Biggest full Moon in over 18 years
On 19 March 2011 everything came together perfectly – in a completely clear sky there was a full Moon and, what is more, at almost the exact time, the Moon passed through the point of closest approach to Earth on its elliptical orbit. This meant we were able to admire an unusually large and bright full Moon. Not wanting to let this opportunity pass, I photographed the Moon through my telescope.
The distance between the Moon and Earth varies between approximately 356,000 and 407,000 kilometres in the course of a month as a consequence of its elliptical orbit. Seen from the Earth, its perceived diameter varies by 14 percent. When the full Moon stage coincides with the Moon's closest approach to Earth, it is particularly clear and appears about 30 percent brighter than it does at greater distances.
At 19:11 CET, the Moon was opposite the Sun and at a distance of 356,577 kilometres from Earth, but the full Moon and its orbit’s closest approach to Earth missed each other by less than an hour. The last time the full Moon was closest to us was on 8 March 1993; it came 46 kilometres closer to Earth, but couldn't be observed from Germany.
Super full Moon on 19 March 2011 at 23:58 CET. Download: High-resolution image. Credit: Rolf Hempel.
This was a great opportunity to observe Earth's satellite, so I wanted to photograph the full Moon through my telescope at a high magnification. (Click here for a description of my equipment.) I extended the original focal length of my telescope from 1200 millimetres to 3570 millimetres using intermediate optics. I used a Canon 5D MK II camera – a full-frame single-lens reflex camera. Despite the large image sensor, only part of the Moon fit into the field of view at this focal length, so I had to capture the Moon in four parts. Combining the photographs into a composite image was easy with modern software.
Unfortunately, when I looked through the telescope, I realised that the air that evening was unusually turbulent. The image was completely blurred, revealing only brief glimpses of textures on the surface. Since the different sections of the Moon never appeared sharp simultaneously, there was only one thing to do: obtain a large number of images and, using a computer, superimpose them to create a sharp composite image. Luckily the specialist software AviStack2 does this almost completely automatically by using only the sharpest areas in each individual image.
Altogether, I took 100 photographs of each of the four partial views. The real work started afterwards. It took more than 50 hours to process the 400 22-megapixel images on my computer. Then, after another four hours of manual editing, the composite image was complete.
The colours of the lunar surface are enhanced in this version of the image. The dark mare surfaces show an exceptionally broad spectrum of colours, showing the varying mineralogical composition of the surface: deep blue titanium-rich basalts alternate with the more brown-coloured low-titanium areas. With their clearly visible, ray-like impact ejecta, a few young craters are easily spotted on the full Moon. Even after millions of years, they give us some idea of the violence with which the material was dispersed when they were formed.
Close-up of the Moon's North Pole. Credit: Rolf Hempel.
The Moon was about five degrees below the plane of Earth’s orbit when I obtained the photographs, so another interesting phenomenon is visible. With ordinary lunar phases, the dividing line between its light and dark side runs along a meridian from the North Pole to the South Pole, the mountains throw particularly long shadows, and craters form an impressive outline. In this case, since we are looking at the Moon ‘from above’, the shadow-casting zone runs from the west side (top left) to the east side (right) over the North Pole. Since the North Pole (top) is tilted nearly seven degrees in our direction, we can see part of the far side of the Moon beyond the pole.
If you missed the opportunity to see it, you won't have to wait too long – it will happen again on 16 November 2016 - and this time the full Moon will be 56 kilometres closer to Earth.