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Graph Article

This graph shows the unemployment rate by year in the United States.

A graph is a picture designed to express words, particularly the connection between one quantity and others.

A simple graph usually shows the relationship between two numbers or measurements in the form of a grid. If this is a rectagular graph, these two measurements will be arranged into two different lines at right angles to one another. One of these lines will be going up (the vertical axis). The other one will be going right (the horizontal axis). These lines (or axes, the plural of axis) meet at their ends in the lower left corner of the graph.

Both of these axes have tick marks along their lengths. You can think of each axis as a ruler drawn on paper. So each measurement is indicated by the length of the associated tick mark along the particular axis.

Another word for graph is chart or diagram. However, a chart or a diagram may not relate two or more quantities to each other. A flowchart or a tree diagram are two examples of charts and diagrams that are not graphs.

How to Draw a Simple Graph

Let's say you wanted to make a graph showing your height as you were growing up. You might show your height in centimeters on the vertical axis and your age in years on the horizontal axis.

For example, say you were 60 centimeters tall at age 1, 85 centimeters tall at age 2 and 95 centimeters tall at age 3. You would draw an imaginary straight line passing through the 50 centimeters height mark on the vertical axis. Then you would draw a second imaginary line passing through the age of 1 year on the horizontal axis. At the place where the two imaginary lines meet (called their intersection), you would then draw a dot. Really, the imaginary lines are usually replaced by graph paper (see below). The drawing of this intersection is called "plotting the point 50 centimeters for year 1".

You would then plot 85 centimeters for year 2 and 95 centimeters for year 3. If you had more heights for more years, you would plot years 4, 5 and so forth. When you had enough points on your graph, you could draw a line through each of the plotted points, making your graph a line graph. For example, the line graph at the upper right shows the unemployment rate (as a percent) on the vertical axis and the year (from 1950 to 2005) on the horizontal axis.

Let's say you wanted a single graph showing both your height and your brother's height. This could be expressed as two sets of plotted points: one for you and one for your bother. You could use different colors to tell your plot from your bother's.

Uses of Graphs

Graphs make information easier to see. This is especially true when two or more sets of numbers are related in some way.

For example, the graph at the beginning of this article (the one about unemployment rates) could be expressed in the form of a table like this:

Year	Unemployment Rate
1950	4.5%
1951	3.1%
1952	3.4%
etc.

But a long string of numbers makes it difficult to see the underlying meaning. It's much simpler to understand when the table is expressed in the form of a graph. In particular, it's easier to see the relationships between the two sets of data. For example, by looking at the graph you can see at a glance that unemployment was relatively low in the late sixties but relatively high in the early eighties.

Scientists and engineers use graphs so that they can get a better understanding of the broad meaning and importance of their data. Salesmen and businessmen often use graphs to add importance to their points in a sales or business presentation. Graphs with many plotted points may be created on a computer rather than being drawn by hand.

Graph Paper

Cartesian graph paper.

Usually, graphs are created on specially-designed paper called graph paper. This paper has evenly drawn horizontal and vertical lines on it. On the right is an example of a sheet of graph paper.

Different types of graphs require different forms of graph paper. What we were talking about in the article above is the commonest form of graphs and graph paper. It is known as a rectangular or Cartesian graphs. Other forms of graphs include: bar graphs, pie graphs, polar graphs, scatter graphs, three-dimensional graphs, logarithmic graphs and many others.

Category:Mathematics

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Hertzprung-Russell Diagram

Hertzsprung-Russell diagram by Richard Powell with permission.

The Hertzprung-Russell Diagram is a graph of many stars. It shows the relation between stars' luminosity (that is, how bright they are) and their temperature (how hot they are). These diagrams are not pictures or maps of the locations of the stars. Rather, Hertzprung-Russell diagrams plot each star on a graph measuring the star's brightness versus its temperature. Hertzprung-Russell Diagrams are also called H-R Diagrams or HRDs.

You can see an example of a Hertzprung-Russell diagram to the right. This diagram is based on measurements from 23,000 stars in our Milky Way galaxy. The Hertzprung-Russell diagram is named after its creators, astronomers Ejnar Hertzsprung and Henry Norris Russell.

Drawing a Hertzprung-Russell Diagram

The vertical axis of a Hertzprung-Russell diagram shows the luminosity or brightness of the stars, as if they were all measured from the same distance. Another term for this is absolute magnitude. The brighter a star is, the higher its plot will be on this chart.

The horizontal axis shows the surface temperature of the stars. However, the temperatures go down, not up, as you move to the right. That is, the left of the diagram contains stars with the highest temperature plots (greater than 30,000 Kelvins) while the right shows stars with temperatures of only 3000K.

In general, the temperature of a star relates to its color. At the top of the chart, along with the temperatures, are the Spectral Classes. The hotest stars are blue-white (class O), those in the middle temperatures are yellow (class G) and the coolest ones are red (class M). (Of course, when we say "coolest" about stars, we must realize that the lowest temperature for a star is almost 5000 degrees Fahrenheit.)

As a matter of fact, when Hertzprung-Russell diagrams were developed in the early 1900's, astronomers didn't know how to find out the temperature of a star. The first diagrams plotted stars' absolute magnitude (where adding one meant the brightness would go down by about two and a half times) against color, represented by the spectral classes from blue-white to red.

Regions of Many Stars

As you can see, stars tend to fall only into certain regions of the diagram when graphed in this way. All stars in a given area of a Hertzprung-Russell diagram share similar luminosities and temperatures. The main region where stars appear is the diagonal curved line, going from the upper-left (hot and bright) to the lower-right (cooler and less bright). This is called the Main Sequence. Above the main sequence is another region containing the red giants. Below is a curved line representing the white dwarfs.

These collections of stars by brightness and temperature have important meanings when talking about stellar evolution. In general, stars are created in the main sequence. (Of course, when we say "in the main sequence" we really mean "having a brightness and a temperature that causes them to be plotted within the main sequence on a Hertzprung-Russell diagram.") After billions of years, they expand into red giants. Then, after another one or two billion years, they shrink into white dwarfs.

It was only in the 1930's and 1940's that scientists began to understand the role of nuclear fusion in creating and keeping stars like our Sun. These days Hertzprung-Russell diagrams are used to present stellar evolution in pictures to students. They are not used much for developing new scientific theories.

On a Hertzprung-Russell diagram, our Sun is plotted very close to the middle of the main sequence at the intersection of luminosity 1 and temperature 5780K. Therefore, the sun is class G or a "yellow star").

Category:Stars Category:Astronomy

Main sequence

Hertzsprung-Russell diagram showing stars in the main sequence.

The main sequence is a region on a Hertzsprung-Russell Diagram where most stars appear. Any star that is plotted within that area is a main-sequence star. The Sun is a main-sequence star. Most of the stars in the Milky Way galaxy and most other galaxies are also main-sequence stars.

Hertzsprung-Russell diagrams are graphs that measure each star's brightness against its temperature or color. The main sequence appears as a band going from the upper-left (hot and bright) to the lower-right (cooler and less bright). You can see an example of the band of main-sequence stars to the right.

Stars are created from nebula and first appear on the main sequence. They stay on the main sequence for millions or billions of years. When a star begins to run out of fuel, it gets much bigger and colder and turns into a red giant. After this happens, the star is no longer on the main sequence.

In general, the hottest and brightest stars (in the upper-left of the Hertzsprung-Russell diagram) also have the most mass. The main sequence is sometimes divided into two parts. Any star that has a mass greater than 1.5 times the Sun's mass is grouped into the upper main sequence; any star with a mass lower than 1.5 solar masses belongs to the lower main sequence.

Stars get the energy they produce through nuclear fusion of hydrogen into helium. The upper main sequence (hot and bright with the most mass) produces energy by one type of nuclear fusion involving only hydrogen and helium. The lower main sequence (cooler and less bright with a lower mass) produces energy by another type of nuclear fusion. This type uses other elements (for example, carbon, nitrogen and oxygen) with higher atomic numbers as nuclear catalysts.

Because of these different types of fusion, stars on the lower main sequence last much longer than stars on the upper main sequence. Our Sun is located on the lower main sequence and is predicted to last between 10 and 12 billion years. A star located on the upper main sequence may only last a few million years.

Nowadays, a new star may be classified as main sequence strictly by its color. A main sequence star of a particular color would have a narrow band of brightness when seen from a standard distance. An astronomer could compute the distance to this newly-discovered star by comparing its brightness as seen from Earth against the brightness for a certain color on the main sequence.

Wikipedia:Basic English combined wordlist

This is the maximum Basic English combined wordlist. It must not be confused with the definition of Basic English: 850 words plus 150 specialty words. This maximum list is simply what the advanced student will know when transiting from the Basic English language to standard English language.

It actually contains well over two thousand words and consists of five subordinate word lists:

• 850 Basic English words
• 179 international words, consisting of:

• 50 international nouns
• 12 names of sciences
• 12 title and organizational names
• 50 general utility names
• 5 onomatopoeic (sounds like) words
• 50 words about time and numbers

• 1293 words used as an addendum
• 215 compound words (made up of Basic English words)
• 91 new words made from adding the allowed endings: -er, -ed, -ing, -ly, -s, and the prefix un-.

Total: 2626 words.

Contents:	Top – 0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Simple Sentence Structure

Simple sentences are more understandable than complex ones. Try to use the simplest sentences that make sense. Remember that this guideline, like all Wikipedia rules, is meant to be used with common sense. It is more important that you follow the spirit of simple sentence structure than reducing every possible sentence to its simplest form.

Guidelines

1. Always start by using simple sentences. For example:

• John Smith walked the dog.

Subject: John Smith

Verb: walked

Direct object: the dog

and

• John Smith walked the dog to the supermarket.

Subject: John Smith

Verb: walked

Direct object: the dog

Indirect object (also prepositional phrase): to the supermarket

2. Try to avoid compound sentences when possible. Write this:

• Good: John Smith walked the dog. Later, he was tired.

instead of:

• Bad: John Smith walked the dog but later he was tired.

But this is not a guideline in favor of short sentences. See the following:

• Good: John Smith walked his big, hairy dog, Bluto, to the supermarket on Main Street. Later, he was so tired that he collapsed onto his bed exhausted.

3. If you must use complex sentences, try to have only one dependent clause, like this:

• John Smith walked his dog to the supermarket because he was hungry.

Subject: John Smith

Verb: walked

Direct object: his dog

Indirect object (also prepositional phrase): to the supermarket

Dependent clause: because he was hungry

For example:

• Bad: John Smith, who was very tired, walked his dog to the supermarket because he was hungry but he returned to his home still hungry and even more tired because the market was closed.
• Clauses: who was very tired; because he was hungry; but he returned to his home; and even more tired and because the market was closed
• Better: John Smith was very tired. He walked his dog to the supermarket because he was hungry. But the market was closed. So he returned to his home still hungry and even more tired.

4. Try not to use compound-complex sentences, with multiple independent and dependent clauses.

• Bad: John Smith walked his dog to the supermarket where he thought he might buy some apples, but Mary Jones, who considered herself superior to John (although many people believed that she didn't have any reason to feel that way), arrived first and spitefully bought the remaining three apples and so John, who was mad as hell at Mary by this time, had to go home hungry.
• Better: John Smith walked his dog to the supermarket. He thought he might buy some apples. But Mary Jones considered herself superior to John. (However, many people believed that she had no reason to feel that way.) She arrived first and bought the remaining three apples, just for spite. By this time, John was mad as hell at Mary. But he had to go home hungry.
  

(The "better" sentences have just one compound-complex sentence and that only has one compound clause and one dependent clause: She arrived first and bought the remaining three apples, [compound, independent clauses] just for spite. [dependent clause])

Refactoring Sentences

"Refactoring" means using a procedure that accomplishes its task almost automatically and mechanically, but not quite.

Here are some refactoring rules to change complex sentence structures into simpler ones. These rules should be applied over and over again to the same sentence until you feel that the sentence structure is simple enough for this Wikipedia. Although listed in order of complexity, these rules can be applied in any order.

(Please note that you probably wouldn't refactor sentences as simple as the first examples below. But, if the sentence was as complex as the one given in guideline number 4 in the sub-section above, then these rules would be a good place to start. Remember that the refactoring process is iterative; that the guidelines should be applied over and over again.)

1. When you see and, or, but, although, except, while and other conjunctionss that link two independent thoughts in the same sentence:

1. Remove the conjunction,
2. Add a period at the end of the word that preceded the conjunction and
3. Capitalize the first word that followed the conjuction.
4. You may have to add new punctuation, usually in the second sentence.

Example: John Smith walked the dog but later he was tired becomes John Smith walked the dog. Later, he was tired.

2. When the subject is missing from the second thought, add the appropriate pronoun.
Example: John Smith walked the dog and later petted the cat becomes John Smith walked the dog. Later, he petted the cat.

3a. When the conjuction expresses significant meaning (usually how or why the subject arrived at the current state), you might consider leaving the conjuction in place as the start of the second sentence.
Example: John Smith walked the dog but he didn't like it becomes John Smith walked the dog. But he didn't like it.
3b. You might also have to rearrange the order of the sentences, changing the conjuction if necessary.
Example: John Smith walked the dog even though he was very tired becomes John Smith was very tired. Even so, he walked the dog.