General Information

Serial #

6939

Part Number

3

Total Parts

4

AKA

N/A

Patents

N/A

General Description

Glass plate/ photographic emulsion

Dimensions

Note: These reflect the general size for storage and are not necessarily representative of the object's true dimensions.

Length

10.1 cm

Width

8.2 cm

Height

N/A

Thickness

N/A

Weight

N/A

Diameter

N/A

Volume

N/A

Lexicon

Group

Photography

Category

Still images

Sub-Category

N/A

Manufacturer

AKA

Unknown

Country

Unknown

State/Province

Unknown

City

Unknown

Context

Country

Canada

State/Province

Ontario

Period

1941+

Canada

A photograph of an astronomical phenomenon used at the David Dunlap Observatory at the University of Toronto, one of Canada’s most important astronomical observatories. The David Dunlap Observatory opened in 1935 as the result of a bequest from the wife of David Dunlap. The telescope was a 74 inch (188 cm) reflector built by Grubb Parsons of Newcastle-upon-Tyne in England. The 74 inch was then the largest telescope in Canada (surpassing the 72 inch telescope of the Dominion Astrophysical Observatory in Victoria) and became the second largest in the world after the 100 inch Hooker Telescope of the Mt. Wilson Observatory outside Los Angeles. DDO's reputation grew and following WWII, it began to graduate most of the astronomers produced in Canada with University of Western Ontario far behind. Beginning in the 1960s a number of other astronomy departments were created but UofT/DDO held its place, a position it probably still holds. The DDO had a good technical staff which gave them an advantage and, with most of the 1940s to early 1970s top astronomers coming from UofT, grants from NRC and then ENSERC were almost guaranteed and allowed UofT's top astronomers -- Hogg, van den Berg, Fernie, Bolton, Kamper, Martin, etc. to acquire or build some of the best equipment available in university observatories. For optical observatories, only the DAO had technical staff and budgets that surpassed those of DDO. In 2007, citing increasing light pollution, the University of Toronto announced plans to sell the Observatory property. In June 2008, it was sold to Corsica Development Inc., a subsidiary of Metrus Development Inc. and the Observatory was closed. In 2009 the Observatory buildings and 80% of the site were designated a cultural heritage landscape. Also in 2009 Corsica and the Royal Astronomical Society of Canada, Toronto Centre announced an agreement allowing the RASC to provide public education and outreach programs at the observatory, and to operate the 188 cm telescope.

Function

A photographic medium upon which is recorded a visual image of astronomical phenomena or events, in two-dimensional format. This is one of a set of two plates used with a blink comparator, an astronomical instrument that shows in rapid succession two images of the same region of the sky taken at different times. It switches back and forth between the two photographs, allowing the user to more easily spot objects in the night sky that have changed position (Refs. 4-5)

Technical

One of a pair photographic plates used with the DDO’s Zeiss Blink comparator. The blink comparator was developed at Carl Zeiss in 1904 and was a major advance in astronomical instrumentation. The comparator showed in rapid succession two images of the same region of the sky taken at different times. Their change in position made celestial bodies stand out in the foreground, thus simplifying the search considerably. One major discovery made with a Zeiss blink comparator was that of Pluto, in 1930 at Lovell Observatory in Arizona. Helen Sawyer Hogg (1905-1993) was a renowned Canadian astronomer who worked at the DDO from 1935 until her death. Dr. Hogg started her work on variable stars in globular clusters while in Victoria. She developed a technique for measuring the distance of galaxies beyond the Milky Way. She took pictures of variable stars and catalogued the cyclical changes in their brightness, which she then used to calculate their distance. Her detailed observations were published in catalogs that are still used today. Dr. Hogg pursued her observations of globular clusters at the David Dunlap Observatory, and she was hired as a research officer in the astronomy department in 1936. Messier 56 (also known as M56 or NGC 6779) is a globular cluster in the constellation Lyra.

Area Notes

Unknown

Details

Markings

Handwriitten black lettering reads '6739'

Missing

Complete

Finish

Black and white image on colourless, transparent glass

Decoration

N/A