Astrophoto: The Bubble Nebula (NGC 7635) by Karel Teuwen

Every clear evening, as twilight dissolves into night, untold thousands of telescopes scattered across the globe turn toward the great beyond that lies above. But, increasingly, a camera is replacing the eyepiece as the favorite way to study the heavens. Taking deep space pictures was once the purview of a small, dedicated group of amateur astronomers. The technology available was daunting, expensive and time consuming. Luck was an important factor in producing an image that resembled its subject. But all that has changed in the past few years- producing deep space images, such as the one seen here, while still not a point-and-click exercise, has become much easier.

The field of amateur astro-photography gained momentum with the introduction of computerized telescopes and CCD digital cameras. Both of these technologies became affordable to the mass market in the late 1990’s. Over the last five or six years, there’s been a virtual explosion of enthusiasts who seldom peer through their telescopes. These night owls opt, instead, to record their observations with a picture that they can share with those who’d prefer to spend their nights sleeping.

Before digital cameras became affordable, astro-photographers relied on film emulsion to produce pictures. This was a hit and miss experience, at best, because the astro-imager did not know how the exposure looked until, at least, the next day when the film could be developed. If the exposure was too short, the picture out of focus or if a large number of other assorted problems developed, the enthusiast was unaware until it was too late to do anything about it. As a result, many enthusiasts lost their enthusiasm and their telescopes gathered dust.

CCD cameras have changed all of that but not just because they are more efficient in gathering dim light. Digital cameras also enable the imager to see a raw form of their picture immediately after it is taken. Problems can be corrected while the photographer is still out under the stars. Today’s novice astro-photographers learn more in a single evening of photographic attempts than folks using film emulsion could understand over a period of weeks! As the speed of mastering the art increased, frustration levels dropped and enthusiasm took off like a rocket!

Computerized telescopes have also contributed to the growth of amateur astronomers who take night sky pictures. Producing an image of a very faint galaxy or nebula requires the camera’s shutter to be left open so that the dim light can be gathered. This has always been and continues to be a challenge, but first there are two problems that the stargazer must overcome- finding their subject in the sky and tracking it.

Locating a deep space object that cannot be seen with the naked eye or finderscope was always a problem before computerized telescopes provided an answer. For example, pick a point located on distant mountain, turn around and lift a soda straw to one eye while closing the other, turn back around and try to find the mountain point through the staw’s small opening. The size of most astronomical objects is smaller than the head of straight pin held at arm’s length. Pinpointing a telescope used to be an exercise in trial and error that could take much more than a few minutes. Now telescopes are equipped with the night sky imprinted in their memories. Many amateurs simply turn on their instruments and global positioning satellites take over. Tens of thousands of night objects are only seconds away from being centered in the field of view.

Tracking is also essential to producing a deep space picture. Consider that you are standing on a globe that is spinning at about 1,000 miles per hour. Everything in the sky is in motion as the world turns below- tiny, dim deep space objects quickly whiz out of your telescope’s view unless you move the instrument in the precise opposite direction. Before telescopes were computerized, tracking was tedious, imprecise and required constant manual intervention. Today, a computer within the mount that holds the telescope can automatically make small corrections to the speed of tracking or the height that the telescope is pointing based on signals sent by the CCD digital camera! This enables the astro-photographer to concentrate on other aspects of the task at hand knowing that their subject will be positioned in the photograph exactly where they left it when the long exposure began.

There are many more challenges facing today’s astro-photographers, however. For example, the weather and the condition of the atmosphere, as evidenced by star twinkling, remain large factors in how the final picture results. But, with experience learned over time by trail and error, many astro-photographers regularly produce stunning images, like the picture of the Bubble Nebula that accompanies this article.

At the heart of the Bubble Nebula is a star that is forty times more massive than our Sun. Located in the northern constellation of Cassiopeia, this spherical nebula requires a large telescope, dark skies and contrast enhancing filters before it can be seen visually due to its low surface brightness.

The bubble, itself, is actually quite large- spanning six light years across and it’s expanding at about four million miles per hour! The bubble was formed by the bright star that is positioned below and to the right of its center. The radiation released from inside that star is so intense that it literally blows its outer surface off into space. The bubble marks the leading edge of the gust from these powerful stellar winds as it plows into denser surrounding material. This scene is approximately 7,100 light years from Earth.

Belgium astronomer Karel Teuwen produced this picture at his private observatory located near the town of Turnhout using a 16 inch telescope and an 11 mega-pixel astronomical camera. The total length of the exposure exceeded 12.5 hours.

Do you have photos you’d like to share? Post them to the Universe Today astrophotography forum or email them, and we might feature one in Universe Today.

Written by R. Jay GaBany