Gallery of Masterpieces
The transits of Venus of 8 June 2004 and 6 June 2012
For the first time since 1882, on 8 june 2004 amateurs had the opportunity to observe and picture the transit of Venus in front of the Sun. Imagine that nobody on Earth had the chance to observe this event for 122 years !
This time Europe was at the first place to observe this event with a sky clear to parly cloudy in most area with temperatures over 20░C. Venus was at 43.1 millions km from the Earth at 0.288 AU only, showing a disk 5 times larger that the one of Mercury and twice as larger as the one of Mars at perihelic opposition, with an angular diameter of 57.7".
In the United States conversely, amateurs could only see the end of the transit because the event had already began several hours before the sunrise. As far as the weather conditions are concerned, in the early morning hours most photographs were recorded under a misty sky or partially cloudy, invaded with cumulus and stratus.
Although the seeing conditions in the United States where not at all favorable for this kind of spectacle, some amateurs didn't hesitate to go out with their apochromatic refractor or their telelens to get some pictures of a great aesthetic value as show the three documents displayed below.
A 7.4 MB Mpeg simulation prepared by GSFC
Let's see now what kind of material used amateurs to record this event. Clubs and groups of amateurs often used optics from 50 to 300 mm wide with an ocular projection on a screen and thus without solar filter. When they worked alone, most amateurs used a solar filter offering a transmission lower than 1/1000th (optical density from 3 to 5), adjusted to the diameter of their objective or off-centered, sometimes simply attached with a rubber band when it was a simple flexible sheet.
Many amateurs used small achromatic refractors (doublets) like Orion ST-80 ED, Tele Vue Pronto 76 or 85, Celestron NexStar 102SLT or an apochromatic refractor equipped with an objective solar filter. Some amateurs fixed it on a simple tripod or on an equatorial mount, others fixed it in piggyback on a larger telescope that, for once, was used as guider.
Some lucky amateurs didn't hesitate to use their large Astro-Physics, Pentax, Takahashi or Zeiss apochromatic refractor from 100 to 200 mm of diameter, their Newton-Cassegrain or their Schmidt-Cassegrain scope from 125 to 300 mm (5-12") of diameter or a solar telescope equipped with an interferential filter.
Among the accessories used in this special occasion, let's quote the sun glasses protected with a polymer film, the Mylar sheet or the Baader AstroSolar film made of alumined polyester, the full-aperture metal-coated glass filter up to 250 mm in diameter (e.g. Orion Telescopes or Thousand Oaks Optical 2+), the Coronado (SolarMax) or Daystar Hα interferential filter, the Herschel wedge, the 1.8 and 2x Barlow lens and long focal eyepieces (32 to 12 mm).
Among the cameras used, for close-ups all amateurs choosed a digital model, from the smallest webcam to the more recent DSLR or simply using HD camcorders.
About the coupling between the ocular system and the digicam, if most amateurs used a special T-ring suited to their body and worked at prime focus of their scope or by ocular projection with an extension ring, in several cases the objective of the digicam, the webcam or the camcorder could not be removed. In this case they worked afocal, placing the eyepiece or the ocular system close to the lens of their digicam, focusing to the infinite when possible and setting the optical zoom mode to the maximum.
They were some accidents without gravity like this amateur, although it was well informed, who saw his solar filter screwed on his eyepiece be broken under the Sun heat (this solution is disadvised for this reason), this other who noted that his Mylar filter was full of pinholes and who had in a hurry to block out all the prick holes with a fine point felt marker and black paint (hence the interest to buy a quality solar filter) to avoid parasitic glare or this other amateur who crashed his CCD camera and had to fall back on his digicam.
Our preparations being finished and the transit being about to start, let's see some among the most beautiful images recorded during this event which, should it be pointed out, will not reproduce again before 2117.
To see : NASA Eclipse Web site
At the first look through the eyepiece, all amateurs where surprised by the size of Venus (we all have in mind the minuscule disk of Mercury) but still more by the sharpness of the disk, like cut with a knife. Indeed, we are used to see its crescent which is a bit fuzzy.
