The Sun sends the Earth more than light and heat. It ejects a continuous stream of fast charged particles in all directions, a phenomenon scientists call the solar wind. Like terrestrial weather, the solar wind goes through cycles, becoming stronger and weaker. Strong solar wind affects electronic equipment such as communications satellites and power lines. The Earth’s natural magnetic field captures most of the solar wind and produces glowing auroral displays at high latitudes.
The Sun
The Sun is mostly made of hydrogen and helium. In the Sun’s core, gravity squeezes atoms together, fusing them into new elements and releasing energy. The Sun’s temperature varies between about 15 million degrees C in the core and 5,500 degrees at the surface. The heat strips electrons from atoms, making an electrically conductive gas called a plasma.
Corona
A glowing layer of plasma called the corona surrounds the Sun. Its temperature runs between 3 and 5 million degrees Celcius. In the corona, the Sun’s heat and magnetic fields churn protons and electrons. Most of them stay in the corona, but the fastest escape the Sun’s gravity at speeds up to 900 km/second. Once in space, these particles become the solar wind.
Mass of Solar Wind
The Sun sends one million tons of matter every second into space as solar wind. Since the Sun’s mass is 2 x 10^27 tons, only a tiny fraction of its total has been lost this way. By the time it reaches the Earth, according to NASA, it thins out to a mere 6 protons per cc.
Coronal Mass Ejection
The Sun produces solar wind slowly and steadily. It also undergoes sudden, violent bursts called coronal mass ejections (CMEs). These highly directional flareups weigh as much as a billion tons and reach speeds up to 1,000 km/second. Since they are so massive, energetic and focused, they can cause trouble if one hits the Earth.
Effects
The Earth’s iron core creates a strong magnetic field that acts as a shield against solar wind and CMEs. On the Moon, beyond the magnetic field’s reach, an unprotected person could be killed by a CME. For this reason, spacecraft must have radiation shielding. On the Earth, even with the safety of the magnetic field, especially strong solar storms can disable communications satellites and burn out electrical power transformers. Not all the effects are destructive, however. The solar wind produces the auroras near the north and south poles. After a strong CME, you might see auroras in the lower 48 states.
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