5184 x 3456 px | 43,9 x 29,3 cm | 17,3 x 11,5 inches | 300dpi
Data acquisizione:
9 maggio 2016
Ubicazione:
Kamloops, British Columbia, Canada
Altre informazioni:
A composite image of the May 9, 2016 transit of Mercury across the Sun, with Mercury at a perfect “inferior conjunction” between the Sun and Earth. Transits happen only rarely, about 13 per century. The next is November 11, 2019. Then in 2032. From my location in Kamloops, British Columbia the early stages of the transit were not visible (the transit was in progress at sunrise) and for the first hour or so after sunrise clouds close to the horizon prevented me from starting a consistent sequence of images until about 7:00 a.m. PDT, some 3 hours into the 7-hour-long transit. From then on I took images every 30 seconds. For this composite I used every 14th image to create a sequence showing Mercury moving across the Sun at 7 minute intervals, until it egressed at lower right at about 11:38 a.m. PDT. I stacked a total of 40 images. For all images I used the 130mm f/6 Astro-Physics refractor with a 2X Barlow for an effective focal length of 1560mm and the Canon 60Da camera (at ISO 100) to yield an image size with the Sun just filling the frame. Exposures were 1/250th second through a Kendrick white light Mylar filter. Yellow colouration of the solar disk added in processing. The telescope was on the Mach 1 equatorial mlount tracking the Sun though imperfectly polar aligned, requiring manual alignment of the disk images in Photoshop to compensate for the image drift. The 40 images of Mercury are not all perfect dots nor equal in size due to the variations in seeing conditions from frame to frame. Some frames were sharper than others. I’ve not “cheated” and placed a perfectly sharp disk image cloned and positioned across the Sun to create a more perfect simulation. The solar disk however, comes from just one of the frames toward the middle of the sequence in mid-morning, when seeing conditions were best. Stacking all the disk images would produce smeared sunpsots and disk detail due to the rotation of the Sun over the 4.5 hours of this sequence. The other