Thanks to eclipse glasses, even naked eye we could see the small black disk of Venus in front of the Sun. Definitely this event had to be spectacular, and it confimed our foreboding all along its evolution.
Venus Transit of 6 June 2012
On 6 June 2012, only observers living in the time zones +7 to +12h GMT (Russia-China-Philippines-Australia-New Zealand) had the opportunity to follow the entire transit of Venus. This time Venus passed in front of the higher part of the Sun as indicated above (the time indicates the greatest transit).
In Europe, the Sun rising only around 4h UT, in Berlin or London the observers only saw the end of the transit (3rd and 4th contact) which began in the U.S.A. by 22h UT. In Europe the Sun was only at 6░ or 14░ above l'horizon at the time of the 3rd contact. Conversely in New-York or Los Angeles amateurs assisted to the first phase of the transit (1st and 2nd contacts) a few times before the sunset.
The black drop effect and the halo
Among the "side effects" that we were all waiting for since 1882, note the "black drop" effect at the instant of the 2d and 3d contact more or less visible on three of the next images (Ayiomamitis, Bishop and Chrisman) and the arc of light or halo in the atmosphere of Venus in three images recorded before the 2d contact and after the 3d contact (Comolli, Smaal and Seip). This effect lasted 20 minutes according to the observation made by Lorenzo Comolli using a 200 mm (8") SCT.
Both phenomena were already noticed by James Cook and Charles Green during an expedition in Tahiti in 1769 as displayed on the sketch at left, by the australian astronomer Henry Chamberlain Russell in 1874 and by the French astronomer Camille Flammarion in 1882.
Usually one told that the "black drop" effect becomes hard to see in scopes over 150 mm (6") of aperture but this time at least two american observers members of the Warren Astronomical Society, and using scopes of 250 mm f/10 (10") and 317 mm f/17 (12.5") observed it as shows very well the last picture at the end of this page. It was taken by Vince when the Sun was only 20░ over the horizon, the scope tracking on Venus to get a stable image. But what is the origin of this strange effect ?
According to Thomas Van Flandern (1940-2009) from Meta Research Institute, "the black drop effect is caused by variable refraction from moving air cells in the Earth's atmosphere".
Bradley Schaefer states that "the ideal image...will suffer smearing...that will produce a somewhat fuzzy image with contour lines (i.e., what is perceived as the edge) that are shaped like the Black Drop. The primary causes of smearing are the usual astronomical seeing (associated with small angle scattering in our Earth's atmosphere) and the usual diffraction in the telescope (the Airy pattern). Other contributing smearing mechanisms that generally do not dominate are imperfections in the telescope's optics, imperfections in the observer's eyes, the finite angular resolution of the detector, and even the physical size of the telescope's aperture".
So for short, the "black drop" effect is first of all depending of the height of the Sun above the horizon (seeing), then of the diffraction effect, while the instrumental resolution, and thus the aperture of the scope comes far behind. Its 's good to know.
Here are the pictures. All images displayed below have been inverted, displaying the north at top and the west to the right, like observing the Sun naked eye. The chronology of events was also respected.
For more information
Planetary transits across the Sun, NASA-GSFC
2004 and 2012 Transits of Venus, by Fred Espenak/NASA-GSFC
Transit of Venus of 9 december 1874, by H.C.Russell
Where was the black drop ?, Sky & Telescope
The black drop effect, by Chuck Bueter
The Black drop effect, by Tom Van Flandern
Orion Telescopes & Binoculars (Metal-coated glass solar filter)
Baader-Planetarium (AstroSolar film made of alumined polyester)
Thousand Oaks Optical (Metal-coated glass filter, black polymer and Hα Lumicon filter)
Coronado (Hα filter)
Daystar (Hα filter)
See also my 1001 Links, Manufacturers.
 Bradley Schaefer, "The Black Drop Effect", Journal for the History of Astronomy 32:4 (Nov. 2001), p334.