Our nearest star is the Sun. The average distance between the Earth and the Sun is 149 597 892 km (1 AU). The lowest distance between them is the perihelium (147 097 000 km), and the highest is the affelium (152 090 000 km).
The Sun's radiation affects the whole Solar System, without the Sun, there would be no planets, so there would be no life on Earth. Considering it's size and radiation, Sun belongs to the average stars, and to the G2V spectral class. It weights 1989 trillion (thirty zeros after the nine) kilogramms, it's diameter is 1 391 960 km. The Sun is 335 000 times heavier and it's diameter is 109 times bigger than the Earth's. The gravitation pickup on the ground is 274,96 m/s2, and the escape velocity is 618,67 km/s.
The Sun is a huge, rotating gas-globe. It's average consistence is 1,41 g/cm3, that is not much higher that the water's (1 g/cm3 ). The temperature in the middle reaches 19 milliů įC, and the consistence is 130 g/cm3 there. The high consistence is made by the upper layers' huge pressure, which can reach 400 billion atmosphere (1 atmosphere is the meteoric pressure on the surface of the Earth) in the middle. The consistence on the surface of the Sun is only 0,001 g/cm3. Despite of the huge consistence, the material of the Sun could everywhere hold it's gas-type. The Sun is mainly made of Hydrogen and Helium (70% Hydrogen, 28% Helium, 2% other). It is rotating like a rigid frame, the equatorial parts are rotating with bigger angle velocity, than the polar ones. The period of the rotation on the equator is 25 days, and on the poles 35 days. 25.
According to our knowledge, the Sun is a big nuclear oven, where the Hydrogen turns into Helium. By the time this transformation-process is running, huge energy gets out. When 1 gramm of Hydrogen transforms, 1012 J energy gets out. The Sun has been transmitting this energy for 5 billion years now, and will be transmitting energy for the next 5 billion years too, as far as itís Hydrogen doesnít run out.
Every single square metres of the Sunís surface transmits 62,86 million J of energy per second, which means that 382,6 trillion J of energy (twenty-three zeros after the 6) gets out on the whole surface in every second. The Earth gets 200 thousand J of energy in every second, which matches 200 billion kW.
The light of the Sun is white-coloured, colours from red to violet give itís spectrum. We can also examine this in the nature, when we see a rainbow.
The Sun is the brightest stars of all in the sky. The unit of the orbsí brilliance is the magnitudo.
The virtual magnitudo is the brilliance we see from the Earth.
The absolute magnitudo is the brilliance the orb would be seen from 10 parsec distance (308,6 billion km).
The scale of the ancient greek astronomer, Hipparkhos helps us to define the brilliance of the stars. He categorized the stars. He was lucky because he made his scale like the stars int he second class were 2,5 times paler than the stars of the first class. This fact was only defined between 1780 and 1800 by William Herchel. He made the first fotometer, which can accurately determine the brilliance of stars, and was the XVIII. centuryís indispensable scientific device.
Later, he modified the 2,5 value to 2,512. This was necessary because the stars in the first class became 100 times brighter than the stars in the sixth class.
Herschel introduced the 0 and the negative classes too. After this, the measure of the brighter orbs became possible. The most pale stars, which are still gross are in the 6th class (6m), the bright Vega, the determining star of the summer sky is int he zero class (accurately 0,02m). Our biggest planetís, the Jupiterís brilliant is between -1,6m and -2,5m.The Venusí approx. -4m, the Moonís at fullmoon is -12m. Our brightest starís the Sunís brilliant is -26m.
The biggest part of the Sun canít be examined directly because of the huge heat and light. The radiation which we can examine comes from the outer parts of the orb, from the corona. The Sunís whole weight is 10 billion times bigger than this.
The bottom part of the Sun, where the examined, continous spectrum arose is called the photosphere. The grossness of this is not more than 200-300 km. We can see the surface as a glowing white disc. The average temperature of the photosphere is 5512įC, itís consistence is so low, we can find only 10 particles per cm3. The photosphere is always moving, because the heat flows push the warmer materials into the outer regions, and int he meantime, the colder goes back to the inner regions.
The picture above illustrates the Sunís chronosphere in the isolated Heliumís discharged ultraviolet area. Helium (neve a gŲrŲg Heliosz = Nap szůbůl) was discovered in 1868 by an english astronomer, Joseph Norman Lockyer, when he broke the Sunís light. His starting idea was that every element makes a unique pattern of straight lines. Once at a solar eclipse, he discovered a not-known spectrum. Later, this was shown ont he Earth, in some minerals. Today we can say that it is the second most common element in the universe. In the picture we can see a protuberance Ė gas eruption. The velocity of these eruptions can reach the 1330 km/s. The knot-shaped formation ont he upper side of the picture floats 400 000 km above the Sunís surface, which is similar to the Earth-Moon distance. The glowing parts, sunspots and eruptions show that the activity of the Sun has reached the maximum, the sunspotmaximum. The period is approx. 11 years.
