that nation’s time. In international
waters, time zone boundaries are meridians 15° apart, except that
<abbr>UT</abbr>−12 and <abbr>UT</abbr>+12 are each 7.5°
wide and are separated by
the 180° meridian (not by the International Date Line, which is
for land and territorial waters only). A captain can change ship’s
clocks any time after entering a new time zone; midnight changes are
common.</li>
</ul>
</section>

<section>
<h2 id="civil">Civil time concepts and history</h2>
<ul>
<li><a href="https:/