My Science School

MOONS

The Solar System has more than 190 moons orbiting six of the planets — only Mercury and Venus are moonless. They range in size from Ganymede, a satellite of Jupiter, which is larger than Mercury, to S/2009 S1, a 300-metre moonlet orbiting within Saturn’s rings. All are made of rock, or rock and ice, and many have surfaces littered with impact craters, formed when the moons were bombarded by asteroids in the past. Nineteen Solar-System moons are more than 400 km (250 miles) wide. These large moons are round but the more numerous smaller moons are irregular in shape.

1. THE MOON: The Moon is Earth’s only natural satellite. It is about a quarter the size of Earth and the fifth largest of all moons. The surface of this dry ball of rock is covered in impact craters.
2. IO: Colourful lo is the most volcanic moon in the Solar System. Its surface is constantly being renewed as molten rock erupts through its thin silicate-rock crust, and fast-moving columns of cold gas and frost grains shoot up from surface cracks.
3. EUROPA: The smallest of Jupiter’s four major moons, Europa has an icy surface criss-crossed with networks of brownish grooves. The crust slowly drifts around on top of a deep ocean of liquid water that might be home to alien life.
4. GANYMEDE: At 5,262 km (3,267 miles) across, Ganymede is the largest moon in the Solar System and belongs to the largest family of moons - the moons of Jupiter. Astronomers know of 79, but the number is likely to rise as smaller moons are detected. Ganymede is made of rock and ice with an icy crust.
5. TITAN: Titan is the largest of Saturn’s 62 moons. On its surface are bright highlands, dark plains, and methane lakes and seas. It is the only moon with a substantial atmosphere, which is rich in nitrogen and extends out for hundreds of kilometres.
6. TITANIA: Titania is the largest of the 27 moons orbiting Uranus. Titania and the planet’s other major moons, Oberon, Umbriel, Ariel, and Miranda, are named after characters in English literature. Impact craters and large cracks are seen on its grey, icy surface.
7. IAPETUS: Iapetus is a moon of contrasts. Most of its crater-covered terrain is bright and icy, but the rest appears to be coated by a dark material. It is one of Saturn’s seven major moons, along with Titan, Rhea, Dione, Tethys, Enceladus, and Mimas.
8. TRITON: Triton is by far the largest of Neptune’s 14 moons, a rock-and-ice ball with a young, icy surface. It is nicknamed the cantaloupe as its linear grooves, ridges, and depressions resemble a melon’s skin.
9. SMALL MOONS Most moons are less than 400 km (250 miles) across and irregular in shape, like Saturn’s Epimetheus and Hyperion. Many of these smaller moons, like Mars’s two moons Phobos and Deimos, may have started off as asteroids or comets.

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SUN

The Sun is the closest star to Earth and the centre of our Solar System. This vast ball consists of hot luminous gas kept together by gravity. About three quarters is hydrogen and almost all the rest is helium, with small amounts of about 90 other elements. More than half of the gas is squashed in the Sun’s core where nuclear reactions convert hydrogen to helium and in the process produce huge amounts of energy. This energy is released through the Sun’s surface, most familiarly as heat and light. The Sun has been producing energy in this way for about 4.6 billion years and will do so for another 5 billion or so. This image shows the Sun not as it appears to the human eye, but in ultraviolet light.

1. SIZE The Sun is the largest body in the Solar System. It measures 1.4 million km (870,000 miles) in diameter, which means that 109 Earths could fit across its face. The Sun is made of 330,000 times more material than Earth, and 1.3 million Earths would fit inside it.
2. PHOTOSPHERE Like other stars, the Sun is not solid but has a visible surface called the photosphere - a violent place where jets and flares of gas constantly shoot into space. It is made of 1,000-km (620-mile) wide short-lived granules of rising gas, which together resemble orange peel.
3. TEMPERATURE The temperature of the surface is 5,500°C (9,900°F), and it is this that gives the Sun its yellow colour. Cooler stars are red, hotter ones are white. Inside is much hotter. The core is 15 million°C (27 million°F) and nuclear reactions here convert 600 million tonnes of hydrogen to helium every second.
4. PROMINENCE Giant clouds and sheets of relatively cool gas that loop and arch from the surface are called prominences. This one extends out the equivalent of about 20 Earths. The gas is propelled from the surface by enormous force built up by magnetic fields inside the Sun.
5. SPICULES Short-lived flame-like jets of gas called spicules continuously leap about 10,000 km (6,200 miles) from the surface.
6. ATMOSPHERE Directly above the surface is the chromosphere, the inner atmosphere that extends out about 2,500 km (1,550 miles). Beyond is the corona, which extends for millions of kilometres into space. Only the inner corona is visible here.
7. FACULAE The hottest areas, which appear almost white, are faculae. They are particularly active regions produced by concentrations in the Sun’s magnetic field.
8. SPIN Unlike Earth, which is solid and spins as a whole, different parts of the Sun spin in different amounts of time. The equator makes one rotation every 25 days; regions near the poles take another five or so days.
9. CORONAL MASS EJECTION This twisting prominence was associated with a coronal mass ejection - a large bubble of billions of tonnes of gas that blasted away from the Sun.

