if you are sailing from San Francisco to Tokyo and reach the International Date Line on a Sunday, what day will it be the moment you have crossed the line

Monday

Explanation:

The International Date Line is the line that is on the total opposite side of the world from here the Prime Meridian is. This imaginary line is the one from which the time is counted, the place from where each new day starts. Just east of the line lie the places that are the most upfront when it comes to the counting of time, while just west of this line lie the places that are the last when it comes to counting the time, so just few cm are actually 24 hours difference in time. If someone is traveling from San Francisco towards Tokyo, and when this line is reached it is Sunday, by simply crossing it everyone enters into the first time zone, so it will be Monday.