Although the Sun was considered a supernatural phenomenon and worshipped as a god in a number of ancient civilisations, it is an average star, a yellow dwarf. It is composed of nearly three-quarters hydrogen, which is converted into helium by nuclear fusion in the Sun’s core,
thereby producing energy (high-energy photons).
The Sun consists of plasma. This is why belts of different latitudes rotate at different rates. Its equatorial areas rotate every 25 days, while polar areas only rotate every 32 days. Its atmosphere is layered (made up of the photosphere, chromosphere and corona), and it gradually merges into the interplanetary medium.
The Sun emits a large amount of energy, mainly in the form of ultraviolet, visible and infrared radiation, but there is also a small amount of other types of radiation, like gamma rays, X-rays and radio waves.
The Characteristics of the Sun
Diameter: 1,392,000 km (109 Earths)
Mass: 1.989 × 1030 kg (333,000 Earths)
Temperature: surface: 5780 K;
nucleus: 13.6 million K; corona: 5 million K
Composition: 73.46% of its mass is made up of hydrogen, 24.85% of helium, 0.77% of oxygen, 0.29% of carbon and 0,63% of other chemical elements (iron, neon, nitrogen, silicon etc.)
Core
The core represents about one fourth of the Sun’s radius. It is the densest and hottest part of the Sun, in which the production of solar energy by thermonuclear fusion takes place. The radiation from the core passes through the layers above it, reaches the photosphere and then exits into space.
Granules
The surface of the Sun has a characteristic grainy texture. The granules, with a diameter of hundreds of kilometres, are the tops of the rising convection currents of hot plasma.
Their outer, dark edges are due to the cooler, descending plasma.
Corona
The outermost, rarefied, but extremely hot part of the solar atmosphere. It can be observed with the naked eye during
total solar eclipses.
The Convective Zone
Large-scale convection takes place in the outer zone of the Sun, which takes up about 25–30%
of the solar radius. This layer is therefore called the convective zone. Heat is transmitted to the photosphere by the flow of the zone’s material. It is then emitted into outer space.
The Radiative Zone
The layer surrounding the core, which is dense and hot enough for the energy produced in the core to pass through in the form of radiation. Its temperature drops gradually outwards from 7 million degrees K to 2 million degrees K.
The Structure of the Solar Atmosphere
The photosphere, composed of granules, is the part of the Sun that is visible and observable to us. It emits 90% of solar radiation. Its average temperature is approx. 5800 K, but
there are also cooler (sunspots) and warmer (faculae) regions.
The chromosphere is the next layer of the atmosphere, made up of rarefied gases and is approx. 5000 km thick. The temperature at the bottom is 6000 K, while at the top it is 20,000 K.
The corona is the outermost, rarefied layer, that is extremely hot in some places, and emits strong X-rays. Solar flares are created when high-speed plasma clouds burst out of the star, and can cause significant damage to our planet if they reach
it. For example, causing geomagnetic storms, and causing auroras to become much more intensive.
Sunspots
Sunspots are dark patches appearing in the photosphere, their temperature is 1–2 thousand degrees K lower than their surroundings. Usually they form groups, and every 11 years there is a significant increase in their numbers.
Solar flares
Occasional changes in the Sun´s magnetic field result in solar flares. These gigantic outbursts of matter can significantly affect living organisms and communication systems on Earth.
The Blazing Sun
Photosphere
Chromosphere
Corona
Our Solar System
15
◄
Our Solar System
14
►
