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As the James Clark Ross makes best speed (we can't go full power due to the high sea temperature and overheating of the engines) to the east and Ascension Island,  the science team on board have been keeping themselves occupied with the putting together of their equipment.  The ship's company have been busy with general maintenance of the ship,  making the most of the excellent weather conditions.  Unlike when in Recife we now have a nice breeze which makes it feel a little bit more comfortable,  unless you are working in the machinery spaces - where it is very warm.

Expedition leader Paul Rose checking out one of the Zodiac inflatable boats.  This will be used for a number of operations when we reach Ascension Island,  which should be some time on the 26th.  When we arrive we will meet up with the fishing vessel Extractor and a number of the team currently on the JCR will move across for the duration of the cruise. 

This is an N70 net.  It has been built by Peter,  on the left,  from a drawing and the original nets were used as part of the Discovery Expeditions.

Two underwater cameras,  designed and built by National Geographic.  One of these has been to the deepest trench on Earth and so has withstood immense pressure.  I am not sure what depths we will be deploying them to but am told that there will be some great footage from them when they are retrieved.

One of the enjoyable perks of working on a ship,  and it does not have to be an Antarctic Survey ship like the James Clark Ross,  is that you get to see some interesting phenomena,  sometimes on a daily basis.  Ships,  because of they tend to spend periods of time in the middle of nowhere are often surrounded by phenomena,  it is just a case of looking out for it.  When deep sea there is a daily occurrence that can lead to phenomena,  being sunrise and sunset.  The Green Flash!

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. 

Sadly for us there was no green flash tonight.  As is often the case the perfectly clear sky that one has enjoyed throughout the day suddenly has a line of cloud on the horizon,  in the exact spot of the setting sun.  The good news is that it is not too uncommon and if one persists on clear days then it will eventually be observed.

Due to the timings of the weather satellites over the ship today,  I don't have a good daylight image to share.

My thanks to Frederic who has advised me that the unknown bird on the blog yesterday was a  caracara chimango.   

 Overnight the clocks will be advanced one hour to GMT -1

Noon Position Report

Latitude: 8 09 S
Longitude: 30 56 W
Bearing: 91 T, 235 Nm from Recife
Course Made Good 032 T
Destination 1: Ascension Island
 TA at 13 knots is 16:00 on 26 May 2017
Destination 2: Ascension Island
ETA at 14 knots is 10:30 on 26 May 2017
Distance Travelled: 235
Total Distance Travelled: 235
Steam Time: 16.9
Total Steam Time: 16.9
Average Speed: 13.9
Total Average Speed: 13.9
Wind: Direction ESE, Force 4
Sea State: Slight
Air Temp: 28.5 C Sea Temp: 29 C
Pressure: 1012.4 Tendency (3 hrs): Falling

 

Previous updates from this trip

Mike Gloistein
gm0hcq @ gm0hcq.com