Saturday, 30 November 2013

The Hubble Space Telescope and Astrophotography

Colour image of NGC 6946 in Cepheus processed from three black-and-white digital photos taken through red, green and blue filters by Chris Gainor on the two-metre Plaskett Telescope at the Dominion Astrophysical Observatory in Victoria, 11-12 September 2002. Image processed by John McDonald.

The Journal of the Royal Astronomical Society of Canada
Vol. 105, No. 5, 199-200
October 2010

This year’s celebrations of the twentieth anniversary of the launch of the Hubble Space Telescope have rightly focused on Hubble’s stunning images of the cosmos and Hubble’s many important contributions to the body of knowledge about our universe.

Almost forgotten in these commemorations is the fact that Hubble helped popularize and revolutionize amateur astronomy because it helped move astrophotography from photographic film to digital detectors. This was driven home to me by a recent article on Hubble by art historian Elizabeth Kessler in the spaceflight history journal Quest

Historians like Kessler look at how society affects art, and vice versa. In this case, she was writing about the cultural impact of the Hubble images that have so captivated the public in the years since Hubble was launched in 1990.

In the 1970s, astronomers and engineers at the U.S. space agency NASA had to decide what kind of electronic detectors would be used for imaging in the proposed orbiting space telescope that became Hubble.  

Photographic film had already been ruled out since it would be difficult to retrieve from space, among other reasons. The electronic detector choice came down to a specialized type of vidicon tube, as was used in television cameras at the time, or the charge coupled device. CCDs had been invented in 1969. CCDs then available had many limitations, but new and better CCDs were being developed for military and commercial purposes.

In spite of the many disadvantages early CCDs had for astronomy, the first astronomical images with CCDs were taken in 1976, and the next year NASA decided to use CCDs for one of the main cameras on Hubble. And while most major telescopes began using CCD cameras in the 1980s, their limitations and expense kept CCDs out of the hands of amateur astronomers until much later.

Computers and software were needed to process CCD images, and in 1990, the same year Hubble was launched with its digital camera, Adobe launched its new image-processing program, Photoshop. In the media and among the public, debate began about the newfound ability to manipulate images.

In common with most major telescopes, Hubble’s camera shoots only monochrome (grayscale) images, and colour images are then produced by combining the monochrome images shot using colour filters. Kessler noted that colour astronomical images had been difficult to produce on photographic film, but digital images provided many new options for processed colour astronomical images. 

Hubble’s first deep sky images were seriously flawed due to an error in Hubble’s mirror curvature. After the problem was repaired in a 1993 shuttle repair mission, the first clear deep sky images from Hubble were taken in 1994, and scientists and technicians at the Space Telescope Science Institute had to decide how to process them for colour, contrast and composition before releasing them to the public. 

Particularly since 1998, when the release of colour images from Hubble became more systematic with the beginning of the Hubble Heritage Program, the Space Telescope Science Institute has not only released images but also descriptions of how those images were processed. 

Indeed, those involved with processing and releasing the images have provided a great deal of detailed information about their work, including academic papers, a 2002 article in Sky & Telescope, presentations to astronomy meetings, a television story on 60 Minutes, and of course information postings on the Hubble Heritage website.

These descriptions answered questions about the trustworthiness of Hubble images, Kessler wrote, and meant that the Hubble images “could stand on their own, as an invitation for further research rather than as a reflection on past achievement.”

Since the Hubble data, including raw images, are available to the public after principal investigators have had exclusive access to the data for a time, members of the public can process their own Hubble images, and many have done so.

Kessler concluded that Hubble has contributed to the public’s cultural acceptance of digital images, which have gone from a being novelty at the time of Hubble’s launch to becoming omnipresent today.

As a historian of technology and someone who has been an amateur astronomer since the days when the Hubble Space Telescope was just an idea, I have pondered the role Hubble played in the transformation of amateur astrophotography, thanks to Kessler’s article.

There is no doubt that the availability of CCD cameras, powerful personal computers, image processing programs, and of course the internet, drove the digital revolution in astrophotography.

While I have only dabbled in astrophotography, I certainly remember that the changeover from film to CCDs was not a painless one for my friends who had spent long hours learning how to hyper and process photographic film and prints. With the arrival of digital cameras, they then had to master the new dark arts of digital processing.

I use the word “arts” deliberately, because of the options made available by processing digital images. Images of distant stars, galaxies and nebulae, be they produced on film or CCD, do not and so far cannot replicate what the eyeball sees through the eyepiece. Therefore each image involves judgment calls by the person processing the final image, which is often produced from multiple originals.

In deciding the “right” colour or orientation, I wonder how often the well-known images taken by Hubble or by astronomers working at facilities such as the Canada-France-Hawaii Telescope influence – consciously and unconsciously – the choices made by amateur astrophotographers when they are sitting at their computer terminals.

Ultimately, this question is one for further study by astronomers and historians, but it is certainly worth consideration today as new cameras, telescopes, processing programs and computers give amateur astronomers new means to better view distant objects.

Further Reading
Elizabeth Kessler. “The Hubble’s Anniversary,” Quest: The History of Spaceflight Quarterly,Vol.17, No. 2, 2010, 34-43.

Robert W. Smith. The Space Telescope: A Study of NASA, Science, Technology, and Politics. Cambridge: Cambridge University Press, 1993.

Ray Villard and Zoltan Levay. “Creating Hubble’s Technicolor Universe,” Sky & Telescope, September 2002, 28-34.

The Hubble Heritage Website:  http://heritage.stsci.edu 

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