table of telescope counterweights required when charting sky photographically
Date: circa 1931
Inventory Number: 1996-1-0539
Classification: Chart
Subject:
Maker: Harvard College Observatory (founded 1839)
Associate Name: Alvan Clark and Sons (1846 - 1958)
Associate Name: J. W. Fecker, Inc. (founded 1926)
Associate Name: Joel Hastings Metcalf (1866 - 1925)
User: Oak Ridge Station (1931 - 2005)
User: George R. Agassiz Station, Harvard (1951 - 1982)
User: Harvard College Observatory (founded 1839)
Cultural Region:
Place of Origin:
Dimensions:
21.1 × 27.5 × 1 cm (8 5/16 × 10 13/16 × 3/8 in.)
DescriptionA typed sheet of bond paper is backed by an 8 x 10 photographic plate and covered with another 8 x 10 glass plate (without any photographic emulsion). The sandwich is secured in a tin frame with 4 eyelet loops on the sides (which were to attach the frame to the wall of the observatory).
The photographic plate is exposed and shows the spectra of stars taken with a photographic telescope. The emulsion is damaged in the middle, which likely explains why the plate was not archived but rather used as scrap material.
The paper is typed with a chart labeled, "LOADS FOR THE 24" REFLECTOR / FOR CHARTING." The columns are labeled with right ascensions in terms of hour angles, "H.A.," 1h - 12h. The last two columns are marked "1D" and "I." The rows are labeled in terms of declinations, "Dec." The declinations are primarily for the northern hemisphere and run from +80 to 0 to -30.
The bottom of the chart reads:
"For prism plates, add to Charting Loads the quantities found in columns D and I, for their respective classes. Double all loads for 16", 8", and 61"."
The photographic plate is exposed and shows the spectra of stars taken with a photographic telescope. The emulsion is damaged in the middle, which likely explains why the plate was not archived but rather used as scrap material.
The paper is typed with a chart labeled, "LOADS FOR THE 24" REFLECTOR / FOR CHARTING." The columns are labeled with right ascensions in terms of hour angles, "H.A.," 1h - 12h. The last two columns are marked "1D" and "I." The rows are labeled in terms of declinations, "Dec." The declinations are primarily for the northern hemisphere and run from +80 to 0 to -30.
The bottom of the chart reads:
"For prism plates, add to Charting Loads the quantities found in columns D and I, for their respective classes. Double all loads for 16", 8", and 61"."
Signedunsigned
Inscribedtyped on paper: LOADS FOR THE 24" REFLECTOR / FOR CHARTING
FunctionThis is a table of telescope counterweights required when charting sky photographically. The addition of a photographic plate holder and objective prism to the telescope changes the telescope's balance. To put it back into equipoise, counterweights are used. The weight load varies with the angle of the telescope, given in terms of the portion of the sky to which it is pointing.
Historical AttributesThis table of telescope counterweights required when charting the sky photographically was used by the Harvard College Observatory at its Oak Ridge Station in Harvard, Massachusetts (later known as the George R. Agassiz Station).
Five telescopes are mentioned in the table in terms of their apertures. These can be identified as the following. The series of photographic plates each telescope took is included in parentheses:
24-inch Clark reflector (H)
built by Alvan Clark & Sons
16-inch Metcalf photographic doublet (MC)
built by Joel Hastings Metcalf
8-inch Ross-Lundin refractor (IR)
61-inch Wyeth reflector (SH)
built by J. W. Fecker
Five telescopes are mentioned in the table in terms of their apertures. These can be identified as the following. The series of photographic plates each telescope took is included in parentheses:
24-inch Clark reflector (H)
built by Alvan Clark & Sons
16-inch Metcalf photographic doublet (MC)
built by Joel Hastings Metcalf
8-inch Ross-Lundin refractor (IR)
61-inch Wyeth reflector (SH)
built by J. W. Fecker
ProvenanceOak Ridge Observatory, Harvard, MA; transfer to CHSI.