AURORAS

1. AURORAS • Aurora 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.

2. Aurora Australis • Looking 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.

3. 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

4. Prime Viewing • Alaska, and northern Canada • Northernmost part of Scandinavia, in Europe • Antarctica

5. Aurora View

6. Aurora View

7. 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.

8. Final Atmospheric Layers Ionosphere & Magnetosphere • The 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 Earth’s atmosphere and contains the magnetic field that surrounds the planet. This layer protects Earth from the bombardment of particles coming from outer space.

9. It All Starts Here! • Moving at a million miles per hour, the Sun’s 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.

10. 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

11. SOLAR WIND • Composed 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.

12. SOLAR FLARE • Intense explosions on the Sun • Occurs because of a very active Sun.

13. 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.

14. Solar Wind Affects Comets • 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.

15. PLASMA APPROACHES THE MAGNETOSPHERE

16. BLAST OF SOLAR WIND AS IT REACHES EARTH’S MAGNETOSPHERE

17. CAUSE OF THE NORTHERN LIGHTS • Sun spews out charged particles from its solar wind that stream toward Earth’s 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 Earth’s 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?

18. ELECTRONS POP BACK INTO ORBITS TO PRODUCE LIGHT • Solar 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 can’t 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.

19. Aurora View

21. Review: HOW IS THE AURORA PRODUCED • Auroral 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