Hall of Precision Astrometry
"When I came to McCormick Observatory - I remember very well there was only one office with four people in it and one measuring engine machine with people standing in line, so to speak. And there was one mechanical desk computer. And these people produced more parallaxes per year than anybody has done ever since; not because they were poor and had limited facilities, but because they relied on what is most important of all, hard work."
-Peter van de Kamp, 1969
Starting in the autumn of 1914, astronomers at McCormick Observatory
undertook an extensive program in photographic astrometry, measuring the distances to stars.
The director of the observatory at that time, Samuel
Alfred Mitchell, realized that photography was a most efficient way to do
this sort of work, for reasons including higher accuracy, permanence of
record, and an ease in the labor involved, as compared to visual
methods. At that time, only the distances to about 100 stars were known
and only a handful of observatories were participating in this work, so
Mitchell decided to dedicate the observatory to the determinations of
During the 1920's, astronomers at McCormick Observatory also became
active in the observation of proper motions of stars, i.e., the relative
angular motions of stars. And then in the 1930's several of the
astronomers turned toward photometry,
which is the science of measuring the brightnesses of stars. Each of
these disciplines -- parallax, proper motion, and photometry -- required
the astronomer to take an image of an object on a photographic plate, to
develop the plate, and then to measure the location or brightness of the
object on that plate. From the time that photography began to be used
in astronomy, engineers developed ways to measure these plates with
increasing precision. Today, images are taken with electronic cameras
and measurements are made on computers. However, over the past century,
a variety of machines have been invented to measure the vast collections
of astronomical photographs in observatories around the world. The
McCormick Observatory at University of Virginia has been taking
photographs for almost one hundred years and its collection of
photographic plates (over 160,000), measuring engines and calculating
and computing machines is quite extensive. Some of the plate measuring
machines and computing machines that have been used at McCormick
Observatory since its early days are listed below, along with the
approximate dates of their acquisition by the observatory.
- One of the first measuring machines ever designed
for photographic work, this engine allowed precise measurements of both
stellar and spectral line positions.
- With similar design as the original Gaertner
engine, this machine was bought to supplement the use of the other as
observers at McCormick Observatory produced more photographic plates to
machine allowed astronomers to examine two plates at one time in order
to more easily detect stellar motions and changes in brightness.
- Variable blink settings, better lighting, and easier
movement of plates allowed for more precise measurements and easier
detections of stellar movement and variability.
- Specially designed to measure astronomical
spectra with a precision down to a small fraction of a micron.
This was the first engine owned by McCormick Observatory which could
measure in two directions using two separate precision screws, allowing
much better accuracy in all measurements.
With a huge projection screen and two-coordinate measuring system, this engine would have been useful for making accurate measurements in two directions.
- The Grant engine required much less skill to operate, was
much faster, and was 10-30% more accurate than previous engines.
The microphotometer was built specially for accurately measuring the positions of spectral lines.
A large measuring stage allowed operators to make very precise
measurements on very large photographic plates and then send them
straight to a computer for analysis.
- Fully automated and microcomputer-controlled,
this machine made faster, extremely accurate, and reproduceable
measurements over a larger range in photographic plate density.
Calculating and Computing Machines
- Classic Electro-mechanical calculating engines.
- One of the first successful programmable calculators, this 78 lb. machine had a magnetic card reader/recorder as well as a keypad for data entry/programming and a drum recorder.
Sun Ultra 5
Work supported by National Science Foundation CAREER Grant AST-97025. Alison F. Schirmer, Steven Majewski and Ricky Patterson
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