As far back as I remember, I was always fascinated both by astronomy and cinema. As a kid, I was mesmerized by the stars shining both on the sky and on the screen of my neighborhood’s cinema. Memories from movies like the Star Wars trilogy or from observing the Perseid meteor shower left a huge impact on me.
Now that I am older, I don’t go outside to admire the stars so often and my neighborhood’s cinema no longer exists, but my love for astronomy and cinema didn’t fade away. I still feel quite excited when I see the latest outstanding snapshot of the oldest light in the Universe by ESA’s Planck satellite or when I see how Wes Anderson use symmetry on his movies, for name a few examples. It’s no wonder then that at some point in my life I wanted to become either a cinema director or an astrophysicist. I went for the latter.
I understand the astrophysicist profession as a craft aimed to decipher cosmic light, showing the true nature of the observable Universe, and that its final aim should be taking this knowledge to everyone. Cinema can also show us the true nature of life but it is just an illusion. An illusion, at 24 frames per second, which fools our eyes into sensing motion when light is projected onto a big screen.
Today, February 13th, marks an important date for the history of cinema: it’s the 120th anniversary of the patent of the cinematograph by the Lumière brothers, who are considered the founding fathers of cinema for creating this primitive motion projector. But, did you know that many historians consider the invention of a French astronomer, Jules Janssen, crucial for the development of motion pictures?
Pierre Jules César Janssen (1824-1907) was a French astronomer and is considered a pioneer among the solar physicists. He is best known for the first detection of helium on the solar atmosphere. He was also an avid inventor and one of his inventions, the so-called ‘photographic revolver’ is considered by historians a turning point in pre-cinema history and the history of photography. The creation of this device was aimed to address one of the scientific challenges of the 19th Century: to precisely determine the mean distance between the Earth and the Sun, the so-called Astronomical Unit (1), taking advantage of the transit of the planet Venus in front of the Sun on 9 December 1874.
The famous astronomer Edmond Halley proposed this method back in 1716. Depending on where you are located on Earth, Venus’ apparent position against the background solar disk changes. You just need two simultaneous measures from two places with different latitudes and to measure the duration of the transit. This is known as solar parallax. It seems easy but actually there are two major problems. First, Venus transits are rare events, there have been only seven in the last five centuries! And second, it is also quite complicated to determine the exact moment the planet begins and ends its transit across the solar disk. In addition, it’s not trivial to agree for different observers when this happens as well as the appearance of the so-called “black-drop effect”, which is an optical effect that distorts the planet’s black silhouette on the moments that get contact with the solar disk.
To overcome the latter problem, the astronomers planning the observation of the Venus transit in 1874 defined different strategies such as using observers especially trained for the event together with standard set of telescopes in different expeditions around the world. Janssen’s approach was different; he developed a technique to register the transit on a series of images at short, regular and adjustable intervals during the periods surrounding the contacts.
For that purpose he designed a device that could be attached to a telescope and would record one image per second on a rotating disk, which could register 48 images in 72 seconds. The disk would turn by means of a system driven by a clockwork mechanism. A rotating disk shutter with adjustable slit width would allow the exposure time to be adjusted.
His invention was called ‘photographic revolver’ because its design resembled the one for the Colt revolver. By 6 July 1874, the instrument was completed and tested on a practice model made for training the observers from the transit. You can watch below a video made out of the pictures taken during these tests.
On 9 December 1874, Janssen’s expedition to Japan to observe the Venus transit took 47 images using his invention. Other expeditions, made by British astronomers, around the world took similar devices to record the transit as well. Unfortunately, even though the results were an improvement from the measurements made on the last Venus transit in 1769, the observations made using this technique were not as precise as expected and were quite similar of other measures using the naked eye and the projection of the Sun on screen.
On the following year, Janssen kept developing his invention and presented the photographic revolver to the Société Francaise de Photographie (French Photograph Society) in 1875. His work later inspired others famous figures in history of cinema such as Étienne Jules Marey or the Lumière brothers who eventually, with the invention of their cinematograph, achieved the illusion of motion, the illusion of cinema. An illusion that is admired by many people around the world and shows that among many other important developments on our society produced by science it can also be the responsible of the development of a new type of art.
(1) The Astronomical Unit (au) is defined as the mean distance between the Earth and the Sun. The au is equal to 149,597,870,700m according to its definition adopted by the XXVIIIth General Asssembly of the International Astronomical Union (IAU 2012 Resolution B2).
Jorge Rivero González (@jorgegrivero) was born in Las Palmas de Gran Canaria, Spain. He is a science communicator working at the European Physical Society (EPS) as the EPS IYL 2015 Outreach Officer. He is also editor of the IYL2015 blog. Before that he spent four years living in Munich while he was doing his PhD in Astrophysics at the University Observatory Munich. Since 2009 he is a member of the GalileoMobile project, a science education programme that brings astronomy closer to young people around the world, and has given him the possibility to share the wonders of astronomy with children in Bolivia, Peru and Brazil in 2009 and 2014.