Basic Astronomy


Probably the Sun is the first and only heavenly body in which human spares much of his time and efforts than any other. This is not only because the Sun is the fundamental source of energy and life in Earth but also for it is the closest star full of so many processes that are likely to happen within any other distant star. This 1.9 x 1030 kg massive star, sitting at the centre of the solar system, 107 km away from Earth contains enormous mysteries and beauties within it.


We were so habituated in Sun that we even started to express astrophysical entities in terms of solar respect. For instance, we measure other star's mass in the unit of solar mass, Mo and radius in units of solar radius Ro. Like any other star, Sun's main source of energy is nuclear fusion, 90 percent of which is P-P chain reaction. Calculation shows age of the Sun is 10 Billion years and it belongs to G2V spectral class. Sun used only 0.1 percent of its mass, which is Hydrogen, as fuel for nuclear reaction and converted it into Helium.

For studying the Sun we distribute it in two main parts: Interior part and the Atmosphere. The atmosphere has three different parts. The inner most part is called Photosphere. It is extended outwards up to 300 to 500 km from the interior. At the inner boundary the temperature is about 8000K while at the outer boundary temperature is reduced to 4500K. The next layer is called Chromosphere. It is 500 km thick. At the inner boundary, it has temperature 4500 K - 6000 K. The outer boundary of this part is called transition region where the temperature reaches 106 K. Chromosphere gradually ends into Corona, which extends into the outer space up to a few solar radii. Corona consists of ionized elements and its temperature is about a million Kelvin. Both Chromosphere and Corona can be visible during total solar eclipse. The interior part consists of radiation zone and convection zone. Nuclear reaction occurs in the radiation zone also called core. The temperature at the core is about 1.5 x 107 K.

Sun spots are the dark patches seen on the surface of Sun. They are very mysterious and were unexplained for long time. However they are helpful to study Sun structure. Basically Sun spots are regions of relatively low temperature, so they emit less photon and appear dark. Number of sunspot changes with a period of nearly 11 years from maximum number to minimum and vice versa.
(source: wikipedia)
Sunspots can be big enough to accommodate even three earths in it. Interesting thing inferred by these sunspots is that the Sun is rotating; more interestingly the period of rotation is 30 days at the Polar Regions while that is 25 days at the equator. This differential rotation brings on pressure gradient which further helps to develop twists in the magnetic field lines within the Sun interior. When twisted lines break up and come out to the surface due to magnetic buoyancy, they create Solar flares. Giant flares can reach even 100,000 Km high from Sun surface. The Sunspots are supposed to be the roots of those unplugged solar magnetic lines. They are also associated with some anomaly in the convection current underlying the sun surface. Beside rotation the Sun is also observed to have periodic vibration in nearly every 5 minutes.

Observing Sun in naked eye or directly with telescope is strongly discouraged as it may hurt your eyes permanently and even may make you blind.

Page Editor: Deb Sankar Bhattacharya

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