[3] [DFN[航海日]]は、[[常用時]]の前日[[正午]]から当日[[正午]]までを[[日]]とする[[時刻系]]でした。

[4] 同様に[[正午]]を[[日界]]とする[[天文時]]とは、1日のずれがありました。

[1] [CITE@en[Nautical time - Wikipedia, the free encyclopedia]] ([TIME[2016-08-16 01:25:30 +09:00]]) <https://en.wikipedia.org/wiki/Nautical_time#Nautical_day>

[FIG(quote)[
[FIGCAPTION[
[2] [CITE@en[International Meridian Conference - Wikipedia, the free encyclopedia]]
([TIME[2016-08-18 17:08:07 +09:00]])
<https://en.wikipedia.org/wiki/International_Meridian_Conference>
]FIGCAPTION]

> That the Conference expresses the hope that as soon as may be practicable the astronomical and nautical days will be arranged everywhere to begin at midnight.

]FIG]


[5] ([TIME[2008-01-19 18:50:15 +09:00]])
<http://www.asj.or.jp/geppou/archive_open/1918/pdf/191812.pdf>