Aarushhh/wikipedia-simple-splitted huggingface dataset:
Indexing 
After the bots crawl content, it can be indexed in the database and arranged in terms of its relevance. If internet content has not been crawled or indexed, it is unlikely to appear in the search results when someone makes a query no matter how relevant that content may be. After the content has been crawled, each of its words is indexed. The search engines also pinpoint where words are located on the crawled pages. During the indexing process, the search engine compares the content to other content with similar ‘words’ and decides how to organize it within its index.
Ranking 
Ranking is a complex process that is dependent on search engine algorithms. When a searcher makes a query on Google looking for anything from 19th-century British landscape painters to New York City plumbers, the search engine will generate a list of good matches to that query. How these matches appear in the list relates to their rank. The search engine lists what it ‘thinks’ are the best answers to the query early in its search results.

Google and other search engines rely on algorithms to interpret the searcher’s query, identify the websites and pages in its index that are related to the request, and it then ranks them in terms of relevance in its presented search results list. What’s important to search engines is to provide searchers with the most relevant matches to their queries possible. Website operators, in turn, use search engine optimization to give their pages a higher rank.

References 

Search engines
Sabbath in Christianity is the day of rest and service to God.  The idea of the Sabbath in Christianity comes directly from the idea
of the Sabbath (or Shabbat) in Judaism.  In fact, the word Sabbath itself comes from the Hebrew word Shabbat.  Like the Jewish Sabbath (Shabbat), the Sabbath in Christianity comes from the Genesis story of Creation.  But unlike Jews, most Christians have Sabbath on Sunday, not Saturday. They also rest, but not the same way as Jews. The exact way depends on the church denomination.

Differing views
Differing views

Most Christians honor the Sabbath on Sunday to remember the Resurrection of Jesus on the first day of the week on the Jewish calendar. They say that there is an analogy between the obligation of the Christian day of worship and the Sabbath-day ordinance. These two rules are not literally identical though. They say that this ordinance is no longer valid, because God has replaced his old creation by a new one. For this reason, the obligation to keep the Sabbath is not the same for Christians as for Jews. They say there are examples in the New Testament, and in other writings surviving from the first few centuries.

Some conservative Christians are "Sabbatarians". Most of these follow the Reformed traditions. Sabbatarians think the first day of the week or Lord's Day is the new Sabbath. This is because the 4th commandment has never been revoked and Sabbath-keeping is in any case a creation ordinance.
Still others believe that the Sabbath remains as a day of rest on the Saturday, reserving Sunday as a day of worship. In reference to Acts 20:7, the disciples came together on the first day of the week (Sunday) to break bread and to hear the preaching of the apostle Paul. This is not the first time Christians assembled together on a Sunday; Jesus appeared to the Christians on the "first day of the week" while they were in hiding. One can maintain this argument in that Jesus himself maintained the Sabbath, although not within the restrictions that were mandated by Jewish traditions;  the Pharisees often tried Jesus by asking him if certain tasks were acceptable according to the Law. This would seem to show that while the Sabbath was still of importance to the Jews, Sunday was a separate day for worship and teaching from Scriptures.
The Seventh-day Adventists and other churches disagree with some of these views. They argue that the custom of meeting for worship on Sunday originated in paganism, specifically Sol Invictus and Mithraism (in which sun god worship took place on Sunday). This is therefore an explicit rejection of the commandment to keep the seventh day holy. Instead, they keep Saturday as the Sabbath as a memorial to God's work of creation believing that none of the Ten Commandments can ever be destroyed. Seventh-day Sabbatarians claim that the seventh day Sabbath was kept by the majority of Christian groups until the 2nd and 3rd century, by most until the 4th and 5th century, and a few thereafter, but because of opposition to Judaism after the Jewish-Roman wars, the original custom was gradually replaced by Sunday as the day of worship
. The history of these changes is certainly not altogether lost regardless of any belief in a suppression of the facts by a conspiracy of the pagans of the Roman Empire and the clergy of the Catholic Church.
Jews had come to be hated in the Roman Empire after the Jewish-Roman wars. This led to the criminalization of the Jewish Sabbath. Hatred of Jews is apparent in the Council of Laodicea (4th Century AD) where Canon 37–38 states: "It is not lawful to receive portions sent from the feasts of Jews or heretics, nor to feast together with them." and "It is not lawful to receive unleavened bread from the Jews, nor to be partakers of their impiety."  In keeping with this rejection of the Jews, this Roman council also criminalized the Jewish Sabbath as can be seen in Canon 29 of the Council Laodicea: "Christians must not Judaize by resting on the Sabbath, but must work on that day, rather honoring the Lord's Day; and, if they can, resting then as Christians. But if any shall be found to be judaizers, let them be excommunicated from Christ."

In the Gospel of Mark 2:28 Jesus says 'the Son of Man is lord even of the sabbath'.

