Auroræ: Their Characters and SpectraCapron, J. Rand
History
Auroræ: Their Characters and Spectra
Capron, J. Rand
Auroras
“But the band is often seen in a perfectly different form. Frequently
it consists of single rays, which, standing close together, point in an
almost parallel direction towards the magnetic pole. These become more
intensely bright with each successive wave of light; hence each ray
appears to flash and dart continually, and their green and red edges
dance up and down as the waves of light run through them. Often, again,
the rays extend through the whole length of the band, and reach almost
up to the magnetic pole. These are sharply marked, but lighter in colour
than the band itself, and in this particular form they are at some
distance from each other. Their colour is yellow, and it seems as if
thousands of slender threads of gold were stretched across the firmament.
A glorious veil of transparent light is spread over the starry heavens;
the threads of light with which this veil is woven are distinctly marked
on the dark background; its lower border is a broad intensely white band,
edged with green and red, which twists and turns in constant motion. A
violet-coloured auroral vapour is often seen simultaneously on different
parts of the sky.
[Sidenote: Aurora in stormy weather. Fragments.]
“Or, again, there has been tempestuous weather, and it is now, let us
suppose, passing away. Below, on the ice, the wind has fallen; but the
clouds are still driving rapidly across the sky, so that in the upper
regions its force is not yet laid. Over the ice it becomes somewhat
clear; behind the clouds appears an Aurora amid the darkness of the
night. Stars twinkle here and there; through the opening of the clouds we
see the dark firmament, and the rays of the Aurora chasing one another
towards the zenith. The heavy clouds disperse, mist-like masses drive on
before the wind. Fragments of the northern lights are strewn on every
side: it seems as if the storm had torn the Aurora bands to tatters,
and was driving them hither and thither across the sky. These threads
change form and place with incredible rapidity. Here is one! lo, it is
gone! Scarcely has it vanished before it appears again in another place.
Through these fragments drive the waves of light: one moment they are
scarcely visible, in the next they shine with intense brilliancy. But
their light is no longer that glorious pale green; it is a dull yellow.
It is often difficult to distinguish what is Aurora and what is vapour;
the illuminated mists as they fly past are scarcely distinguishable from
the auroral vapour which comes and goes on every side.
[Sidenote: Bands. Rays reach the pole. No noise.]
Public-domain text, read in full here on John Shaqi.
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