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Imaging the Orion-Eridanus Superbubble: commercially available cameras and software allow today's amateurs to create unprecedented images.

From the night sky's brightest star and most-illustrious nebulae, to large sweeps of glowing hydrogen that few readers have ever seen before, there's a tremendous range of deep-sky detail visible on the previous two pages. But that's not surprising given the vast area of sky involved. Centered roughly on the constellation Orion, the view stretches 65[degrees] along the celestial equator from Monoceros at left to Eridanus at right. It's only part of a mosaic that we created earlier this year. Covering more than 4,000 square degrees, the full view records almost 10% of the sky visible from Earth.

Just a few years ago, images like this would have been all but impossible to produce. The fact ours was made with readily available equipment and image-processing software emphasizes some of the rapid advances taking place in astrophotography. Furthermore, our exposures were made from a suburban-Boston backyard that's surrounded by some of the world's most light-polluted skies.

Even astrophotographers familiar with wide-field views may need a moment to orient themselves within the mosaic, since prominent nebulosity appears in areas usually thought to be devoid of deep-sky objects. Dominating the bottom center of the image is the constellation Orion and Barnard's Loop, the distinctive crescent-shaped nebula around the celestial giant's Sword. The Orion and Horsehead nebulae, though two of the most famous deep-sky objects in the heavens, are almost lost in the general tangle of nebulosity inside the arc of Barnard's Loop.

A large circular glow in the head of Orion, enveloping the 3rd-magnitude star Lambda (?) Orionis, carries the prosaic designation Sh2-264, but is popularly known as the Angelfish Nebula. To its lower left is Betelgeuse, one of but a few stars standing out prominently in this view. Another is Sirius, the brightest nighttime star, near the lower left edge of the field.

Like pearls on a necklace, large and small patches of glowing hydrogen stretch along a band running from Canis Major at lower left to Auriga at top center. They roughly define the plane of our galaxy in what we northerners know as the winter Milky Way. The bright complex in Perseus at upper right includes the California Nebula, though the state gets a noteworthy border revision because of the faint nebulosity recorded here. The Pleiades, dwarfed by the scale of the mosaic, are prominent along the right side of the image. The dazzling star Aldebaran, in the familiar V-shaped asterism forming the head of Taurus, lies to the right of the image's center.

Beneath the Pleiades, running along an imaginary north-south line at roughly 4h right ascension, is a sinuous nebula known as the Eridanus Loop. The 30[degrees]-tall feature, though prominent in this view, is rarely photographed and likely to be new to many amateurs. Even less familiar is the rippling veil of nebulosity permeating the region.

[ILLUSTRATION OMITTED]

The Orion-Eridanus Superbubble

The Orion Nebula is famous for being a stellar nursery, but the whole central area of the constellation is a massive star-formation region. Collectively called the Orion OB 1 Association, it comprises several subgroups of hot, young stars. At the upper right of Orion's Belt, the oldest and closest subgroup, Orion OB 1a, has stars roughly 8 to 12 million years old, which lie about 1,100 light-years away. The Orion Nebula is part of the youngest subgroup, Orion OB 1d, with stars less than 2 million years old and lying about 1,400 light-years away.

Stellar winds and the aftermath of an estimated 10 to 20 supernova explosions within the Orion OB 1 Association during the past 12 million years have blown a large bubble in the surrounding interstellar medium. Recognized since the 1970s, it's known as the Orion-Eridanus Superbubble. In the red light of hydrogen-alpha emission (656.3 nanometers wavelength), Barnard's Loop is the brightest part of the bubble. Some 40[degrees] to its west, the Eridanus Loop marks another side. This is also the section closest to us, at an estimated distance of about 600 light-years. Barnard's Loop, on the other hand, is thought to be about 1,300 light-years away.

For those who want to learn more about this intensely studied region, star-formation expert John Bally (University of Colorado) has written an overview in the Handbook of Star Forming Regions: Volume I, The Northern Sky. The new book is part of the Astronomical Society of the Pacific's Monograph Publications, and it's available electronically on the ASP's website (astrosociety.org).

Work in Progress

Our mosaic is a work in progress. Indeed, the view here started out merely as a map to locate the extent of the Orion-Eridanus Superbubble that we could record. We're currently working on a new version with images that are deeper and have better resolution.

The view here, however, is made from 15 frames totaling more than 50 megapixels. We acquired them mainly with an SBIG STL-11000 CCD camera, Astrodon 3-nm H[alpha] filter, and 80-mm Hasselblad medium-format lens. But there are also exposures made with a Baader 7-nm H[alpha] filter and 50-mm Hasselblad lens. We did various aspects of the image processing with MaxIm DL, CCD-Stack, RegiStar, and Adobe Photoshop.

[ILLUSTRATION OMITTED]

Although we've lost track of the mosaic's total exposure time (because of frames rejected due to clouds), the initial exposures exceed 40 hours. The original is a 100-megabyte file, which contains more detail than we can show here. For readers who want a better look, we've placed a version on our website (skyandtelescope.com/skytel). We made it a 3-megabyte file by halving the original resolution and saving it in jpeg format.

We're sure there will be an ever-increasing number of spectacular and unusual views of the night sky as amateurs continue to exploit new digital tools. Techniques that weren't even dreamed of by photographers working in darkrooms are now accomplished with just a few mouse clicks. There's never been a better time for astrophotographers to let their imaginations soar.

Sky & Telescope's resident astrophotographers, Dennis di Cicco and Sean Walker, collaborate on many projects.
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Title Annotation:Ultra-Wide-Field Imaging
Author:Di Cicco, Dennis; Walker, Sean
Publication:Sky & Telescope
Geographic Code:1USA
Date:Apr 1, 2009
Words:1000
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