# 1er partie : Le transit de Vénus devant le Soleil le matin du 8 juin 2004 # 2e partie : Des images # 3e partie : " Les observations de l'effet de la goutte noire" # 4e partie : Des animations / L' explication du phénomène goutte noire / Un questionnaire # 5e partie : Une explication proposée (la goutte noire) /Une animation # 6e partie :Notre section qui traite des images du satellite TRACE (Transition Region and Coronal Explorer) # Part 6 : Images from satellite TRACE (Transition Region and Coronal Explorer) Anglais # 7e partie A ...(1 de 2) : Nous avons tenté de reproduire par logiciel la goutte noire !!! # 7e partie B ...(2 de 2) : Les effets détectables de la goutte noire (Isophotes et ...) # 8e partie : Détermination de la fréquence de coupure et de la fonction de transfert de modulation, et du Point spread function (PSF), des télescopes mentionnés dans ce document. # JSRAC colors " The transit of Venus against the Sun on June 8, 2004 " by MICHEL DUVAL, ANDRE GENDRON, GILBERT ST-ONGE AND GILLES GUIGNIER Amateur Astronomy Clubs of Dorval (CDADFS) and Montreal (SAM), RASC # JSRAC couleurs Le transit de Vénus devant le Soleil le matin du 8 juin 2004 par MICHEL DUVAL, ANDRE GENDRON, GILBERT ST-ONGE et GILLES GUIGNIER du club d'astronomie de Dorval CDADFS, et de la SAM (RASC).

TRACE section #6B : By members of Dorval Astronomy Club (CDADFS) Mainly G. St-Onge, L. Morin and G. Guignier - The images (in raw format) used in this section come for the website " TRACE DATA CENTER " at the following URL: http://vestige.lmsal.com/TRACE/Data/trace_cat.html - Some processed images used in this page are from Dr. Jay M. Pasachoff (Williams College, Williamstown, Massachusetts, USA) and Dr. Glenn Schneider (Steward Observatory, University of Arizona, Tucson, Arizona, USA), at http://nicmosis.as.arizona.edu:8000/ECLIPSE_WEB/TRANSIT_04/TRACE/ToV_TRACE.html - Page making, methodology and elaboration of this section by G. St-Onge and L. Morin - Translation and Text revision by : G. Guignier

- Summary of this document - Our objectives - Description of the images in this section : TRACE .FITS - Black drop progression at 3rd contact (from images in FITS format) - Images of the 2nd Contact (from images in FITS format ) - Conclusion

Thank you to the TRACE Team ! Images from satellite TRACE (Transition Region and Coronal Explorer) This section presents the work we have done on some TRACE raw images  (originally in non-compressed FITS format) in the  WL domain (White Light). This work has allowed us to detect on these images the Black-Drop effect. " TRACE DATA CENTER " http://vestige.lmsal.com/TRACE/Data/trace_cat.html

-   Somes images are compared to processed images available on Dr. Jay M. Pasachoff (Williams College, Williamstown, Massachusetts, USA) and Dr. Glenn Schneider (Steward Observatory, University of Arizona, Tucson, Arizona, USA) website. These images have been captured by TRACE (Transition Region and Coronal Explorer), which is supported by the Committee for Research and Exploration of the National Geographic Society and the NASA. These images are available on the website : http://www.eclipses.info or by direct access to the site : TRANSIT OF VENUS 08 JUNE 2004 TRACE WHITE LIGHT INGRESS/EGRESS IMAGING with the kind authorization from Dr. Jay M. Pasachoff and Dr. Glenn Schneider. Pictures coming from  : http://nicmosis.as.arizona.edu:8000/ECLIPSE_WEB/TRANSIT_04/TRACE/ToV_TRACE.html -   From Glenn Schneider, Steward Observatory, University of Arizona gschneider@as.arizona.edu, http://nicmosis.as.arizona.edu:8000/ ------------------- In collaboration with Jay Pasachoff, Williams College Jay.M.Pasachoff@williams.edu

