Whether travelling to the West or to the East from the Prime Meridian (zero Longitude) the International Date Line is 180 degrees Longitude.
121 degrees east longitude
International Date Line
The international date line
The major line of longitude located at 180 degrees longitude is the International Date Line.
The international date line (or there abouts)
180 degrees
180 degrees
International Date Line. Nominally 180 degrees east (or west) longitude. Opposite the Prime Meridian.
180 degrees of longitude.
180 degrees longitude is the meridian that should be the International Date Line. But in actuality, the date line was drawn with several zigs and zags in it, in order to avoid cutting across land, which would have placed different parts of the same country in different calendar dates. So the Date line deviates from the 180 meridian in several places.
The International Dateline approximately follows the meridian of 180° longitude.
No. 90 degrees longitude is not a major line of longitude. Only 0 and 180 degrees longitude, which are the Greenwich Meridian and the International Date Line respectively, are major lines of longitude.