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Volume 76, 1946-47
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Coordinates of the 9-Inch Refracting Telescope at the Carter Observatory, Wellington, and Nearby Stations.

In November, 1941, the new Carter Observatory building was nearing completion, and the galvanised iron building, known as the Wellington City Observatory since its erection in 1924, which had housed the 9-inch refracting telescope, was due to be demolished. It was felt at this time that the position of the old observatory with respect to the new building should be determined for the purposes of historical record, as well as the geographical coordinates for the new position of the telescope. The difficult circumstances produced by the war meant that surveyors were not available, and surveying instruments were difficult to obtain. Mr. W. M. Jones, of the Department of Scientific and Industrial Research, kindly loaned a mountain theodolite and measuring tape, and with these the writer made such measurements as could be done with the greatest speed, ease, and minimum of assistance. The methods were perhaps not in strict accordance with usual surveying practice, but after reducing the results in November, 1945, it is considered that they are sufficiently accurate for the purposes required.

A document found on the old records concerning the Wellington City Observatory kept by the late Dr. C. E. Adams, gives positions for that building determined by the Wellington City Corporation's Engineer's Office in 1928 as follows:—

  • In Links from Mt. Cook Initial Station:

  • North East corner of building, 8449.88 N. 3945.72 W.

  • South East corner of building, 8393 52 N. 3946.04 W.

  • South West corner of building, 8393.51 N. 3974.53 W.

The last point was more or less lost when the New Zealand Astronomical Society added a room to the building as a library, and of course there is now no trace of any part of the building. These positions were obtained by establishing a station near the radio aerial mast (since renewed) alongside the Astronomical Observatory of the Royal Society of New Zealand (Wellington Branch), from the standard survey point South Etako. From the above figures Dr. Adams estimated the position of the 9-inch telescope to be 8435.8 North, 3960.2 West, and they also indicate that the eastern wall of the building had a bearing of 000° 19′ from the south end.

No easy means were available for measuring with reasonable accuracy long distances over sloping ground, and the great growth of surrounding vegetation prevented sights along certain lines without cutting them. Therefore two pegs were placed, one in front of the Wellington City Observatory and the other in front of the Carter Observatory, such that they were on the same level. From

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these pegs, as well as from South Etako, as many bearings as possible were taken on all observable points and distances measured to the nearest 0.5 inch (0.06 link). For purposes of record the main readings are tabulated as follows:—

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Station. Station Observed. Bearing. Distance (Inches).
Peg I Wind vane, Dominion Obs. 000° 00′
S.E. corner, City Obs. 174 49 437
N.E. corner, City Obs. 232 18 490
N.E. corner, foundation 9-in. room, Carter Obs. 237 53
N.E. corner, foundation, library room, Carter Obs. 244 21
Peg II 252 31 980
Peg II Wind vane, Dominion Obs. 000 00
Peg. I 055 37 980
N.E. corner, City Obs. 073 39
N.W. corner, City Obs. 097 45
N.W. corner, N.Z.A.S. Library 111 43
S.E. corner, E. wall, Carter 123 45 740
S.E. corner, foundation, 9-in. room, Carter Obs. 134 12 476.5
N.E. corner, foundation, 9-in. room, Carter Obs. 172 40 332
N.E. corner, E. wall, Carter, library room 210 04 467
Wind vane, Meteor. Office 338 56
South Etako Wind vane, Dominion Obs. 000 00
Wind vane, Meteor. Office 040 56
S.E. corner, 9-in. room, Carter Obs. 292 06
S.E. corner, 9-in. room, Carter N.E. corner, 9-in. room 298.5
N.E. corner S.E. corner, Carter Obs. 519
S.E. corner, City obs. N E. corner, City Obs. 448

From these observations, two methods of determining the eastern corners of the 9-inch room of the Carter Observatory were available.

(a)

A direct bearing and calculated distance from South Etako to the S.E. corner of the 9-inch room.

(b)

By accepting the coordinates determined by the Wellington City Engineer's Office, determining the positions of the two pegs and hence the corners of the 9-inch room.

Although internal checks and calculated and observed distances showed very satisfactory agreements wherever possible by the first method, when the co-ordinates of the eastern corners of the Wellington City Observatory were computed, systematic differences amounting to 1.3 links North and 2 6 links West, compared with the City Engineer's figures, were found. The second method was therefore adopted for the final result.

The co-ordinates of South Etako and the bearing and distance from it of the wind vane of the Dominion Observatory are available(1). Since the transit pier of the Dominion Observatory is the spot from which the most recent longitude observations have been made,(2) (3) concentration has centred on differences from this position. Owing to the small distances the work can be considered plane, and trials with more detailed working(4) shows that this is pretty well the case even when working from Mount Cook Initial Station.

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To estimate the accuracy finally required in the measurements, interpolations from Tables III and IV of Close's “Textbook of Topographical Surveying” 2nd Ed. 1913 (Clarke's First Figure, 1858) show that:

(a)

In longitude, 1sec. arc (1/15 sec. time) = 76.3496 feet—i.e., 0.01 sec. (time) = 11 45 feet = 17.35 links.

(b)

In latitude, 1 sec. arc = 101 2135 feet—i.e., 0″ .01 (arc) = 1.012 feet = 1.535 links.

Since 0.01 link = 0 079 inch, figures quoted to 0.01 link must be presumed to be the result of extremely careful measurement.

