SOME GALAXY FACTS

GALAXY FACTS

Galaxies are groups of billions of stars that are held  together by the force of gravity . Most galaxies are either spiral or elliptical , but some are irregular in shape .

THE MILKY WAY

The best known galaxy is the milky way . The word galaxy itself comes from the Greek word for milk .  This is because before telescope were powerful enough to prove that they were made up of individual stars , galaxies looked like milky or cloudy areas in the sky . Our relatively small solar system is only one of 100-200 billion stars in the milky way galaxy . Which is 100,000 light years in diameter . The sun and all the planets take about 200,000,000 years to complete one orbit around its center .

BRIGHTEST GALAXY

The large magellanic cloud . which is visible only in the southern hemispere , is 170,000 light years from earth and 39,000 light years in diameter .

LARGEST GALAXY

The central galaxy of the abell 2029 galaxy cluster was discovered in 1990 . It is 1070 million light years distant and has a diameter of 5.6 million light years , 80 times the diameter of our own galaxy . It has a total light output equivalent to 2 trillion times that of the sun .

NEAREST GALAXY

The sagittarius Dwarf , discovered in 1994 , is more than 70,000 light years from earth and is being torn apart .

REMOTEST VISIBLE OBJECT 

The most distant thing in the universe that can be seen with the naked eye is the andromeda galaxy , which is 2,309,000 light years from earth . This galaxy has 300 billion stars and a diameter of 180,000 light years . The light we see now from andromeda left there just after the first humans appeared on earth .

MOST DISTANT GALAXY

In 2004 , astronomers at the european southern observatory , chile announsed the discovery of galaxy Abell 135 IR 1916 . It exists an astonishing 13.2 billion light years from earth .

CONSTELLATIONS

Groups of stars form patterns in the night sky , which are called constellations . There are 88 known constellations . The sumerians a middle eastern civilizations , probably named them about 5,000 years ago . They called them after the shapes , objects or animals that they thought they looked like or after mythological characters .

The largest is hydra , the sea serpent and the smallest is crux australis , the southern cross  . Centaurus the centaur has the most stars that can be seen with the naked eye . Others include Aquila the Eagle , Draco , the Dragon , Canis , Major , the Great dog and Orion the Hunter .

SOLAR SYSTEM

The solar system was formed about 4,560 million years ago . It is made up of the nine planets - Mercury , Venus , Earth , Mars , Jupiter , Saturn , Uranus , Neptune and Pluto , as well as their moons , comets and other bodies . These all orbit around our Sun to which they are attracted by gravity . Lets see the planets one by one .

1. MERCURY

Diameter : 4,880 km 

Mass : 3,302,000,000,000 tonnes

Average distance from sun : 57,909,175 km

Rotation : 58.6462 days

Avg temperature : + 166.86`c

Moons : 0

Mercury was named after the speedy messenger of the god because it seemed to move more quickly than the other known planets . In 2004 NASA launched MESSENGER probe , which is due to reach Mercury in 2011 .

2. VENUS

Diameter : 12,103.6 km

Mass : 48,690,000,000,000 tonnes 

Avg distance from sun : 108,208,903 km

Rotation : 243.0187 days

Orbit : 224.701 days

Avg temperature : +456.85`c

Moons : 0

In size , mass , density and volume Venus is the planet most similar to Earth . Venus rotates backwards , from east to west , so the Sun would appear to rise in the east and set in the west . In april 2006 the European Space Agency Venus express spacecraft reached Venus . 

3. EARTH

Diameter : 12,756.3 km

Mass : 59,720,000,000,000 tonnes 

Avg distance from sun : 149,600,000 km

Rotation : 0.99727 days

Orbit : 365.256 days

Avg temperature : +15`c

Moons : 1

Earth is a watery planet 70 % of its surface appears blue and the only one that can support life . From space astronauts have observed cities , forest fires , roads , airports , dams and other large structures such as the Great Pyramid and the Great wall of China .

4. MARS

Diameter : 6,794 km

Mass : 6,421,900,000,000 tonnes 

Avg distance from sun : 227,940,000 km

Rotation : 1.025957 days

Orbit : 686.98 days

Avg temperature : -63`c

Moons : 2

Several space probes have flown past or landed on Mars , providing information on its atmosphere and features , such as the volcano Olympus Mons . This stands 27 km high more than three times the height of Mount Everest . The latest craft to visit the red planet is Mars Reconnaissance Orbiter , which began a four year orbit in 2006 .

