Published by Patrick Mutisya · 14 days ago
The Sun is a typical medium‑sized star located at the centre of our Solar System. Its main characteristics are:
The Sun is composed almost entirely of two elements:
| Element | Mass Fraction (%) |
|---|---|
| Hydrogen (H) | ≈ 73 |
| Helium (He) | ≈ 25 |
| Heavier elements (metals) | ≈ 2 |
The Sun generates energy through nuclear fusion of hydrogen nuclei into helium in its core. The overall power output (luminosity) can be expressed by the Stefan‑Boltzmann law:
\$L = 4\pi R^{2}\sigma T^{4}\$
where \$L\$ is the luminosity, \$R\$ the solar radius, \$T\$ the surface temperature, and \$\sigma\$ the Stefan‑Boltzmann constant.
Although the Sun emits across the entire electromagnetic spectrum, most of its energy reaches Earth in three main regions:
| Region | Wavelength Range | Typical Example | Approx. Fraction of Solar Output |
|---|---|---|---|
| Infrared (IR) | 700 nm – 1 mm | Heat radiation | ≈ 50 % |
| Visible Light | 400 nm – 700 nm | Yellow‑white light (peak around 500 nm) | ≈ 40 % |
| Ultraviolet (UV) | 10 nm – 400 nm | UV‑A, UV‑B, UV‑C | ≈ 10 % |
When observed from space the Sun’s spectrum peaks in the green part of the visible range, giving it a white appearance. Atmospheric scattering removes much of the shorter‑wavelength blue light, so the Sun looks yellow to an observer on Earth.