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This picture shows material from the Sun coming towards the Earth. It is the Sun's magnetic field carried in this material that causes magnetic storms.

What is Space Weather?

What are we talking about when we describe the weather on Earth? We usually think of temperature, the speed and direction of the wind, air pressure, whether rain or snow is falling...Basically, when we say "weather" we mean conditions in our atmosphere that change from time to time.

"Weather" in Space?

There is a kind of weather in space, too. It isn't quite the same as weather on Earth (you can't really have wind if there is no air!), but it is similar in some ways. When you hear someone talk about "space weather", they are discussing conditions in space that change from time to time. Sometimes the Sun gives off more radiation, sometimes it gives off less. A flow of charged particles (not air!) called the "solar wind" constantly streams outward from the Sun. The speed and pressure of this "solar wind" change all the time. Space is filled with magnetic fields, which control the motions of charged particles. The strengths and directions of the magnetic fields often shift. Changes in radiation, the solar wind, magnetic fields, and other factors make up space weather, just like changes in temperature, rainfall, and winds make up weather on Earth.

Space Weather Starts at the Sun

Most of space weather starts at the Sun. The amazing amount of energy the Sun gives off is what makes space weather go. Sometimes there are storms on the Sun, called solar flares and Coronal Mass Ejections (CMEs). These storms fling showers of radiation and powerful magnetic fields outward through our Solar System. Most storms miss Earth completely, but some storms hit our home planet. Those are the space weather storms we care about the most!

Space Weather Around Earth

When space weather from the Sun reaches Earth, it runs into our planet's magnetic field and its atmosphere. The radiation and magnetic fields in space weather swirl around Earth in very complex patterns. Earth is surrounded by a sort of magnetic bubble called the "magnetosphere". How do space weather storms affect Earth? Partly this depends on what the storms from the Sun are like. But it also depends on how those storms flow around and through Earth's magnetosphere.

Changing Space Weather

Like weather on Earth, space weather is always changing. Some space weather storms form in minutes or hours. An "active region" on the Sun can last for many days or weeks, causing space weather storms for that whole time. Earth's weather has long cycles, such as the gradual changes in temperature that come with the changing seasons. The Sun, too, has cycles; for example, the 11-year long sunspot cycle that brings along stormy and calmer space weather at different times in the cycle. On Earth, we call long-term trends in weather "climate". Space weather also has trends lasting decades or centuries, which we can think of as the "climate" of space weather. Finally, the Sun has changed during the billions of years it has been around. These changes in the Sun have caused long term "climate change" effects in our space weather.

Space Weather and People - Why Should I Care?

Why are people interested in space weather? Why should you care about space weather? The Sun is the main source of energy for our planet. It makes plants grow and makes our weather go. Changes in the Sun could make a big change in our weather and climate on Earth. Radiation from space weather storms can damage satellites, like the ones used for cell phone communications. That radiation can also harm astronauts, or even people on some kinds of jet airplane flights. Really powerful space weather storms can even knock out the electricity over large areas. But not everything about space weather is bad. Effects of space weather can be beautiful, too. When radiation from a storm crashes into our atmosphere, it sometimes makes really cool light shows. These light shows are called the aurora, or the Northern Lights and the Southern Lights.

Last modified February 7, 2007 by Randy Russell.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA