En route to Chefoo, China, on June 19, 1936, an interesting possibility for a longitude sight developed. After 17 or 18 days of generally overcast and foggy weather, the sky very obligingly cleared up on the afternoon of the 19th and conditions became ideal for taking sights. A noon latitude had been established and the sky had cleared just before the sun was on the prime vertical, so a fairly reliable dead reckoning was determined for the sights to follow.
The writer, radio officer of the vessel and amateur navigator, with the co-operation of the first and second officers took sextant altitudes of the sun and the moon at the instant when the sun appeared to be in its fullest eclipse (as the vessel was not quite in the path of the total eclipse it was rather difficult to determine offhand the exact moment that the sun was in this condition). This difficulty was partially overcome by having another observer observe the side limbs or tips of the sun’s crescent form and mark when they touched the horizon together, or as near that time as could be determined. The accuracy of this observation would of course depend upon the angle that the moon crossed the sun; however, the angle was quite acute at this point and the error would be small.
One observer observed the moon’s lower limb, another observer and the writer observed the sun’s lower limb, and the resulting sights were obtained and worked by the writer. To followers of the discussions pro and con on “The Fallacy of the Time Sight,” let it here be noted that one mate would not even attempt to work out the moon sight. The other mate worked it out with the time-sight method once, found a discrepancy of 8 minutes in longitude between it and the sun sight, and gave up in disgust, declaring the moon was too complicated to work. By using the hour-angle method the moon sights are no more difficult than any other sights. It has been my experience though to find the same attitude toward the moon sights throughout the Merchant Marine service.
As already stated, the writer is but an amateur navigator and hasn’t had enough experience to make any definite statements as to the relative merits of the old and modern methods of navigation. Having learned the modern methods before the older ones, a prejudice may have been formed against the latter. However, when sights can be worked out and plotted on the chart so quickly, accurately, and with such ease with H.O. 208 and H.O. 211, it is hard to understand why these methods are not more popular in the Merchant Marine service.
It is regretted that there was no preliminary information available concerning the taking of sights during an eclipse. Had there been, better preparations could have been made and perhaps some interesting results obtained.
At 1708 June 19, 1936, in D.R. latitude 35°-35’ N.; 154°-00’ E. observed the sun’s and moon’s lower limbs as:
Sun
GCT | 06-50-09 |
| Hs | 23-25-00 | |||
GHA | 282-16.1 | Cor | 7-48 | ||||
Assumed Long | 153-43.9 | H0 | 23-42-48 | ||||
t | 436-00.0 | Hc | 23-58-40 | ||||
t | 76 W. |
| a | 15’-52’’ away | |||
L | 34 N. |
| |||||
d | 23-25.8 N. | A | 22616 | C | 95 | Z’ | 24.0 |
b | 19-43.9 N. | B | 16491 | D | 28 | Z’’ | 53.0 |
d±b | 43-09.7 | A+B | 39107 | C+D | 123 | Z N. | 77.0 W. |
Moon H.P. 59.0
GCT | 06-50-09 |
| Hs | 23-39-00 | |||
GHA | 281-19.6 | Cor | 01-02-12 | ||||
Assumed Long | 153-40.4 | H0 | 24-41-12 | ||||
t | 435-00.0 | Hc | 24-59-30 | ||||
t | 75 W. | a | 18’-18’’ away | ||||
L | 34 N. |
| |||||
d | 23-52.4 N. | A | 22261 | C | 97 | Z’ | 25.6 |
b | 20-59.6 N. | B | 15153 | D | 2 | Z’’ | 51.5 |
d±b | 44-52.0 | A+B | 37414 | C+D | 99 | Z N. | 77.1 W. |
1708 position 33°-35’ N. 153°-56.5’ E.
The resulting lines of positon, when plotted on the plotting sheet, were identical.