AURORASAurora borealis (northern lights)Aurora australis (southern lights) Beautiful, dynamic, light displays seen in the night sky in the northern and southern latitudes, near the poles.

Aurora AustralisLooking toward the south, the crew of the Space Shuttle Endeavor made this stunning time exposure of the aurora australis (southern lights) in April of 1994.

Sailing upside down, 115 nautical miles above Earth, the crew of the Space Shuttle Endeavor made this spectacular time exposure of the southern aurora (aurora australis) in October of 1994. The dark object at lower left is the Earth.

A Side View of Aurora Australis

Prime ViewingAlaska, and northern CanadaNorthernmost part of Scandinavia, in EuropeAntarctica

Aurora View

Aurora View

ATMOSPHERIC LAYERS

Thermosphere: Temperatures can reach 2000 degrees F because high energy x-rays are being absorbed into this layer. Mesosphere: The mesosphere also contains ozone. Ozone filters out powerful ultraviolet rays from the sun. This zone has the coldest temperatures in the atmosphere.Stratosphere: The stratosphere is the layer in which jets most often travel. It is clear and cold and contains clouds. A special form of oxygen, called ozone is also found in the stratosphere.Troposphere: This is the lowest layer of the atmosphere and the layer in which you live. Almost all weather takes place in the troposphere.

Final Atmospheric Layers Ionosphere & MagnetosphereThe ionosphere is the region of the atmosphere that contains many electrically charged particles, called ions. These charged particles result from powerful cosmic rays that collide with the atoms of the atmosphere. The ionosphere extends from approximately 70 to over 400 miles above the surface of the Earth.

The magnetosphere is the farthest layer of Earths atmosphere and contains the magnetic field that surrounds the planet. This layer protects Earth from the bombardment of particles coming from outer space.

It All Starts Here!Moving at a million miles per hour, the Suns hot ionized gas, called plasma, carries particles and magnetic fields from the Sun outward past the planets. This stream of charged particles is called the solar wind.

Ultraviolet image of the 1 million degree plumes from the sun's surface near the south pole. Taken by the Solar and Heliospheric Observatory (SOHO), March 7, 1996

SOLAR WINDComposed mainly of hydrogen ions (protons) and electrons. It carries the magnetic field from the Sun into interplanetary space. Speed and density vary tremendously. Its speed and density tend to go up when it comes from active regions on the Sun, like sunspots, solar flares, and coronal holes. The solar wind streams outward through the solar system at an average speed of 400 km/sec (1,440,000 km/hr, 893,000 mi/hr). At the distance of the Earth from the Sun, 93 million miles, it has an average density of 8 particles per cubic centimenter. On average, solar wind originating from around the equator on the Sun takes approximately four days to reach Earth.

SOLAR FLAREIntense explosions on the Sun

Occurs because of a very active Sun.

Gaseous eruptions occur when a significant amount of cool dense plasma or ionized gas escapes from the normally closed, low-level magnetic fields of the Sun's atmosphere. Eruptions travel out into space and can produce major disruptions in the near Earth environment, affecting communications, navigation systems and even power grids.

Solar Wind Affects CometsThe tail of a comet always points away from the Sun because of the force of the solar wind. The tail of comet Hyakutake, visible in this (March 26, 1996) color image, is composed of dust and gas driven off the icy comet nucleus by the Sun's heat and blown away by the solar wind. Bathed in sunlight, the gas molecules break down and are excited, producing a characteristic glow. This glow is responsible for visible light from the tail.

PLASMA APPROACHES THE MAGNETOSPHERE

BLAST OF SOLAR WIND AS IT REACHES EARTHS MAGNETOSPHERE

CAUSE OF THE NORTHERN LIGHTSSun spews out charged particles from its solar wind that stream toward Earths magnetosphere.The particles speed up as they travel down the magnetic field lines toward the poles. The particles gain a lot of energy so that when they blast into the Earths atmosphere they collide with ionized gas particles of oxygen and nitrogen gas, causing the brilliant light show of the auroras.

But, how do particle collisions make the sky glow?

ELECTRONS POP BACK INTO ORBITS TO PRODUCE LIGHTSolar wind particles blast into the oxygen and nitrogen atoms in the magnetosphere - energy is given off and the electrons jump into a higher energy shell around their nucleus. Electrons want to return to their normal shell because they cant keep this energy for long. When the electrons return to their lower energy level (shell), the energy they give off is a small burst of light, called a photon of a particular wavelength. The wavelength determines the color of the light. (Nitrogen gas ions produce pink and magenta color of light whereas oxygen ions emit greenish light)Billions of atoms and molecules undergoing these electron excitations are what produce the light in the auroras. The color of the light is determined by the amount of energy absorbed and released by the atom or molecule.

Aurora View

Review: HOW IS THE AURORA PRODUCEDAuroral light is from the air glowing as high-energy electrons stream down Earth's magnetic field lines and collide with molecules in the atmosphere. Each gas in the atmosphere glows with a particular color, depending on whether it is neutral or charged, and on the energy of the particle that hits it. Red aurora over Alaska

The aurora is a very large-scale phenomenon encircling the entire polar regions, but when one views a particular display from the ground only a very small portion is visible. Most auroras have a ribbon-like form but they can also form in the shapes of rays, arcs and flames. Astronauts looking down on the polar region are in a much better position than those of us who are earthbound to observe the aurora. Though the aurora appear to come near to the ground, the light originates high in the atmosphere. The lowest aurora are about 100 kilometers or 62 miles above the ground, with the highest extending to 4 times that distance. This is much higher than clouds or the highest flying aircraft (besides the Space Shuttle).

The aurora is a permanent feature of the earth's upper atmosphere. It is actually an oval centered on the magnetic north and south poles.

In Fairbanks and Nome, Alaska, the northern lights can be seen almost 200 days a year.The ionosphere is the region of the atmosphere that contains many electrically charged particles, called ions. High energy particles strip electrons from the atoms of oxygen and nitrogen, giving them a specific charge. These charged particles result from powerful cosmic rays that collide with the atoms of the atmosphere. The ionosphere extends from approximately 50 to over 400 miles above the surface of the Earth.

The magnetosphere is the farthest layer of Earths atmosphere and contains the magnetic field that surrounds the planet. This layer holds in the electrically charged particles of the ionosphere.

The Sun is a stormy place and has its own weather. It is so hot and dynamic that it cannot keep its atmosphere contained by its gravity. Instead, energy flows out from the Sun toward the Earth in a stream of electrified particles.

The solar wind is constantly streaming toward Earth from the Sun. When the Sun is more active, observed as sunspots and other changes, the solar wind blows harder.Composed mainly of hydrogen ions (protons) and electrons. It carries the magnetic field from the Sun into interplanetary space. The solar wind varies tremendously in speed and density. Its speed and density tend to go up when it comes from active regions on the Sun, like sunspots, solar flares, and coronal holes. The solar wind streams outward through the solar system. At the distance of the Earth from the Sun, one astronomical unit or 93 million miles, it has an average density of 8 particles per cubic centimenter and an average speed of 400 km/sec (1,440,000 km/hr, 893,000 mi/hr). On average, solar wind originating from around the equator on the Sun takes approximately four days to reach Earth.

NASA's Skylab during an active phase in 1973.

An "eruptive prominence" or blob of 60,000-degree gas, over 80,000 miles long, was ejected at a speed of at least 15,000 miles per hour. The gaseous blob is shown to the left in each image. These eruptions occur when a significant amount of cool dense plasma or ionized gas escapes from the normally closed, confining, low-level magnetic fields of the Sun's atmosphere to streak out into the interplanetary medium, or heliosphere. Eruptions of this sort can produce major disruptions in the near Earth environment, affecting communications, navigation systems and even power grids.

Observations of comet tails gave scientists the first hint that the Sun produced a solar wind composed of particles. The tail of a comet always points away from the Sun because of the force of the solar wind. The tail of comet Hyakutake, visible in this (March 26, 1996) color image, is composed of dust and gas driven off the icy comet nucleus by the Sun's heat and blown away by the solar wind. Bathed in sunlight, the gas molecules break down and are excited, producing a characteristic glow. This glow is responsible for visible light from the tail.

Here is a blast of the solar wind (in white) traveling toward the Earth and its magnetosphere which are depicted as curved lines coming from the Earth. Also note the satellites NASA has launched to study the solar wind.

After the energy is given off, energy is absorbed causing a "quantum leap" in the electrons making them move to outer shells or orbits in their atom.

The color of the light is determined by the particular "quantum" of energy absorbed and released by the atom or molecule.

Auroral light is similar to light from a color television set. In the picture tube, a beam of electrons strikes the screen, making it glow in different colors, depending on the type of chemicals that coat the picture tube. The chemicals are called phosphors and glow red, green or blue.Atomic oxygen, about 60 miles up, is the source of the greenish-white light common in aurora displays. High altitude atomic oxygen, about 200 miles up, can also emit a dark red light under some circumstances resulting in the "bloody red" auroras produced during great magnetic storms.

Nitrogen molecules, lower in the atmosphere, produce a red light when they are struck by electrons. This is the faint red that is often seen along the bottom edge of a aurora curtain. High in the atmosphere nitrogen molecules can become ionized and emit blues and violets.