Auroras can help us understand the Earth's magnetic field and how it changes over time. Because the Earth's magnetic field is three-dimensional, the aurora appears as an oval ring around the pole. This has been observed from satellites, the International Space Station and the space shuttle. It isn't a perfect circle because the Earth's magnetic field is distorted by the solar winds.
The auroral ring can vary in diameter. Auroras can be seen as far south as the southern United States, but not frequently. In general, they stay near the polar regions. They also occur in pairs -- when we see an aurora borealis , there is a corresponding aurora australis in the southern hemisphere learn why on the next page. Because auroras are caused by the interactions of solar winds and solar flares with the magnetic fields of a planet, you'd think they'd happen on other planets as well.
What you need is:. So, with these conditions, we have observed auroras on Jupiter and Saturn. Both planets have powerful magnetic fields and atmospheres with ionized gases, mainly hydrogen and helium. The Hubble Space Telescope caught images of auroras on Jupiter, and the Cassini probe orbiting Saturn has photographed auroras there.
Sign up for our Newsletter! Mobile Newsletter banner close. But on October 17, , skywatchers in Finland and Sweden noticed that the Northern Lights were spreading out horizontally , undulating like a wave and stretching toward the equator.
The sight led to new research as well as the revelation that this style of aurora has been spotted in other places as well, including the United States and Canada. The phenomenon had actually been known to photographers for decades, but it gained attention in when the scientific community began to investigate its origin.
It turns out, STEVE is formed in a different atmospheric level and in a different way than auroras are. The different colors—pink, green, yellow, blue, violet, and occasionally orange and white—are released when the resulting energy starts to wear off. The new aurora shape looks like a wave and can stretch out hundreds of miles towards the horizon.
Arcs resemble a rainbow, a curve from one side of the horizon to the other. They are the most common type of aurora and usually occur when aurora conditions are quiet or growing in intensity. These ribbon-like aurora formations are the ones you are probably hoping to see. They appear when auroral conditions are more active, so arcs can turn into bands. Also called beams or rays, pillars can be seen alone as a streak or two in the sky or a cluster of streaks.
But they can also be a feature of an active arc or band aurora. These are the vertical bars of light that seem to reach upwards. They can sometimes be as tall as miles from the green base and purple canopy.
Similar to pillars, diffuse is both a shape of aurora and a way to describe other types. But auroras can also present as light glow known as diffuse, which has no discernible shapes or features. Essentially, the light of auroras is emitted when charged particles in the solar wind excite the electrons of atmospheric atoms through collisions.
As the electrons return to their original energy levels, these atoms, primarily oxygen and nitrogen, emit photons of visible light of distinct wavelengths to create the colors of the auroral display.
The wavelength of the light depends upon the electronic structure of the atoms or molecules themselves, and on the energy of the charged particle colliding with the atom or molecule.
These charged particles, mostly protons and electrons, have their own magnetic field. They reach Earth at speeds of to km per second. The solar wind is not constant, but follows an eleven-year cycle of activity.
Coronal holes are spots, usually near the equator, where fast-flowing "gusts" of material flow out from the sun. Even more dramatic are coronal mass ejections, or CMEs.
Complex magnetic fields on the solar surface eject billions of tons of plasma at extraordinarily high speeds. Recent investigation by NASA has confirmed that magnetic reconnection is responsible for sudden increases in the brightness and movement of the auroras. Magnetic reconnection is a model of the process where magnetic field lines are broken and reformed, giving off kinetic energy and heat.
The THEMIS measurements support the model of substorms following magnetic reconnection, which is followed by the dancing and brightening of auroral light towards the poles. An alternative model from plasma physics explains this phenomenon in terms of exploding double layers and electrical discharge. The auroral ovals mark out the spots on Earth where the aurora is most likely to be seen, usually in rings that run roughly around the Arctic and Antarctic circles.
At the busiest point in the eleven-year cycle of solar activity, auroras may be observed over a much wider span of latitudes. A dark sky also increases the visual effect of the aurora, so it is best observed away from the airglow of cities and industrial sites.
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