Abstract

Altitudes of celestial objects were observed with the bubble sextant from a 950 ton ship and a 12 ton craft at sea. For moderate sea conditions individual altitudes were occasionally as much as 60 minutes of arc in error and averages of 5 consecutive observations were usually correct within 30 minutes of arc. On the 950 ton ship a portion of the error was due to the vibration of the ship caused by wind, engines, etc., and a larger portion was due to the horizontal acceleration arising from the roll and pitch of the ship. If the roll were simple harmonic the latter error could be partially eliminated by taking the sextant altitude at the midpoint of the roll. A small pendulum device was arranged to sound a buzzer signal at the midpoint of the roll and the sextant observations were made simultaneously with the buzzer signal. This improved the accuracy of the bubble sextant altitudes by roughly a factor of 2, so that individual observations were rarely more than 30 minutes of arc in error and averages of 5 consecutive altitudes were usually correct within 15 minutes of arc for a moderate sea.

© 1933 Optical Society of America

Full Article  |  PDF Article

References

  • View by:
  • |
  • |
  • |

  1. Descriptions of and experiments with artificial horizon sextants, mostly from the standpoint of aerial navigation, are given by Eaton, , 1922, and Beij, , 1924, Nat. Advisory Committee for Aeronautics; H. N. Russell, Proc. Ast. Soc. Pacific 31, 129 (1919); Gatty, Jr. Soc. Aut. Eng. 30, 153 (1932).
    [Crossref]
  2. Kaster, Proc. U. S. Inst. Naval Eng. 56, 607 (1930).

1930 (1)

Kaster, Proc. U. S. Inst. Naval Eng. 56, 607 (1930).

Eaton,

Descriptions of and experiments with artificial horizon sextants, mostly from the standpoint of aerial navigation, are given by Eaton, , 1922, and Beij, , 1924, Nat. Advisory Committee for Aeronautics; H. N. Russell, Proc. Ast. Soc. Pacific 31, 129 (1919); Gatty, Jr. Soc. Aut. Eng. 30, 153 (1932).
[Crossref]

Kaster,

Kaster, Proc. U. S. Inst. Naval Eng. 56, 607 (1930).

Proc. U. S. Inst. Naval Eng. (1)

Kaster, Proc. U. S. Inst. Naval Eng. 56, 607 (1930).

Other (1)

Descriptions of and experiments with artificial horizon sextants, mostly from the standpoint of aerial navigation, are given by Eaton, , 1922, and Beij, , 1924, Nat. Advisory Committee for Aeronautics; H. N. Russell, Proc. Ast. Soc. Pacific 31, 129 (1919); Gatty, Jr. Soc. Aut. Eng. 30, 153 (1932).
[Crossref]

Cited By

OSA participates in Crossref's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (4)

Fig. 1
Fig. 1

Dots are bubble sextant altitudes, crosses are averages of five consecutive dots, broken lines are true altitudes. a, sun, observed from land; b, sun, observed while under way at 12 knot speed in Chesapeake Bay; c, sun, observed while at anchor in a moderate sea, roll 2° to 4°; d and d′, star Rigel, observed while under way at 12 knot speed in a moderate sea. b, c, d and d′ were observed from the USS Cormorant.

Fig. 2
Fig. 2

Dots are bubble sextant altitudes, crosses are averages of five consecutive dots, broken lines are true altitudes. a and b, sun, observed from a 30 foot ketch sailing over a smooth and a moderate sea; c and c′, star Altair, observed while at anchor in a moderate sea, roll 2° to 7°, with and without the midpoint indicator; d, d′ and d″, star Rigel, observed while under way at 12 knot speed in a moderate sea, roll up to 7°, with and without the midpoint indicator. c, c′, d, d′ and d″ were observed from the USS Cormorant.

Fig. 3
Fig. 3

Diagrammatic sketch of the midpoint indicator.

Fig. 4
Fig. 4

Photograph of the midpoint indicator.

Equations (4)

Equations on this page are rendered with MathJax. Learn more.

x = x 0 sin ( 2 π / p ) t ,
x 0 = h tan α 0 ,
f = - ( 4 π 2 / p 2 ) h tan α 0 sin ( 2 π / p ) t .
d = tan f / g ,