Earthshine during a total solar eclipse J. Brit. Astron. Assoc., 107, 2, 1997, pp. 106–107
(Note: The Association is not responsible for individual opinions expressed in articles, reviews, letters or reports of any kind.)
Earthshine during a total solar eclipse From Mr Mike Harlow
Regarding Graham Young's letter in the February Journal, it would appear that it is not possible to see the Earthshine during a total solar eclipse. Although Earthshine can appear quite bright in the night sky, the sky during totality is considerably brighter, in fact about 10 times brighter than Earthshine itself. A diagram illustrating this can be found in Harold Zirin's excellent book on the Sun.[1]
Mike Harlow
Orwell Astronomical Society, Ipswich. ( mike.harlow@bt-sys.bt.co.uk)
[1] Zirin, H., Astrophysics of the Sun, Figure 8.5, p. 222, Cambridge University Press, 1988
From Mr Patrick Poitevin
Of the ten total eclipses I have observed, I have seen the dark side of the Moon quite a few times. With a small telescope, a 70cm refractor or since 1992 a C90 Celestron, you can see the structure on the black disk of the Moon during totality. It is of course not in the colours you will observe on the Moon and its dark limb during lunar observations. It is very dark, dark grey and black. Colours are very deep and less pronounced.
I have never seen a photograph of this effect. I believe the main reason observers do not see the dark side of the Moon during totality is because they are spending too much time making pictures and forget all the beauties of the phenomenon. Every eclipse, I notice observers are missing a lot. It does not have anything to do with experience or otherwise. They seem to be focused on their camera and not the spectacle of the eclipse and its surroundings. In contradiction to astrophotography, where you will make pictures of what you cannot see and never will, at solar eclipses you can never photograph what you have seen or experienced.
Patrick Poitevin
Eclipse Section, VVS Belgium, Pulsebaan 16, 2275 Lille-Wechelderzande, Belgium. ( ppoitevin@innet.be)
From Mr Andrew Langley
I read with interest the paper by Thomas Dobbins regarding his use of video equipment to observe the Moon and planets. (Journal 1996 December). His results are of a high standard clearly demonstrating the great potential of this technique.
As Mr Dobbins rightly points out the Moon is largely monochromatic, but there are subtle colour differences which, under suitable conditions, can be emphasised by the use of a colour camera such as a domestic camcorder. This may be useful in some aspects of TLP research for instance.
Following the example, and with the encouragement, of Gerald North I have been using a VHS-C Palmcorder camera at the eyepiece of my 22cm Newtonian reflector, primarily for recording the Moon. This arrangement is rather more bulky than that of Mr Dobbins and is of intrinsically lower resolution, but still yields very pleasing results. To avoid vignetting the camera is used at or near its maximum zoom setting and in 'sport' or 'portrait' mode to ensure a large physical lens aperture.
My efforts at 'hardcopy' of the video images have so far been by photographing still-frame images from a colour television screen. These exhibit the undesirable qualities described by Mr Dobbins. In particular the raster lines become increasingly obvious on enlargement and the grid of colour elements can also be observed.
An approach with which I have been experimenting to reduce these effects has been briefly discussed in a Lunar Section Circular. During the printing of negatives a fine glass plate (a microscope slide) is placed in the beam immediately below the enlarger lens. During exposure this plate is continuously rocked backwards and forwards about an axis parallel with the projected image of the raster lines. This causes a small displacement of the image which can be adjusted (following observation with a magnifying focus finder) so as to 'blend' adjacent raster lines hence smoothing the image. The raster pattern is somewhat subdued in the processed version without a significant reduction in image quality.
A more elegant method of image processing is described by de Frutos & Gonzales Vismanos.3 In this case a transparency of the television image is illuminated by laser light and the resulting diffraction pattern examined. A suitable mask is then constructed to eliminate diffracted beams due to regular screen features, while allowing the underlying image information to pass relatively unaffected.
Andrew Langley
'Awelon', Hirwaun Road, Aberdare, Mid Glamorgan.
From Mr Mike Frost
I was on my (late) summer holiday in Turkey during the partial eclipse of the Sun on Saturday October 12. Earlier in my holiday I had observed several sunsets (in a fruitless attempt to see the green flash again) from the restaurant at the east end of the beach. The barman was used to tourists making their way up to watch the sunset – I don't think he had encountered too many people who proceeded to try and burn the Sun's image into the wall of his bar with a pair of binoculars. To keep the barman happy I ordered a drink; then I noted the progress of the eclipse. 10 to 15 percent of the disk of the Sun was covered and it was only ten minutes from sunset – so yes, I was going to see a sunset eclipse.
As the Sun sank, and more and more sunlight was scattered, it became possible to observe the eclipse safely with the naked eye. In the last few seconds of the sunset binocular observations became possible. As the Sun approached the horizon, its reflection in the calm waters of the Mediterranean became clearer and clearer, and I saw a mirror image of the eclipse reflected in the blue sea. Finally, as the Sun began to sink below the horizon, there was a stunning sight. As the Moon touched the horizon, the fiery red of the Sun was split into two by the utter blackness of the eclipsing Moon, and for a few seconds I had two separated sunsets – deep red diamonds of light shrinking rapidly into the ocean. Moments later, first one and then the other Sun flickered out, and I was left with a smooth red horizon.
Unfortunately there was no green flash, as I was in a position to see a unique double green flash as each of the two segments set separately. But what I saw through my binoculars was a sight every bit as awe-inspiring as a view of totality: two beautiful lozenges of red slipping into an azure sea.
Mike Frost
70 Arbour Close, Bilton, Rugby, Warwicks. CV22 6EH
From the editor of Network
I should like to thank Pete Seiden for his unstinting work as editor of Network from its inception until the autumn 1996 issue. From relatively little straw, he produced a very sound brick and I shall do my utmost to maintain the standards which he set.
Since it is clearly inappropriate for me, as Network editor, to remain as the Association's Area Representative for Derbyshire and Nottinghamshire, there is urgent need for a replacement. At the same time, there are still other areas of the country without a BAA representative. If you are interested, please contact either myself or the office at Burlington House.
Mike Carson–Rowland
Barnstead, 141 Ecclesfield Road, Chapeltown, Sheffield S30 4TD
From Mr T. J. C. Moseley
I fully agreed with the advice given in Dr P. M. R. Hemphill's letter in the February Journal, in which he quoted polar alignment instructions from the late Dr W. H. Steavenson. I have always found the method simple and accurate.
However, one minor correction is now necessary: the effects of precession since Dr Steavenson's time mean that the true Pole now lies much closer to a line from Polaris to Kocab (Beta UMi) than from Polaris to Eta UMa. The angle between the line from Polaris to the Pole and the line to Kocab is 19 minutes (RA), compared with 44 minutes (RA) for the line to Eta UMa. Polaris is now about 44 minutes of arc from the true Pole.
Terry Moseley
6 Collinbridge Drive, Glengormley, Co. Antrim, N. Ireland BT36 7SX
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