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Recently, the European Space Agency released the third batch of data from the Gaia satellite, a public catalog that provides the positions and velocities of more than a billion stars. This is our latest attempt to answer some of the age-old questions in astronomy: How do stars (and nebulae) spread across the sky? How many are there, how far away are they, and how bright are they? Do they change in position or brightness? Are there new kinds of things unknown to science?
For centuries, astronomers have tried to answer these questions, and the work has been painstaking and time-consuming. It’s not always easy to record what you can see through the eyepiece of a telescope – if you’re lucky enough to own a telescope.
Now imagine the emergence of a new technology that in its time offered some of the advantages of Gaia’s indexing technology. It can record what you see automatically and impartially, and anyone can use it.
This technique is photography.
This article tells how photography changed astronomy and how hundreds of astronomers formed the first international scientific collaboration to create the Carte du Sel (literally, “map of the sky”), a complete photographic survey of the sky. This collaboration resulted in a century-long struggle to process thousands of photographic plates taken over decades, and manually measure the locations of millions of stars to create the largest catalog of the night sky.
Unfortunately, the Carte du Seal project came at a time when our ability to collect measurements of the natural world and our ability to analyze them did not match. During the implementation of the project, new instruments made it possible to study physical processes in distant celestial bodies, keeping scientists away from surveys by providing the opportunity to develop new models to explain the world.
For the astronomers working on the Carte de Sel, there is still no model that can sum up the locations of millions of stars into a theory of how our galaxy formed; Instead, the researchers only had a hunch that photographic techniques would be useful for mapping the world. They were right, but it took more than a century and a lifetime for the intuition of many astronomers to come true.
photography and astronomy
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Louis Daguerre’s photographic techniques were introduced to the world by astronomer and explorer François Arago, head of the Paris Observatory. Daguerre built on the work of Nicephorus Knipes and discovered how to create permanent images on metal plates.
For centuries, astronomers have struggled to record what they saw in the night sky through hand-drawn notes and drawings. Staring at the distorting optics of old instruments, it’s not always easy to draw what you can see. You may notice things that are not there; The canals and plants on Mars that poor Schiaparelli took from the Milan Observatory were nothing more than an optical illusion caused by the turbulent atmosphere. Only a few highly trained astronomers, such as Caroline and William Herschel, were immediately able to spot a new star in a familiar galaxy – a sign of a distant catastrophic event?
Photography can change all that. Arago immediately recognized the huge potential of this technology: images captured in the depths of the night might be adequately and quantitatively analyzed in broad daylight. Measurements can be accurate and can be checked frequently.
Daguerre received a pension and allowed Arago to open up the details of his operation, which led to an explosion of portrait studios in Paris and around the world. But as it turns out, Daguerre’s method was neither sensitive nor practical enough to capture anything but bright stars, the sun, or the moon. The next hot new technology, wet collodion emulsions, wasn’t much better; The plates tend to dry out during the long exposures required to capture faint astronomical objects.
Astronomers had to wait 40 years until the 1880s before ultra-sensitive dry photographic plates finally became available.