Observatories that I have visited:
the Astrograph at
Stockholm's "new" Observatory, Sweden

Content:

1. Introduction
2. The excursion to Saltsjöbaden
3. Historical background
4. What is an astrograph?
5. Optical performance
6. Finder telescope
7. Tracking and motor operation
8. Object tracking, finder telescope
9. The elevator
10. The Dome
11. Glass plates (film)
12. What research was done with this astrograph?
13. Who has worked on this astrograph?
14. How it ended?

13: Who has worked on this astrograph?

Kerstin Lodén says:

"This instrument was mainly used for determination of the distribution of stars in the Milky Way. The astrograph was involved from the beginning of the observatory existence. Bertil Lindblad, the first director, had developed a method of so called short spectra, i.e. not very detailed ones, determine stellar absolute magnitudes. By also measuring the same stellar apparent magnitudes we could get stars distances.

There was a method which was suitable for statistical use:
You have to observe many stars to get good results. The person who most used the instrument was Jöran Ramberg, Tord Elvius and I self. Of course, there was also other observations with this telescope, such as Comet Arend-Roland in 1957, but the above was the astrograph original area of use."

In addition, Gösta Gahm on Astronomical Department told that Bertil Lindblad was probably engaged in the purchase of the astrograph. Another astronomer, Per-Olof Lindblad's research work was to determine the Milky Way's structure, Per-Olof is otherwise son of Bertil.

At last Kerstin Lodén tells about the exciting work at the astrograph:

"The telescope was pretty handy, not so slowly turning as the big double refractor. But the dome and the knob to rotate the the dome was tough when it became cold and severe cold, occasionally put a stop to my observations. As to the photographic plates. In order to determining magnitudes must also be the same pre photographed plate having a sequence of stars whose magnitudes were known, reference stars.

In the processing done later in a photometer at daytime compared new stars with reference stars. Such a sequence was the area around the North Star where some astronomers had previously determined magnitudes for a number of stars of different brightness. We must therefore when you had finished the exposure of its interesting field turning the telescope up against Polaris, and - on the same plate - exposing this area. After one usually short exposure moved the telescope slightly in declination and exposed again to yield two images of Polaris Stars. This is to be to distinguish the stars to: You then got double images of reference stars. North Star self that is so bright was of course a large light circle that could not be used as a reference.

I remember the first time I did this I discovered that the North Star is double. On each plate had thus three exposures. It could happen in rich star field that the stars interfered with each other. On spectral plates needed no photographed default stars. There, the spectra of stars small rectangles. It sometimes happen that some stellar spectra fell on each other more or less. Then it was necessary to turn the prism 90 degrees, in the daytime of course, and it took a new plate with another dispersions direction.

Spectral plates, which had a larger size, was mounted in cartridges that was very heavy and cumbersome and was difficult to handle in the dark. The day after when woke up everything would be developed. It was important that during the observation time had noticed all the plates (what was up and down plate!) and that it had been wrote down correctly in the observation book over all photographed fields, exposure times and any cloud disruption. On good nights, several instruments was running and it was crowded in dark rooms after the session. The result of reductions of all observations in this program, covered many fields appropriately distributed across the sky, eventually led to an understanding of how the number of faint stars are distributed if you go up or down from the Milky Way's plane. They then got a confirmation on the assumption that our galaxy is a disc where the stars is concentrated in certain areas. A similar programs in the southern sky were carried out by J.M. Ramberg and by me on Boyd Observatory South Africa in the 1950s. There were instruments that was suitable. After a while more confirmations collects on how our galaxy looks, it was found by radio observations of the spiral arms for example. And you could perform observations smoother with photoelectric photometry."

This dial seems to have had an important function, we managed however, not clear out what. Kerstin think it had with the focus to do, perhaps some of our readers know?