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STARS

Stars are huge spinning balls of hot, luminous gas. Each one is unique because stars differ in colour, temperature, size, brightness, and mass. Over time, characteristics change and the star evolves from one stage of star life to another. The key to a star’s life is its mass - the amount of gas it is made from. Mass determines the star’s life span, as well as its other characteristics and how these change.

• STAR BIRTH Stars are formed inside vast clouds of hydrogen gas, such as the Eagle Nebula. A small fragment of cloud collapses under gravity. It becomes increasingly squashed and eventually forms a spinning ball of gas termed a protostar - the first sign of a new star.
• MID-LIFE STARS Most stars glow steadily for most of their lives. During this stage they are known as main sequence stars - the Sun is one. Planets orbit around some stars; others, such as Fomalhaut, have discs of dusty material that may form planets.
• YOUNG STARS A protostar gets denser and hotter as its gas becomes more squashed. When its core reaches about 10 billion °C (18 billion°F), nuclear reactions start. Hydrogen is converted to helium, energy is produced, and the star shines. Stars born at the same time and from the same region of cloud exist as a cluster. Some clusters remain together for millions of years, but eventually their stars drift apart.
• SUDDEN DEATH Ageing stars with eight or more times the mass of the Sun swell into enormous, unstable supergiant stars, which can end their lives in a sudden and spectacular explosion known as a supernova. The exploding star creates an extremely hot gas cloud called a supernova remnant, while its core can collapse to become a rapidly rotating, very dense pulsar or a black hole (where the core collapses in on itself under gravity until it is a hole in space). The material dispersed into space forms clouds, which in turn can give birth to new stars.
• DYING STARS when a star with a mass of up to eight times that of the Sun runs out of hydrogen, it swells up, cools, and becomes a red giant. Eventually, the giant star ejects its outer layers and becomes a planetary nebula. The ejected gas slowly disperses, leaving behind a white dwarf – the tiny, slowly cooling core of the original star.

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CONSTELLATIONS

Stargazers have always looked for patterns in the night sky, using imaginary lines to link stars and form the shape of a creature or object. Known as constellations, these patterns help us navigate the sky. The first of them were used about 4,000 years ago. Today, Earth’s sky is divided into 88 constellations. Just over half are characters from Ancient Greek mythology, such as Orion and Taurus.

NIGHT SKY The region of sky above is centred on the constellation of Orion. Orange lines mark a constellation’s boundary, white lines link its bright stars, and the imaginary pattern is shown in light blue.

1. GEMINI The two brightest stars in Gemini mark the heads of the mythological twins Castor (right) and Pollux (left). Castor’s head is in fact six stars, and Pollux’s is an orange-coloured giant star.
2. TAURUS The head of Taurus the bull is drawn around the Hyades, a V-shaped star cluster. Aldebaran, a red giant star, is the brightest of his eyes. The Pleiades star cluster marks his back.
3. CANIS MINOR AND MAJOR Orion’s dogs are known as Canis Major and Canis Minor. Canis Major, the larger dog, contains Sirius, sometimes called the Dog Star, the brightest star in the night sky.
4. MONOCEROS The unicorn Monoceros was introduced in 1613. It lies in the path of the Milky Way - the glowing band of stars that stretches across the sky.
5. ORION The hunter Orion is visible from nearly everywhere on Earth. His raised arms hold a club and a lion’s head. The red star in one of his shoulders is the red supergiant Betelgeuse.
6. ERIDANUS This constellation is the sixth largest in the sky and represents the river into which Phaethon, the son of the Greek sun god Helios, plunged when he lost control of his father’s golden chariot.
7. PUPPIS According to Greek myth, Puppis is the stern of the ship sailed by legendary hero Jason. Other parts of the ship are represented by the constellations Carina (the keel) and Vela (the sails).
8. LEPUS Orion’s larger dog chases Lepus the hare across the sky. It is one of more than 40 creatures in the night sky. There are also 13 human figures and two centaurs (half-man, half-horse).
9. COLUMBA It is thought that Columba, the dove, is the bird that was sent from Noah’s ark to find dry land, as told in the Bible. It may also represent a dove sent out to guide Jason in Ancient Greek myth.

