Читать книгу Exploring the Solar System - Peter Bond - Страница 36

The Sun is our nearest star, some 270,000 times closer than the next closest stars of the Alpha Centauri system. When compared with other stars, there is nothing out of the ordinary about the Sun. However, since it accounts for more than 99% of the mass of the Solar System, the Sun is undoubtedly the dominant influence over the local galactic neighborhood. It is the Sun's gravitational influence which holds the planets in their orbits and controls a region of space that extends in all directions for several light years.

The Sun influences every aspect of our lives, most obviously through its tremendous output of light and heat. Plants grow upward toward the Sun and soon die if the supply of light is cut off. Humans require sunlight to produce vitamin D. If sunlight is blocked by thick clouds or disappears at night, the temperature drops noticeably. In winter, when the Sun is above the horizon for shorter periods, the lower temperatures often result in frost and prolonged snow cover. If the Sun was extinguished tomorrow, Earth would soon turn into a frozen, lifeless planet, blanketed in ice.

In recent decades, space observatories have examined our nearest star in incredible detail and at many different wavelengths. Nevertheless, there are still many mysteries that remain to be unraveled, including the causes of solar flares, the mechanism that causes such extreme heating of the corona, and the origin of its 11‐year periodic cycle of surface activity.