================== Our contribution : Summary of this document - This section of our work, based on the TRACE images, contains some of the observations we made from these pictures. We have been able to put in evidence the black drop effect (a dark region between the edge of Venus disk and the edge of the solar face) using TRACE images  (in a non-altered FITS format), while Venus was approaching the 3rd contact and slightly after the 2nd contact. These effects are also seen the processed images issued from Dr. Jay M. Pasachoff and Dr. Glenn Schneider website. - We have been brought to conclude that the black-drop effect, also observed on some TRACE images in jpeg format, is something real, and not a artificial bias effect that would have been produced by image processing techniques. - We do not claim explaining all the mechanics of the black-drop effect on the TRACE images, but we have tried only to show this phenomenon is also present on the satellite images, just as we have observed it on our own pictures. - In the particular TRACE case, we have to consider that the satellite imager is not subject to atmospheric turbulence and thus is able to achieve a high image resolution (~ 0,5 arcsec/pixel). Therefore, we have concluded that the influence of the Earth atmosphere, as discussed on some other section of this document, onto the TRACE images does not apply. In order to propose an explanation of the black-drop effect on TRACE images, we have assumed that the edges of Venus and Sun disks displays halos as observed on our own images (please refer to Part 5 and in the JSRAC colors section of this work). - In our analysis, we have taken into account that the TRACE imager detector is not perfectly adapted to high-contrast imaging. Therefore, TRACE images are prone to be altered by high contrasts such as the ones observed during the Venus transit. They also could be affected by a contrast drop that may occur resulting from Venus and Sun halos interferences (Part 8), in addition to the limb darkening effect mentioned by Dr. Jay M. Pasachoff and  Dr. Glenn Schneider. - We think that the FITS images from TRACE show quite well that the black-drop effect is a consequence of the optical performance of the imaging instruments, without any contribution of the atmosphere. The black drop appears well on these two images and more evidently on image #1B. Image TRACE #1A Image from " TRACE DATA CENTER " Image TRACE #1B " Image from TRACE DATA CENTER " - The left image #1A is a typical RAW image of the TRACE satellite. We can see a pale dark band between the edge of Venus disk and the edge of the Sun. - On the right, image #1B  has been adjusted to reveal some contaminating scattering of the raw image. This contaminants have been addressed by Dr. Glenn Schneider et Dr. Jay M. Pasachoff during image processing. - The following image #1C, is a pre-processed image by Dr. Glenn Schneider and Dr. Jay M. Pasachoff. A slight darkening between Venus and Sun disks can be seen. Black-drop effect still remains on these processed images  (in blue on color image #1D). Image TRACE #1C (Courtesy of Jay M. Pasachoff and Glenn Schneider) Image TRACE #1D (Courtesy of Jay M. Pasachoff and Glenn Schneider) Image TRACE #1E (Courtesy of Jay M. Pasachoff and Glenn Schneider) Image TRACE #1F (Courtesy of Jay M. Pasachoff and Glenn Schneider) Images TRACE # 1E - # 1F are also processed images by Dr. Glenn Schneider and Dr. Jay M. Pasachoff. Image # 1E appears in an original document from the authors. On Image # 1F, contrast has been adjusted and colour palette has been re-defined show evidently the apparent bridging cavity between Venus and the background. - On some processed images from Dr. Glenn Schneider and Dr. Jay M. Pasachoff, one can also distinguish a dark line on the sky background. In this case, it is an artefact resulting from the image processing. - We observe from the first image on which Venus disk is very close from the Sun edge, and from second image where Venus disk is outside of the Sun disk, a dark line on the sky background. On the contrary, on the corresponding raw FITS images, (TRACE DATA CENTER), this feature can not be seen. It can be concluded that these artefacts have resulted from image processing operations. ================ Description of the images in this section (acquisition by satellite TRACE in the WL (White Light) band). TRACE WL : - The first set of images allows seeing the commencement and the evolution of the black-drop phenomenon just before contact #3. In Dorval (Quebec, Canada), we could only observe contacts #3 and #4. - On some of the pictures, we have issued a contour plot that shows the apparent depression of the sun edge towards Venus disk, resulting from the black-drop effect. - Then, we have included a second series of images that specifically shows the second contact and the black drop effect. - And finally, another website, where TRACE images with the black drop effect are shown, should be mentioned: http://vestige.lmsal.com/TRACE/transits/venus_2004/

