His Angels, His Books, and His Messengers. (They say,) ‘We make no distinction between one another of His Messengers’ — and they say, ‘We hear, and we obey. (We seek) Your forgiveness, our Lord, and to You is the return (of all)’." (Quran 2:285)

Islam has two primary sources, the Quran, and the authentic traditions of Prophet Muhammad, that explain and sometimes expand on that of the Quran.

“And We have not sent down the Book (the Quran) to you (O Muhammad, except that you may explain clearly unto them those things in which they differ, and (as) a guidance and a mercy for a folk who believe.” (Quran 16:64)

The Quran was delivered to Prophet Muhammad by the Angel Gabriel and revealed in stages over a period of 23 years.

“And (it is) a Quran which We have divided into parts, in order that you might recite it to men at intervals. And We have revealed it by stages.” (Quran 17:106)

Prophet Muhammad was commanded by God to convey the Quran to all of humankind and the responsibility weighed heavily upon him. Even in his farewell address he called on the people present to bear witness that he had delivered the message.

The Quran explains the concept of God, it explains in detail what is permissible and what is forbidden, it explains the basics of good manners and morals, and gives rulings about worship. It tells stories about the Prophets and our righteous predecessors, and describes paradise and hell. The Quran is a guidance, a mercy and a book of glad tidings for those who have submitted themselves to God. (Quran 16:89) The Quran was revealed for all of humankind.

The book in which the Quran (the words of God) are contained in is called a mus haf. The Quran is considered so unique in content and style that it cannot be precisely translated; therefore, any translation is considered an interpretation of the meanings of Quran.

When God sent Prophets to the various nations He often allowed them to perform miracles that were relevant to their particular time and place. In the time of Moses magic and sorcery were prevalent therefore Moses’ miracles appealed to the people he was sent to guide. In the time of Muhammad, the Arabs, although predominantly illiterate, were masters of the spoken word. Their poetry and prose was considered outstanding and a model of literary excellence.

When Prophet Muhammad recited the Quran – the words of God – the Arabs were moved tremendously by its sublime tone and extraordinary beauty. The Quran was Prophet Muhammad’s miracle from God. Muhammad was unable to read or write therefore the Arabs knew that he was unlikely to have produced such eloquent words, but even so some refused to believe that the Quran was the word of God. God therefore challenged them, in the Quran, to produce a rival text.

“And if you (Arab pagans, Jews, and Christians) are in doubt concerning that which We have sent down (i.e. the Quran) to Our slave (Muhammad), then produce a chapter of the like thereof and call your witnesses (supporters and helpers) besides God, if you are truthful.” (Quran 2:23)

Of course they were unable to do so. In contrast to those who questioned the origin of the Quran, many Arabs converted to Islam after hearing the recitation. They knew immediately that such sublime beauty could originate only from God. Even today it is possible to see Muslims moved to tears while listening to or reciting the Quran. In fact some people, unable to understand even one word of the Arabic language are moved by the intrinsic beauty of the Quran.

After establishing that Quran is the word of God and that it is a recitation, it is also important to understand that Quran has remained unchanged for more than 1400 years. Today when a Muslim in Egypt holds his mus haf in his hands and begins to recite you can be sure that in far away Fiji another Muslim is looking at and reciting the exact same words. There are no differences. The child in France holding his first mus haf is tentatively reciting the same words that flowed from the lips of Prophet Muhammad.

God assures us in Quran that He will surely protect His words. He says, “Verily, it is We Who have sent down the Quran and surely, We will guard it (from corruption).” (Quran 15:9) This means that God will guard against anything false being added or any part of it being taken away.[1] It is protected from tampering and if anyone attempts to distort the meanings of Quran, God will guide someone to expose the deception.[2] Muslims believe that the previous revelations from God, including the Torah and the Gospels of Jesus were either lost in antiquity, or changed and distorted, so it is a source of comfort to them knowing that God’s words – the Quran – are now well guarded.