To determine the longitude astronomically to 0.01 sec. of time accurately is very difficult, so that the tolerance of 17.35 links shows that if any change is to be made for future values of the longitude of the Carter Observatory, it will be due to a change in the value of the fundamental longitude. At the present time it is doubtful if the longitude is known exactly to 0.01 sec., as is shown by the following recent determinations, Greenwich-Wellington:—

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Date, Observer. Range in Values. No. of Observations. Mean Value Adopted.
Sec. (time). h. m. s.
1926 Adams 0.26 6 11 39 04.03 E.
1933 Hayes 0.29 10 11 39 04.00 E.
1933 Thomsen 0.22 15 11 39 03.94 E.
1933 Hayes & Thomsen (Present accepted mean) 11 39 03.97 E.

In 1926, Adams' results were based on handkey observations of transits instead of the impersonal micrometer, and so are not strictly comparable with the 1933 observations. The range between the two observers in the 1933 work is equivalent to 0″ .9 (arc), and in linear measure to 68.7 feet (104.1 links). Similar differences may be found in the analysis of the results of many overseas observatories, but it would be of great interest and value if it were possible to have continuous longitude work in progress such as is done at Dehra Dun, India(5), and Uccle, Belgium(6), where monthly and annual averages are obtained.

The latitude of the Dominion Observatory transit pier is taken as -41° 17′ 3″.75 as deduced by Dr. C. E. Adams in 1914 from observations at Mount Cook Observatory by Mr. C. W. Adams in 1883(7). It would appear that observations at the present time with a good zenith telescope, the improved star places now available, and modern knowledge of latitude variation, might be well worth while.

After determining the coordinates for the foundation corners of the 9-inch room of the Carter Observatory, the coordinates of the 9-inch were estimated from the architect's plan on a scale of ½ inch to the foot, and those of the second spare pier and coelostat pier of the spectrohelioscope from another plan, scale ⅛ inch to the foot. The position of the 5-inch refractor housed in the Astronomical Observatory of the Wellington Branch of the Royal Society of New Zealand has also been deduced from available data(1) for reference purposes

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[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Coordinates of Points Observed or Estimated.
Station. Coordinates from Mt. Cook Initial. Coordinate Differences from Dominion Obs. Transit. Geographical Differences from Transit. Deduced (South) Lat. (East) Long.
North. West. North. West. Lat. Long. -41° 17′ 11h.39m.
South Etako 8434.55 3534.69 -83.95 -0.34
Dominion Observatory, Transit Pier 8518.50 3535.03 00.00 00.00 3″.75 3s.97
City Observatory
  S.E. corner 8393.52 3946.04
  N.E. corner 8449.88 3945.72
  9-in. old position 8435.8 3960.2 −82.7 +425.2 S. 0″.54 W. 0s.24 4.29 3.73
Carter Observatory
  S.E. corner 9-in. room 8472.7 4007.2
  N.E. corner 9-in. room 8510.5 4007.1
  9-in. new position 8491.6 4026.9 -26.9 +490.9 S. 0.18 W. 0.28 3.93 3.69
  Second pier 8442 4064 -76 +529 S. 0.49 W. 0.30 4.24 3.67
  Coelostat pier 8558 4083 +40 +548 N. 0.26 W. 0.32 3.49 3.65
Royal Soc Observatory
5-in. telescope 8297.97 3758.04 -220.53 +223.01 S. 1.44 W. 0.13 5.10 3.84
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When the builders suddenly arrived to commence the new Carter Observatory building, they requested that a north-south line be provided. The complete lack of instruments as well as the urgency of the matter caused the writer to use the shadow of a long plumbline, when the sun was calculated to be on the meridian. Calculations from the observations above, give a bearing of the eastern wall of the 9-inch room, from the south end, of 000° 22′, and of the main eastern wall of 000° 14′. It may be assumed, therefore, that the building as a whole has a bearing of 000° 18′, which is probably satisfactory considering the means available.

By means of a water level sight made from the base of the 9-inch dome on the Dominion Observatory, and with data supplied by the Acting Director, Mr. R. C. Hayes, the height of the equatorial head of the 9-inch telescope above mean sea level is taken as 424 feet.

The summarised data for the 9-inch telescope for practical astronomical purposes are therefore as follows:—

     Longitude (λ) 11h. 39m. 3s.69 E. of Greenwich. = 174° 45′ 55″ E.
     Latitude (ϕ) 41° 17′ 3″.9 South
     Geocentric Latitude (ϕ′) 41° 05′ 34″.5 South
     Radius/Equatorial Radius (ρ) 0.99856
     ρ sin ϕ′ -0.656336 (Log. = 9.817126n)
     ρ cos ϕ′ 0.752560 (Log. = 9.876541)
     tan ϕ′ -0.872138 (Log. = 9.940585n)
8.8 ρ sin ϕ′ -5.78 (Log. = 0.762n)
8.8/15 ρ cos ϕ′ 0.442 (Log. = 9.645)

For nearly all purposes the geocentric coordinates will be applicable without perceptible error to any position in the Observatory area at Kelburn, Wellington.

References.

(1) Lands and Survey Dept., Annual Report of Survey Operations for 1914–15, Appendix III, Wellington City Triangulation.

(2) Dominion Observatory Bulletin No. 69: International Longitude Observations, 1926.

(3) Dominion Observatory Bulletin No. 115. Extract from N.Z. Journ. of Science and Tech., vol. 18, p. 512, 1936. International Longitude Determinations, 1933.

(4) Tables of Geodetic Factors for use on the Brunsviga Calculating Machine, by C. E. Adams. Dominion Observatory Bulletin No. 71. Extract from Transactions Australasian Association for the Advancement of Science, 1904.

(5) Survey of India. Geodetic Reports. 1922 to 1923.

(6) Bulletin Astronomique de l'Observatoire Royal de Belgique, à Uccle.

(7) Dominion Observatory Bulletin No. 66. Extract from Trans. N.Z. Inst., vol. 47, p. 590, 1914. The Longitude, Latitude, and Height of the Hector Observatory, Wellington, New Zealand.