Eyes on the Skies by Govert Schilling

Author:Govert Schilling
Language: eng
Format: epub
Publisher: Wiley
Published: 2011-12-01T00:00:00+00:00

NGC 7635 — THE BUBBLE NEBULA

Three shells of gas surround this massive star in the constellation Cassiopeia to form the Bubble Nebula. About six light-years in diameter, it glows because the gas in the shell is ionised by energetic radiation from the star. Magenta wisps near the bottom right of this photo are thediluted remains of a super-nova explosion that occurred thousands of years ago.

The big advantage of digital images is that they are all set and ready for computer processing. Astronomers use sophisticated and specialised software to clean, tweak and improve their snapshots of the sky. They can calculate results directly from the data in the images and extract interesting information that can be plotted and visualised. The images can be stretched or contrast enhanced to show the faintest regions of nebulae or galaxies. Colour coding brings out structures that would otherwise remain invisible. By combining three images made through different colour filters, glorious composites can be produced, blurring the boundary between science and art.

There are other knock-on benefits from electronic astronomy. Never before has it been so easy to find spectacular images of the cosmos. The newest Hubble photos or the latest images from space probes orbiting distant planets are just one mouse click away! Semiprofessional amateurs use Photoshop to apply their image processing skills to images taken with the big telescopes or to digitised versions of old photographic plates to create strikingly beautiful colour composites for everyone to enjoy. Amateur astronomers with small backyard telescopes that use cheap and simple webcam technology can routinely obtain images of planets that show much more detail than the best photographs taken with the 5-metre Hale Telescope half a century ago.

The digital revolution has also made it possible to automate the observing process completely. Robotic telescopes, equipped with sensitive electronic detectors, keep watch over the sky. Advanced computer software compares images that are made a few hours or days apart, picking up the slightest change to detect asteroids in the Solar System, variable stars and extrasolar planets in our Milky Way or supernova explosions in distant galaxies.

The art of blinking

For the better part of the twentieth century, astronomers have been using blink comparators in their hunt for asteroids, variable stars and other changes in the sky. The idea is simple. Two photographic plates of the same part of the sky, each containing tens of thousands of stars, are compared side by side by looking through the eyepiece of the blink comparator. A mirror flips the observer’s view between the two plates every second or so. For most stars, the observer won’t notice any difference, but if a star changes position or brightness, it will appear to jump to and fro, or to switch on and off. With the advent of digital images and powerful computers, this tiresome technique has finally become obsolete: sky images can now be compared automatically simply by subtracting one from the other to reveal any changes between the exposures.

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