THE SUN - Inside The Sun

INSIDE THE SUN

Our Nearest Star, The Sun, is a huge globe of hot gas. It is 109 times the diameter of planet Earth and has a mass 745 times bigger than all the planets in the Solar System put together. Without the continuous warming rays of our Sun there would be no life at all on Earth. The source of the Sun’s scorching heat is a huge nuclear furnace deep beneath the Sun’s photosphere. It has been blazing for about 4.6 billion years and will continue to burn for about the same time again until its hydrogen and helium fuel runs out.

SUN’S STRUCTURE

The sun’s energy is generated in the core, where it is so hot-15 million °C-that atoms of gas are ripped apart, leaving just their bare nuclei, or centers. The energy travels through the radiative zones to the surface, or photosphere, where it leaves the Sun, mostly as light and infrared radiation. On the way, it passes through the Sun’s atmosphere, which extends millions of kilometers into space.

NUCLEAR REACTIONS

At the Sun’s core, energy is released as hydrogen changes into helium during nuclear fusion reactions. Four hydrogen nuclei (protons) fuse, or join together, to make one helium nucleus. Particles called positrons and neutrinos are released, along with packets of radiation energy called gamma-ray photons.

JOURNEY OF A PHOTON

Aphoton of radiation from the core takes 30,000 years to reach the surface. It collides with gas particles, giving it a random path. At each collision, the photon loses energy and may split into many more photons. Starting as a gamma ray in the core, it emerges from the surface the as a burst of visible light.

CORE	RADIATIVE ZONE	CONVECTIVE ZONE
Core is the central region where nuclear reactions occur. It occupies 2% of the volume of the Sun, but contains 60% of its mass.	Radiative zone is region where energy leaves the core in the form of streams of photons.	Convective zone is region where energy is carried by convection cells-rising and falling currents of hot gas.
PHOTOSPHERE	BEYOND PHOTOSPHERE	SUN’S ENERGY
Photosphere is the Sun’s visible surface.	Beyond the photosphere is the solar atmosphere, which consists of the chromosphere and the corona.	The Sun pours out enough energy each second to meet the needs of the whole world for more than 1,000 years.

SOLAR NEUTRINOS

Neutrinos produced by nuclear reactions in the Sun’s core travel out into space. Most of these ghostly particles pass through the earth, but neutrino telescopes can detect a few. The Sudbury Neutrino Observatory, Canada, is 2 km underground to protect it from cosmic rays, which would affect its measurements. Astronomers are puzzled because they find less than half the number of neutrinos they expect.

SOLAR OSCILLATIONS

The photosphere - the Sun’s surface – moves up and down in complex patterns of vibration. Most of these vibrations, of solar oscillations, are caused by sound waves generated below the surface in the convective zone and trapped inside the Sun. By carefully mapping the vibration patterns of the photosphere, scientists can work out the Sun’s internal structure.

SUN QUAKES

Some solar oscillations may be caused by sunquakes. These are shock waves that spread out from the edges of turbulent circulations of hot gas called convection cells. The energy carried by the shock waves is equal to the energy that would be released by detonating 1.2 billion tonnes of high explosive.

SOLAR COMPOSITIONS

The Sun’s outer layers are 73 per cent hydrogen, 25 per cent helium, and 2 per cent other elements. In the core, where more than 600 million tonnes of hydrogen are converted into helium every second, the amount of hydrogen is only about 34 per cent, while the amount of helium is about 64 per cent.

VITAL STATISTICS
Distance from Earth	147.1 million km
Diameter	1.4 million km
Mass (Earth = 1)	330,000
Average density (water = 1)	1.41
Luminosity	390 quintillion megawatts
Average surface temperature	5,500 °C
Core temperature	15 million °C
Rotation period	25.4 days (at equator)
Age	4.6 billion years

EVOLUTION OF SOLAR THEORIES

In the early 19^th century some scientists believed that the Sun’s was a vast lump of burning coal. Others thought that it was covered with volcanoes, or that it was kept hot by meteorites bombarding the surface.

In 1854, German physicist Hermann von Helmholtz (1821-94) proposed that the Sun was being heated as it shrank under its own weight.

Scientists in the 1920s realized that nuclear reactions power the Sun.

In1928, German physicists Hans Bethe (1906- ) and Carl von Weizsäcker (1912- ) independently worked out how hydrogen converts into helium inside the Sun.