8 Observe the Sabbath and keep it holy. 9 You have six days in which to do your work, 10 but the seventh day is a day of rest dedicated to me (Exodus 20:8 - 10)
While the fourth commandment gives us a very basic idea of what to do and not do on the Sabbath (e.g. keep it holy but do not work) no specific instructions are given regarding WHEN to keep the day. The absence of an exact time within the Ten Commandments may be indicative of God's wisdom in revealing a law adaptable to various geographical locations.
Do sunsets define a day?
There are many reasons why sunset is used as the starting point not only for the Sabbath but also for God's Feast days as well.
The holy day known as Atonement, occurring in the Fall of the year, states that the day's fasting needed to occur from the evening of the 9th and continue until the 10th day at even (Leviticus 23:27 - 32). Another reason is, in Biblical times, the setting of the sun denoted the end of the work day. Jesus' parable of workers in a vineyard alludes to this when the owner of the fields, at evening, calls all those working to him so that they can be paid (Matthew 20:8).
Do the New Testament writers define the end of a day as occurring at a fixed time (e.g. 6 p.m.), or when evening starts, or when the sun sets? The gospel of Mark states that when the sun had set all kinds of sick people and those possessed by an evil spirit came to Jesus to be healed (Mark 1:32).
"When the sun was setting, all those who had any that were sick with various diseases brought them to Him; and He laid His hands on every one of them and healed them." (Luke 4:40)
Clearly, the evening in these phrases that mark the end of the day, especially the Sabbath, is sunset.
God's rest in the Arctic
Trying to observe God's day of rest using sunset, within the Arctic circle, is virtually impossible. This is because the sun does not set below the visible horizon for a period of time in the summer and does not come ABOVE the horizon during parts of winter. The problem of observance is also compounded by the fact that, just before the sun goes below the horizon for a period in winter, it sets at noon. Under such factors the keeping of God's Sabbath day is a real problem since it requires the abrupt stopping of all work before noon on Friday and the starting of a regular day on noon Saturday.
Although no quick solutions exist on keeping the fourth commandment in such regions as the Arctic, some acceptable alternatives include the following.
When there are no sunsets during winter, the end of twilight, as indicated by astronomical tables, could be looked upon as the start of God's rest day.
The fourth commandment can also be kept by using astronomical computations to determine when the sun is closest to the horizon, or at its zenith on Friday, until it returns to this same location on Saturday.
One can also define, in such regions, the starting and ending of the Sabbath based on when the sun sets just south of the Arctic Circle.
In the area of the Arctic the sun can set very early, very late, or even not at all. It is therefore suggested that the Sabbath be observed from 6 p.m. to 6 p.m., according to the equatorial sunset time. This method preserves the integrity of the sixth working day, is compatible with the sunset time of Bible lands, and respects the working schedule of most people living in these regions.
The arctic circle begins at latitude 66° 33' (66 degrees 33 minutes) and includes all regions north of this line. Within this circle the sun is above and below the horizon for 24 straight hours at least once per year. The Arctic Ocean within the circle, the smallest of the earth's five main oceans (the others being the Atlantic, Pacific, Indian and Southern), comprises on area of roughly 5,427,051 square miles. The equivalent polar circle in the Southern Hemisphere is the Antarctic Circle.
The fact that no instruction exists within the Fourth of the Ten Commandments in regard to when the day of rest should begin or end lends itself to the conclusion that God had decided to leave such determinations open in order to allow all mankind to keep His law no matter where they live on the planet. Additionally, the reasons that made sunset the point from which the fourth commandment was kept are still important today.