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Aurora from space

Auroral zones of the Earth IMAGE spacecraft.

The Earth's magnetosphere impacted by the solar wind.

The Earth's magnetosphere

Earth's Magnetosphere

Aurora Borealis

Aurora Borealis

Aurora Borealis

Aurora Borealis

Aurora Borealis

Aurora Borealis

Aurora Borealis


The relationship between the Sun and the Earth is at the heart of a complex, dynamic system we do not yet fully understand. At the center of our solar system is the Sun, a magnetically variable star. This variability has impacts on life and technology that are felt here on Earth and throughout the solar system. Earth is the only planet we know to be capable of sustaining life. It is our lifeboat in the vast expanse of space. Earth can sustain life thanks to the existence of water, atmosphere and oxygen. This life-sustaining environment came into being 4 billion years ago, and has not changed substantially since then. Unlike Venus and Mars, the Earth has a magnetic field. This field creates a protective wall that stops the solar wind from blowing directly into its atmosphere. High-energy particles such as radiation belt are produced in the magnetic field.

The Earth's magnetosphere
Earth's magnetosphere is an extension into space of the familiar magnetic field that causes compass needles to point North. Our planet sits at the heart of a fuel-efficient magnetic bubble, which occupies a volume at least 1000 times greater than Earth itself. The magnetosphere protects us from solar wind gusts and from potentially deadly solar flares. Without it, Earth might be as barren as Mars or the Moon, two worlds without magnetospheres. The magnetosphere not only shields us from solar radiation but it also acts something like a solar sail. The solar wind pushes on the magnetosphere constantly, but fortunately Earth is just too massive to blow away.

Every square meter of the Earth is pierced by a line of magnetic force, which loops from deep inside the Earth, and far into space, only to return back in a great closed circuit thousands of kilometers away. If there were no Sun or solar wind, the Earth's magnetic field would extend far beyond the orbit of the moon and millions of kilometers into interplanetary space

When the solar wind and the magnetosphere are taken together they operate like a powerful, but invisible system. Depending on the magnetization of the particles in the solar wind the field can be southward or northward attracting or repelling the Earth's field.

The solar wind is composed of charged particles, so it actually draws out the solar magnetic field into interplanetary space and gives rise to a very weak interplanetary magnetic field (IMF) outside the Earth’s magnetosphere. The magnitude of the IMF is 5,000 time smaller than the Earth's magnetic field at the Earth's surface.

The Earth's magnetic field has two poles, north and south, but the fields' pull extends far beyond the surface of the Earth. An average of 50 tons of plasma per day in this field flows against the gravitational pull of the Earth, much as the solar wind flows away from the sun. This plasma contains hydrogen, helium, oxygen and nitrogen atoms and ions.

A magnetosphere has many parts, such as the bow shock, magnetosheath, magnetotail, plasmasheet, lobes, plasmasphere, radiation belts and many electric currents. It is composed of charged particles and magnetic flux. These particles are responsible for many wonderful natural phenomena such as the aurora and natural radio emissions such as lion roars and whistler waves.

The particles move and circulate about the magnetosphere and even generate storms. The magnetosphere changes constantly, even flipping its orientation every few thousand years.

Magnetic Storms and Aurora Borealis

The most spectacular manifestation of the connection between the Sun and the Earth is the Aurora Borealis (Northern Lights) and the Aurora Australis (Southern Lights). Aurora often accompanied magnetic 'storms' and an unsettled magnetosphere; they were produced by flows of charged particles entering the atmosphere; they came and went with the sunspot cycle; and their colors were the product of excited oxygen and nitrogen atoms about a hundred miles above the surface of the Earth.

Auroras are not caused by the direct flow of particles from the Sun into the polar regions, guided by Earth's magnetic fields. Instead, these currents are generated in the distant, comet-like tail of Earth's magnetosphere, whenever solar activity and severe solar storms are in progress. During a solar storm, some of the energy stored in the tail of the Earth's magnetic field is transformed into high-speed currents of charged particles. These accelerated particles flow into the equatorial regions of near-Earth space and become trapped as the ring current. Positively charged particles drift westward while negatively charged particles drift eastward. In a process scientists don't fully understand, some of these particles also flow along the magnetic field into the polar regions. As they enter the upper atmosphere they are accelerated to even higher energies before colliding with atoms of oxygen and nitrogen to produce the aurora's colors. These million-ampere currents not only cause the spectacular displays we see as aurora, but they also heat the upper atmosphere and ionosphere.

Lights in the Northern Sky

The solar storms fueling these auroras were the result of the biggest sunspot cluster seen in a decade, which developed on the upper right quarter of the side of the sun visible from Earth according to satellite readings. A sunspot is a cooler, darker region on the sun’s surface caused by a concentration of temporarily distorted magnetic fields. It spawns tremendous eruptions, or flares, into the sun’s atmosphere, hurling clouds of electrified gas toward Earth at speeds in excess of a million miles (1.6 million kilometers) per hour.

The short answer to how the aurora happens is that energetic electrically charged particles (mostly electrons) accelerate along the magnetic field lines into the upper atmosphere, where they collide with gas atoms, causing the atoms to give off light.

In the ionosphere, the speeding electrons collide violently with gas atoms. This gives the gas atoms energy, which causes them to release both light and more electrons. In this way, the gases of the ionosphere glow and conduct flowing electric currents into and out of the polar region. The electrons flowing back out don't have as much energy as the speedy incoming ones had - that energy went into creating the aurora!

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