Shop Windows to the Universe

Please help support Windows to the Universe, and our activities to help Earth and space science teachers, with a tax-exempt donation today!
Illustration of Lagrange Points
Original Windows graphic, by Sarah Joseph

Lagrange Points

We could learn a lot about the solar wind if we could fix a satellite in a certain location in space. Changes in magnetic fields and particle flows could be measured. Most importantly, if the satellite is between Earth and the Sun, it could be an early warning system. It would let us know about any changes in the solar wind about an hour before they reached the Earth.

The problem with fixing a satellite in a certain location is that it is impossible. To resist gravity, a satellite has to be moving in an orbit. Nearly as helpful though would be if the satellite were to orbit the Sun in a one-year orbit. Then, it could keep a fixed position relative to the Earth. However, Kepler's laws show that any satellite closer to the Sun must orbit more quickly than the Earth. A satellite farther away would have an orbit longer than one year.

There is one way around this problem. The Lagrangian Point L1, named after French mathematician Joseph Lagrange, is one of five Lagrangian points in the Sun-Earth system. Also called libration points, these five points are places where a satellite could stay in a fixed position relative to the Earth as the Earth goes around the Sun. L1 is just inside Earth's orbit, the best place for an early warning system. At the L1 point, the Earth's gravity pulls in the opposite direction of the Sun's gravity. This cancels out the effects of the Sun's gravity, which allows the satellite to orbit the Sun with less velocity. Here the satellite can have an orbit of one year, matching the orbit of the Earth.

The ACE and SOHO spacecraft are both at L1, which means they will stay in a relatively constant position with respect to the Earth. This point is about one-hundredth of the distance to the Sun, or 1.5 million km from the Earth.

Last modified June 26, 2001 by Jennifer Bergman.

Shop Windows to the Universe Science Store!

Cool It! is the new card game from the Union of Concerned Scientists that teaches kids about the choices we have when it comes to climate change—and how policy and technology decisions made today will matter. Cool It! is available in our online store.

Windows to the Universe Community

News

Opportunities

You might also be interested in:

ACE Mission Page

Have you ever wondered what you are made of? Where did the elements come from that make up your body? The elements that make up your body are the same elements found on the Earth. Where did those Earth...more

SOHO Mission Page

Have you ever wondered why your favorite radio station doesn't always come in? Solar activity, such as solar wind, sometimes causes this and other problems. Scientists are trying to find ways to understand...more

How do Satellites & Spacecraft Monitor Space Weather?

Satellites and other spacecraft help us observe space weather. They collect data about the Sun, Earth's magnetosphere, Earth's atmosphere, and space weather throughout the rest of our Solar System. Spacecraft...more

IMF

IMF stands for Interplanetary Magnetic Field. It is another name for the Sun's magnetic field. The Sun's magnetic field is huge! It goes beyond any of the planets. The Sun's magnetic field got its name...more

Coronal Mass Ejections

"Without warning, the relatively calm solar atmosphere can be torn asunder by sudden outbursts of a scale unknown on Earth. Catastrophic events of incredible energy...stretch up to halfway across the visible...more

Solar Activity

The Sun is not a quiet place, but one that exhibits sudden releases of energy. One of the most frequently observed events are solar flares: sudden, localized, transient increases in brightness that occur...more

The Solar Atmosphere

The visible solar atmosphere consists of three regions: the photosphere, the chromosphere, and the solar corona. Most of the visible (white) light comes from the photosphere, this is the part of the Sun...more

The Solar Interior

To understand how our Sun works, it helps to imagine that the inside of the Sun is made up of different layers, one inside the other. The core, or the center of the Sun, is the region where the energy...more

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