References

Liturgical calendar
Statistics is a branch of applied mathematics that deals with collecting, organising, analysing, reading and presenting data. Descriptive statistics make summaries of data. Inferential statistics makes predictions. Statistics helps in the study of many other fields, such as science, medicine, economics, psychology, politics and marketing. Someone who works in statistics is called a statistician. In addition to being the name of a field of study, the word "statistics"  can also mean numbers that are used to describe data or relationships.

History 
The first known statistics are census data. The Babylonians did a census around 3500 BC, the Egyptians around 2500 BC, and the Ancient Chinese around 1000 BC.
Collecting data 
Before we can describe the world with statistics, we must collect data. The data that we collect in statistics are called measurements. After we collect data, we use one or more numbers to describe each observation or measurement. For example, suppose that we want to find out how popular a certain TV show is. We can pick a group of people (called a sample) out of the total population of viewers. Then we ask each viewer in the sample how often they watch the show. The sample is data that one can see, and the population is data that one cannot see (assuming that not every viewer in the population are asked). For another example, if we want to know whether a certain drug can help lower blood pressure, we could give the drug to people for some time and measure their blood pressure before and after.
Descriptive and inferential statistics 
Numbers that describe the data one can see are called descriptive statistics. Numbers that make predictions about the data one cannot see are called inferential statistics.

Descriptive statistics involves using numbers to describe features of data. For example, the average height of women in the United States is a descriptive statistic: it describes a feature (average height) of a population (women in the United States).
Once the results have been summarized and described, they can be used for prediction. This is called inferential statistics. As an example, the size of an animal is dependent on many factors. Some of these factors are controlled by the environment, but others are by inheritance. A biologist might therefore make a model that says that there is a high probability that the offspring will be small in size—if the parents were small in size. This model probably allows to predict the size in better ways than by just guessing at random. Testing whether a certain drug can be used to cure a certain condition or disease is usually done by comparing the results of people who are given the drug against those who are given a placebo.

Methods 
Most often, we collect statistical data by doing surveys or experiments. For example, an opinion poll is one kind of survey. We pick a small number of people and ask them questions. Then, we use their answers as the data.
The choice of which individuals to take for a survey or data collection is important, as it directly influences the statistics. When the statistics are done, it can no longer be determined which individuals are taken. Suppose we want to measure the water quality of a big lake. If we take samples next to the waste drain, we will get different results than if the samples are taken in a far-away and hard-to-reach spot of the lake.

There are two kinds of problems which are commonly found when taking samples:
If there are many samples, the samples will likely be very close to what they are in the real population. If there are very few samples, however, they might be very different from what they are in the real population.  This error is called a chance error (see also Errors and residuals in statistics).
 The individuals for the samples need to be chosen carefully. Usually, they will be chosen randomly. If this is not the case, the samples might be very different from what they really are in the total population. This is true even if a great number of samples is taken. This kind of error is called bias.

Errors 
We can reduce chance errors by taking a larger sample, and we can avoid some bias by choosing randomly. However, sometimes large random samples are hard to take. And bias can happen if different people are not asked, or refuse to answer our questions, or if they know they are getting a fake treatment. These problems can be hard to fix. See standard error for more.

Descriptive statistics
Finding the middle of the data 
The middle of the data is called an average. The average tells us about a typical individual in the population. There are three kinds of average that are often used: the mean, the median and the mode.

The examples below use this sample data:

Mean 
The formula for the mean is

Where  are the data and  is the population size (see also Sigma Notation).

This means that one calculates the mean by adding up all the values, and then divide by the number of values. For the example above, the mean is:
The problem with the mean is that it does not tell anything about how the values are distributed. Values that are very large or very small change the mean a lot. In statistics, these extreme values might be errors of measurement, but sometimes the population really does contain these values. For example, if there are 10 people in a room who make $10 per day and 1 who makes $1,000,000 per day. The mean of the data is $90,918 per day. Even though it is the average amount, the mean in this case is not the amount any single person makes, and thus is not very useful for some purposes. 

The mean described above is the "arithmetic mean". Other kinds are useful for some purposes.
Median 
The median is the middle item of the data. For a given data , this is sometimes written as . To find the median, we sort the data from the smallest number to the largest number, and then choose the number in the middle. If there is an even number of data, there will not be a number right in the middle, so we choose the two middle ones and calculate their mean. In our example above, there are 10 items of data, the two middle ones are "57" and "64", so the median is (57+64)/2 = 60.5.
As another example, like the income example presented for the mean, consider a room with 10 people who have incomes of $10, $20, $20, $40, $50, $60, $90, $90, $100, and $1,000,000. Here, the median is $55, because $55 is the average of the two middle numbers, $50 and $60.  If the extreme value of $1,000,000 is ignored, the mean is $53.  In this case, the median is close to the value obtained when the extreme value is thrown out.  The median solves the problem of extreme values as described in the definition of mean above.

Mode 
The mode is the most frequent item of data. For example, the most common letter in English is the letter "e". We would say that "e" is the mode of the distribution of the letters.

As another example, if there are 10 people in a room with incomes of $10, $20, $20, $40, $50, $60, $90, $90, $90, $100, and $1,000,000, then the mode is $90, because $90 occurs three times and all other values occur fewer than three times.
There can be more than one mode. For example, if there are 10 people in a room with incomes of $10, $20, $20, $20, $50, $60, $90, $90, $90, $100, and $1,000,000, the modes are $20 and $90. This is bi-modal, or has two modes. Bi-modality is very common, and it often indicates that the data is the combination of two different groups.  For instance, the average height of all adults in the U.S. has a bi-modal distribution.  This is because males and females have separate average heights of 1.763 m (5 ft 9 + 1⁄2 in) for men and 1.622 m (5 ft 4 in) for women.  These peaks are apparent when both groups are combined.

The mode is the only form of average that can be used for data that can not be put in order.
Finding the spread of the data 
Another thing we can say about a set of data is how spread out it is. A common way to describe the spread of a set of data is the standard deviation. If the standard deviation of a set of data is small, then most of the data is very close to the average. If the standard deviation is large, though, then a lot of the data is very different from the average.

The standard deviation of a sample is generally different from the standard deviation of its originating population . Because of that, we write  for population standard deviation, and  for sample standard deviation.
If the data follows the common pattern called the normal distribution, then it is very useful to know the standard deviation. If the data follows this pattern (we would say the data is normally distributed), about 68 of every 100 pieces of data will be off the average by less than the standard deviation. Not only that, but about 95 of every 100 measurements will be off the average by less than two times the standard deviation, and about 997 in 1000 will be closer to the average by less than three standard deviations.

Other descriptive statistics 
We also can use statistics to find out that some percent, percentile, number, or fraction of people or things in a group do something or fit in a certain category.

For example, social scientists used statistics to find out that 49% of people in the world are males.

Related software
In order to support statisticians, many statistical software have been developed:

 MATLAB
 R
 SAS Institute
 SPSS (made by IBM)

References

Other websites 

Statistics
Speed is a measure.
It is velocity but without the direction.

Finding speed 
Speed is the distance an object moves in a given amount of time.
The distance is never negative.
If a train takes 1 hour to travel 100 kilometers, it has a speed of .
In fact this is the average speed.
During this one hour, the train may become slower and faster, it may even drive backwards.
The average speed of an object in a certain time is the distance the object traveled divided by the time.
The instantaneous speed is the average speed when the time is very small, almost zero.

Units 
There are many units of measurement.
Since the 20th century following units were widely used by humans:

 miles per hour (mph),
 kilometers per hour (km/h), and
 meters per second (m/s), which is the SI-unit for speed.

Different units are used for different applications.
People controlling planes and ships frequently use Knot (speed).
Sometimes a Mach number is used.
Range 
The smallest speed is .
A “negative speed” would be in fact a velocity.
The biggest speed is the speed of light.
You can write bigger speeds, but they are not possible in this universe.

Read also 

 Orbital speed
 Speedometer – a thing showing speed
 Speed limit – a law telling people a maximum speed
 Speed of sound
 Wind speed

Sources 

Measurement
Physical quantity
A server log records what is happening on a server at any time.  For example, an HTTP server runs a web site.

internet
Software
Servers

de:Logdatei
For servers and clients to talk to each other, they need to be connected to a network.  They need to use the same communication protocol, a set way for machines to talk to other machines.  It is like a language.  For example, the Wikipedia server runs the HTTP to send web sites to your computer, and your computer uses the HTTP Protocol to ask Wikipedia for pages.

Overview 
Usually, servers are specially made to be more powerful and reliable.  They are usually more expensive than normal computers.  Sometimes, servers can be clustered, which means many servers are working together to do one service.

The server might slow down if there are too many people accessing the server at the same time, resulting in a high load.  An overloaded server might also shut itself down automatically.

In a peer-to-peer system, every computer is both a client and a server to the others. This is commonly put into file sharing and VOIP.  However, this can help in attempts at piracy.
Typical server operating systems are Linux, FreeBSD, NetBSD, and OpenBSD.  Unlike other computers, a server often has no monitor, keyboard, or mouse.  When a server doesn't have to do very much, server software can run on a computer that is also doing other things.Initially, such servers were connected to clients known as terminals that did not do any actual computing. These terminals, referred to as dumb terminals, existed simply to accept input via a keyboard or card reader and to return the results of any computations to a display screen or printer. The actual computing was done on the server. Servers also have a special ip number that other devices use to find the servers.

Web server

A web server is a type of server that is used to host websites.  Examples of web server software include Apache or IIS.  A web server can host one, or many, websites.  The default port for a web server to listen to is port 80 (HTTP) or 443 (HTTPS).
Some web servers do other things than just serving a web page.  For example, they may have something called SSI that makes building a website easier.

Web servers use services like CGI to let software on the server make web pages. Some of the programming languages that can use CGI are scripting languages like Perl, Python, PHP, or ASP. Some are compiled languages like C++ or Java.

Reference

Related pages  
File server

Reference
Internet
Servers
Computer science
A simile is a figure of speech that compares two different things, usually by using the words 'like' or 'as'. It is used to make a direct and clear comparison between two things .Similes may be confused with metaphors, which do the same kind of thing. Similes use comparisons, with the words 'like' or 'as'. Metaphors use indirect comparisons, without the words 'like' or 'as'.

Similes:
Like a hungry wolf, he ate the food.
A dragonfly is like a plane: they both fly and cannot close their wings.
 He fought like a lion.
 The color yellow is like walking into a surprise birthday party. 

The other team's quarterback is as big as a redwood tree
Kingda Ka is as green as a pine tree

Other websites
"On substantiation through transitive relations" is an old manuscript written by the Arabic scholar Sayf al-Din al-Amidi. He talks about similes. 

Figures of speech
In politics, a state is a the government of a country which has control over a geographic area or territory. States have three main features:
Control over a geographic area, or territory
A people, the population of the state.
Institutions which have the power to make laws.

There are different forms of government a state may have, for example a republic or a monarchy. Sometimes states form their own countries. In its origin the United States had different kinds of states, but they agreed to join together. Most states also have armed forces, civil service, law and police. 

Government institutions in a country are commonly referred to as "the state".

Different definitions 
The definition above is very broad. It  is based on ideas by Georg Jellinek (1851-1911). Other people had other ideas:
Max Weber (1864-1920) had another definition: According to him, a state is a community of people which has "the monopoly to legitimately use physical force within a well-defined area". 
 Another definition  is from political science: A state is a system of public institutions which are there to regulate the  issues of a society.
 Some philiospohers, such as Aristotle, Rousseau and Hegel had a moralistic view: In their opinion, a state arises when individuals reach their goals and that of society. According to Hegel,  the state is the reason God came into the world; it is the power of reason. This reason manifests as His will. 

Because of the different definitions, there's no universally accepted definition of state. The one given at the start of the article is now part of international law.

History
History

Early states 
The earliest states could not be just human settlements. They had to be more than tribes. An example is New Guinea, which has many small tribes, but no larger organisations. Amazonia in the 18th century was also like this, with many small tribes. They are not states. To be a state, tribes have to be bounded together, for example, by a monarch. They may also be bonded by their language, and by living in the same region.

An example of monarchy is early Egypt under the Pharaohs.  Similar military-based states included the Babylonian Empire and the huge Roman Empire and early China.
Some early states were based on cities.  Some Ancient Greek city-states had democracy in a limited form.  Other states had inheritance of kingship or even challenges and fighting to decide leadership.  Early city states had a feature that modern society cannot match.  Every man got to see and know the leading citizens.  "Man" because most city-states limited the vote to male heads of families. One reason was that the adult men would do the fighting if the group were attacked.

From military to modern state 
When the military-based state, the Roman Empire, fell, lots of little states were made and each was also military-based and controlled by a king. These states did not often work together and war raged. However, once people within the state itself started fighting (what's called a Civil war), the kings had to make peace and start parliaments.

Modern states
Modern states 

Modern states soon started in the late 15th century. The main states in Europe were:
England under the Tudors
Spain under the Habsburg
France under the Bourbons
Russia under Catherine the Great and Alexander II of Russia

These states all tried to improve their politics and economy. They became more and more like the states today. They formed proper boundaries for their lands and worked with the powers in the state, such as the Church and the nobility. They made armies, tax systems and embassies to make them more powerful and stable.

Different types of state 
Types of state can be separated into two categories: democracy and dictatorship. However, just because a group of states are all democratic does not mean that they follow the same rules. Iran, Pakistan, France, Germany and the United States of America are all states. Each of them sees itself as a democracy. Each of them however has a different idea of what democracy really means.
Different states of the same 'category' can also function differently. For example, two democratic states may be quite different if one has a well-trained police or army while the other does not. Therefore, the word 'state' only tells us what type of government that state follows (democratic or dictatorship) and does not tell us about the country itself.

Sub-categories of state 
There are lots of sub-types of state branching off from democracy and dictatorship. The main ones are Pluralism, Marxism and Institutionalism.

Pluralism 
Pluralism has been very popular in the United States. It shows the state as a neutral place for settling arguments between other states. Pluralism allows each group of people to tell the state what to do. This type of state is called a polyarchy.

Also in a pluralist state, politics, the military and the economy are all united and work together. This means that all power in the state is 'diffused' across the people who live there.
Marxism 
Marxism is an ideology advocating for the rights of workers and labourers of society. It was started by Karl Marx and Friedrich Engels. Marxism rejects the idea that a state is there to protect business interest, and is definitely not a neutral place for settling arguments.

The main job of a Marxist state is to protect the labour and financial situation of the working classes. With such reforms, a Marxist state focuses on collectivising resources and creating a planned economy to ensure the well-being of the workers. 

Both Marxist and Pluralist states have to react to the activities of groups of people in the state itself. Institutionalist states do not see themselves as 'instruments' to be controlled, they are more just geographical areas. In this area, the people just form groups themselves. An institutionalist state can be made up of both Marxist and Pluralist people, both which have the power to control themselves and not influence the other parties of the state.
Anarchism 
Anarchism is when a group of people have complete freedom and do not believe in having a state at all. Anarchists are a lot like Marxists, but they believe (opposite to Marxists) that a country can work without without a state forcing people to do anything. Law and order are not necessary.

Anarchists (such as Bakunin and Kropotkin in the 19th century), often want a form of Marxism but ignoring some of their rules. They want workers to manage themselves and simply get paid for what they do, rather than getting paid in wages.

Related pages 
 Country
 Sovereign state
 International relations
 List of sovereign states
 Montevideo Convention
 Nation
 Social contract
 U.S. state
 Unitary state
 Province
 Political economy
 Constitutional economics
 Local government

References

International law
A stream is a natural flow of water moving across land between banks.  It is smaller than a river. 

The primary meaning of stream is a body of water, confined within a bed and banks, and detectably flowing.  Synonyms or related words include river, creek, tributary, run, branch, brook, bourne, wash, and fork. Navigable streams are sometimes called waterways, though the term may apply to any size of permanent and natural water feature except oceans.

In the United States, an intermittent stream is one that only flows for part of the year and is marked on topographic maps with a line of blue dashes and dots.  In desert areas of the American Southwest, this also includes washes, which only flow after thunderstorms or other significant rains.  A blue-line stream is one which flows for most or all of the year and is marked on topographic maps with a solid blue line. In Australia, an intermittent stream is usually called a creek, and marked on topographic maps with a solid blue line.
Generally, streams that form only during and immediately after precipitation are termed ephemeral streams.

Streams in geographic terms are awarded order designations.  A stream of the first order is a blue-line stream which does not have any other blue-line stream feeding into it.  A stream of the second order is one which is formed by the joining of two or more blue-line streams.  A third-order stream is one below the confluence of two or more second-order streams; a fourth-order stream is formed by the confluence of at least two third-order streams, and so forth.

Typically, streams are said to have a particular profile, beginning with steep gradients, no flood plain, and little shifting of channels, eventually evolving into streams with low gradients, wide flood plains, and extensive meanders.  The initial stage is sometimes termed a "young" stream, and the later state a "mature" or "old" stream.  However, a stream may meander for some distance before falling into a "young" stream condition.
The gradient of a stream is a critical factor in determining its character, and is entirely determined by its base level of erosion.  The base level of erosion is the point at which the stream either enters the ocean, a lake or pond, or enters a stretch in which it has a much lower gradient, and may be specifically applied to any particular stretch of a stream.  In geologic terms, the stream will erode down through its bed to achieve the base level of erosion throughout its course.  If this base level is low, then the stream will rapidly cut through underlying strata and have a steep gradient, and if the base level is relatively high, then the stream will form a flood plain and meanders.
When a stream flows over an especially resistant stratum and forms a waterfall or cascade, or the same results because for some reason the base level of erosion suddenly drops, perhaps as a result of a fault, the resulting sudden change in stream elevation is called a nickpoint.  The stream, of course, expends kinetic energy in "trying" to eliminate the nickpoint.

Meanders are looping changes of direction of a stream.  These may be somewhat sine-wave in form.  Typically, over time, the meanders don't disappear but gradually migrate downstream.  However, if some resistant material slows or stops the downstream movement of a meander, a stream may erode through the neck between two legs of a meander to become temporarily straighter, leaving behind an arc-shaped body of water termed an oxbow lake or bayou.  A flood may also result in a meander being cut through in this way.
The point of origin of a stream is often called the headwaters or source.  The entire basin drained by the stream is termed the watershed.  Every watershed is made up of smaller watersheds, while most watersheds are parts of larger watersheds.  For instance, the Continental Divide in North America divides the Atlantic Ocean watershed from the Pacific Ocean watershed, but the Atlantic Ocean watershed may be first divided into the Atlantic Ocean drainage and the Gulf of Mexico drainage.  This delineation within the United States is termed the Eastern Divide.  The Gulf of Mexico watershed may be divided into Mississippi River basin and a number of smaller watersheds, such as the Tombigbee River watershed.

The Mississippi River watershed includes the Ohio River watershed, which in turn includes the Kentucky River watershed, and so forth.

The point at which a stream empties into an ocean or other large body of relatively level water is termed the mouth.  There may often be an estuary or delta at the mouth.
Some streams flow underground through unconsolidated sediments or through caves.  Especially with caves, a stream may flow aboveground for part of its course, and underground for part of its course.  When a stream emerges from an underground course, it is termed a spring.

The study of streams and waterways in general is known as surface hydrology and is important in environmental geography or environmental geology.

Related pages
waterfall
river
waterway
lake
marsh
swamp
ocean
spring
Bodies of water
The Solar System is the Sun and all the objects that orbit around it. The Sun is orbited by planets, asteroids, comets and other things. 

The Solar System is about 4.568 billion years old. The Sun formed by gravity in a large molecular cloud. It is mainly hydrogen, which it converts into helium through nuclear fusion. The planets are in a flattened orbiting disk. This disk was left over from the cloud that formed the Sun. Eventually, the gas and dust of the disk came together into planets. It is thought that almost all stars and their planets form this way.

The Sun is a star. It makes up 99.9% of the Solar System's mass. This means that it has strong gravity. The other objects are pulled into orbit around the Sun. The Sun is mostly made out of hydrogen, and some helium and higher elements. All heavier elements, called metals in astronomy, account for less than 2% of the Sun's mass. Oxygen is about 1% of the Sun's mass. Iron (0.2%) is the most plentiful of the other elements.
There are eight planets in the Solar System. From closest to farthest from the Sun, they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The first four planets are called terrestrial planets. They are mostly made of rock and metal, and they are mostly solid. The last four planets are called gas giants. This is because they are much larger than other planets and are mostly made of gas.

Six of the planets, and the six largest dwarf planets, are orbited by moons. There are more than 200 moons in the Solar System. Mercury and Venus have no moons, and Jupiter and Saturn have the largest number of moons. The largest moon is Ganymede which is a moon of Jupiter. Titan is one of Saturn’s moons. It is the only moon in the Solar System to have an atmosphere, which is mainly composed of nitrogen.
The Solar System also contains other things. There are asteroid belts, mostly between Mars and Jupiter. Further out than Neptune, there is the Kuiper belt and the scattered disc. These areas have dwarf planets, including Pluto, Makemake, Haumea, Ceres and Eris. There are thousands of very small objects in these areas. There are also comets, centaurs, and interplanetary dust.

In Ancient Greece, Aristarchus of Samos proposed the heliocentric model of the Solar System, where the Sun, is at the center of the known universe. He is sometimes known as the "Greek Copernicus".

Evolution of the Solar System 

The formation and evolution of the Solar System began 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud.

Most of the collapsing mass collected in the centre, forming the Sun, while the rest flattened into a protoplanetary disk of loose dust, out of which the planets, moons, asteroids, and other Solar System bodies formed.
This model, known as the nebular hypothesis, was developed in the 18th (1700s) century by Emanuel Swedenborg, Immanuel Kant, and Pierre-Simon Laplace. It has been adjusted by scientific disciplines such as astronomy, physics, geology, and planetary science. As our knowledge of space has grown, the models have been changed to account for the new observations.

The Solar System has evolved considerably since its initial formation. Many moons have formed from circling discs of gas and dust around their parent planets, while other moons are believed to have formed and were later captured by their planets. Others, such as the Earth's Moon, may be the result of giant collisions.

Many collisions between bodies have occurred, and have been important to the evolution of the Solar System. In the early stages, the positions of the planets sometimes shifted, and planets have switched places. This planetary migration is thought to have been responsible for much of the Solar System's early evolution.
Grand tack hypothesis 
Astronomers now think that the order of the planets was not always as it is today. Knowing what we know today, we can see the Solar System is strange. Most other planetary system we are able to study have their largest planet closer to their star. Also we have noticed other oddities in the Solar System. Mars is smaller than it ought to be, and the asteroid belt has been disturbed.

So, astronomers have put forward the grand tack hypothesis. In it Jupiter was earlier closer to the Sun, and (for some unknown reason) moved out to its present position.

Orbits of the planets 
The Earth's orbit around the Sun is nearly a perfect circle, but in a very slightly oval shaped orbit, an elliptical orbit. The other planets in the Solar System also orbit the Sun in slightly elliptical orbits. Mercury has a more elliptical orbit than the others, and some of the smaller objects orbit the Sun in very eccentric orbits. The planets all orbit the Sun in the same direction.
A full account of the planetary motion needs an account of the n-body problem, which is not treated on this wiki. A page can be found on En wiki.

Discovery and exploration
For thousands of years, people had no need for a name for the "Solar System". They thought the Earth stayed still at the center of everything (geocentrism). The Greek philosopher Aristarchus of Samos suggested that there was a special order in the sky. Nicolaus Copernicus was the first to develop a mathematical system that described what we now call the "Solar System". This was called a "new system of the world". In the 17th century, Galileo Galilei, Johannes Kepler and Isaac Newton began to understand physics more clearly. People began to accept the idea that the Earth is a planet that moves around the Sun, and that the planets are worlds, and that all worlds are governed by the same same physical laws. More recently, telescopes and space probes sometimes let us see details directly. All inner planets have surface features. The gas giants (as the name suggests) have surfaces whose make-up is gradually being discovered.

The eight planets
The eight planets 

In their order from the Sun:
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune

The planets are the biggest objects that go around the Sun.  It took people many years of using telescopes to find the objects that were farthest away.  New planets might still be found, and more small objects are found every year.  Most of the planets have moons that orbit around them just as the planets orbit the Sun. There are at least 200 of these moons in the Solar System.

Dwarf planets 

Pluto was discovered by American astronomer Clyde Tombaugh and was declared the 9th planet of the Solar System in 1930. 

This all changed on August 24, 2006, when the International Astronomical Union (IAU) decided on the correct definition for the word "planet" for the first time. By this definition, Pluto was not a planet anymore due to its irregular orbit and size. It became a "dwarf planet" along with Eris and many others.
Eris was 27% more massive than Pluto. After this, Pluto was put on the list of minor planets and was downgraded in 2006. Instead they defined a new category of dwarf planet, into which Pluto did fit, along with some others. These small planets are sometimes called plutinos.
 Pluto
 Ceres
 Haumea
 Eris
 Makemake

Structure 
There are a few main parts of the Solar System. Here they are in order from the Sun, with the planets numbered, and the dwarf planets marked with the letters a to e.

Inner solar system 

The first four planets closest to the Sun are called the inner planets. They are small and dense terrestrial planets, with solid surfaces. They are made up of mostly rock and metal with a distinct internal structure and a similar size. Three also have an atmosphere. The study of the four planets gives information about geology outside the Earth.
Terrestrial planets region contains the four planets closest to the sun, all are rocky planets
 (1) Mercury
 (2) Venus
 (3) Earth
 (4) Mars
 Asteroid belt region contains;
 (a) Ceres (the only dwarf planet in this region)
 Asteroids

Outer solar system 

 Gas giant planets region contains;
 (5) Jupiter
 (6) Saturn
 (7) Uranus
 (8) Neptune

Trans-Neptune region 
 Kuiper belt region contains;
 (b) Pluto
 (c) Haumea
 (d) Makemake
 Kuiper belt objects and possibly other dwarf planets
 short-period comets
 Scattered disc region contains;
 (e) Eris
 Scattered disk objects and possibly other dwarf planets

Oort Cloud  
The Oort cloud is separate from the trans-Neptune region, and much farther out. It contains the long-period comets.
Ecliptic plane 
The plane of the ecliptic is defined by the Earth's orbit around the Sun. All of the planets orbit the Sun roughly around this same orbital plane. The farther away from this plane a planet orbits, the more inclined is its orbit to the ecliptic. If you could look at the Solar System "edge on" then all the planets would be orbiting more or less in the plane of the ecliptic.

References

More reading

Other websites 

 Views of the Solar System
 Your Weight on Other Worlds
 Solar System Citizendium
The Planets in the Solar System
Saturn is the sixth planet from the Sun in the Solar System. 

Saturn is one of the four gas giant planets in the Solar System, with Jupiter, Uranus, and Neptune. It is the second largest planet in the Solar System (Jupiter is larger).

Saturn was named after the Roman god Saturnus. He was the Roman equivalent of the Greek god Kronos. Saturn's symbol is ♄ which is the symbol of Saturnus' sickle.

Inside Saturn is probably a core of iron, nickel, silicon and oxygen compounds, surrounded by a deep layer of metallic hydrogen, then a layer of liquid hydrogen and liquid helium and finally, an outer gaseous layer.
Saturn has 145 known moons orbiting the planet.  The largest moon is Titan. Titan is larger in volume than the planet Mercury. It is the second-largest moon in the Solar System. The largest moon is a moon of Jupiter, Ganymede. There are also many rings around Saturn. These rings are made of ice with some rocks and dust. Some people think that that the rings were made by a moon impact or other event. Saturn is about 1,433,000,000 km (870,000,000 mi) on average from the Sun. Saturn takes 29.6 Earth years to move around the Sun.

Physical features 

Saturn is an oblate spheroid. This means that it is flattened at the poles and wider around the equator. The planet's equatorial diameter is . Its polar diameter (the distance from the north pole to the south pole through the centre) is . This is a 9% difference. Saturn has a flattened shape because of its very fast rotation. It rotates once every 10.8 hours.
Saturn is the only planet in the Solar System that is less dense than water. Even though the planet's core is very dense, it has a gaseous atmosphere. This makes its average density is 0.69 g/cm3. This means if Saturn could be placed in a large pool of water, it would float.

Atmosphere 
The outer part of Saturn's atmosphere is made up of about 96% hydrogen, 3% helium, 0.4% methane and 0.01% ammonia. There is also some acetylene, ethane and phosphine.
Saturn's clouds show a banded pattern. This is like the cloud bands seen on Jupiter. Saturn's clouds are much fainter and the bands are wider at the equator. Saturn's lowest cloud layer is made up of water ice. It is about  thick. The temperature there is quite low, at 250 K (-10°F, -23°C). However, scientists do not all agree on this. The layer above is made up of ammonium hydrosulfide ice. It is about  thick. Above it is a layer of ammonia ice clouds which are  thick. The highest layer is made up of hydrogen and helium gases. It goes to between  and  above the water cloud tops. Auroras can be seen in Saturn in the mesosphere. The temperature at Saturn's cloud tops is very low, at 98 K (-283 °F, -175 °C). The temperatures in the inner layers are much higher than the outside layers because of the heat made by Saturn's inside. Saturn's winds are some of the fastest in the Solar System. They can reach 1,800 km/h (1,118 mph), ten times faster than winds on Earth.
Storms and spots 
Saturn's atmosphere can make oval shaped clouds. This is like the clearer spots seen on Jupiter. These oval spots are cyclonic storms, the same as cyclones seen on Earth. In 1990, the Hubble Space Telescope found a very large white cloud near Saturn's equator. Storms like the one in 1990 were known as Great White Spots. These unique storms only exist for a short time and only happen about every 30 Earth years, at the time of the summer solstice in the Northern Hemisphere. Great White Spots were also found in 1876, 1903, 1933, and 1960.

The Voyager 1 spacecraft found a hexagonal cloud pattern near Saturn's north pole at about 78°N. The Cassini−Huygens probe later confirmed it in 2006. Unlike the north pole, the south pole does not show any hexagonal clouds. The probe also found a hurricane-like storm on the south pole that showed an eyewall. Until this finding, eyewalls had only been seen on Earth.
Interior 
Saturn's inside is similar to Jupiter's inside. It has a small rocky core about the size of the Earth at its center. It is very hot. Its temperature reaches 15,000 K (). Saturn is so hot that it gives out more heat energy into space than it gets from the Sun. Above it is a thicker layer of metallic hydrogen, about  deep. Above that layer is a region of liquid hydrogen and helium. The core is heavy, with about 9 to 22 times more mass than the Earth's core.
Magnetic field 
Saturn has a natural magnetic field that is weaker than Jupiter's. Like the Earth's, Saturn's field is a magnetic dipole (it has a North and a South). Saturn's field is unique in that it is perfectly symmetrical, unlike any other known planet. This means the field is exactly in line with the planet's axis. Saturn generates radio waves, but they are too weak to be detected from Earth. The moon Titan orbits in the outer part of Saturn's magnetic field and gives out plasma to the field from the ionised particles in Titan's atmosphere.

Rotation and orbit 
Saturn's average distance from the Sun is over 1,400,000,000 km (869,000,000 mi). This is about nine times the distance from the Earth to the Sun. It takes 10,759 days, or about 29.8 years, for Saturn to orbit around the Sun. This is known as Saturn's orbital period.
Voyager 1 measured Saturn's rotation as being 10 hours, 14 minutes at the equator, 10 hours, 40 minutes closer to the poles, and 10 hours, 39 minutes, 24 seconds for the planet's inside. This is known as its rotational period.

Cassini measured the rotation of Saturn as being 10 hours, 45 minutes, 45 seconds ± 36 seconds. That is about six minutes longer than the radio rotational period measured by the Voyager 1 and Voyager 2 spacecrafts, which flew by Saturn in 1980 and 1981.

Saturn's rotational period is calculated by the rotation speed of radio waves given off by the planet. The Cassini−Huygens spacecraft found that the radio waves slowed down. This suggested that the rotational period increased. Since scientists do not think Saturn's rotation is actually slowing down, the explanation may be that the magnetic field causes the radio waves.

Planetary rings
Planetary rings 

Saturn is best known for its planetary rings which are easy to see with a telescope. There are seven named rings: A, B, C, D, E, F, and G. They were named in the order they were found, which is different to their order from the planet. From the planet the rings are ordered: D, C, B, A, F, G and E.

Some scientists think that the rings are material left after a moon broke apart. A new idea says that it was a very large moon, most of which crashed into the planet. This left a large amount of ice to form the rings and some of the moons. This includes Enceladus, which is thought to be made of ice.
The rings were first found by Galileo Galilei in 1610, using his telescope. They did not look like rings to Galileo. He called them "handles". He thought that Saturn was three different planets that were right next to each other. In 1612, when the rings were facing edge on with the Earth, the rings disappeared, then reappeared again in 1613, further confusing Galileo. In 1655, Christiaan Huygens was the first person to say that Saturn was surrounded by rings. Using a much more powerful telescope than Galilei's, he said that Saturn "is surrounded by a thin, flat, ring, nowhere touching...". In 1675, Giovanni Domenico Cassini found that the planet's rings were in fact made of smaller rings with gaps. The largest ring gap was later named the Cassini Division. In 1859, James Clerk Maxwell showed that the rings cannot be solid, but are made of small particles, each orbiting Saturn on their own. Otherwise, it would become unstable or break apart
. James Keeler studied the rings using a spectroscope in 1895 which proved Maxwell's theory.