Midnight.
No. That would be the International Date Line.The Prime Meridian is defined as zero longitude.
Most world maps are drawn with the Prime Meridian at or near the center and the International Date Line at or near the left and/or right edge(s).
This is called the Prime meridian, it passes through Greenwich, England.
I have a feeling that the meaning of "it" in this question is of paramount significance, and that if we but knew it, an answer would be possible.
nominally 12 hours
It is sometimes called the Greenwich meridian or 0° longitude.
That would be the Prime Meridian.
The prime Meridian is 0 degrees longitude.
The prime meridian is the zero degree vertical longitude line on the globe of the Earth. An example sentence would be: She used to live close to the prime meridian.
Ideally, the International Date Line should be the meridian of 180° longitude. Actually, it has been zigged and zagged to avoid cutting across any island or country, since to do so would put two different calendar dates in the same country simultaneously. If the IDL coincided with the 180° meridian, then together with the Prime Meridian, it would form a great circle on the earth, passing through the north and south poles as well as through Greenwich. As it is now, the Prime Meridian, the 180° meridian, and all other meridians of longitude are semi-circles, that begin and end at the poles.
The 180th meridian or antimeridian is the meridian which is 180° east or west of the Prime Meridian ... It is common to both east longitude and west longitude. It runs through the Pacific Ocean, and was the nominal guideline for the position of the International Dateline, although the dateline itself had to depart from the antimeridian in several places.
It depends on the connotation of Prime Meridian. Although there are a number of meridians defined as prime meridians, the Greenwich Meridian was established as the international prime meridian in 1884 and is at 0 degrees longitude. The opposite is 180 degrees longitude. Vietnam is located between 100 and 110 degrees east longitude and between 0 and 25 degrees north latitude. To locate Vietnam using west longitudinal reference it would be between 250 and 260 degrees west longitude. Since the distance from the prime latitude to Vietnam is shorter in the eastward direction than the westward direction it would be considered east of prime meridian.