About twenty years ago while I was still teaching classes in astronomy for a local adult and continuing education program, an elderly student of mine gave me a very special gift – a couple of boxes filled with glass lantern slides that her father had used decades earlier in his lectures on astronomy. These slides included many produced by the University of Chicago Press during the 1920s and 1930s showing photographs taken by the Yerkes Observatory as well as slides from other sources. These were the old time equivalent of the photographic slides I had been using during my astronomy lectures at the time (which have since been replaced by electronic presentations).
A few months ago while digging through my archives, I found these slides and decided to sort through them for the first time in a long time. Among these were a pair of slides of Mars taken at the Yerkes and Mt. Wilson Observatories. A little digging quickly revealed that they were taken during an especially favorable perihelic opposition of Mars in 1909 providing the best views of the Red Planet to Earth-bound observers in 15 years. Between the advances in telescopes and especially photography during the intervening years, these were considered the best images of Mars ever taken up to that time. And given that astronomers like Percival Lowell used their visual observations during this favorable opposition to bolster their claims about the existence of canals on Mars (as well as life on the Red Planet – see “A Cautionary Tale of Extraterrestrial Chlorophyll“), these images provided an unambiguous visual record free from the vagaries of human artistic interpretation.
A contemporary diagram showing the positions of the Earth and Mars during the 1909 opposition. Click on image to enlarge. (Rolston)
The first of these images was taken by American astronomer and astrophotography pioneer, E.E. Barnard (1857-1923) (after whom Barnard’s Star is named – see Barnard’s Star page), using the 40-inch (one-meter) refracting telescope at the Yerkes Observatory – the largest astronomical telescope of this type even to this day. With Mars reaching opposition on September 23, 1909, Barnard took a series of photographs of the Red Planet on September 24 and 28 through a yellow filter (to reduce the effects of atmospheric scattering and improve surface feature visibility) using Cramer Instantaneous Isochromatic plates. These comparatively sensitive photographic plates in combination with the Yerkes 40-inch telescope allowed Mars to be recorded with exposure times of just two or three seconds. While the photographs taken on September 24 were of less than satisfactory, those from September 28 were excellent by the standards of the day.
The Yerkes 40-inch (1-meter) refracting telescope used by Barnard to photograph Mars in 1909. (Yerkes Observatory)
On the evening of September 28, Mars was 59.4 million kilometers away (just a bit more than the minimum distance of 58.3 million kilometers attained on September 18) and presented a disk with a diameter of 23.6 arc seconds. Each column of images in the slide seen below were taken within a few seconds of each other. The images in the left column were taken at about 15:44 GMT, at 16:24 GMT for the middle column and 16:44 GMT for the right column. Centered on the triangular-shaped classical feature called Syrtis Major (today known as Syrtis Major Planum), they clearly show the rotation of Mars during the hour of elapsed time. Also clearly visible in the image is the remnant of the south polar cap.
The images of Mars were taken by Barnard on September 28, 1909. The images in each column were taken just a few seconds apart with the left column taken at about 15:44 GMT, the middle column at about 16:24 GMT and the right column taken at 16:44 GMT. Click on image to enlarge to a scale of ~0.15 arc seconds/pixel (the effective resolution is closer to an arc second). (Yerkes Observatory)
The second lantern slide showed a pair of images taken by American astronomer George Ellery Hale (1868-1938) who had founded the Mt. Wilson Observatory in California. The instrument he used was the 60-inch (1.5-meter) reflecting telescope, which saw first light in December 1908 and was the largest operational telescope in the world at the time. As an interesting historical aside, Professor Hale also played a central role in developing the California Institute of Technology into a leading research university. As part of this push, the Guggenheim Aeronautical Laboratory at the California Institute of Technology (GALCIT) was founded in 1936 to research rocket propulsion. This lab was renamed the Jet Propulsion Laboratory in 1943 and would go on to send the first successful probe to Mars 55 years after the 1909 Mars opposition.
