Sun

History

The Sun was worshipped since ancient times. In the 19th century, Joseph Fraunhofer discovered dark lines in its spectrum, and in 1925, Cecilia Payne-Gaposchkin proved that the Sun consists mainly of hydrogen. In the 20th century, physicists uncovered the source of its energy — thermonuclear fusion.

How it works

In the Sun's core, under enormous pressure and temperature, hydrogen nuclei fuse into helium, releasing energy. This energy slowly pushes through the star's bulk to the surface and is radiated into space. Thus the Sun has been shining for 4.6 billion years and will last about as long again.

History

The Sun was worshipped since ancient times. In the 19th century, Joseph Fraunhofer discovered dark lines in its spectrum, and in 1925, Cecilia Payne-Gaposchkin proved that the Sun consists mainly of hydrogen. In the 20th century, physicists uncovered the source of its energy — thermonuclear fusion.

How it works

In the Sun's core, under enormous pressure and temperature, hydrogen nuclei fuse into helium, releasing energy. This energy slowly pushes through the star's bulk to the surface and is radiated into space. Thus the Sun has been shining for 4.6 billion years and will last about as long again.

History

The Sun has been an object of worship and study since ancient times. A scientific breakthrough occurred in 1814 when Joseph von Fraunhofer systematically described the dark lines in the solar spectrum. In 1925, Cecilia Payne-Gaposchkin, applying ionization theory, proved that the Sun and stars consist mainly of hydrogen. The mechanism of thermonuclear fusion was revealed by Hans Bethe and Carl von Weizsäcker in the 1930s. In the second half of the 20th century, helioseismology allowed probing the Sun's interior, and spacecraft studied the solar wind and corona.

How it works

The Sun's equilibrium is described by the hydrostatic equation: dP/dr = -G M(r) ρ / r². The rate of thermonuclear reactions strongly depends on temperature: for the proton-proton chain ε ∝ ρ T⁴. The energy release in the core is about 0.3 μW/cm³. In the radiative zone, energy is transported by radiation (opacity coefficient κ), in the convective zone by convection, according to the Schwarzschild criterion. The magnetic field is generated in the tachocline through the Ω-effect, and the α-effect is realized by turbulent convection. Flares are explained by magnetic reconnection — the rapid release of energy, described by magnetohydrodynamics. Doppler measurements allow studying surface motion and internal oscillations. The radiation spectrum is modeled by Planck's law with corrections for chemical composition and opacity. Detection of solar neutrinos confirms the models of thermonuclear burning.

Open problems & fun facts

The solar neutrino problem: partly solved by the discovery of oscillations, but discrepancies remain in the low-energy region.; The mechanism of solar corona heating to millions of degrees is not fully established.; The nature of the 11-year activity cycle: why it is stable and whether future cycles can be predicted.

💡 The solar corona's temperature exceeds 2 million degrees, which is more than 200 times hotter than the photosphere. This contradicts everyday experience: moving away from a heat source, we expect cooling, but here the outer layers of the star turn out to be much hotter than the inner ones.