If it is Sunday just east of the International Dateline, what day is it just west of the International Dateline?
http://worldatlas.com/aatlas/infopage/dateline.htm
If it is Sunday just east of the International Dateline, it will be Saturday just west of the International Dateline. The International Date Line is an imaginary line that runs generally north-south in the Pacific Ocean, and it serves as the dividing point between calendar days. When you cross the International Date Line from east to west, you "lose" a day, meaning you move back one day. So, if it is Sunday just east of the International Dateline, when you cross over to the west, it becomes Saturday.
The International Date Line is not a straight line but zigzags around certain island groups to avoid splitting them into two different calendar days. It generally follows the 180° meridian of longitude, but it deviates to ensure that it does not cut through certain regions.
You can find more information about the International Date Line and its exact location by referring to a resource like worldatlas.com, which provides detailed maps and explanations. The link you provided (http://worldatlas.com/aatlas/infopage/dateline.htm) is a good resource to learn more about the International Date Line and its significance.