The 60-inch (1.5-meter) reflecting telescope at the Mt. Wilson Observatory used by Hale to photograph Mars in the fall of 1909. (Mt. Wilson Observatory)
The first of these images was taken on October 5, 1909 when Mars was at a range of 61.4 million kilometers presenting a disk that was 22.8 arc seconds across. As with Barnard’s photographs taken a week earlier, this image is centered on Syrtis Major with the bright circular classical feature known as Hellas visible to the south (now known to be an ancient 2,300-kilometer impact basin called Hellas Planitia).
An image of Mars taken by Hale on October 5, 1909. Click on image to enlarge to a scale of ~0.07 arc seconds/pixel (the effective resolution is closer to an arc second). (Mt. Wilson Observatory)
The second image was taken on November 3, 1909 when Mars had receded to a distance of 80.4 million kilometers with a disk that was 17.4 arc seconds across. This image records a part of the Red Planet to the west of the earlier view showing the classic feature known as Sinus Meridiani. Today this is known as Meridiani Planum and would be the landing site of NASA’s long-lived Opportunity rover 94 years later (see “Meridiani Planum in 1969 – Our First Closeup View of Opportunity’s 2004 Landing Site”).
An image of Mars taken by Hale on November 3, 1909. Click on image to enlarge to a scale of ~0.05 arc seconds/pixel (the effective resolution is closer to an arc second). (Mt. Wilson Observatory)
Although these images were the best photographs of Mars of the time, atmospheric seeing and the seconds-long exposure times limited their effective resolution to something on the order of an arc second or about 300 to 400 kilometers on the surface of Mars. While some of the features visible in these photographs corresponded to some of the canals identified by Lowell and other visual observers, the vast networks of fine linear features mapped by these astronomers were not visible in these or subsequent images of Mars taken over the following half century. The explanation was that the visibility of the canals was too ephemeral to be recorded in photographs but could be observed visually only during brief periods when the atmospheric seeing steadied for a moment to improve the view substantially. It would not be until after NASA’s Mariner 4 mission reached Mars in July 1965 that the first closeup, kilometer-scale images of the Red Planet showed no signs of the classical canals but a cratered Moon-like landscape instead (see “Mariner 4 to Mars”). It has since been shown that the canals were an optical illusion caused by the mind connecting isolated dark blotches scattered across the Martian landscape.
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Related Reading
“A Cautionary Tale of Extraterrestrial Chlorophyll”, Drew Ex Machina, October 5, 2014 [Post]
“Mariner 4 to Mars”, Drew Ex Machina, July 14, 2015 [Post]
“Meridiani Planum in 1969 – Our First Closeup View of Opportunity’s 2004 Landing Site”, Drew Ex Machina, August 8, 2020 [Post]
“The Famous Mars Image that Never Was”, Drew Ex Machina, April 4, 2014 [Post]
General References
E. M. Antoniadi, “On some Drawings from Photograph of Mars taken in 1909 by Professor Barnard and Professor Hale”, Monthly Notices of the Royal Astronomical Society, Vol 71, pp 714-715, June 1911
E. E. Barnard, “Photographs of the Planet Mars, etc.”, Monthly Notices of the Royal Astronomical Society, Vol 71, pp 471-472, March 1911
William E. Rolston, “The Approaching Opposition of Mars”, Nature, Vol 81, No 2081, pp 336-338, September 16, 1909
An Illustrated Catalog of Astronomical Photographs (3rd Edition), The University of Chicago Press, April 1923
While the images are too blurry to show any straight lines, I can see how some of them hint at what could be several canals branching off from that main dark region. It is almost like Mars was teasing Earth observers.
Does that pic of the Yerkes 40-inch refractor remind anybody else of Marvin the Martian from Bugs Bunny cartoons?
Absolutely fantastic post Drew!
Thanks! It was a fun one to research and write 🙂
Very nice. It is probably worth bearing in mind that the actual images at the time, as observed by eye, would have been a lot more detailed. Atmospheric effects have resulted in these photographs being less detailed.