Jupiter was king of the Gods in Roman mythology.

All of the planets in the Solar System can fit into Jupiter. 1400 Earth's can fit into Jupiter. Jupiter's mass is only 318 times bigger than Earth's. , but the planet's Its density is Earth, indicating that the planet consists of gas. ¼ of the It takes only to rotate around its own axis. This speed results 10 hours in a bulge in its equator. Its colourful surface is caused by the clouds. One famous cloud is the rust-coloured GREAT RED SPOT. The colour is formed by chemicals which were affected by UV waves, lightning, electric discharges and heat. Some people believe that some of these compounds have a relationship with the organic substances which formed life on Earth. MOONS: Jupiter has 16 moons. The largest 4 are Lo, Europa, Ganymede and Callisto.

In Roman mythology, Saturn was Jupiter's father.

Saturn is the 2nd largest planet in the Solar System although its son is bigger than it. Galileo discovered in 1610 Saturn's rings with his telescope. He thought that the rings were attached to the planet, so he called them ansae (handles).

In 1655, Huygens described the rings correctly. He wrote a group of letters in code. When his letters were translated it said, "It is girdled by a thin flat ring, nowhere touching, inclined to the ecliptic." The rings are named in order of their discovery. From the planet outwards they are known as D,C,B,A,F,G,E. In the 19th century, James Clerk Maxwell discovered that each ring is made out of 100,000 tiny particles. Each one had it's own orbit.

In the 1980's a famous theory called CHAOS started to develop. One of the phenomena of this theory occurs in Saturn's rings. Each particle has its own orbit. It always stays in its orbit and never moves 1 mm towards any direction. Using mathematics, it was discovered that if any particle moved, it will be "kicked" out of Saturn instantly. It will be released and it will travel away for ever.

MOONS: Saturn has at least 18 moons, more than any other planet. Its largest is Titan (that's from where Titanic got its name. It's the Latin word for large).

Uranus was in Roman mythology the God of heavens, Saturn's father and Jupiter's grandfather.

Uranus is as bright as a star. Its orbit intersects with Saturn's and Neptune's. It was accidentally discovered in 1781 by Sir William Herschel accidentally.

It was originally called Georgium Sidus (Star of George) in honour of King George III. Later, it was called Herschel. Finally, it got its name Uranus which was proposed by German astronomer Johann Elert Bode in the late 1800's. It's unique for its rotation. Its axis is 50 degrees to its equator. In other words it revolves sideways. Sometimes the "North" pole faces the Sun directly, which means that it's summer there. It has at least 11 rings.

MOONS: It has 15 moons. The largest 5 are Miranda, Ariel (two characters in Shakespeare's play), Umbreil, Titania and Oberon.

Neptune was the Roman god of the sea. It was given this name because of its blue surface. Neptune is the fourth largest planet in the Solar System. Its average distance from the sun is 4,500000000 km. Its diameter is about 50,000 km or 4 times bigger than the Earth's. It's 72 times bigger in volume but 17 times bigger in mass. That's because it has a low density. It's a "gas giant" planet with an atmosphere surrounding a liquid surface which sometimes solidifies into a solid core. It's mainly made out of hydrogen and helium. Its blue colour comes from methane which makes up only 3% of the atmosphere. Its core has more metals and rocks than the other gas giant planets. Its magnetic field is tilted more than 50 degrees to the rotation axis. MOONS: Neptune has 8 moons; only 2 can be seen from Earth. Its largest moon, Triton has a surface made out of ice that is cracked.

Early Developments

In the past 100 years astronomists, chemists, meteorologists and physicists improved the understanding of the Universe, stars and Earth. In the 7th and 6th centuries BC, the Greek philosophers Thales and Pythagoras said that the earth is a sphere; in the 3rd century BC the astronomer Aristarchus said that the earth moved around the sun. Hipparchus, another Greek philosopher, prepared information about stars and the motions of the moon. In the 2nd century AD Ptolmey of Alexandria was the first to place the Earth at the center of the solar system in the Ptolemaic system.
 
 

Scientific Discoveries
 
 

1400 years later, Polish astronomer, Copernicus explained the Ptolmaeic system in more details involving other planets orbiting the Sun. Danish astronomer, Tycho Brahe influenced the laws of planetary motion made by Johannes Kepler. One of his 3 laws stated that orbits were elliptical. Galileo, Halley, Herschel and James Jeans made contributions to astronomy.

In 1654 the German physicist Otto von Guericke proved that a vacuum could be maintained, proving that earlier theories were wrong. Sir Isaac Newton wrote down the laws of forces and universal gravitation and motion. His laws helped scientists to design rockets and predict the motion of satellites. His equation:

F= GMm/d2

is probably one of the most important equations in the history of physics. In this equation, M and m were the masses of 2 objects, G was a universal constant (a very small number) and d was the distance between the 2 objects.
 
 

Cosmology
 
 

Cosmology is the study of the universe as a whole; its future and origin.

The Dutch astronomer Jan Hendrik Oort found that the sun takes approximately 250 million years to travel once around the center of our galaxy, so he was able to calculate that the mass of the Milky Way is roughly 100 billion times the mass of the sun.

Several of the stars which Hubble studied were pulsating stars called Cepheid variables. By measuring their period of pulsation, astronomers can determine the brightness of these stars. By comparing the real brightness of these Cepheids with the known brightness of nearby Cepheids, Hubble proved that these nebulas lie far outside the galaxy. This meant that the thousands of spiral and elliptical nebulas were galaxies outside the Milky Way Galaxy with each containing hundreds of billions of stars.
 
