Skip to main content

What the hell is Aurora?

An aurora is a natural light display in the sky particularly in the high latitude (Arctic and Antarctic) regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere (thermosphere). The charged particles originate in the magnetosphere and solar wind and, on Earth, are directed by the Earth's magnetic field into the atmosphere.Most aurorae occur in a band known as the auroral zone, which is typically 3° to 6° in latitudinal extent and at all local times or longitudes. The auroral zone is typically 10° to 20° from the magnetic pole defined by the axis of the Earth's magnetic dipole.
 Photo credit:astrofotografen.se
During a geomagnetic storm, the auroral zone expands to lower latitudesAurorae are classified as diffuse or discrete. The diffuse aurora is a featureless glow in the sky that may not be visible to the naked eye, even on a dark night. It defines the extent of the auroral zone. The discrete aurorae are sharply defined features within the diffuse aurora that vary in brightness from just barely visible to the naked eye, to bright enough to read a newspaper by at night. Discrete aurorae are usually seen in only the night sky, because they are not as bright as the sunlit sky. Aurorae occasionally occur poleward of the auroral zone as diffuse patches or arcs (polar cap arcs), which are generally invisible to the naked eye.

History of aurora theories

  • Seneca speaks diffusely on auroras in the first book of his Naturales Quaestiones, drawing mainly from Aristotle; he classifies them ("putei" or wells when they are circular and "rim a large hole in the sky", "pithaei" when they look like casks, "chasmata" from the same root of the English chasm, "pogoniae" when they are bearded, "cyparissae" when they look like cypresses), describes their manifold colors and asks himself whether they are above or below the clouds. He recalls that under Tiberius, an aurora formed above Ostia, so intense and so red that a cohort of the army, stationed nearby for fireman duty, galloped to the city.
  • Walter William Bryant wrote in his book Kepler (1920) that Tycho Brahe "seems to have been something of a homœopathist, for he recommends sulphur to cure infectious diseases “brought on by the sulphurous vapours of the Aurora Borealis.
  • Benjamin Franklin theorized that the "mystery of the Northern Lights" was caused by a concentration of electrical charges in the polar regions intensified by the snow and other moisture.
  • Auroral electrons come from beams emitted by the Sun. This was claimed around 1900 by Kristian Birkeland, whose experiments in a vacuum chamber with electron beams and magnetized spheres (miniature models of Earth or "terrellas") showed that such electrons would be guided toward the polar regions. Problems with this model included absence of aurora at the poles themselves, self-dispersal of such beams by their negative charge, and more recently, lack of any observational evidence in space.
  • The aurora is the overflow of the radiation belt ("leaky bucket theory"). This was first disproved around 1962 by James Van Allen and co-workers, who showed that the high rate of energy dissipation by the aurora would quickly drain the radiation belt. Soon afterward, it became clear that most of the energy in trapped particles resided in positive ions, while auroral particles were almost always electrons, of relatively low energy.
  • The aurora is produced by solar wind particles guided by Earth's field lines to the top of the atmosphere. This holds true for the cusp aurora, but outside the cusp, the solar wind has no direct access. In addition, the main energy in the solar wind resides in positive ions; electrons only have about 0.5 eV (electron volt), and while in the cusp this may be raised to 50–100 eV, that still falls short of auroral energies.

 

Popular posts from this blog

LG’s first flexible OLED phone due before the year is out

LG plans to launch a flexible OLED smartphone before the end of the year, the company’s VP of mobile has confirmed, though it’s unclear to what extent the work-in-progress handset will actually flex. The OLED panel in question is the handiwork of LG Display according to VP of LG mobile Yoon Bu-hyun, the WSJ  reports, with the proposed device set to launch sometime in Q4. LG Display’s work on flexible OLEDs has been underway for some time, though the company’s efforts have perhaps been overshadowed somewhat by rival Samsung’s YOUM development. Last year, according to a Korea Times report, LG Display was preparing for

Bing Apps for Windows 8 get major updates

Late least year, Microsoft rolled out a half dozen Bing Apps for Windows 8 users, each one focused on a specific category, such as travel and sports. The apps were designed to offer “immersive vertical experiences,” and now, about six months later, a big line of updates for them is being pushed out. Users can grab the updates now by heading into the Windows Store and selecting the updates notification.

How to fix black spot on Phone Screen!

An honest talk about how to fix the damaged Phone screens in a very short time.