Last updated: Tuesday 17th April 2018  Time Zone:  GMT   

The Royal Research Ship James Clark Ross crossed the Equator at 20:13 UTC

I mentioned flying fish the other day and did not have a picture to accompany that statement.  However I asked Richard,  our Purser,  as he has a few taken over the years and he has kindly let me use this one.  Picture Richard Turner.

This part of our journey normally produces wonderful sunsets (see yesterdays photos for a post sunset picture) and one think that we look out for is the 'Green Flash'.  Some say that this does not exist,  but having seen it myself I am happy to say it is no myth and the following is taken from the Mariners Handbook:

THE GREEN FLASH

At sunset,  the small segment of the upper part of the sun's disc,  which is the last to disappear,  may turn emerald-green or bluish-green at the instant of its setting.  The phenomenon thus usually lasts only a fraction of a second,  which is the reason for calling it the 'green flash',  but longer durations of the colour are occasionally seen. 

The green flash is not always seen and when it is seen it is not always equally brilliant.  It can range from a green of extreme brilliance and purity, conspicuous without optical aid,  down to a trace of grey-green coloration observable only with binoculars.

The green flash is produced by the last rays of sunlight emanating from the upper limb of the sun, at sunset,  being refracted before reaching the observer's eye.  The shorter waves which appear as violet,  blue and green light suffer greater refraction than the orange and red longer waves of the white sunlight.  The fringes of the upper limb cannot usually be seen while the main body of the sun is still above the horizon,  as the general sunlight is too strong,  but when most of this is cut off by the horizon they spring suddenly into view.  Normally,  only the green fringe is seen,  the light of still shorter wavelengths usually being scattered by its horizontal passage through the lower atmosphere.  The flash is,  however, occasionally seen as a blue one,  or as green quickly changing to blue.  On very rare occasions the violet colour has been seen.

The green colour occasionally appears in other ways.  Sometimes when refraction is marked,  and the sun's disc is perhaps distorted, the use of shaded binoculars will show that the upper limb appears to be 'boiling', giving off shreds or tongues of green 'vapour'.  Occasionally the sun's upper limb has been seen with a narrow green rim when half or more of the disc remained above the horizon.

A sea horizon is not essential for observing the green flash;  it may be equally well seen when the sun sets behind a distant land surface.  It has also often been seen when the upper limb sinks below a bank of hard-edged cloud at low altitude,  and if there are several parallel bars of cloud in the clear sky the phenomenon may be seen more than once on the same evening.  When the lower line of the sun disappears from behind cloud near the horizon the converse phenomenon,  the 'red flash's has sometimes been seen.

Moon and planets.  The green flash occurs also with the moon,  but has seldom been observed,  presumably because it is fainter and rarely looked for.  On the other hand,  it has been frequently seen at the setting of the bright planets Venus and Jupiter,  and an observation of a blue flash from Venus is on record.  Many interesting varieties of phenomena may occur before these planets set,  the observation usually requiring binoculars.  Colour changes may be seen, usually between white,  red and green,  or two images may appear of the same or different colours.  The planet may exhibit slow 'shimmering' movements,  obviously due to abnormal refraction.

The most favourable conditions for seeing the green flash,  at any rate brilliantly,  is probably some degree of abnormal refraction, whereby the vertical extent of the colour separation described above is greater than that produced by normal refraction.  In addition,  the green flash is most likely to be seen when the air is relatively dust-free, and without mist or haze,  so tha the sun remains brighter  and less red than usual at low altitudes.  The green flash has been well observed at sunrise,  but less frequently,  perhaps because it is less often looked for.  Also, owing to its short duration the phenomenon is liable to be missed unless the exact spot at which the sun will appear is known.

The green flash has sometimes been called,  rather inappropriately,  the 'green ray'.  It will be obvious from the remarks made above that it exhibits a considerable variety of appearances at different times. 

Previous updates from this trip can be found HERE

Latitude: 01 16.6 S
Longitude: 014 05.2 W
Bearing: 150 T, 1118 Nm from Praia (Cabo Verde)
Course Made Good 330 T
(1) Destination 1: Immingham
(1) ETA at 10.2 knots is 07:20 on 03 May 2018
Distance Travelled: 259
Total Distance Travelled: 1007
Steam Time: 24.0
Total Steam Time: 90.4
Average Speed: 10.8
Total Average Speed: 11.1
Wind: Direction SSE, Force 3
Sea State: Slight
Air Temp: 29.8 C Sea Temp: 28.2 C
Pressure: 1013.9 Tendency (3 hrs): Falling

 

Mike Gloistein
gm0hcq @ gm0hcq.com