2
G.M.T.
Zenith Distance
Diff.
True Bearing.
0800
87° 47'.5
53'.8
247° 55'
0805
88 41 .3
53 .6
247 08
0810
89 34 .9
53 .1
246 21
0815
90 28 .0
53 .0
245 34
0820
91 21 .0
52 .5
244 46
0825
92 13 .5
243 58
The time of setting for Venus may be interpolated or extrapolated by the above table for the following factors:-
(a) At sea level with no refraction, Z.D. = 90° 00'
(b) At sea level for refraction of 34', Z.D. = 90° 34'
(c) At 8,000 feet and no refraction, Z.D. = 91° 28'
(A.N.T. tables give dip for 8,000 feet as 88')
(d) At 8,000 feet and refraction of 40', Z.D. = 92° 08'
The allowance for refraction at 8,000 feet is generous, in that a table in the Air Almanac gives a refraction of about 1° 40' for altitude 8,000 feet, and would make the time of setting much later, since a Z.D. of 93° 08' is then required.
4. POSITION LINES FOR SETTING TIMES OF VENUS:
While the accuracy of data in Section (3), has been verified by various partial checks, it may be argued that since they apply to only one point, the results may be different for other points. To cover this contingency the following lines for equal times of setting (or position lines for given zenith distances at given times) have been calculated. They have been calculated for a height of 8,000 feet (dip 88') but no allowance for refraction. Variations in the times of these position lines for various factors can be allowed for in conjunction with the table in Section (3).
G.M.T./Lat.
35°S
36°S
37°S
38°S
39°S
40°S
0800
176°58'
177°35'
178°09'
178°44'
179°20'
179°57'
0805
175 43
176 20
176 54
177 29
178 05
178 42
0810
174 28
175 05
175 39
176 14
176 50
177 27
0815
173 14
173 50
174 24
174 59
175 35
176 12
0820
171 59
172 35
173 09
173 44
174 20
174 57
0825
170 44
171 21
171 54
172 29
173 05
173 42
0830
169 29
170 06
170 39
171 14
171 50
172 27
For arguments of G.M.T. in the left hand vertical column, and latitude in the top horizontal row, the body of the table gives longitudes east of Greenwich.
Plotting these values on a chart exhibits quite clearly that Venus would be visible from the aircraft during the whole flight, except for any cloud that might be present.
5. ALTAZIMUTH COORDINATES FOR SATURN:
Assumed position: Latitude 39°S
Longitude 174° 11' E.
No allowance for dip or refraction.
The assumed position of 1' further east was an accidental error