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UNIVERSE

The Universe is everything that exists, from the smallest particle on Earth to the vast galaxies of deep space. Every part of it, including space and time, came into existence in the Big Bang - a huge explosion that occurred about 13.8 billion years ago. At that time, the Universe looked nothing like it does today, and it has been expanding, cooling, and changing ever since. The hydrogen and helium of the very young Universe formed stars, which in turn produced all the other elements in today’s Universe, including those that make Earth and everything on it, including you.

COSMIC BACKGROUND By looking at the heat left over from the Big Bang, known as the cosmic microwave background radiation, scientists are able to build up a picture of the early Universe. This image is a heat map of the Universe 380,000 years after the Big Bang. It shows that matter was not evenly distributed - the hotter areas (red) are more densely packed regions, where galaxies will form.

THE BIG BANG In the beginning, the Universe was unimaginably small, dense, and incredibly hot. Within a trillionth of a second it ballooned from being smaller than an atom to bigger than a galaxy. It was made of tiny particles of energy that turned to particles of matter. Within three minutes, the Universe was made almost entirely of the nuclei of hydrogen and helium atoms.

FORMATION OF GALAXIES Over millions of years, hydrogen and helium clumped together to form vast clouds. These broke into fragments, which collapsed under gravity and became stars. About one billion years after the Big Bang, a Universe of dwarf galaxies had formed. These collided, merged, and changed shape to become spiral and elliptical galaxies.

BIRTH OF THE SOLAR SYSTEM The Solar System formed from a cloud of gas and dust within the disc of the Milky Way galaxy. The spinning cloud, known as the solar nebula, collapsed in on itself under the force of gravity. It first formed a central sphere - the young Sun - and then the unused material surrounding the Sun formed the planets, moons, asteroids, and comets.

YOUNG MILKY WAY The Milky Way galaxy, the galaxy we live in, formed at the same time as the other galaxies. Not all of today’s Milky Way stars existed at that time. Since its beginning, the galaxy has produced stars that shine brightly for millions or billions of years, but that dies eventually. Their remains produce a new generation of stars.

FORMATION OF THE MOON Earth formed as ever-larger lumps of unused material collided and joined together. Young Earth was hit by a Mars-sized asteroid. Molten rock from the collision splashed into space. This formed a ring of rubble around Earth which clumped to form a large sphere – Earth’s Moon.

HOME PLANET Earth, the third rock planet from the Sun, is the only place in the Universe where life is known to exist. Life started in its oceans at least 3.7 billion years ago. Bacteria-like cells evolved into sea creatures, then land-based plants, and animals. Humans first walked on Earth about 1 million years ago.

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GALAXIES

A galaxy is a vast group of stars held together by gravity — it is thought that there could be some 2 trillion in our Universe. They are not scattered randomly but exist in clusters, vast distances apart. All the galaxies together take up just two millionths of space.

