This nice video musing about (among other things) the US Naval Observatory's $3,500 expedition to Baker City or at least Baker County Oregon to observe the June 18, 1918 solar eclipse, there is a photograph of the expedition showing both normal-sized portable telescopes, and in the background a very long telescope (at least 6 meters, can't see the end) held up by a ladder, with an even longer tent extending backward from the shack sitting at the bottom of the telescope along the ground.

What is this instrument? How does it function optically, and what kind of data does it produce?

below: Screenshot from the video, photo credits available at the end.

enter image description here


1 Answer 1


This construct was a telescope. Citing this article:

Owing to the difficulty of erecting a double tower, most other astronomers follow the mechanically simpler plan of laying the camera tube horizontally and allowing the sunlight to be fed into it by means of a plane mirror driven by clockwork to counteract the westward motion of the sun.
pg. 255

A Popular Astronomy article also discusses the eclipse observation in detail. They describe the primary telescopes used for photography. The first was a 65-foot telescope (that measurement being the length, not the aperture).

This instrument was in charge of W. A. Conrad, who was assisted by W. L. Veale. The camera was horizontal and was directed toward the sunrise point. Light from the corona was reflected from a silvered glass mirror 10 inches in diameter attached to a coelostat controlled by clockwork. The lens was 7 1/2 inches in aperture and the plates were double coated special coronal, 17x20 inches, made by the Eastman Kodak Co. The diameter of the sun's image on the plates is about 7 1/4 inches. Five exposures were made of 5, 15, 35, 15, and 5 seconds duration respectively.

They also had a 105-inch telescope which was also laid horizontally and had the light directed into it via a coelostat. While I can't be completely sure which telescope is pictured in that image, given the size, my guess would be the 65-foot telescope.

  • $\begingroup$ Thanks for finding these historical links, this is great! I'm still not sure what the covered item is that is pointing up at an angle in the top right (arrow here: i.stack.imgur.com/Drkzf.jpg) — the same direction that the other telescopes are pointing. Perhaps that's yet another telescope? It will take me some time to read those historical papers, it's probably explained well there. Great stuff! $\endgroup$
    – uhoh
    Jul 24, 2017 at 18:25
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    $\begingroup$ I believe it's just a part of the coelostat used to catch and direct the light, but I could be wrong. $\endgroup$
    – zephyr
    Jul 24, 2017 at 18:34
  • $\begingroup$ I've read through both articles again, and counting cameras and people described in the second column of page 255 in the Natural History article by S. A. Mitchell one interpretation is that there were actually five cameras; 65-foot camera (W. A. Conrad), 104 and 36 inch cameras (G. H. Peters & C. C. Wylie), and “Two smaller cameras pointing directly at the sun were employed by Mr. Kempton Adams". But if they are smaller than 104 and 36 inches they would not account for the tall sun-pointing tower at extreme right (neither would the three spectrographs). So it remains a mystery. Thanks again! $\endgroup$
    – uhoh
    Jul 30, 2017 at 5:00
  • $\begingroup$ During the re-reading I noticed the mention of the observation of a new nova in the evening following the eclipse, so I've asked the follow-up question What was the “brilliant new star in Aquila” on June 8, 1918, just after the solar eclipse?. $\endgroup$
    – uhoh
    Jul 30, 2017 at 11:35
  • $\begingroup$ @uhoh I'm confused as to why you think the object you're asking about might be the "two smaller cameras". The most likely answer is that the object you're asking about is the 65 foot camera, as I said in my answer. $\endgroup$
    – zephyr
    Jul 31, 2017 at 16:55

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