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from the home of NASA’s Hubble Space Telescope

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Building a Constellation Image Library

by John Stoke

We are converting beautiful engravings from a classic star atlas into images suitable for use in a variety of media projects (and now available for use).

Few things in astronomy are immutable. Among those that are, the classical mythological forms of the constellations visible from the Northern Hemisphere, developed long before the study of the stars was a modern science, are perennial public favorites. A ghostly image of a lion appearing among the stars of Leo is just as likely to elicit a chorus of ‘Oohs’ and ‘Ahhs’ from young visitors to a planetarium as is the latest picture from Hubble!

Fanciful mythological illustrations may have little to do with science, but they’re part of astronomy’s great cultural heritage, and to acknowledge that heritage in media projects that involve the identification of constellations (particularly, the Skylines presentations in the online version of ViewSpace), we decided that we really should have a library of constellation images available to overlay atop photographic or synthesized starfields.

With kind help from the US Naval Observatory’s Library in Washington, DC, we perused a variety of centuries-old star atlases, each of which contained a rich treasure of constellation illustrations. It didn’t take long to settle on the late 17th century Firmamentum Sobiescianum sive Uranographia by Johannes Hevelius. This atlas features exquisite engravings that are simply a privilege to behold.

The first step, carried out by our graphic designer John Godfrey and exhibit coordinator Lucy Albert, was to spend a long day at the library digitally scanning the pages of the Hevelius atlas in high resolution. This yielded a collection of digital images containing all of the beauty of the images, but also all of the flaws of the medium, including paper creases and print-through, as shown in this typical page scan:

Leo the Lion as seen in the unretouched star atlas

In addition to the defects noted above, each constellation illustration was ‘marred’ (at least from the point of view of our intent!) with lines demarcating important celestial reference circles and star illustrations showing the then-current positions of bright stars.

Our goal was to have the engravings of the mythological forms alone against pure white. To do this, while remaining faithful to the original style of the illustrations, Godfrey devoted dozens of hours per image to painstaking retouching using Adobe Photoshop software. In many instances features such as entire limbs had to be created in a style that would blend seamlessly with the original engravings. The results speak for themselves:

Leo the lion isolated against white background

When reversed and applied as a layer (in Photoshop screen mode with partial transparency applied to the constellation art layer), the effect is lovely:

Leo the lion against a star field

One interesting thing we learned about Hevelius: He pictured the sky as it would be seen from outside the celestial sphere! Therefore, the images need to be flipped before applying to a starfield.

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