5. JUPITER

Diameter : 142,984 km

Mass : 18,986,000,000,000,000 tonnes 

Avg distance from sun : 778,412,010 km

Rotation : 9 hours 53 minutes

Orbit : 11 years 314 days

Avg temperature : +14.85`c to +19.85`c

Moons : 63

Jupiter is the largest planet in the solar System and is big enough to contain more than a thousand Earths . Four of its many moons were among the first ever astronomical discoveries made with a telescope , by Galileo in 1610 . More were identified by later astronomers and in 1979 by the space probe Voyager2.

6.SATURN

Diameter : 120,536 km

Mass : 5,684,600,000,000,000 tonnes 

Avg distance from sun : 1,426,725,400 km

Rotation : 10 hours 34 minutes 

Orbit : 29 years 168 days

Avg temperature : -139.5`c

Moons : 34

Saturn is the second largest planet but the least dense . Its distinctive rings are made of pieces of ice and rock which were probably parts of comets and asteroids . These rings are being examined by the joint NASA/European Space Agency project Cassini/Huygens . Launched in 1997 , cassini began a four year orbit of the ringed planet in july 2004 .

7.URANUS

Diameter : 51,118 km

Mass : 868,320,000,000,000 tonnes 

Avg distance from sun : 2,870,972,200 km

Rotation : 17 hours 17 minutes

Orbit : 84 years 4 days

Avg temperature : -197.15`c

Moons : 27

All the named satellites of Uranus are called after characters from either William Shakespeare's plays or Alexander Pope's poem " The Rape of the Lock " . Some have only recently been discovered and as yet do not have names . Uranus has rings like those of Saturn , but they are visible only with a powerful telescope .

8.NEPTUNE

Diameter : 49,522 km

Mass : 1,024,700,000,000,000 tonnes 

Avg distance from sun : 4,498,252,900 km

Rotation : 16 hours 7 minutes

Orbit : 164 years 298 days

Avg temperature : -200.15`c

Moons : 13

The orbits of Neptune and Pluto cross each other . Neptune is the furthest of the nine planets currently , and for 20 years of every 248 . Surface winds are the strongest of any planet at up to 2,000 km/hr . Neptune's year is so long that it has not completed an orbit round the Sun since its discovery and will not until 2011 .

9.PLUTO 

Diameter : 2,390 km

Mass : 129,000,000,000 tonnes 

Avg distance from sun : 5,913,520,000 km

Rotation : 6 days 9 hours 18 minutes

Orbit : 247 years 256 days

Avg temperature : -215.35`c

Moons : 3 ( Charon and two unnamed , discovered in 2005 )

Though discovered by an American , Pluto's name was suggested by an 11 year old British school girl , Venetia Burney .

SUN FACTS

The sun is 149,597,893km from Earth and has a diameter of 1,391,940 km . This is more than 100 times larger than Earth . Its mass is equivalant to 99.98 per cent of the mass of the entire Solar System .

Elements 

The sun is mostly made up of two light gases , 75 per cent hydrogen and 23 per cent helium , with relatively small quantities of other elements , including metals such as gold . Helium was discovered in the Sun before it was detected on Earth . Its name comes from helios , the Greek word for sun .

Temperature

The sun has a surface temperature of 5,880k but it can be 56,000,000k at its core . ( k represents kelvin , which is an astronomical temperature , it can be converted to Celsius by substracting 273.16. ) at the Sun's center , nuclear fusion constantly changes hydrogen into helium and the energy and heat released from this process rise to the surface . The yellow surface we see is called the photosphere .

The corona 

The outermost layer of the Sun extends millions of kilometers  into space but is visible only during eclipses . At a height of 75,000km in the corona , the temperature may reach 2,000,000k .

Rotation 

The Sun rotates once every 25.4 days , but because it is not solid like a planet or moon , the poles spin at diffrent rate , taking as much as 36 days to complete a single revolution .

Solar eclipses

When the moon lies between the Earth and the Sun , its blocks out the light causing either a partial or total eclipse . At this time astronomers are able to observe the corona in detail .

MOON FACTS

Earth's Moon is the most familiar and also the largest satellite in relation to its planet in the entire Solar System . It is the first body in the Solar System on which vehicles from Earth landed , and the only one to be explored by humans .

Diameter : 3,475.6 km

Distance from Earth : 406,711km ( furthest , 1912 )

                                   to 356,375km ( closest , 1984 ),

                       384,403km ( average )

Mass : 734,556,000,000 tonnes 

Rotation : 27 days 7 hours 43 minutes 11.5 seconds

Surface temperature : -163`c to +117`c

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