Orwell Astronomical Society (Ipswich)
Atmospheric Phenomena, 30 March 1980 - 29 May 2021
Images of atmospheric phenomena captured by members of OASI are below.
1. Andy Gibbs. A 22° solar halo, taken with an iPhone SE outside Suffolk Food Hall on 28 May 2021.
2. Alan Smith. A 22° lunar halo, captured with Alan's all-sky camera on 04 April 2020, 03:14-03:15 UT. Canon 1100D, Sigma 4.5 mm fisheye lens, ISO 1600, 58 s exposure.
3. Neil Morley. A sun pillar captured at 04:16 UT (around sunrise) on 16 July 2019 from location 48.9525° N, 1.05684° W, Tessy Sur Vire, northern France. The location was on a hilltop with an unobstructed view to the eastern horizon. Equipment: FV-5 camera app installed on a handheld Huawei Y.635 Smartphone, using automatic settings with focus set manually to infinity.
4. Alan Smith. A sun pillar photographed using a phone camera on 27 May 2012 from east Felixstowe.
5. Alan Smith. A solar halo photographed on 22 April 2008. At times the halo spanned a full 360° - unfortunately I did not have a wide angle lens to hand so could not capture the phenomenon in its entirety. However, the image gives a general impression of the phenomenon.
6. Nigel Evans. A green flash from the setting sun, partially eclipsed, photographed from Woomera, Australia on 04 December 2002.
7. Sue Brown. A 22° solar halo and a much rarer and fainter parhelic circle (going up to top left) which passes through the Sun and intersects the 22° halo. It also captures a circumscribed halo which shows as a shoulder on the 22° halo - but this isn't very obvious. Taken from Newbourne, near Ipswich, on 01 June 2001, using a 16 mm fish-eye lens.
8. Alan Smith. On 30 March 1980, at 19:45 UT, several members of OASI saw phenomena caused by the light from a full Moon shining through high level cirrus clouds. The most noticeable feature was a 22° halo around the Moon together with several rays that appeared to emanate from the Moon itself. The halo was yellow/orange in colour; the inner edge had a red tint and the outer edge a green tint. One of the rays struck a cloud and caused a rainbow halo, again at 22°. At first the halo appeared rather dim, but by 20:00 UT had brightened considerably over about 15° of its circumference and, by using averted vision, could be traced around a full circle. Over the bright portion of the circumference, the halo exhibited an orange colour, the inner edge continued to exhibit a red tint and the outer edge a grey tint.
Explanations of some atmospheric phenomena are as follows.
Many atmospheric spectacles are created by the Sun's rays falling on ice crystals in the atmosphere, usually at an altitude of 5–10 km. The solar halo and lunar halo are fairly common. They are visible when light from the Sun or Moon shines through ice crystals associated with a thin, whitish veil of cirrostratus cloud. The halo appears as a faint ring around the Sun or Moon at a distance of approximately 22° and can vary in colour. The space inside the ring is generally very faint white. If the halo is strongly defined, a red tint may be visible on its inner edge and a yellow tint on its outer. Occasionally, a halo can be centred on the zenith, rather than the Sun or Moon.
The Sun pillar and Moon pillar are caused by the reflection of light from the Sun or Moon on the vertical sides of columnar crystals in the atmosphere. The sun pillar appears as a column of either red or white light extending vertically above and below the Sun. Sometimes, the vertical column is crossed by a similar horizontal bar, when the phenomenon is called a heavenly cross. The sun pillar is rarely seen in the British Isles and the heavenly cross is even more rare.
In hazy conditions caused by dusk or smoke in the atmosphere, the Sun's rays produce sunbeams known as crepuscular rays. They are usually red or yellow, due to the scattering of other colours of light by the atmosphere.
The green flash appears as a brilliant emerald colouration on the very last edge of a setting Sun or the very first edge of a rising Sun. It generally lasts no longer than one or two seconds. It is caused by the refraction of sunlight in the atmosphere, effectively causing the colours to separate.
When there is a considerable quantity of airborne dust, such as may occur after a large volcanic eruption, strange spectacles can occur in the sky. After the great eruption of Krakatoa in 1883, a blue Sun was reported from many parts of the world: it rose a bright light blue, shone a deep azure blue throughout the day and set a dark blue. The eruption had carried particles of dust to a great height in the upper atmosphere and created a dense haze which resulted in the unusual colours. A blue Sun has also been reported for two or three consecutive days after major dust storms in the Sahara. Sometimes dust in the atmosphere can result in the Sun appearing yellow: over Cairo during a great dust storm, it appeared pale yellow while the sky immediately surrounding it appeared pale blue and, at night, the Moon also appeared pale yellow, surrounded by a similar blue tint.
Among other types of unusual weather phenomena are coloured rain and snow. Rain has been known to fall as red or blue, as it did for example during March 1935 in the Shetland Isles after a heavy thunder storm; descriptions spoke of it looking very much like blue-black ink diluted with water. The accepted explanation was localised pollution and atmospheric conditions. There have also been many reports of coloured rain falling in Italy. Red rain has been reported falling in New Zealand: one such occasion was on 26 October 1929, following two days of a curious smoky haze over South Island. The haze disappeared after the storm of red rain. The only time red rain has fallen over England was on 21 and 23 February 1903 when it was believed to be caused by dust raised into the atmosphere by a storm over the Sahara and carried northwards to Europe by the winds. Coloured snow has been reported from various parts of the world, usually red or green and sometimes yellow or brown. The colours are caused by minute vegetable organisms known as Protococcus Nivalis.
One phenomenon which is astronomical, but can be mistaken for an atmospheric feature, is the Gegenschein or counterglow. This is a very faint glow visible on the ecliptic, opposite the position of the Sun, only slightly lighter than the general illumination in the sky; it is visible sometimes, on clear moonless nights, from dark-sky locations. Spectral analysis reveals it to be sunlight scattered by minute dust particles in the interplanetary medium in the inner solar system.
As is widely known, the rainbow is associated with showery weather and always appears opposite the Sun in the sky. Under ideal conditions it is possible to see two bows: the larger is the secondary and the smaller the primary. The colours occur in the opposite order in the two bows. A particularly brilliant rainbow can exhibit up to seven distinguishable colours, in the following order from the outer band inwards:
From the ground it is possible to observe only the half circle of a bow, but from an aeroplane at sufficient height it is possible to observe the complete circle.