A new panoramic image of the full night sky — with the Milky Way as its centerpiece — has been made by piecing together 3,000 individual photographs.
The panorama's creator, Axel Mellinger of Central Michigan University, spent 22 months and traveled over 26,000 miles to take digital photographs at dark sky locations in South Africa, Texas and Michigan.
"This panorama image shows stars 1,000 times fainter than the human eye can see, as well as hundreds of galaxies, star clusters and nebulae," Mellinger said.
To combine these images, a simple cutting and pasting job would not suffice. Each photograph is a two-dimensional projection of the celestial sphere. As such, each one contains distortions, in much the same way that flat maps of the round Earth are distorted. In order for the images to fit together seamlessly, those distortions had to be accounted for. To do that, Mellinger used a mathematical model — and hundreds of hours in front of a computer.
Another problem he had to deal with was the differing background light in each photograph.
"Due to artificial light pollution, natural air glow, as well as sunlight scattered by dust in our solar system, it is virtually impossible to take a wide-field astronomical photograph that has a perfectly uniform background," Mellinger said.
To fix this, Mellinger used data from the Pioneer 10 and 11 space probes. The data allowed him to distinguish star light from unwanted background light. He could then edit out the varying background light in each photograph and fit them together so that they wouldn't look patchy.
Mellinger describes the image-making process in the November issue of the journal Publications of the Astronomical Society of the Pacific.
The result is an image of our home galaxy that no star-gazer could ever see from a single spot on earth. Mellinger plans to make the giant 648 megapixel image available to planetariums around the world.