Current phase of Earth's moon

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Aurora Meter

Image: Berkeley SSL

Current UV image of the Aurora

A sprite is a little-known phenomenon that is a result of energy leaking from the top of the largest of thunderstorms during lightning discharge. This energy discharge makes different colored sprites. Colors like red are observed in this phenomenon, but little else is known. To the right is an example of a red sprite.

Aurora Borealis (Northern Hemisphere) and Aurora Australis (Southern Hemisphere) are caused by high-enegy particles colliding with atoms in our atmosphere. These high-energy particles are ejected from the Sun at very fast velocities on the order of 400KM/s (a million miles per hour!). These particles of the solar wind sneak through the Magnetosphere into our Ionosphere through a process called merging (or reconnection). These particles hit atoms in our atmosphere, upon which the atoms absorb the energy from the collision. The energy that is absorbed makes the electrons of the atoms excite, and jump to higher energy levels. These higher energy levels are not stable, so the electrons jump back down to their most stable energy level after the collision. As you know, energy is neither created nor destroyed, so the electrons release the extra energy in the form of a photon; a photon is a "particle" of light. There are many different kinds of atoms in our atmosphere, and each atom has a different "base" energy level. Since this is the case, many colors are visible in some Auroral displays. The different colors in the Northern Lights are the result of particles of different energy striking different atoms in the atmosphere. For example, Oxygen can produce both red and green-color auroral displays..

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Seeing Aurora Borealis depends on many factors. First and foremost is your location. Locations at high latitudes (>60 degrees North) can see Aurora frequently during active periods. This, of course, depends on the time of year, since locations above the arctic circle get 24-hour "days" (light) in the summer time. The sky should also be free of clouds and the moon should not be visible to get the best viewing of Aurora. (Check the Moon's rise/set times here). For locations in mid-latitudes, a geomagnetic event is required. These events are a result of Solar Flares, Proton Events, and Coronal Mass Ejections (CMEs). The level of the geomagnetic storm determines how far south of the magnetic pole the Aurora will be visible (for us in the northern hemisphere). The duration of these events can be anywhere from minutes to days. Check here to see the Aurora forecast for Alaska, or here to use the interacative map.

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To view aurora (Northern Lights) most effectively, you should first start with clear, moonless night; the best viewing time to see aurora is around local midnight. Most aurora should be visible with the naked eye, barring any type of light pollution. In times of extreme activity, aurora have been seen in parking lots of the Bronx! The longer days in the summer makes it harder to see aurora, since the long days keep the sky light until late in the evening.

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Where Can I See It?

The best place in the sky to look is to the north, and even right overhead sometimes! Aurora patterns change rapidly, so they should be discernable from ordinary clouds. Light pollution interferes with aurora viewing, since the stray light from street lights and houses scatters easily in the particulate-laden air near urban areas. Of course, seeing the northern lights is much easier for those us up here in the woods of Maine without all of that light pollution!

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