Aurora Borealis


The Aurora Borealis, Or Northern Lights

This phenomenon is frequently observed in the northern heavens. It occurs in many forms, but the most common is that of a luminous arch whose summit is in the magnetic meridian of the place of observation, and from which vivid flashes of light dart towards the zenith. A like phenomenon in the southern heavens is denominated the Aurora Australis. Auroras are most frequent and brilliant in the polar regions, and diminish in intensity towards the equator.

Aurora Borealis  (´rẽ-ā´lĭs ), i. e., northern daybreak; popularly called northern lights. A luminous meteoric phenomenon, visible only at night, and supposed to be of electrical origin. This species of light usually appears in streams, ascending toward the zenith from a dusky line or bank, a few degrees above the northern horizon. Occasionally the aurora appears as an arch of light across the heavens from east to west. Sometimes it assumes a wavy appearance. They assume a variety of colors, from a pale red or yellow to a deep red or blood color.

The Aurora Australis  (aws-trā´lĭs ) is a corresponding phenomenon in the southern hemisphere, the streams of light ascending in the same manner from near the southern horizon.

Splendour of the Aurora Borealis

Humboldt thus beautifully describes this phenomenon:

The intensity of this light is at times so great, that Lowenörn (on June 29, 1786) recognised its coruscation in bright sunshine. Motion renders the phenomenon more visible. Round the point in the vault of heaven which corresponds to the direction of the inclination of the needle the beams unite together to form the so-called corona, the crown of the Northern Light, which encircles the summit of the heavenly canopy with a milder radiance and unflickering emanations of light. It is only in rare instances that a perfect crown or circle is formed; but on its completion, the phenomenon has invariably reached its maximum, and the radiations become less frequent, shorter, and more colourless. The crown, and the luminous arches break up; and the whole vault of heaven becomes covered with irregularly scattered, broad, faint, almost ashy-gray, luminous, immovable patches, which in their turn disappear, leaving nothing but a trace of a dark smoke-like segment on the horizon. There often remains nothing of the whole spectacle but a white delicate cloud with feathery edges, or divided at equal distances into small roundish groups like cirro-cumuli.—Cosmos, vol. i.

Among many theories of this phenomenon is that of Lieutenant Hooper, R.N., who has stated to the British Association that he believes “the Aurora Borealis to be no more nor less than the moisture in some shape (whether dew or vapour, liquid or frozen), illuminated by the heavenly bodies, either directly, or reflecting their rays from the frozen masses around the Pole, or even from the immediately proximate snow-clad earth.”

What is the aurora borealis or northern lights?

Luminous appearances  seen in the sky  at night-time. Sometimes streaks of blue, purple, green, red, etc., and sometimes flashes of light, are seen.

What is the cause of the aurora borealis or northern lights?

Electricity  in the higher regions of the atmosphere is undoubtedly an active agent in producing this phenomenon.

Is the aurora ever seen in other parts of the heavens than towards the north?

In the northern hemisphere it always appears in the north, but in the southern hemisphere it appears in the south : it seems to originate at or near the poles of the earth, and is consequently seen in its greatest perfection within the arctic and antarctic circles.

What is known concerning the extent of the aurora?

It is not local, but it is seen simultaneously at places widely remote from each other, as in Europe and America.

What calculations have been made respecting the height of the aurora?

The height of the appearances varies from one to two hundred miles ; they sometimes appear within the region of the clouds, and very near to the earth.

Do the auroras appear at any particular seasons and times?

They appear more frequently in the winter  than in the summer, and are only seen at night.

Do they also occur in the day-time?

The aurora is known to affect the magnetic needle  and the telegraph; and as the effects upon these instruments are noticed by day as well as by night, there can be no doubt of the occurrence of the aurora at all hours. The intense light of the sun renders the auroral light invisible during the day.

Of what utility are the auroral appearances in the polar regions?

During the long polar night, when the sun is absent, the aurora appears with a magnificence unknown in other regions, and affords light sufficient  for many of the ordinary outdoor employments.