God sent down Quran, from above the heavens, to the angel Gabriel in the glorious month of Ramadan. The story of how this recitation was revealed and how Quran came to be available worldwide, with an interpretation of the meanings translated into over 100 languages[3] will be covered in part 2. </div>

ASTRONOMY AND SPACE

 

astronimy and space
From : A.Armada Pahla Mashad, M.Pd.
Solar System
“And God of Allah which have created noon and night, moon and sun. Everyone of both that circulate in its orbit..” (LQ:21.33)
‘’And God of Allah have subdued ( pula) for you continuous moon and sun circulate ( in its orbit); and have subdued for you noon and night.’’ (LQ:14.33)
INTRODUCTION
Solar System
the Sun and everything that orbits 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 (see Extrasolar Planets). In this article, 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 mi). The most distant known planet, Pluto, orbits about 39 AU from the Sun. Estimates for the boundary where the Sun’s magnetic field ends and interstellar space begins—called the heliopause—range from 86 to 100 AU. The most distant known planetoid orbiting the Sun is Sedna, whose discovery was reported in March 2004. A planetoid is an object that is too small to be a planet. At the farthest point in its orbit, Sedna is about 900 AU from the Sun. Comets known as long-period 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, when astronomers discovered a planet about 0.6 times the mass of Jupiter orbiting the star 51 Pegasi. Jupiter is the most massive planet in our solar system. 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. Most astronomers think it likely that solar systems of some sort are numerous throughout the universe. See Astronomy; Galaxy; Star. 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, dense interior (see Nuclear Energy). Although this nuclear fusion is transforming 600 million metric tons of hydrogen each second, the Sun is so massive (2 × 1030 kg, or 4.4 × 1030 lb) that it can continue to shine at its present brightness for 6 billion years. This stability has allowed life to develop and survive on Earth. 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, samples of which were brought back from the Moon’s surface by piloted United States Apollo spacecraft (see Space Exploration; Apollo program). The Sun’s activity also influences the heliopause, a region of space that astronomers believe marks the boundary between the solar system and interstellar space. The heliopause is a dynamic region that expands and contracts due to the constantly changing speed and pressure of the solar wind. In November 2003 a team of astronomers reported that the Voyager 1 spacecraft appeared to have encountered the outskirts of the heliopause at about 86 AU from the Sun. They based their report on data that indicated the solar wind had slowed from 1.1 million km/h (700,000 mph) to 160,000 km/h (100,000 mph). This finding is consistent with the theory that when the solar wind meets interstellar space at a turbulent zone known as the termination shock boundary, it will slow abruptly. However, another team of astronomers disputed the finding, saying that the spacecraft had neared but had not yet reached the heliopause. 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 known to have abundant liquid water and life. However, in 2004 astronomers with the National Aeronautics and Space Administration’s Mars Exploration Rover mission confirmed that Mars once had liquid water on its surface. Scientists had previously concluded that liquid water once existed on Mars due to the numerous surface features on the planet that resemble water erosion found on Earth. Mars’s carbon dioxide atmosphere is now so thin that the planet is dry and cold, with polar caps of frozen water and solid carbon dioxide, or dry ice. However, small jets of subcrustal water may still erupt on the surface in some places. 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. One of Jupiter’s largest moons, Io, has volcanoes that produce the hottest surface temperatures in the solar system. At least four of Jupiter’s moons have atmospheres, and at least three show evidence that they contain liquid or partially frozen water. Jupiter’s moon Europa may have a global ocean of liquid water beneath its icy crust. Saturn rivals Jupiter, with a much more intricate ring structure and a similar number of satellites. One of Saturn’s moons, Titan, has an atmosphere thicker than that of any other satellite in the solar system. 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. See also Planetary Science. OTHER ORBITING BODIES The asteroids are small rocky bodies that move in orbits primarily between the orbits of Mars and Jupiter. Numbering in the thousands, asteroids range in size from Ceres, which has a diameter of 1,003 km (623 mi), to microscopic grains. Some asteroids are perturbed, or pulled by forces other than their attraction to the Sun, into eccentric orbits that can bring them closer to the Sun. If the orbits of such bodies intersect that of Earth, they are called meteoroids. When they appear in the night sky as streaks of light, they are known as meteors, and recovered fragments are termed meteorites. Laboratory studies of meteorites have revealed much information about primitive conditions in our solar system. The surfaces of Mercury, Mars, and several satellites of the planets (including Earth’s Moon) show the effects of an intense bombardment by asteroidal objects early in the history of the solar system. On Earth that record has eroded away, except for a few recently found impact craters. Some meteors and interplanetary dust may also come from comets, which are basically aggregates of dust and frozen gases typically 5 to 10 km (about 3 to 6 mi) in diameter. Comets orbit the Sun at distances so great that they can be perturbed by stars into orbits that bring them into the inner solar system. As comets approach the Sun, they release their dust and gases to form a spectacular coma and tail. Under the influence of Jupiter’s strong gravitational field, comets can sometimes adopt much smaller orbits. The most famous of these is Halley’s Comet, which returns to the inner solar system at 75-year periods. Its most recent return was in 1986. In July 1994 fragments of Comet Shoemaker-Levy 9 bombarded Jupiter’s dense atmosphere at speeds of about 210,000 km/h (130,000 mph). Upon impact, the tremendous kinetic energy of the fragments was released through massive explosions, some resulting in fireballs larger than Earth. Comets circle the Sun in two main groups, within the Kuiper Belt or within the Oort cloud. The Kuiper Belt is a ring of debris that orbits the Sun beyond the planet Neptune. Many of the comets with periods of less than 500 years come from the Kuiper Belt. In 2002 astronomers discovered a planetoid in the Kuiper Belt, and they named it Quaoar. The Oort cloud is a hypothetical region about halfway between the Sun and the heliopause. Astronomers believe that the existence of the Oort cloud, named for Dutch astronomer Jan Oort, explains why some comets have very long periods. A chunk of dust and ice may stay in the Oort cloud for thousands of years. Nearby stars sometimes pass close enough to the solar system to push an object in the Oort cloud into an orbit that takes it close to the Sun. The first detection of the long-hypothesized Oort cloud came in March 2004 when astronomers reported the discovery of a planetoid about 1,700 km (about 1,000 mi) in diameter. They named it Sedna, after a sea goddess in Inuit mythology. Sedna was found about 13 billion km (about 8 billion mi) from the Sun. At its farthest point from the Sun, Sedna is the most distant object in the solar system and is about 130 billion km (about 84 billion mi) from the Sun. Many of the objects that do not fall into the asteroid belts, the Kuiper Belt, or the Oort cloud may be comets that will never make it back to the Sun. The surfaces of the icy satellites of the outer planets are scarred by impacts from such bodies. The asteroid-like object Chiron, with an orbit between Saturn and Uranus, may itself be an extremely large inactive comet. Similarly, some of the asteroids that cross the path of Earth’s orbit may be the rocky remains of burned-out comets. Chiron and similar objects called the Centaurs probably escaped from the Kuiper Belt and were drawn into their irregular orbits by the gravitational pull of the giant outer planets, Jupiter, Saturn, Neptune, and Uranus. The Sun was also found to be encircled by rings of interplanetary dust. One of them, between Jupiter and Mars, has long been known as the cause of zodiacal light, a faint glow that appears in the east before dawn and in the west after dusk. Another ring, lying only two solar widths away from the Sun, was discovered in 1983. 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. Within this maze of motions, some remarkable patterns exist: Mercury rotates on its axis three times for every two revolutions about the Sun; no asteroids exist with periods (intervals of time needed to complete one revolution) 1/2, 1/3, …, 1/n (where n is an integer) the period of Jupiter; the three inner Galilean satellites of Jupiter have periods in the ratio 4:2:1. These and other examples demonstrate the subtle balance of forces that is established in a gravitational system composed of many bodies. THEORIES OF ORIGIN Despite their differences, the members of the solar system probably form a common family. They seem to have originated at the same time; few indications exist of bodies joining the solar system, captured later from other stars or interstellar space. Early attempts to explain the origin of this system include the nebular hypothesis of the German philosopher Immanuel Kant and the French astronomer and mathematician Pierre Simon de Laplace, according to which a cloud of gas broke into rings that condensed to form planets. Doubts about the stability of such rings led some scientists to consider various catastrophic hypotheses, such as a close encounter of the Sun with another star. Such encounters are extremely rare, and the hot, tidally disrupted gases would dissipate rather than condense to form planets. Current theories connect the formation of the solar system with the formation of the Sun itself, about 4.7 billion years ago. The fragmentation and gravitational collapse of an interstellar cloud of gas and dust, triggered perhaps by nearby supernova explosions, may have led to the formation of a primordial solar nebula. The Sun would then form in the densest, central region. It is so hot close to the Sun that even silicates, which are relatively dense, have difficulty forming there. This phenomenon may account for the presence near the Sun of a planet such as Mercury, having a relatively small silicate crust and a larger than usual, dense iron core. (It is easier for iron dust and vapor to coalesce near the central region of a solar nebula than it is for lighter silicates to do so.) At larger distances from the center of the solar nebula, gases condense into solids such as are found today from Jupiter outward. Evidence of a possible preformation supernova explosion appears as traces of anomalous isotopes in tiny inclusions in some meteorites. This association of planet formation with star formation suggests that billions of other stars in our galaxy may also have planets. The high frequency of binary and multiple stars, as well as the large satellite systems around Jupiter and Saturn, attest to the tendency of collapsing gas clouds to fragment into multibody systems. See separate articles for most of the celestial bodies mentioned in this article. See also Exobiology. Contributed By:Tobias C. Owen Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved.