the-french-artist/wikipedia_20220301.simple_sentence_split huggingface dataset:
The flesh of the fruit is firm with a taste anywhere from sour to sweet.
Apples used for cooking are sour, and need to be cooked with sugar, while other apples are sweet, and do not need cooking.
There are some seeds at the core, that can be removed with a tool that removes the core, or by carefully using a knife.
The scientific name of the apple tree genus in the Latin language is Malus.
Most apples that people grow are of the Malus domestica species.
Most apples are good to eat raw (not cooked), and are also used in many kinds of baked foods, such as apple pie.
Apples are cooked until they are soft to make apple sauce.
Apples are also made into the drinks apple juice and cider.
Usually, cider contains a little alcohol, about as much as beer.
The regions of Brittany in France and Cornwall in England are known for their apple ciders.
Apple cultivars
If one wants to grow a certain type of apple it is not possible to do this by planting a seed from the wanted type.
The seed will have DNA from the apple that the seeds came from, but it will also  have DNA from the apple flower that pollinated the seeds, which may well be a different type.
This means that the tree which would grow from planting would be a mixture of two.
In order to grow a certain type of apple, a small twig, or 'scion', is cut from the tree that grows the type of apple desired, and then added on to a specially grown stump called a rootstock.
The tree that grows will only create apples of the type needed.
There are more than 7,500 known cultivars (varieties) of apples.
Different cultivars are available for temperate and subtropical climates.
One large collection of over 2,100 apple cultivars is at the National Fruit Collection in England.
Most of these cultivars are grown for eating fresh (dessert apples).
However, some are grown simply for cooking or making cider.
Cider apples are usually too tart to eat immediately.
However, they give cider a rich flavor that dessert apples cannot.
Most popular apple cultivars are soft but crisp.
Colorful skin, easy shipping, disease resistance, 'Red Delicious' apple shape, and popular flavor are also needed.
Modern apples are usually sweeter than older cultivars.
This is because popular tastes in apples have become different.
Most North Americans and Europeans enjoy sweet apples.
Extremely sweet apples with hardly any acid taste are popular in Asia and India.
In the United Kingdom
In the United Kingdom there are about 3000 different types of apples.
The most common apple type grown in England is the 'Bramley seedling', which is a popular cooking apple.
Apple orchards are not as common as they were in the early 1900s, when apples were rarely brought in from other countries.
Organizations such as Common Ground teach people about the importance of rare and local varieties of fruit.
In North America
Many apples are grown in temperate parts of the United States and Canada.
In many areas where apple growing is important, people have huge celebrations:
Annapolis Valley Apple Blossom Festival - held five days every spring (May-June) in Nova Scotia
Shenandoah Apple Blossom Festival - held six days every spring in Winchester, Virginia.
Washington State Apple Blossom Festival - held two weeks every spring (April-May) in Wenatchee, Washington
Varieties of apples
Cox's Orange Pippin
Fuji (apple)
Golden Delicious (sometimes called a Green Delicious Apple)
McIntosh
Red Delicious
Apples are in the group Maloideae.
This is a subfamily of the family Rosaceae.
They are in the same subfamily as pears.
Potter D. et al 2007.
Phylogeny and classification of Rosaceae.
Plant Systematics and Evolution.
266 (1–2): 5–43.
An Abrahamic Religion is a religion whose followers believe in the prophet Abraham.
They believe Abraham and his sons/grandsons hold an important role in human spiritual development.
The best known Abrahamic religions are Judaism, Christianity and Islam.
Smaller religious traditions sometimes included as Abrahamic religions are Samaritanism, Druze, Rastafari, Babism and Bahá'í Faith.
Mandaeism (a religion that holds many Abrahamic beliefs) is not called Abrahamic because its followers think Abraham was a false prophet
True Abrahamic religions are monotheistic (the belief that there is only one God).
They also all believe that people should pray to God and worship God often.
Among monotheistic religions, the Abrahamic religions have the world's largest number of followers.
They are also all ethical monotheistic religions.
This means they have rules that they have to follow.
Algebra (from Arabic: الجبر‎, transliterated "al-jabr", meaning "reunion of broken parts") is a part of mathematics.
It uses variables to represent a value that is not yet known.
When an equals sign (=) is used, this is called an equation.
A very simple equation using a variable is: .
In this example, , or it could also be said that " equals five".
This is called solving for .
Besides equations, there are inequalities (less than and greater than).
A special type of equation is called the function.
This is often used in making graphs because it always turns one input into one output.
Algebra can be used to solve real problems because the rules of algebra work in real life and numbers can be used to represent the values of real things.
Physics, engineering and computer programming are areas that use algebra all the time.
It is also useful to know in surveying, construction and business, especially accounting.
People who do algebra use the rules of numbers and mathematical operations used on numbers.
The simplest are adding, subtracting, multiplying, and dividing.
More advanced operations involve exponents, starting with squares and square roots.
Algebra was first used to solve equations and inequalities.
Two examples are linear equations (the equation of a straight line,  or ) and quadratic equations, which has variables that are squared (multiplied by itself, for example: , , or ).
Early forms of algebra were developed by the Babylonians and the Greek geometers such as Hero of Alexandria.
However the word "algebra" is a Latin form of the Arabic word Al-Jabr ("casting") and comes from a mathematics book Al-Maqala fi Hisab-al Jabr wa-al-Muqabilah, ("Essay on the Computation of Casting and Equation") written in the 9th century by a Persian mathematician, Muhammad ibn Mūsā al-Khwārizmī, who was a Muslim born in Khwarizm in Uzbekistan.
He flourished under Al-Ma'moun in Baghdad, Iraq through 813-833 AD, and died around 840 AD.
The book was brought into Europe and translated into Latin in the 12th century.
The book was then given the name 'Algebra'. (
The ending of the mathematician's name, al-Khwarizmi, was changed into a word easier to say in Latin, and became the English word algorithm).
Sue has 12 candies, and Ann has 24 candies.
They decide to share so that they have the same number of candies.
How many candies will each have?
To have the same number of candies, Ann has to give some to Sue.
Let  represent the number of candies Ann gives to Sue.
Sue's candies, plus , must be the same as Ann's candies minus .
This is written as:
Subtract 12 from both sides of the equation.
This gives: . (
What happens on one side of the equal sign must happen on the other side too, for the equation to still be true.
So in this case when 12 was subtracted from both sides, there was a middle step of .
After a person is comfortable with this, the middle step is not written down.)
Add  to both sides of the equation.
This gives:
Divide both sides of the equation by 2.
This gives .
The answer is six.
This mean that if Ann gives Sue 6 candies, they will have the same number of candies.
To check this, put 6 back into the original equation wherever  was:
This gives , which is true.
They each now have 18 candies.
With practice, algebra can be used when faced with a problem that is too hard to solve any other way.
Problems such as building a freeway, designing a cell phone, or finding the cure for a disease all require algebra.
Writing algebra
As in most parts of mathematics, adding  to  (or  plus ) is written as ;
subtracting  from  (or  minus ) is written as ;
and dividing  by  (or  over ) is written as  or  .
In algebra, multiplying  by  (or  times ) can be written in 3 different ways: ,  or just .
All of these notations mean the same thing:  times .
The symbol "" used in arithmetic is not used in algebra, because it looks too much like the letter , which is often used as a variable.
When we multiply a number and a variable in algebra, we can simply write the number in front of the letter: .
When the number is 1, then it is not written because 1 times any number is that number () and so it is not needed.
And when it is 0, we can completely remove the terms, because 0 times any number is zero ().
As a side note, you do not have to use the letters  or  in algebra.
Variables are just symbols that mean some unknown number or value, so you can use any letter for a variable (except  (Euler's number) and  (Imaginary unit), because these are mathematical constants).
and  are the most common, though.
An important part of algebra is the study of functions, since they often appear in equations that we are trying to solve.
A function is like a machine you can put a number (or numbers) into and get a certain number (or numbers) out.
When using functions, graphs can be powerful tools in helping us to study the solutions to equations.
A graph is a picture that shows all the values of the variables that make the equation or inequality true.
Usually this is easy to make when there are only one or two variables.
The graph is often a line, and if the line does not bend or go straight up-and-down it can be described by the basic formula .
The variable  is the y-intercept of the graph (where the line crosses the vertical axis) and  is the slope or steepness of the line.
This formula applies to the coordinates of a graph, where each point on the line is written (, ).
In some math problems like the equation for a line, there can be more than one variable ( and  in this case).
To find points on the line, one variable is changed.
The variable that is changed is called the "independent" variable.
Then the math is done to make a number.
The number that is made is called the "dependent" variable.
Most of the time the independent variable is written as  and the dependent variable is written as , for example, in .
This is often put on a graph, using an  axis (going left and right) and a  axis (going up and down).
It can also be written in function form: .
So in this example, we could put in 5 for  and get .
Put in 2 for  would get .
And 0 for  would get .
So there would be a line going through the points (5,16), (2,7), and (0,1) as seen in the graph to the right.
If  has a power of 1, it is a straight line.
If it is squared or some other power, it will be curved.
If it uses an inequality ( or ), then usually part of the graph is shaded, either above or below the line.
In algebra, there are a few rules that can be used for further understanding of equations.
These are called the rules of algebra.
While these rules may seem senseless or obvious, it is wise to understand that these properties do not hold throughout all branches of mathematics.
Therefore, it will be useful to know how these axiomatic rules are declared, before taking them for granted.
Before going on to the rules, reflect on two definitions that will be given.
Opposite: the opposite of  is .
Reciprocal: the reciprocal of  is .
Commutative property of addition
'Commutative' means that a function has the same result if the numbers are swapped around.
In other words, the order of the terms in an equation does not matter.
When two terms (addends) are being added, the 'commutative property of addition' is applicable.
In algebraic terms, this gives .
Note that this does not apply for subtraction (i.e.  except if ).
Commutative property of multiplication
When two terms (factors) are being multiplied, the 'commutative property of multiplication' is applicable.
Note that this does not apply for division (i.e. , when  and , except if ).
Associative property of addition
'Associative' refers to the grouping of numbers.
The associative property of addition implies that, when adding three or more terms, it doesn't matter how these terms are grouped.
Algebraically, this gives .
Note that this does not hold for subtraction, e.g.  (see distributive property).
Associative property of multiplication
The associative property of multiplication implies that, when multiplying three or more terms, it doesn't matter how these terms are grouped.
Note that this does not hold for division, e.g. .
The distributive property states that the multiplication of a term by another term can be distributed.
For instance: . (
Do not confuse this with the associative properties!
For instance: .)
Additive identity
'Identity' refers to the property of a number that it is equal to itself.
In other words, there exists an operation of two numbers so that it equals the variable of the sum.
The additive identity property states that any number plus 0 is that number: .
This also holds for subtraction: .
Multiplicative identity
The multiplicative identity property states that any number times 1 is that number: .
This also holds for division: .
Additive inverse property
The additive inverse property is somewhat like the opposite of the additive identity.
When we add a number and its opposite, the result is 0.
Algebraically, it states the following: , which is the same as .
For example, the additive inverse (or opposite) of 1 is -1.
Multiplicative inverse property
The multiplicative inverse property means that when we multiply a number and its inverse, the result is 1.
For example, the multiplicative inverse (or just inverse) of 2 is 1/2.
To get the inverse of a fraction, switch the numerator and the denominator: the inverse of  is  .
This includes how to use a matrix to solve many linear equations at once.
Abstract algebra is the study of things that are found in equations, going beyond numbers to the more abstract with groups of numbers.
Many math problems are about physics and engineering.
In many of these physics problems time is a variable.
The letter used for time is .
Using the basic ideas in algebra can help reduce a math problem to its simplest form making it easier to solve difficult problems.
Energy is , force is , mass is , acceleration is  and speed of light is sometimes .
This is used in some famous equations, like  and  (although more complex math beyond algebra was needed to come up with that last equation).
Khan Academy: Algebra theory and practice
algebrarules.com: A free place to learn the basics of Algebra
Khan Academy: Origins of Algebra, free online micro lectures
Fields of mathematics
Atoms are very small pieces of matter.
There are many different types of atoms, each with its own name, mass and size.
These different types of atoms are called chemical elements.
The chemical elements are organized on the periodic table.
Examples of elements are hydrogen, carbon, chlorine, and gold etc.
Atoms are very small, but their exact size depends on the element.
Atoms range from 0.1 to 0.5 nanometers in width.
One nanometer is about 100,000 times smaller than the width of a human hair.
This makes atoms impossible to see without special tools.
Scientists discover how they work and interact with other atoms through experiments.
Atoms can join together to make molecules: for example, two hydrogen atoms and one oxygen atom combine to make a water molecule, and many separate molecules make up a glass of water.
When atoms join together it is called a chemical reaction.
Atoms can join together without forming separate molecules, in this case every atom is connected to a giant web of atoms, these are called crystals.
Atoms are made up of three kinds of smaller particles, called protons, neutrons and electrons.
The protons and neutrons are heavier, and stay in the middle of the atom, which is called the nucleus.
The nucleus is surrounded by a cloud of light-weight electrons, these are attracted to the protons in the nucleus by the electromagnetic force because they have opposite electric charges.
The number of protons an atom has defines what chemical element it is, this number is sometimes called its atomic number.
For example, hydrogen has one proton and sulfur has 16 protons.
Because the mass of neutrons and protons is very similar, and the mass of electrons is very small, we can call the amount of protons and neutrons in an atom its atomic mass.
Atoms move faster when they are in their gas form (because they are free to move) than they do in liquid form and solid matter.
In solid materials, the atoms are tightly packed next to each other so they vibrate, but are not able to move (there is no room) as atoms in liquids do.
The word "atom" comes from the Greek (ἀτόμος) "atomos", indivisible, from (ἀ)-, not, and τόμος, a cut.
The first historical mention of the word atom came from works by the Greek philosopher Democritus, around 400 BC.
Atomic theory stayed as a mostly philosophical subject, with not much actual scientific investigation or study, until the development of chemistry in the 1650s.
In 1777 French chemist Antoine Lavoisier defined the term element for the first time.
He said that an element was any basic substance that could not be broken down into other substances by the methods of chemistry.
Any substance that could be broken down was a compound.
In 1803, English philosopher John Dalton suggested that elements were tiny, solid balls made of atoms.
Dalton believed that all atoms of the same element have the same mass.
He said that compounds are formed when atoms of more than one element combine.
According to Dalton, in a certain compound, the atoms of the compound's elements always combine the same way.
In 1827, British scientist Robert Brown looked at pollen grains in water under his microscope.
The pollen grains appeared to be jiggling.
Brown used Dalton's atomic theory to describe patterns in the way they moved.
This was called brownian motion.
In 1905 Albert Einstein used mathematics to prove that the seemingly random movements were caused by the reactions of atoms, and by doing this he conclusively proved the existence of the atom.
In 1869, Russian scientist Dmitri Mendeleev published the first version of the periodic table.
The periodic table groups elements by their atomic number (how many protons they have.
This is usually the same as the number of electrons).
Elements in the same column, or period, usually have similar properties.
For example, helium, neon, argon, krypton and xenon are all in the same column and have very similar properties.
All these elements are gases that have no colour and no smell.
Also, they are unable to combine with other atoms to form compounds.
Together they are known as the noble gases.
The physicist J.J. Thomson was the first person to discover electrons.
This happened while he was working with cathode rays in 1897.
He realized they had a negative charge, and the atomic nucleus had a positive charge.
Thomson created the plum pudding model, which stated that an atom was like plum pudding: the dried fruit (electrons) were stuck in a mass of pudding (nucleus).
In 1909, a scientist named Ernest Rutherford used the Geiger–Marsden experiment to prove that most of an atom is in a very small space, the atomic nucleus.
Rutherford took a photo plate and covered it with gold foil, and then shot alpha particles (made of two protons and two neutrons stuck together) at it.
Many of the particles went through the gold foil, which proved that atoms are mostly empty space.
Electrons are so small they make up only 1% of an atom's mass.
In 1913, Niels Bohr introduced the Bohr model.
This model showed that electrons travel around the nucleus in fixed circular orbits.
This was more accurate than the Rutherford model.
However, it was still not completely right.
Improvements to the Bohr model have been made since it was first introduced.
For example, any atom with 2 protons should be a helium atom.
Usually, a helium nucleus also contains two neutrons.
However, some helium atoms have only one neutron.
This means they truly are helium, because an element is defined by the number of protons, but they are not normal helium, either.
Soddy called an atom like this, with a different number of neutrons, an isotope.
To get the name of the isotope we look at how many protons and neutrons it has in its nucleus and add this to the name of the element.
So a helium atom with two protons and one neutron is called helium-3, and a carbon atom with six protons and six neutrons is called carbon-12.
However, when he developed his theory Soddy could not be certain neutrons actually existed.
To prove they were real, physicist James Chadwick and a team of others created the mass spectrometer.
The mass spectrometer actually measures the mass and weight of individual atoms.
By doing this Chadwick proved that to account for all the weight of the atom, neutrons must exist.
In 1937, German chemist Otto Hahn became the first person to create nuclear fission in a laboratory.
He discovered this by chance when he was shooting neutrons at a uranium atom, hoping to create a new isotope.
However, he noticed that instead of a new isotope the uranium simply changed into a barium atom, a smaller atom than uranium.
Apparently, Hahn had "broken" the uranium atom.
This was the world's first recorded nuclear fission reaction.
This discovery eventually led to the creation of the atomic bomb.
Further into the 20th century, physicists went deeper into the mysteries of the atom.
Using particle accelerators they discovered that protons and neutrons were actually made of other particles, called quarks.
The most accurate model so far comes from the Schrödinger equation.
Schrödinger realized that the electrons exist in a cloud around the nucleus, called the electron cloud.
In the electron cloud, it is impossible to know exactly where electrons are.
The Schrödinger equation is used to find out where an electron is likely to be.
This area is called the electron's orbital.
Structure and parts
The complex atom is made up of three main particles; the proton, the neutron and the electron.
The isotope of Hydrogen Hydrogen-1 has no neutrons, just the one proton and one electron.
Protons have a positive electric charge and electrons have a negative charge.
A positive hydrogen ion has no electrons, just the one proton.
These two examples are the only known exceptions to the rule that all other atoms have at least one proton, one neutron and one electron each.
Electrons are by far the smallest of the three atomic particles, their mass and size is too small to be measured using current technology.
They have a negative charge.
Protons and neutrons are of similar size and weight to each other, protons are positively charged and neutrons have no charge.
Most atoms have a neutral charge; because the number of protons (positive) and electrons (negative) are the same, the charges balance out to zero.
However, in ions (different number of electrons) this is not always the case, and they can have a positive or a negative charge.
Protons and neutrons are made out of quarks, of two types; up quarks and down quarks.
A proton is made of two up quarks and one down quark and a neutron is made of two down quarks and one up quark.
The nucleus is in the middle of an atom.
It is made up of protons and neutrons.
Usually in nature, two things with the same charge repel or shoot away from each other.
So for a long time it was a mystery to scientists how the positively charged protons in the nucleus stayed together.
They solved this by finding a particle called a gluon.
Its name comes from the word glue as gluons act like atomic glue, sticking the protons together using the strong nuclear force.
It is this force which also holds the quarks together that make up the protons and neutrons.
The number of neutrons in relation to protons defines whether the nucleus is stable or goes through radioactive decay.
When there are too many neutrons or protons, the atom tries to make the numbers the same by getting rid of the extra particles.
It does this by emitting radiation in the form of alpha, beta or gamma decay.
Nuclei can change through other means too.
Nuclear fission is when the nucleus splits into two smaller nuclei, releasing a lot of stored energy.
This release of energy is what makes nuclear fission useful for making bombs and electricity, in the form of nuclear power.
The other way nuclei can change is through nuclear fusion, when two nuclei join together, or fuse, to make a heavier nucleus.
This process requires extreme amounts of energy in order to overcome the electrostatic repulsion between the protons, as they have the same charge.
Such high energies are most common in stars like our Sun, which fuses hydrogen for fuel.
Electrons orbit, or travel around, the nucleus.
They are called the atom's electron cloud.
They are attracted towards the nucleus because of the electromagnetic force.
Electrons have a negative charge and the nucleus always has a positive charge, so they attract each other.
Around the nucleus, some electrons are further out than others, in different layers.
These are called electron shells.
In most atoms the first shell has two electrons, and all after that have eight.
Exceptions are rare, but they do happen and are difficult to predict.
The further away the electron is from the nucleus, the weaker the pull of the nucleus on it.
This is why bigger atoms, with more electrons, react more easily with other atoms.
Some elements, and many isotopes, have what is called an unstable nucleus.
This means the nucleus is either too big to hold itself together or has too many protons or neutrons.
When this happens the nucleus has to get rid of the excess mass or particles.
It does this through radiation.
An atom that does this can be called radioactive.
Unstable atoms continue to be radioactive until they lose enough mass/particles that they become stable.
All atoms above atomic number 82 (82 protons, lead) are radioactive.
Alpha decay is when the atom shoots out a particle having two protons and two neutrons.
This is essentially a helium nucleus.
The result is an element with atomic number two less than before.
So for example if a beryllium atom (atomic number 4) went through alpha decay it would become helium (atomic number 2).
Alpha decay happens when an atom is too big and needs to get rid of some mass.
Beta decay is when a neutron turns into a proton or a proton turns into a neutron.
In the first case the atom shoots out an electron.
In the second case it is a positron (like an electron but with a positive charge).
The end result is an element with one higher or one lower atomic number than before.
Beta decay happens when an atom has either too many protons, or too many neutrons.
Gamma decay is when an atom shoots out a gamma ray, or wave.
It happens when there is a change in the energy of the nucleus.
This is usually after a nucleus has already gone through alpha or beta decay.
There is no change in the mass, or atomic number or the atom, only in the stored energy inside the nucleus.
Every radioactive element or isotope has what is named a half-life.
This is how long it takes half of any sample of atoms of that type to decay until they become a different stable isotope or element.
Large atoms, or isotopes with a big difference between the number of protons and neutrons will therefore have a long half life, because they must lose more neutrons to become stable.
Marie Curie discovered the first form of radiation.
She found the element and named it radium.
She was also the first female recipient of the Nobel Prize.
Frederick Soddy conducted an experiment to observe what happens as radium decays.
He placed a sample in a light bulb and waited for it to decay.
Suddenly, helium (containing 2 protons and 2 neutrons) appeared in the bulb, and from this experiment he discovered this type of radiation has a positive charge.
James Chadwick discovered the neutron, by observing decay products of different types of radioactive isotopes.
Chadwick noticed that the atomic number of the elements was lower than the total atomic mass of the atom.
He concluded that electrons could not be the cause of the extra mass because they barely have mass.
Enrico Fermi, used the neutrons to shoot them at uranium.
He discovered that uranium decayed a lot faster than usual and produced a lot of alpha and beta particles.
He also believed that uranium got changed into a new element he named hesperium.
Otto Hahn and Fritz Strassmann repeated Fermi's experiment to see if the new element hesperium was actually created.
They discovered two new things Fermi did not observe.
By using a lot of neutrons the nucleus of the atom would split, producing a lot of heat energy.
Also the fission products of uranium were already discovered: thorium, palladium, radium, radon and lead.
Fermi then noticed that the fission of one uranium atom shot off more neutrons, which then split other atoms, creating chain reactions.
He realised that this process is called nuclear fission and could create huge amounts of heat energy.
General information on atomic structure
Atomic structure timeline
Atom (science) -Citizendium
Astronomy (from the Greek astron (ἄστρον) meaning "star" and nomos (nόμος) meaning "law") is the scientific study of celestial bodies.
The patterns in the night sky are called constellations.
The objects studied include stars, galaxies, planets, moons, asteroids, comets and nebulae.
Phenomena that are studied include supernovae explosions, gamma ray bursts, and cosmic microwave background radiation.
Astronomy concerns the development, physics, chemistry, meteorology and movement of celestial bodies, as well as the structure and development of the Universe.
Ancient Greek people used the positions of the stars to navigate, and to find when was the best time to plant crops.
Astrophysics is an important part of astronomy.
A related subject, cosmology, is concerned with studying the Universe as a whole, and the way the universe changed over time.
Astronomy is not the same as astrology, the belief that motion of the stars and the planets may affect human lives.
Since the 20th century there have been two main types of astronomy, observational and theoretical astronomy.
Observational astronomy uses telescopes and cameras to observe or look at stars, galaxies and other astronomical objects.
Theoretical astronomy uses maths and computer models to explain the observations and predict what might happen.
Working together, theories predict what should happen and observations show whether the predictions work.
The main work of astronomy is to explain puzzling features of the universe.
For many years the most important issue was the motions of planets; now many other topics are studied.
Early astronomers used only their eyes to look at the stars.
They made maps of the constellations and stars for religious reasons and calendars to work out the time of year.
Early civilisations such as the Maya people and the Ancient Egyptians built simple observatories and drew maps of the stars positions.
They also began to think about the place of Earth in the universe.
For a long time people thought Earth was the center of the universe, and that the planets, the stars and the sun went around it.
This is known as geocentrism.
Ancient Greeks tried to explain the motions of the sun and stars by taking measurements.
A mathematician named Eratosthenes was the first who measured the size of the Earth and proved that the Earth is a sphere.
A theory by another mathematician named Aristarchus was, that the sun is in the center and the Earth is moving around it.
This is known as heliocentrism.
Only a few people thought it was right.
The rest continued to believe in the geocentric model.
Most of the names of constellations and stars come from Greeks of that time.
Arabic astronomers made many advancements during the Middle Ages including improved star maps and ways to estimate the size of the Earth.
They also learned from the ancients by translating Greek books into Arabic.
Renaissance to modern era
During the renaissance a priest named Nicolaus Copernicus thought, from looking at the way the planets moved, that the Earth was not the center of everything.
Based on previous works, he said that the Earth was a planet and all the planets moved around the sun.
This brought back the old idea of heliocentrism.
A physicist called Galileo Galilei built his own telescopes, and used them to look more closely at the stars and planets for the first time.
He agreed with Copernicus.
The Catholic Church thought Galileo was wrong.
He spent the rest of his life under house arrest.
Heliocentric ideas were soon improved by Johannes Kepler and Isaac Newton, who invented the theory of gravity.
After Galileo, people made better telescopes and used them to see farther objects such as the planets Uranus and Neptune.
They also saw how stars were similar to our Sun, but in a range of colours and sizes.
They also saw thousands of other faraway objects such as galaxies and nebulae.
Modern era
In the early 1920s it began to be accepted that the galaxy in which we live, the Milky Way, is not the only galaxy.
The existence of other galaxies was settled by Edwin Hubble, who identified the Andromeda nebula as a different galaxy.
It was also Hubble who proved that the universe was expanding.
There were many other galaxies at large distances and they are receding, moving away from our galaxy.
That was completely unexpected.
In 1931, Karl Jansky discovered radio emission from outside the Earth when trying to isolate a source of noise in radio communications, marking the birth of radio astronomy and the first attempts at using another part of the electromagnetic spectrum to observe the sky.
Those parts of the electromagnetic spectrum that the atmosphere did not block were now opened up to astronomy, allowing more discoveries to be made.
The opening of this new window on the Universe saw the discovery of entirely new things, for example pulsars, which sent regular pulses of radio waves out into space.
The waves were first thought to be alien in origin because the pulses were so regular that it implied an artificial source.
The period after World War 2 saw more observatories where large and accurate telescopes are built and operated at good observing sites, normally by governments.
For example, Bernard Lovell began radio astronomy at Jodrell Bank using leftover military radar equipment.
By 1957, the site had the largest steerable radio telescope in the world.
Similarly, the end of the 1960s saw the start of the building of dedicated observatories at Mauna Kea in Hawaii, a good site for visible and infra-red telescopes thanks to its high altitude and clear skies.
The next great revolution in astronomy was thanks to the birth of rocketry.
This allowed telescopes to be placed in space on satellites.
Space telescopes gave access, for the first time in history, to the entire electromagnetic spectrum including rays that had been blocked by the atmosphere.
The X-rays, gamma rays, ultraviolet light and parts of the infra-red spectrum were all opened to astronomy as observing telescopes were launched.
As with other parts of the spectrum, new discoveries were made.
Discoveries broadly come in two types:  bodies and phenomena.
Bodies are things in the Universe, whether it is a planet like our Earth or a galaxy like our Milky Way.
Phenomena are events and happenings in the Universe.
White dwarf stars
Neutron stars
Galaxy clusters
Superclusters
Burst events are those where there is a sudden change in the heavens that disappears quickly.
These are called bursts because they are normally associated with large explosions producing a "burst" of energy.
Supernovas
Periodic events are those that happen regularly in a repetitive way.
The name periodic comes from period, which is the length of time required for a wave to complete one cycle.
Periodic phenomena include:
Variable stars
Noise phenomena tend to relate to things that happened a long time ago.
The signal from these events bounce around the Universe until it seems to come from everywhere and varies little in intensity.
In this way, it resembles "noise", the background signal that pervades every instrument used for astronomy.
The most common example of noise is static seen on analogue televisions.
The principal astronomical example is: cosmic background radiation.
Telescopes are the main tool of observing.
They take all the light in a big area and put in into a small area.
This is like making your eyes very big and powerful.
Astronomers use telescopes to look at things that are far away and dim.
Telescopes make objects look bigger, closer, brighter.
Spectrometers study the different wavelengths of light.
This shows what something is made of.
Many telescopes are in satellites.
They are space observatories.
The Earth’s atmosphere blocks some parts of the electromagnetic spectrum, but special telescopes  above the atmosphere can detect that radiation.
Radio astronomy uses radio telescopes.
Aperture synthesis combines smaller telescopes to create a phased array, which works like a telescope as big as the distance between the smaller telescopes.
There are way  astronomers can get better pictures of the heavens.
Light from a distant source reaches a sensor and gets measured, normally by a human eye or a camera.
For very dim sources, there may not be enough light particles coming from the source for it to be seen.
One technique that astronomers have for making it visible is using integration (which is like longer exposures in photography).
Astronomical sources do not move much: only the rotation and movement of the Earth causes them to move across the heavens.
As light particles reach the camera over time, they hit the same place making it brighter and more visible than the background, until it can be seen.
Telescopes at most observatories (and satellite instruments) can normally track a source as it moves across the heavens, making the star appear still to the telescope and allowing longer exposures.
Also, images can be taken on different nights so exposures span hours, days or even months.
In the digital era, digitised pictures of the sky can be added together by computer, which overlays the images after correcting for movement.
Data analysis is the process of getting more information out of an astronomical observation than by simply looking at it.
The observation is first stored as data.
This data will then have various techniques used to analyse it.
Fourier analysis in mathematics can show if an observation (over a length of time) is changing periodically (changes like a wave).
If so, it can extract the frequencies and the type of wave pattern, and find many things including new planets.
Subfields of astronomy
Pulsars pulse regularly in radio waves.
These turned out to be similar to some (but not all) of a type of bright source in X-rays called a Low-mass X-ray binary.
It turned out that all pulsars and some LMXBs are neutron stars and that the differences were due to the environment in which the neutron star was found.
Those LMXBs that were not neutron stars turned out to be black holes.
Solar astronomy
Solar astronomy is the study of the Sun.
The Sun is the closest star to Earth at around 92 million (92,000,000) miles away.
It is the easiest to observe in detail.
Observing the Sun can help us understand how other stars work and are formed.
Changes in the Sun can affect the weather and climate on Earth.
A stream of charged particles called the Solar wind is constantly sent off from the Sun.
The Solar wind hitting the Earth's magnetic field causes the northern lights.
Planetary astronomy
Planetary astronomy is the study of planets, moons, dwarf planets, comets and asteroids as well as other small objects that orbit stars.
The planets of our own Solar System have been studied in depth by many visiting spacecraft such as Cassini-Huygens (Saturn) and the Voyager 1 and 2.
Galactic astronomy
Galactic astronomy is the study of distant galaxies.
Studying distant galaxies is the best way of learning about our own galaxy, as the gases and stars in our own galaxy make it difficult to observe.
Galactic astronomers attempt to understand the structure of galaxies and how they are formed through the use of different types of telescopes and computer simulations.
Gravitational wave astronomy
Gravitational wave astronomy is the study of the Universe in the gravitational wave spectrum.
So far, all astronomy that has been done has used the electromagnetic spectrum.
Gravitational waves are ripples in spacetime emitted by very dense objects changing shape, which include white dwarves, neutron stars and black holes.
Because no one has been able to detect gravitational waves directly, the impact of dravitational wave astronomy has been limited.
Satellite (natural)
Astronomy site specifically designed for kids and their parents.
Architecture is designing the structures of buildings.
It uses both art and engineering.
Examples include houses, churches, hotels, office buildings, roads, viaducts, tunnels and bridges.
Architecture is the profession of an architect.
Usually, a person must study at an institution of higher education (university) to become an architect.
There were architects long before there was higher education.
They learnt by being an apprentice to an established architect.
Architecture can do small designs, such as for a garage, or large designs, such as for a whole city.
The capital cities of Brasília, and Canberra were designed.
Architecture often overlaps with structural engineering, and architects and engineers often work together.
In the past, people built huts and wood houses to protect themselves from the weather.
For safety, they were often close together.
Great civilizations like the Ancient Egyptians built large temples and structures, like the Great Pyramids of Giza.
The Ancient Greeks and Romans made what we now call "Classical Architecture".
The Romans, working over 2000 years ago, copied the arch from the Etruscans, who copied it from the Mesopotamians.
Classical architecture was formal, and it always obeyed laws.
It used symmetry, which really means balance, and it used proportion between shapes.
The Golden Mean was a rule which said, (to put it simply) if you are making a room, or any other thing, it will work best if you always make the long side 1.6 times as long as the short side.
There are many 'laws' in classical architecture, like how high the middle of an arched bridge needs to be (which depends on how wide the bridge needs to be).
These laws were learned from thousands of years of experience and they are often used today.
However, today more notice is taken of specific facts, such as what wind speeds occur once or twice in a century.
Several bridges have blown down because that was not properly taken into consideration.
In some parts of the world, like India, the architecture is famous for carving the stone on temples and palaces.
Different architectural styles occur in China, Japan, Southeast Asia, Africa, Mexico, and Central and South America.
Architects in Western Europe in the Middle Ages made Romanesque architecture, then Gothic architecture.
Gothic buildings have tall, pointed windows and arches.
Many churches have Gothic architecture.
Castles were also built at this time.
In Eastern Europe, churches usually had domes.
People added their own ideas and decoration to the Classical Architecture of the past.
The Renaissance brought a return to classical ideas.
In the late 18th century with the Industrial Revolution, people began to invent machines to make things quickly and cheaply.
Many factories and mills were built during, or after this revolution.
Decades later, in the Victorian era, architects like George Fowler Jones and Decimus Burton still followed the Gothic style to build new churches.
Up to this point, buildings were limited in size and style by the strength of the wood and masonry used to construct them.
Gothic cathedrals were among the largest buildings because the gothic arch when combined with buttresses allowed stone buildings to be built taller.
For example, the cathedral in Ulm, Germany is over 500 feet tall.
However, building with stone has its limits, and building too tall could result in collapse.
This happened to the Beauvais Cathedral, which was never completed.
Towards the end of the 19th Century with a second Industrial Revolution, steel became much cheaper.
Architects began to use inventions like metal girders and reinforced concrete to build.
An example is the Eiffel Tower in Paris.
Buildings can now be built taller than ever before.
We call them skyscrapers.
This new technology has made us free from traditional limitations, and because of the new possibilities presented by these materials, many traditional methods of construction and ideas about style were reevaluated, replaced, or abandoned.
Cheap, strong glass soon brought transparent exterior walls, especially for office buildings.
Modernism is the name for the architectural style which developed because of these new building technologies, and its beginnings can been seen as early as 1890.
Modernism can also refer to a specific group of architects and buildings from the early to late 20th century, and so may not be the proper term to use for many building built since then, which are sometimes called "post-modern".
World Heritage Sites
Australian Institute of Architects
Royal Architectural Institute of Canada
New Zealand Institute of Architects
Architecture Citizendium
Architecture sciences
Anatomy is the study of the bodies of people and other animals.
Anatomy is the study of the inside of the body and outside the body.
Anatomy notes the position and structure of organs such as muscles, glands and bones.
A person who studies anatomy is an anatomist.
The history of anatomy dates back to 1600 BC when Egyptians began studying human anatomy.
They discovered the functions of many organs like the liver, spleen, kidneys, heart etc.
and were the first to discover the structure and functions of the lymphatic system.
Academic human anatomists are usually employed by universities, medical schools and teaching hospitals.
They are often involved in teaching and research.
Gross anatomy studies parts of the body that are big enough to see.
Micro-anatomy studies smaller parts.
Body systems
An asteroid is a space rock.
It is a small object in the Solar System that travels around the Sun.
It is like a planet but smaller.
They range from very small (smaller than a car) to 600 miles (1000 km) across.
A few asteroids have asteroid moon.
The name "asteroid" means "like a star" in the ancient Greek language.
Asteroids may look like small stars in the sky, but they really do move around the Sun, while stars only seem to move because the Earth spins.
Like planets, asteroids do not make their own light.
Because of this, some people think "asteroids" is not a good name, and think that the name "planetoid" ("like a planet") would be a better name.
Giuseppe Piazzi found the first asteroid, in 1801.
He called it Ceres, and it is the biggest object in the asteroid belt.
Others, like Juno, Pallas, and Vesta were found later.
In the 1850s so many had been found, that they were numbered by a Minor planet designation starting with 1 Ceres.
Today, astronomers using computerized telescopes find thousands of asteroids every month.
Asteroid impact prediction is one of the purposes.
Asteroids are the leftover rock and other material from the formation of the Solar System.
These rocks were too small to come together to make a planet.
Some are made of carbon or metal.
Depending on what's on the surface, they are classified into various asteroid spectral types including Type M (metal), Type S (stone), and Type C (carbon).
Most asteroids in our Solar System are in the asteroid belt between Mars and Jupiter.
Many are not in the main asteroid belt.
The ones that come close to Earth are called Near-Earth asteroids.
Many scientists think asteroids striking the Earth killed off all the dinosaurs and caused some of the other extinction events.
Afghanistan, officially the Islamic Emirate of Afghanistan (Pashto/Dari: ), is a country in South Asia.
It borders Pakistan in the south and east, Iran in the west, Turkmenistan, Uzbekistan and Tajikistan in the north, and China in the far northeast.
Kabul serves as the country's capital city.
Afghanistan is currently governed by the Taliban, after the collapse of the internationally recognized Islamic Republic of Afghanistan on 15 August 2021.
In early times people passed through it with animals and other goods as it connected China and India with Central Asia and the Middle East.