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What is Solar Wind? - Definition & Facts

Instructor: Joanne Abramson

Joanne has taught middle school and high school science for more than ten years and has a master's degree in education.

Did you know that there is wind on the Sun? Read on to learn more about solar wind, what causes it, its speed and temperature, and how you can witness it on Earth.

Wind on the Sun

Think about the strongest wind that you have ever experienced. Did you feel it pushing against your car when you were driving? Did the wind blow your umbrella away and you had to chase it?

Mt. Washington, New Hampshire is the windiest location in the United States, with an average wind speed of 35 mph. At this speed, trees start to sway and it becomes difficult to walk. Barrow Island, Australia has the highest wind speed ever recorded on Earth at 253 mph. This is strong enough to blow the roofs off of most buildings and uproot trees and shrubs. That is a pretty strong wind. But this is a drop in the bucket compared to the wind on the Sun.

Solar wind is more than 4000 times as strong as the wind speed recorded on Barrow Island. Additionally, it reaches temperatures of around 1 million degrees Celsius, almost 15,000 times the hottest recorded temperature on Earth.

The solar wind refers to the steady stream of highly charged particles that continually blow off the Sun in all directions. It is caused by the solar corona expanding into space. The corona is the outer atmosphere of the Sun. You can see it as a glowing halo around the Sun during a solar eclipse.

An eclipse highlights the solar corona, the outer atmosphere of the Sun.
Picture of the Sun in a total solar eclipse.

The corona is so hot that the Sun's gravity cannot hold it in. Instead, it streams off the Sun as protons and electrons shooting through space at speeds of around 400 km/s (about 1 million miles per hour). At that speed, you could travel from New York to Los Angeles in 10 seconds!

The solar wind causes the Sun to lose more than 1 million tons of mass per second. That may seem like a really big number, but consider this: The Earth's mass is about 6.5 sextillion tons. If you write that out it would be 6,500,000,000,000,000,000,000 tons. The Sun's mass is 333,000 times that of Earth. If you think about it like that, 1 million tons per second isn't actually that much.

The solar wind escapes from coronal holes, which are generally found at the Sun's poles. A coronal hole is an area in the corona that is thinner and less dense than the surrounding areas. It appears as a dark spot on the Sun's surface since it is also a cooler temperature than the surrounding corona.

Since the coronal hole is a cooler temperature than its surroundings, it appears as a dark spot at the pole.
X-ray image of the Sun.

Observing the Solar Wind from Earth

If you are lucky enough, and in the right place at the right time, you can see the effects of the solar wind right here on Earth!

The auroras, or the northern and southern lights, are caused by particles from the solar wind becoming trapped in Earth's magnetic field. (The magnetic field is what causes your compass to always point north.) The colors are created when the high energy electrons collide with oxygen and nitrogen in the atmosphere, exciting the molecules into higher energy levels.

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