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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//

Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

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Page 1: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

Auroras

Lights in the Sky… Why??

Gallery of photos

Photo credit: Background photo and example photographs – Jan Curtishttp://www.geo.mtu.edu/weather/aurora/images/aurora/jan.curtis//

Page 2: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

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?

Page 3: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

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.

Page 4: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

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.

Page 5: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

“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.

Page 6: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

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.

Page 7: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

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

Page 8: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

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.

Page 9: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

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.

Page 10: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

A gallery of Auroras

Bands with ray structure (at left)

Page 11: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

A gallery of Auroras

Yellow-Green (Oxygen at lower altitudes) is the most prominent type of Aurora

Page 12: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

A gallery of Auroras

Homogeneous Bands

Page 13: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

A gallery of Auroras

Draperies – still yellow green (oxygen)

Page 14: Auroras Lights in the Sky… Why?? Gallery of photos Photo credit: Background photo and example photographs – Jan Curtis

A gallery of Auroras

Comet Hale-Bopp (1997) with luminous glow near horizon