Sir, – Methinks that Margaret Butler (April 10th) is winding us all up in relation to the clock times of noon and midnight.
Midnight clock time, is exactly 12 hours before midday, and it is correct to call it 12am, since am is the abbreviation for ante meridiem (from Latin “before midday”).
While the exact time of noon or midday is neither before nor after midday, calling noon 12pm is a convention in civil time. All times after 12pm until midnight are designated pm (post meridiem “after midday”).
On a word of caution, am and pm relate to midday, not meridian. While meridian is itself related to midday (meridianum), it is a circle of constant longitude around the earth, passing through a place on the Earth’s surface and the poles. In astronomical terms the sun crosses a local meridian at noon.
Of course the use of 24-hour clock time would make these pedantic niceties redundant and would restore the romance and poetry of the use of the words, noon, midday and midnight. – Yours, etc,