Back in the late 1990s, 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 lantern 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 collections. These were the old time equivalent of the photographic 35 mm slides I had been using during my astronomy lectures at the time (which have long since been replaced by electronic presentations).
A scan of a glass lantern slide showing the Triangulum Galaxy, M33. The image was taken by George W. Ritchey in September 1902 using the 24-inch reflector telescope he designed at the Yerkes Observatory. Click on image to enlarge. (Yerkes Observatory)
Last year while digging through my archives, I found these lantern slides and decided to sort through them for the first time in a long time. Among the gems I found was an image of what is today called the Triangulum Galaxy, also known as M33 from the famous Messier catalog of nebulae and star clusters. The image was taken by famed American telescope maker and astronomer, George W. Ritchey (1864-1945), using the then-new 24-inch (0.61-meter) reflecting telescope at the Yerkes Observatory operated by the University of Chicago. Designed by Ritchey and built at the observatory where it entered service in 1901, the 23½-inch (0.597-meter) clear aperture, f/4 reflecting telescope employed parabolic optical surfaces instead of the easier-to-grind spherical surfaces used in most telescopes. This was done to minimize optical distortions towards the edge of the field of view so that the telescope could be used for high quality, wide-angle astrophotography. The image of M33 was recorded on the nights of September 4 and 6, 1902 with a total exposure of four hours on a 7 by 8-inch (18 by 20-centimeter) glass photographic plate – the cutting edge imaging technology of the day.
Here is a view of the Yerkes Observatory’s 24-inch (0.61-meter), wide-angle reflector telescope designed by George W. Ritchey which entered service in 1901. (University of Chicago Photographic Archive, Hanna Holborn Gray Special Collections Research Center, University of Chicago Library)
Probably discovered by the Italian astronomer Giovanni Battista Hodierna (1597-1660) before 1654, the Triangulum Galaxy was cataloged by the French astronomer Charles Messier (1730-1817) in 1764 receiving the designation Messier 33. Located in the constellation of Triangulum (where it gets its popular name), the object was classified as a “spiral nebula” in the Milky Way when Ritchey photographed it at the turn of the last century. It was not until 1926, when American astronomer Edwin Hubble (1889-1953) measured the distance of M33 for the first time, that it was discovered to reside far outside the Milky Way and was another “island universe” or galaxy like our own. Today we know that the Triangulum Galaxy is a spiral-type galaxy located about 2.7 million light years away. With a diameter of 60,000 light years and the home of perhaps 40 billion stars, M33 is the third largest member of the Local Group after the Andromeda Galaxy and the Milky Way.
The VLT Survey Telescope (VST) at ESO’s Paranal Observatory in Chile captured this beautifully detailed image of the Triangulum Galaxy released in 2014. It was recorded using the 256 million pixel OmegaCAM CCD imager. Click on image to enlarge. (ESO)
Because of its proximity to us, the Triangulum Galaxy has been the subject of close study for a century now. The modern image of M33 shown above was taken with the VST (VLT Survey Telescope) at the European Southern Observatory’s (ESO’s) Paranal Observatory in the Atacama Desert of northern Chile. The VST, which saw first light in 2011, is a 2.61-meter aperture, modified Ritchey-Chrétien reflector design invented in the early 1910s by French astronomer Henri Chrétien (1879-1956) and George W. Ritchey – the same person who designed the Yerkes 24-inch reflector and took the photograph of M33 discussed earlier. The Ritchey-Chrétien design employs hyperbolic optical surfaces to further reduce optical distortions in wide-angle images compared to Ritchey’s earlier designs. The VST uses additional precision optical elements to reduce optical distortions further. The new image of M33 was acquired using OmegaCAM which uses a mosaic of 32 individual CCD focal plane arrays with a total 256 million pixels covering a one-degree square field of view. Multiple digital images taken through various filters were combined to create this color view released by ESO in August 2014. A full resolution version of the VST image of the Triangulum Galaxy can be accessed here (beware – this is 647 MB TIFF file!!!).
Here is a view of the 2.6-meter VLT Survey Telescope (VST) at ESO’s Paranal Observatory in the Atacama Desert of northern Chile. It is housed in an enclosure immediately adjacent to the four VLT Unit Telescopes on the summit of Cerro Paranal. (ESO/G. Lombardi)
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Related Video
Here is a brief ESO video “Zooming in on the Triangulum Galaxy”:
Related Reading
“The Best Images of Mars – 1909”, Drew Ex Machina, October 8, 2020 [Post]
General References
G.W. Ritchey, “The Two-Foot Reflecting Telescope of the Yerkes Observatory”, The Astrophysical Journal, Vol. 14, No. 4, pp. 217-233, November 1901
G.W. Ritchey, “Astronomical Photography with the Forty-Inch Refracting and the Two-Foot Reflector of the Yerkes Observatory”, Publication of the Yerkes Observatory, Vol. 2, pp. 389-415, 1904
An Illustrated Catalog of Astronomical Photographs (3rd Edition), The University of Chicago Press, April 1923
“Triangulum Galaxy Snapped by VST”, ESO Photo Release eso1424, August 6, 2014 [Link]
“VLT Survey Telescope”, ESO website (last accessed June 26, 2021) [Link]
Hi Andrew,
Have you thought of digitizing your plates ?
Variability and proper motion could be studied by comparing them with archival photos such as those from the Harvard patrol plates and also more recent images. There is the potential for some interesting science from this.
David
An interesting suggestion but ultimately impractical. The glass lantern slides I have are at least 2nd generation copies of the original glass plates Ritchey exposed with his telescope – a photographically reduced inter-negative from the original plate was then used to create a photographic copy in the form of a lantern slide. Each reproduction step would add additional distortions in the image scale as well as degrade the photometric quality of the image. While the lantern slides make for “pretty pictures” we can admire even a century later, any precision scientific work would best be done with the original glass plates in the Yerkes Observatory archives.
Andrew, an extended version of this piece would make a good post on Centauri-Dreams. Have you thought of contacting Paul Gilster to suggest this?
You really think so? It has been a few years since I contributed anything to CD. Actually, I have already been considering preparing new pieces like this about other objects as a semi-regular thing on this website 🙂
I know that on CD you are mostly known for your interpretation of the type and habitability of exoplanets. The site does a lot of posts on telescopes and new technology and analytics that can be used to enhance their capabilities. There are also interesting posts on a range of related topics, for example, Larry Kales SciFi movie retrospectives.
I think this article fits nicely into the history of astronomy category. As a non-astronomer, I would like to know more about the techniques of recording astronomical images and how they have evolved. In this particular case, the glass plate is a long exposure of all the visible light reaching the plate, whilst I think the comparison image of M-33 is a composite image that teases out more information. There is also the improved resolution – is that due to the larger mirrors, the light recording CCDs, or some post processing algorithms? These are the sorts of questions that could be answered in a fleshed-out article suitable for readers like me.
That is my 2 cents.
Best,
Alex
Done! I’ve contacted Paul and he is very interested. I’ll have to get on this. I appreciate your suggestion 🙂