 

Big Bang Theory
 
 

In 1929 Hubble compared the distances he had estimated for various galaxies with the red shifts determined by Slipher for the same galaxies. He found that the more remote the galaxy, the higher was its velocity. This important relationship has become known as the law of the red shifts, or Hubble's law; it states that the velocity of a galaxy is proportional to its distance. The ratio of the velocity of a galaxy to its distance (the Hubble constant) is estimated to be between 50 and 100 km/sec per megaparsec (one megapersec is about 3 million light years).

Because galaxies in all directions seem to recede from the Milky Way, it might appear that the Milky Way is at the center of the universe. This is not the case, however. One can imagine a balloon with evenly spaced dots painted on it. As the balloon is blown up, an observer on each spot would see all the other spots expanding away from it, just as observers see all the galaxies receding from the Milky Way. The Universe is expanding like a balloon.

At the present time, estimates of the age of the universe range between 7 and 20 billion years, so they do not conflict with the age of the earth. Lower estimates in this range, however, seem to conflict with the age of the oldest stars, which are believed to be about 16 billion years old.

2 scientists found the idea of a sudden beginning to the universe which was unsatisfactory. It stated that the Universe appeared the same from any location, but not for all times. They proposed that the decrease in the density of the universe caused by its expansion is exactly balanced by the creation of matter condensing into galaxies, thereby maintaining forever the present appearance of the universe. The steady-state theory is no longer accepted by most cosmologists, after the discovery of cosmic background radiation in 1965.

In 1948 the Russian-American physicist George Gamow suggested the Big Bang Theory. Gamow proposed that the universe was created in a gigantic explosion and that the various elements observed today were produced within the first few minutes after the big bang, when the extremely high temperature and density of the universe would fuse subatomic particles (e.g. electrons, protons, positrons, neutrinos, etc.) into the chemical elements (e.g. hydrogen, helium, lithium, etc.). Hydrogen and helium would have been the primary products of the big bang, with heavier elements being produced later within stars, that's because there's less energy needed to produce such elements. This theory, however, provided a basis for understanding the earliest stages of the universe and its subsequent evolution. The extremely high density within the primeval atom would cause the universe to expand rapidly. As it expanded, the hydrogen and helium would cool and condense into stars and galaxies. This explains the expansion of the universe and the physical basis of Hubble's law.

According to Gamow's theory, as the universe expanded, the radiation from the big bang would continue to cool. By today it should be a temperature of about 3 K (about -270° C/-454° F). This relic radiation was detected by radio astronomy in 1965, thereby providing what most astronomers consider to be confirmation of the big bang theory. The radiation was probably gamma rays which has a lot of energy. This radiation's wavelength increased slowly into radio waves which is very cold. One day, there will be no heat at all in the Universe (absolute zero, 0K).
 
 

Evolution of the Universe

One of the unresolved problems in the expanding universe model is whether the universe is open (that is, whether it will expand forever) or closed (whether the universe will contract again).

One approach to solving this problem is to determine whether the mean density of matter in the universe is more than the critical value in Friedmann's model. The mass of a galaxy can be measured by observing the motion of its stars. If the mass density of the universe is estimated by multiplying the mass of each galaxy by the number of galaxies, the density is found to be only 5 to 10 percent of the critical value. The mass of a cluster of galaxies can be determined by measuring the motion of the galaxies within it. Multiplying this mass by the number of clusters of galaxies results in a much higher mean density, one approaching the critical limit that would indicate the universe is closed. Scientists believe that there's more mass than we can see. The so-called dark matter, inside the cluster but outside visible galaxies. This dark matter can be a series of black holes. Until the missing mass phenomenon is understood, this method of determining the fate of the universe will be useless.

Because light from the most remote galaxies has been traveling for billions of years, the universe can be observed as it appeared in the distant past. If a star is 13 billion light years away, we will look at it and see what happened to it 13 billion light years ago. When you are in Nasa recording what a probe can see, you can't say, "Oh, please, can the probe zoom in?" By the time the message of zooming reaches the probe, the probe itself will move for a few thousand km! Using new, highly sensitive infrared detectors called large format arrays, astronomers at Mauna kA Observatory have recorded hundreds of the faintest galaxies ever observed, most of them clustered at a distance of 6 billion light years. This proves that the universe of 6 billion years ago was not a mixture of galactic types, instead only one type can be seen; a class of small, galaxies containing far fewer stars than the Milky Way or others of its kind. The young spiral and elliptical galaxies observed today may thus have formed from the combination of low-mass galactic fragments late in the history of the universe, long after the big bang, and represent just one of a series of stages in the evolution of the universe.

Much current work in cosmology is concentrated on developing a better understanding of the processes that must have shaped the big bang. Inflationary theory, made in the 1980s, made difficulties in Gamow's theory by involving recent advances in particle physics. Such theories have also led to the possibility of an infinity of universes produced according to the inflationary model. Most cosmologists, however, are more intent on locating the whereabouts of dark matter, while a minority, following the Swedish Nobel physicist Gosta Alfvén, believe the idea that plasma (sub-atomic particles separated from atoms) phenomena—not just gravity—can help us to understand the history of the Universe.