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Archive for the ‘Optical Phenomena’ Category

Carneddau Rainbows

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Primary and secondary rainbows.  Looking towards the Carneddau mountains.

Primary and secondary rainbows. Looking towards the Carneddau mountains.

Date

7 June 2014
Location

Bethesda

SH 63395 66545; 53.17841°N, 4.04548°W

Information

Optical Phenomena

 

Written by Graham Stephen

June 29, 2014 at 11:44 am

Moel y Ci Rainbow

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Looking towards Moel Wnion from Moel y Ci

Looking towards Moel Wnion from Moel y Ci

Date

12 August 2013
Location

Parc y Bwlch, Moel y Ci

SH 59382 66403; 53.17608°N, 4.10541°W

 

Written by Graham Stephen

August 15, 2013 at 7:11 pm

Montaña de Arena, Fuerteventura

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Looking towards Montaña de la Blanca from the summit of Montaña de Arena.  The apparently converging 'anti-crepuscular rays' are formed by shadows being cast by clouds on the opposite side of the sky.

Looking towards Montaña de la Blanca from the summit of Montaña de Arena. The apparently converging ‘anti-crepuscular rays’ are formed by shadows being cast by clouds on the opposite side of the sky.

Date

3 April 2013
Location

La Oliva, Fuerteventura

28.633835°N, 13.929066°W

Information

Created 185,000 years ago, Montaña de Arena (422m) was declared a Natural Monument in 1994. The mountain is located 2.5km north of La Oliva in northern Fuerteventura, and its volcanic ‘bad lands’ plain, the Malpaís de la Arena, stretches some 6km from La Oliva northwards to Lajares. There are two conjoined craters at the top of the volcano’s pyroclastic cone, which stands 120m above the base of the mountain.

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Holyhead Breakwater

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At 1.7 miles long, Holyhead Breakwater, completed in 1873, is the longest in the UK.

Date

17 June 2012
Location

Holyhead, Anglesey

SH 25661 84774; 53.33106°N, 4.61950°W

Information

Holyhead’s role as a port for mail-packet crossings to Ireland dates back to the 16th century, but it was in the 19th century that major changes were made as part of a programme of improvements to the mail route from London to Dublin. A new harbour of refuge, where boats could shelter in bad weather, was created when a long breakwater was built off Soldiers Point. Construction began in 1845 and was completed in 1873, with the work initially supervised by James Meadows Rendel and after Rendel’s death in 1856, by John Hawkshaw. The mock castle at Soldiers Point was built in 1848 as the Superintendent Engineer’s residence.

The 19m-high lighthouse at the end of the breakwater, with its unusual square tower, was probably designed by Hawkshaw and was completed in 1873. It is operated by Trinity House and was automated in 1961.

At 1.5 miles long, the breakwater is the longest in the UK. Seven million tons of quartzite extracted from the quarries on Holyhead Mountain were used in its construction.

In August 2011 the breakwater’s owners, Stena Line, were criticised for their lack of maintenance of the structure. The issue of its proper upkeep has been linked to Conygar Stena’s Holyhead waterfront development plans.

Holyhead Breakwater (Royal Commission on the Ancient and Historical Monuments of Wales);
Holyhead Breakwater Lighthouse (Royal Commission on the Ancient and Historical Monuments of Wales);
Fears over condition of Holyhead breakwater (The Bangor and Anglesey Mail, 24 Aug 2011)

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Written by Graham Stephen

June 20, 2012 at 6:42 pm

Carneddau Halos

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Solar halos over Carnedd Llewelyn and Yr Elen

Date

28 January 2012
Location

Carnedd Gwenllian, Carneddau

SH 68520 66535; 53.17961°N, 3.96883°W

Information

This impressive display of atmospheric optical phenomena – caused by ice crystals in high cirriform clouds refracting and reflecting the light from the sun – was witnessed around 2pm on 28 January 2012. It was viewed from a spot on the slopes of Carnedd Gwenllian (formerly known as Garnedd Uchaf) looking south over Carnedd Llewelyn and Yr Elen in the Carneddau range of mountains in North Wales. The various components of the display are described below.

Individual components of the optical display

Circumzenithal Arc
The circumzenithal arc (CZA) is a vividly coloured arc centred on the zenith and extending for about 90°. Appearing like an ‘upside down rainbow’, this arc is caused by horizontal plate crystals acting as 90° prisms (light passes through a horizontal hexagonal face and one of the vertical side faces).

Supralateral Arc
This coloured arc is caused by horizontally oriented columnar crystals acting as 90° prisms (light passes through a vertical end hexagonal face and one of the long side faces of the column).

Upper Tangent Arc
The gull-wing shaped arc above the 22° halo is formed by refraction through side faces inclined at 60° to each other of horizontally oriented hexagonal column crystals.

22° Halo
A solar halo is a bright circle centred on the sun and is formed by refraction. The 22° halo is the most common and occurs when hexagonal crystals with a range of different orientations act as tiny 60° prisms (light enters through one side of the hexagonal cross section and exits through a next-to-adjacent side).

Parhelion
Also known as a ‘mock sun’ or ‘sundog’, a parhelion is a bright, coloured spot seen on either side of and at the same height as the sun. Parhelia are most commonly seen 22° away from the sun and are formed by refraction through the vertical side faces (inclined at 60° to each other) of horizontal plate crystals.

Parhelic Circle
Caused by reflection off vertical faces of ice crystals (both externally and internally), this faint white circle forms parallel to the horizon at the same height as the sun and can extend for as much as 360°.

Paranthelion
This is a sundog appearing 120° away from the sun and occurs when light passing through horizontal plate crystals is reflected internally multiple times.

Warning: when looking for solar halos, never look directly at the sun.

(Featured in Atmospheric Optics Picture of the Day)

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Sun dog over Moel y Ci (‘Dog Hill’) (2)

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Sun dog over Moel y Ci

Date

5 August 2011
Location

Viewed from Bethesda, Wales

SH 63219 66497; 53.17793°N, 4.04809°W

Information

A sun dog (or parhelion) is a luminous spot on one or both sides of the sun at the same height as the sun. It is formed by refraction through hexagonal plate crystals of ice in high cirrus clouds.

Featured in NASA Earth Science Division’s Earth Science Picture of the Day, 12 October 2011.

Sun dog over Moel y Ci (‘Dog Hill’), 1 September 2010
Sundogs, Parhelia, Mock Suns (Atmospheric Optics)
Sundog formation (Atmospheric Optics)

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Written by Graham Stephen

August 6, 2011 at 12:18 pm

Moon, Jupiter and Lunar Halo

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Moon, Jupiter, Lunar Halo

Date

13 December 2010
Viewed from

Bethesda

SH 63218 66487; 53.17784°N, 4.04811°W

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Written by Graham Stephen

December 13, 2010 at 9:15 pm

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