Auroras

1. Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis http://www.geo.mtu.edu/weather/aurora/images/aurora/jan.curtis//

2. Auroras … • Seem to happen near the poles • Seem to happen after Solar Flares and Coronal Mass Ejections (CMEs) • Have many different characteristic patterns which can indicate what is happening • Have amazed everyone, the world over, for MANY years. Check out this video! • So, we’ll look at what happens, and why?

3. What is an Aurora? • Auroras are: • Patterns of light in the night sky usually seen in northern latitudes. • Related to Sunspot activity • Related to Coronal Mass Ejections by the sun • Auroras can: • Look like curtains, ribbons, or point sources of light emanating from a place near the celestial poles.

4. What causes an Aurora • A little Technical background: • Earth has a magnetic field with “lines of force” , it’s Magnetosphere, extending (roughly) from North pole to the South pole. • The Sun creates a Solar Wind of subatomic particles (protons & electrons) which, when it gets to the earth, is diverted by the earth’s magnetosphere.

5. “Cutting to the chase…”So when do Auroras Occur? • When there are CME’s or high sunspot activity: • Solar wind pressure creates an electric voltage between the magnetosphere and the earth’s poles, like the voltage between the two terminals of a battery. • It can reach about 10,000 volts! • The voltage pushes electrons (with little mass) toward the magnetic poles • Accelerates the electrons to high speeds, much like the electrons in a TV picture tube that accelerate to hit the screen. • Electrons zoom along the field lines towards the ground to the north and south, • Huge numbers of electrons are pushed down into the upper layer of the atmosphere, the ionosphere.

6. Finally, In the Ionosphere… • The speeding electrons collide violently with gas atoms. • This gives the gas atoms energy. • This causes them to release both light and more electrons. • So, the gases of the ionosphere glow and conduct flowing electric currents into and out of the polar region. • Check out this video of an aurora viewed from space.

7. What about the colors? Where do the colors come from? • An Analogy… Neon signs glow different colors due to the concentration of neon atoms inside the glass tube • Colors in the Auroral display are formed by high energy photons hitting gas particles in the upper atmosphere Accelerated particles move along the magnetic lines of force into the poles energize gas particles

8. What do specific colors mean? • Red Auroras are caused by high-altitude oxygen in the ionosphere • Yellow-Green is caused by Oxygen at lower altitudes. (This is the most common and brightest color of auroras) • A light blue is caused by ionized nitrogen molecules • Neutral nitrogen glows in a weak tint of red • Nitrogen creates the purplish-red lower borders and ripple edges of an aurora.

9. When can I see auroras? • Auroras are usually coupled with Sunspot activity • Auroras will follow Coronal Mass Ejections (CMEs) • So when you hear of Coronal Mass Ejections, Auroras will probably follow within a day or two.

10. A gallery of Auroras Bands with ray structure (at left)

11. A gallery of Auroras Yellow-Green (Oxygen at lower altitudes) is the most prominent type of Aurora

12. A gallery of Auroras Homogeneous Bands

13. A gallery of Auroras Draperies – still yellow green (oxygen)

14. A gallery of Auroras Comet Hale-Bopp (1997) with luminous glow near horizon