Question: Does not the international date line create uncertainty about which day should be observed as the seventh day?
ANSWER: The international date line creates uncertainty primarily for travelers who have either to add or to drop a day from their calendar when crossing such a line in the Pacific Ocean.
It may be helpful to explain that the date line is a north-south line which runs through the Pacific Ocean, approximately along the 180th meridian. Meridians are lines which extend from the North to the South pole and which divide the globe into 360 equally spaced lines. At the line of the 180th meridian the date changes, so that east of it is one day earlier and west of it is one day later.
Need for Date Line. The date line is necessary because the earth is divided into 24 one-hour time zones (of 15 degrees longitude each) which make up a full day upon the earth. Since the earth rotates eastward, when people travel westward or eastward, they must of necessity either drop a day from or add a day to their reckoning of time.
In October 1884 the commercial nations of the world agreed to make the meridian going through the astronomical observatory at Greenwich, England, as the prime meridian from which all other meridians were to be numbered. As a result of this decision, the international date line, which is the 180th meridian, runs from north to south through the Pacific Ocean. In some places the date line bulges eastward and in other places westward to enable certain land areas and islands to have the same day.
Though the date line was established on the basis of geographical, political, economic, and social considerations, the decision must be accepted as appropriate, since it has produced order out of that which would otherwise have been confusion.
Date Line Israel. Some Sabbathkeepers argue that the international date line should be located at the eastern border of Israel where there is the time zone line. Their reasoning is that since the Sabbath was first given to the Jews, then Jerusalem must be the place where the seventh day must begin and end (Is 2:3; Mic 4:2).
This reasoning, in my view, is faulty:
Millions of people would have had to constantly add or drop a day whenever crossing the date line. This problem is largely avoided by the present date line, which, because of its location mostly in the open waters of the Pacific Ocean, affects only very few inhabited areas.
Providential Decision. In the absence of any Biblical injunction, it is perfectly right for human judgment to determine the location of the date line. The fact that the decision to place the line at the 180th meridian in the Pacific Ocean has produced order and has met the satisfaction of all the world, must be seen as an indication of providential guidance on the matter.
The Scriptures teach that political powers are instituted by God (Rom 13:1) and when they exercise their powers legitimately to ensure law and social order, they are fulfilling a divine mandate. In the case of the date line, the decision of the international community must be accepted as divinely sanctioned, because it detracts no honor from God, it exalts no individual, political, or religious organization, and it benefits all people.
Adoption of Local Calendar. The travelers who reach the islands of the Pacific from the East or from the West, should adopt the day of the people who inhabit the islands, as it is customary to adopt the time of the day of any place one goes.
It is important to remember that in a round, rotating earth the seventh-day cannot possibly be observed at the same time everywhere. When the Sabbath is beginning in Los Angeles, California (Friday evening), it is already ending in Sydney, Australia (Saturday evening).
The principle of Sabbathkeeping consists not in observing the seventh day at the same time everywhere around the globe, but rather in observing the seventh day when it arrives in the part of the earth where one lives. This principle applies both to the hour for beginning the Sabbath and to the day for observing it. Obedience to the Fourth Commandment demands that we observe the seventh day as it comes to us in the place where we live.
From Sabbath in the New Testament by Samuele Bacchiocchi pp.164-166