- Our objectives: Our objectives consisted in detecting the black drop effect on the WL raw images from TRACE satellite and on the already-processed images, provided the instrument has contributed to this phenomenon. We would expect to find on these images, which have been acquired from above the atmosphere, the same effect as on the pictures we have captured from the ground. The analysis we have made on our own images (please refer to Venus Transit Part 5 , Part 7B , Part 8 and Venus Transit, back to the first part ), has permitted to build a model which describes quite well the construction and the evolution of the black-drop effect. - From this model, we have tried to detect on the TRACE images signs of the black-drop effect. Parameters we have used on these pictures: - Images from the TRACE DATA CENTER are originally in FITS format. They have been converted in JPG format in order to be posted online on this website. - The same visualization thresholds were applied (High = 4095 and Low = 167). - The colour coding used is the thermal palette of Pises Atlas-PRISM98 software edited by the Société Astronomique de Montpellier (authors : C. Cavadore, B. Gaillard, P. Martinole). - Isophotes and contour plots are also used on some images in order to highlight the black-drop effect on some images. - Our results seem to be of interest and worthy to be part of the present document. These images and the analysis we propose along bring another point of view on this captivating phenomenon of the black-drop effect. Enjoy your visit !

Black-drop progression at the 3rd contact TRACE's WL pass band (White Light) (WL transmission : ~ 200nm à ~900nm) Time is expressed in UT Image #1 - 10h 58 12 - This image does not show any sign of the black drop. Image #1B - 10h 58 12 Using a contour plot rendering, this picture does not show any apparent depression of the sun edge in the region of Venus disk. Image #2 - 10h 58 29 One can barely see first signs of the black drop (diffuse). Image 2B The first signs of the black-drop effect!!! Image #3 - 10h 58 41 The black drop is more evident on this picture as the dark bridge between Venus and sun edges is getting darker. Image #3B - 10h 58 41 On this image (contour plot mode), the apparent depression of the sun edge towards Venus disk can be well observed. Image 3C - 10h 58 41 Magnification of the previous picture. Image #4 - 10h 58 49 The region of the black drop is larger and darker. Image #4B - 10h 58 49 The Isophote image shows an apparent bridging cavity at the darker location of the black drop. Image #5 - 10h 58 58 This image uses a Black and White palette and it may show the black-drop effect at its best. Pictures of the 2nd contact TRACE's WL pass band Image #6 - 05h 39 02 This picture show clearly the black-drop effect, with a Black and White palette. The darker band between Venus disk and the edge of the sun can be seen as well. Image #6B - 05h 39 02 The use of the thermal palette allows to highlight the black drop even more. Image #6C - 05h 39 02 This image in contour plot permits to see the depression of the sun disk edge which seems to fall onto Venus disk. Image #7 - 05h 39 25 The black-drop effect is still visible.

Original Images taken by satellite TRACE Extracted from the " TRACE DATA CENTER " This set of pictures was originally in FITS format (without any compression nor quality loss). They have been converted into the JPEG format before their insertion in this page. - The same visualization thresholds were applied (High = 4095 and Low = 167). - The colour coding used is the thermal palette of Pises Atlas-PRISM98 software edited by the Société Astronomique de Montpellier (authors : C. Cavadore, B. Gaillard, P. Martinole). Time is expressed in UT Just before the 3rd contact , Image #1

Image #1 at 10h 58 12 UT " TRACE DATA CENTER "

Image #1B at 10h 58 12 UT " TRACE DATA CENTER "

This image coming from the TRACE DATA CENTER still does not show any significant sign of the black drop.

Image #2 at 10h 58 29 UT " TRACE DATA CENTER "	Image #2B at 10h 58 29 UT " TRACE DATA CENTER "

Some faint signs of the black drop are now visible on image #2. Note the apparent depression of the sun disk edge on image #2B at the tip of the leader.