The photosphere is granular in construction, these granulesí size is 200 Ė 1800 km (approx. Size of Hungary), and they are detached by darker parts. Although their life last for only a few minutes, their brightness and temperature are much more higher than the darker parts. These granules can only be seen with bigger telescopes, at good conditions.
The sunspots are easier to see. Some spots can be seen without telescopes (but with a filter!). These are the photosphereís colder, and darker regions. The parts of it can easily be seen: the darker ones are called the umbra, the lighter ones are called the penumbra. The formation of sunspots is due to the Sunís magnetic activity. The life-span of these formations depend on the size of them. The smaller ones can be seen for only a couple of hours, the bigger ones can be seen for months.
Weíll find the chromosphere above the photosphere. It has a much more higher temperature. Itís consistence immensely small, it usually keeps disappearing in the brightness of the sun-disk. We can only examine it at total eclipse, or with complicated devices, such as a spectrohelioscop or a monochromatic filter. The chromosphere is often shot by the spiculas. These are the amusing flows of the erupting gases.
The size of them is 2000 km, but they can lift up to 10 000 km high. They are only seen for 3-4 minutes. The formation of them may be connected to the granules.
The protuberances are giant shapes, which are mainly Hydrogen-plasmatic gasclouds. They erupt from the surface of the Sun with great velocity, and burst into the corona. The frame of them is a strong magnetic space, which is approx. 10 times stronger than the whole Solar systemís. As the height grows, the gas cools down, the magnetic space weakens, the shapes dissolves. In a calm state, they can even last for a couple of months. They can shove 30 000 km height off the surface. The protuberances put an end on their lives with a huge, powerful explosion. The sun flares are amongst the protuberances too.
This picture was made by the SOHO space capsule. The brightest parts have been uncovered. The white circle shows the size of the Sun.
We usually call the huge sun flares coronal flows too. If there is an eruption, more than 100 million tons of plasm can get into the space. The plasm flows near the surface for a while, and suddenly begins to get further away. Suddenly the gas dilates, and pushes the forcelines high into the corona. The magnetic space brokes, and the gas goes away in a bubble. Donít be afraid! The Sun arose 4,6 billion years ago, but lost only 0,1% of itís weight.
The Sun transmits not only electro-magnetic radiations, but particles too (corpuscular radiation). This is called the sunwind. The sunwind is made up of plasm (ions) and electrons. The sunwind near the Earth is 10-100 particles per cm3. If these particles crash in the atmosphere of the Earth, we can see a light. These are called the polar lights.
The solar eclipse is an amusing, but rare phaenomena. It has made up peopleís interest ages ago. We know from antic memos that they knew the periodicity of the solar eclipse and predicted them.
This natural phenomenon is due to a random coincidence. The Sunís diameter and distance are 400 times bigger than the Moonís, so it can hide the Sun. The eclipses are in connection with the Moonís movement. If teher is a solar eclipse, the Moon is located between the Earth and the Sun. Our Moon goes round the Earth monthly, but why isnít there a solar eclipse in every month? The reason is that there is a 5į angle between the orbit of the Moon and the ecliptics, so the shadow projects to somewhere other place. So there could only be a solar eclipse, when there is new moon, and the Moon is near the ordbital level.
Because of the Earthís complex movement, the shadow of the Moon moves from the west to the east at 0,6 km/s velocity, so we can observe it for a short time. (Max. 7,5 minutes, average 1-4 minutes, but the full procedure lasts for 2,5 hours).
The total eclipse is one of the natureís most beautiful events. Besides the jet black disk, you can admire the brilliant blue corona.
The future of the Sun is not so lucky for us. When the Sunís Hydrogen will go out (approx. 5 billion years later), there will be an irreversible process. The Sunís inside will be made of Helium, and the outer parts will be Hydrogen. The intensity of the thermonuclear processes will decrease, and the shrinking will begin. Suddenly, the Hydrogene atom will start the transformation as though there will have been an explosion, which would blow up the Sun 100 times bigger, and 1000 times brighter, than before. It will drop itís outer gaslayer, which will slowly cover all the planets and orbs of the Solar system, like the fog covers a city. An outsider will see a beautiful gascloud, which has our elf-sized Sun in the middle.