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Sun Science

The Sun - A star 

The Sun A Star
The Sun is a small and faintly lit star in comparison to many of the millions of other stars in the universe, it is a mere speck in our Milky Way galaxy and our galaxy is just one of the billions of galaxies that we know of. 
However if the dimensions of our Sun are compared to those of the Earth then the Sun is very impressive. It has a diameter of 864,988 miles (1,392,000 kilometres) whilst the Earth’s diameter is 7,927 miles (12,756 kilometres). The Sun’s size is almost incomprehensible - one hundred and nine Earths could fit across the diameter of the Sun, it would take one million Earths to fill the inside of the Sun. Given these statistics the Sun should look closer to the Earth than it does, however it is 93 million miles (150 million kilometres) away from the Earth. The Sun is located on one of the spiral arms of the Milky Way galaxy. In its position within the Milky Way it is the centre of, and by far the largest object in the solar system spinning round once every 27.4 days. It is estimated that the Sun is around 5 billion years old. 
The Sun is made up of several layers, working from the centre outwards these are: the core, the radiative zone, the convective zone, the photosphere, the chromosphere and the corona. The corona stretches out millions of kilometres into space but is only visible during eclipses.
The Sun’s surface is an extremely hot ball of plasma that is neither liquid, gas nor solid. Its surface temperature is 6,000°C or 10,800°F and at the core it is an incredibly hot 15 million degrees Celcius. 
Sun cut
Schematic view of the inner structure of the Sun Image courtesy of NASA 
The Sun’s energy output is produced by nuclear fusion reactions it loses approximately 4 million tons of energy every second in the form of gamma rays. The energy travels out toward the Sun’s surface, during this process the energy is continuously absorbed and re-emitted at lower and lower temperatures so that by the time it reaches the surface it is primarily visible light. 
Sun date
Image of the solar corona in white light (outer circle, blue and white) and X-Rays (inner circle, red, yellow, and black) on April 22, 1994, courtesy of the High Altitude Observatory and the Yohkoh Science team. The dashed circle is the solar radius. 
As well as heat and light the Sun gives off solar wind. This is particles that fly outward from the Sun’s corona at temperatures of approximately one million degrees Celcius and speeds between 300 and 700 kilometres per second. Solar wind can have a dramatic effect on the Earth ranging from power line surges to radio interference and the beautiful aurora borealis.
Sunspots are cooler areas on the surface of the Sun and because of this they seem to be darker than the rest of the Sun’s surface. They are 3,000°C cooler than the rest of the Sun. Sunspots have a great effect on Earth, the magnetic activity that accompanies them can have important consequences for the Earth’s upper atmosphere and weather.


Sun Reference Data 
Diameter: 1. millon km Age:

4.5 billion years

(870,000 miles)

Mass: 330,00 x Earth Distance from Earth:

149.6 million km

(93 million miles)

Density: 1.41 (water = 1) Distance to neares Star: 9.46 million million km
Solar Wind Speed: 3 million km/hr         Luminosity: 390 billion billion Megawatts
Solar Cycle: 8 - 11 years Temperature at Surface: 5,500 °C (9,923 °F)
Core:  14 million °C 

4,000 °C (7,232  °F)

(22 million  °F)

Rotation Periode At Equator:      25 Earth days Rotation Period At Poles:     35 Earth days



For more information on this subject: 

The Sun - Views of the Solar System  An extensive educational site with information on the many effects of the sun on the Earth and Man. Includes Culture, Science, History, hot Sun Facts, Teachers’ Guide and Activities. Easy to navigate and very informative. 

Windows to the Universe -  UCAR University Coporation for Atmospheric Research
Very good site with extensive scientific coverage of the Universe. Section on The Sun contains information ranging from scientific to mythological, games and images. Levels covered - beginner, intermediate and advanced.