Image #3 at 10h 58 41 UT " TRACE DATA CENTER "

Image #3B at 10h 58 41 UT " TRACE DATA CENTER "

Image #3 : The effects induced by the black drop are getting more important. Image #3B : In this image in contour plot, the depression is clearly visible.

Image #3C at 10h 58 41 UT Magnification of image #3 : This image has been adjusted in order to reinforce the apparent depression of the sun disk edge in the contact region. Note the leader tip pointing at the depression as a clear effect of the black drop. " TRACE DATA CENTER "

Image #4 at 10h 58 49 UT " TRACE DATA CENTER "

Image #4B at 10h 58 49 UT " TRACE DATA CENTER "

Image #4 The region covered by the black drop is larger and darker now Image #4B This image in isophote rendering displays the bridging cavity at the location where the black-drop effect is the most important.

Image #5 at 10h 58 58 UT " TRACE DATA CENTER "

Image #5 This image has been adjusted in a different manner in order to enhance the black drop effect.

Image #6C at 05h 39 02 UT " TRACE DATA CENTER "

Image #6C - 05h 39 02 This image displayed in contour plot allows to visualize the depression of the Sun disk edge oriented towards Venus disk.

Image #7 at 05h 39 25 UT " TRACE DATA CENTER "

Image #7 - 05h 39 25 The black drop effect is still visible (green colour).

To go further : - In the website http://vestige.lmsal.com/TRACE/transits/venus_2004/ it is possible to find a picture taken by TRACE showing the black-drop effect. The following legend is associated with this image : 2006-06-08 at 10:57:52UT - 11:01:24 UT, black drop effect. Conclusion : - The TRACE scientific satellite has not been designed to image high contrast picture such as the Venus transit across the Sun disk. - Therefore, TRACE images can be affected by some high contrast conditions during the transit: refer to Image TRACE #1B at the beginning of this page where dispersions affect the raw picture extracted from the TRACE Data center. - In addition to the previous point, the images are also affected by a contrast drop occurring from Venus and Sun halos interferences. We would also mention that the limb darkening on the Sun disk may play a role in the black-drop effect observation. Please consult section Part 8  of this study where MTF and PSF are discussed. There is a shared aspect between TRACE images and the pictures CDADFS members are taken relatively to the black-drop effect : - It may be important to consider the apparent curvature at the Sun edge (depression towards Venus) when the planet disk close to the contact phase. This factor can be associated with the black-drop phenomenon, and hence to the contrast drop. This depression effect can be observed on André Gendron s and Gilles Guignier s images (refer to Part 4 "les animations", and sections Part 7 and Part 7B of this study. - We conclude this page by stating that there are certainly detectable effects of the black-drop phenomenon on the satellite TRACE images, and that these effects are induced by the imaging instrument characteristics. - The black-drop effect may not be considered as an intrinsic effect due to Venus and Sun disks, but rather a phenomenon caused by instruments and seeing condition (optics collimation, MTF, PSF, thermal balance of the telescope, stability of the atmosphere, limb darkening, ...). References: - "TRACE DATA CENTER" http://vestige.lmsal.com/TRACE/Data/trace_cat.html - Glenn Schneider, Steward Observatory, University of Arizona gschneider@as.arizona.edu, http://nicmosis.as.arizona.edu:8000/ ------------------- In collaboration with Jay Pasachoff, Williams College Jay.M.Pasachoff@williams.edu http://nicmosis.as.arizona.edu:8000/ECLIPSE_WEB/TRANSIT_04/TRACE/TOV_TRACE.html - Le transit de Vénus devant le Soleil Le matin du 8 juin 2004 Tel qu'observé de Dorval et de Montréal (Pointe-aux-Trembles) Québec Canada. Par des membres du CDADFS Transit de Vénus, retour à la première partie - Schneider, G., Pasachoff, J. M., and Golub, L., 2004, "Space Observations of the 15 November 1999 Transit of Mercury and the Black Drop Effect for the 2004 Transit of Venus," Icarus 168 (April), 249-256. - Pises Atlas-PRISM98 from the Société Astronomique de Montpellier, C. Cavadore, B. Gaillard, P. Martinole (astronomical image processing software).

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