Header Twilights

Had the fierce ashes of some fiery peak
Been hurled so high they ranged about the globe?
For day by day, thro’ many a blood-red eve,
In that four-hundredth summer after Christ,
The wrathful sunset glared…

Tennyson (1892)

Volcano twilight
A volcanic sunset afterglow photographed from Marden (Kent) in 1983

The eruption of Krakatoa, between Java and Sumatra, began on May 20, 1883, and culminated in four huge explosions on August 26 - 27.
An enormous volume of dust was expelled to a height of at least 17 miles (27 kilometres). The dust was then carried eastward by high-velocity winds (whose existence had previously been unsuspected). Three days after the final eruption (on August 26 - 27) the dust had reached the eastern coast of equatorial Africa. On August 31 it was over Brazil, and after 13 days the dust had encircled the globe at the tropics. By November it had spread to cover most of Europe and North America. Its progress was marked by coloured suns and moons and strange vivid sunsets. This was the first occasion on which post-volcanic sunsets had attracted general attention, although the post-sunset purple light had been observed in 1553.

The volcano El Chicon in south-east Mexico erupted on March 28, 1982. The eruption lasted for several months. Several villages were destroyed and thousands of persons were killed. Before the eruption, El Chicon was considered to be merely a solfatara, or a sulphurous hot spring. Dust rose to a height of 30 kilometres.

Sunsetsmall 1982 09 13
September 13, 1982. King’s Cross, London, about 7:40 p.m. (BST). Sunset was at 7:20 p.m.
Illuminated clouds at sunset, however spectacular, do not indicate a volcanic twilight. By the time the volcanic layer is fully illuminated, all lower clouds, even cirrus, are dark, and the glows are best seen when the sky is cloudless.

Sunset 1982 09 18
September 18, 1982. Marden, Kent. 7:25 p.m.

Sunsetsmall 1982 09 21
September 21, 1982. Camden, London, 7:20 p.m. A white glow over the sun’s position at 7:15 p.m. illuminated extensive delicate bands or ripples parallel to the horizon. The purple light appeared at 7;20 p.m. An orange stratum on the horizon at 7:40 p.m.

Sunset 1982 11 10 dust Clouds 1982 11 10
November 10, 1982. Marden, Kent, 4:48 p.m. Sunset was at 4:18 p.m. Upper: The dust stratum became visible as a continuous layer with billows at 4:28 p.m. (GMT). Red dot shows point of sunset. The billows were faintly seen at 4:10 p.m., just before sunset. Lower: The purple light appeared at 4:35 p.m. and grew steadily brighter until 4:45 p.m., when it reached 30 degrees above the horizon. It then shrank and withdrew to an orange glow on the horizon at 4:52 p.m.

Volcanic billows 01
December 18, 1982. Marden, Kent, 3:53 p.m. (Sunset was at 3:46 p.m.) Billows in a volcanic dust layer become visible.
The billows appeared in a clear sky just after sunset. Before sunset, the sky appeared to be cloudless. As the billows faded, the purple light and twilight glows began. The purple light appeared 15 minutes after sunset.

Volcanic billows 02
December 18, 1982. Marden, Kent, 4 p.m. The billows become distinct.

Volcanic billows 03
December 18, 1982. Marden, Kent, 4:20 p.m. Billows on the horizon. The red dot (left) marks the point of sunset.

The Reverend S.E. Bishop, in Honolulu (Hawaii) said that the dust from the eruption of Krakatoa in 1883 was visible as a “haze stratum…at a height far above that of the highest cirrus, a slight wavy ripple being noticeable in its structure.”
The billows have been described as stratospheric haze, ultracirrus, or twilight cirrus. F. H. Ludlam records that stratospheric haze is only visible from ground level when the sun is near the horizon, and usually appears at an altitude of below 30 degrees. It appears most distinct just before the purple light appears. The haze in concentrated in very long streaks, with a ‘waved or rolled’ underside. It was seen after the eruptions of Mount Spurr (Alaska) in 1953, Bezymianny (Siberia) in 1956, and Mount Agung (Bali) in 1963. A flight in 1953 found that the haze layer was at a height of 15 kilometres above the earth, and only about 150 metres thick. The wavelength of the undulations was from 1.4 to 4.2 kilometres.

Volcanic beam 01Volcanic beam 02
January 8, 1983. Marden, Kent. Upper, 4:35 p.m. (GMT). Lower, 4:41 p.m. The purple light after sunset was divided by a dark band about 6 degrees wide and reaching about 20 degrees above the horizon.
Volcanic glow 01
January 8, 1983. Marden, Kent. 4:56 p.m. The afterglow 10 degrees above the horizon, 45 minutes after sunset (at 4.11 p.m).
Using a graph in Sunsets, Twilights and Evening Skies, by A. and M. Meinel, this indicates that the ‘glow stratum’ was at an altitude of 102,000 feet (19 miles 1,680 feet, 31.090 kilometres).

Clouds 1983 03 04
March 4, 1983. Manchester. The sky cleared after sunset, which was at 5:52 p.m. Ripples and billows in the dust layer were visible in the western sky at 6 p.m., to an altitude of 20 degrees.

Volcanic afterglow 02
April 15, 1983. Twilight colours and purple light, Marden, Kent, 8:5 p.m., with the Moon (about 22 degrees above the horizon) and Venus.

Sunsetsmall1983 10 29 cirrus
October 29, 1983. Marden, Kent, about 5:05 p.m. Cirrus clouds, the highest type of common cloud, at a height of about 5 miles, show dark against the afterglow.

Clouds 1984 01 13
January 13, 1984. South London. The ‘purple light’ often arrayed itself into beams, and this was one of the most striking displays. Five or six beams radiated from the western horizon to a height of about 20 degrees