1. SIZE Galaxies are huge. The largest are more than a million light-years across (one light-year is the distance that light travels in a year). The smallest, called dwarf galaxies are a few thousand light-years wide. Andromeda measures 220,000 light-years from side to side.
2. SHAPE A single galaxy is made of billions or trillions of stars arranged in one of four basic shapes: spiral, barred spiral, elliptical, or irregular. Spirals and barred spirals are disc-shaped with arms of stars. In a spiral, such as Andromeda, the arms wind out from a central bulge, while in a barred spiral, they flow from the ends of a central bar of stars. Elliptical galaxies are ball-shaped. Irregular galaxies have no clear shape.
3. ORBITING STARS Galaxies do not behave like solid objects. Each star follows its own orbit around the centre of the galaxy. Stars in a spiral galaxy typically take a few hundred million years to make an orbit. Those further away take longer than those closest to the core.
4. SPIRAL ARMS Stars exist throughout a spiral galaxy’s disc. The arms simply stand out because they are full of very bright young stars.
5. CORE The core of a spiral galaxy typically consists of old red and yellow stars, with a supermassive black hole in its centre. Andromeda’s black hole is as massive as 30 million Suns.
6. DUST LANES Dense clouds and lanes of dust within the galaxy’s disc hide stars from view.
7. DWARF GALAXY M110 is one of the dwarf elliptical galaxies that orbit Andromeda. It is held in its orbit by Andromeda’s gravity.

ANDROMEDA GALAXY Andromeda is one of the closest galaxies to our own, the Milky Way. It is a spiral galaxy 2.5 million light-years away from us - the most distant object that can be seen by the naked eye from Earth.

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Yuri Alekseyevich Gagarin?was a Soviet pilot and cosmonaut who became the first human to journey into outer space, achieving a major milestone in the Space Race; his capsule, Vostok 1, completed one orbit of Earth on 12 April 1961. Gagarin became an international celebrity and was awarded many medals and titles, including Hero of the Soviet Union, his nation's highest honour.

Gagarin was born in the Russian village of Klushino, and in his youth was a foundryman at a steel plant in Lyubertsy. He later joined the Soviet Air Forces as a pilot and was stationed at the Luostari Air Base, near the Norwegian border, before his selection for the Soviet space programme with five other cosmonauts. Following his spaceflight, Gagarin became deputy training director of the Cosmonaut Training Centre, which was later named after him. He was also elected as a deputy of the Soviet of the Union in 1962 and then to the Soviet of Nationalities, respectively the lower and upper chambers of the Supreme Soviet.

On 27 March 1968, while on a routine training flight from Chkalovsky Air Base, Gagarin and flight instructor Vladimir Seryogin died when their MiG-15UTI crashed near the town of Kirzhach. The bodies of Gagarin and Seryogin were cremated and their ashes interred in the walls of the Kremlin. Wrapped in secrecy, the cause of the crash that killed Gagarin is uncertain and became the subject of several theories. At least three investigations into the crash were conducted separately by the Air Force, official government commissions, and the KGB.

Alexei Leonov, who was also a member of a state commission established to investigate Gagarin's death, was conducting parachute training sessions that day and heard "two loud booms in the distance". He believes that a Sukhoi Su-15 was flying below its minimum altitude and, "without realizing it because of the terrible weather conditions, he passed within 10 or 20 meters of Yuri and Seregin's plane while breaking the sound barrier". The resulting turbulence would have sent the MiG-15UTI into an uncontrolled spin. Leonov said the first boom he heard was that of the jet breaking the sound barrier and the second was Gagarin's plane crashing.

According to some conspiracy theories, Gagarin's death was ordered by Soviet leader Leonid Brezhnev, who supposedly was jealous of Gagarin's popularity, overshadowing him at public events.

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Americans were stunned when the Soviets launched the world's first satellite, Sputnik, on Oct. 4, 1957. A month later, Sputnik 2 orbited with a dog as a passenger.

Plans to launch an American satellite began in 1954 and despite strong advocacy from the ABMA, the Eisenhower Administration chose the U.S. Navy’s Vanguard project to lead the nation's efforts for the IGY. However, the first attempt to orbit a Vanguard satellite ended in a launch pad explosion on Dec. 6, 1957.

The job of launching America's first satellite then was given to ABMA, which had been waiting for just such an opportunity. Taking on the task of designing and building the Explorer 1 satellite was the Jet Propulsion Laboratory (JPL) of the California Institute of Technology in Pasadena, California, directed by Dr. William Pickering.

The Explorer 1 effort included the work of the satellite's principal investigator, Dr. James Van Allen, professor of physics and astronomy at the University of Iowa. He had been studying cosmic rays around the Earth. Van Allen developed instrumentation to measure the concentration of ions and electrons in space and to detect cosmic rays. By Jan. 11, 1958, the work of assembling and testing the 30.8-pound, 6-foot, 9-inch Explorer 1 satellite was complete.

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