🔍 Key Concepts

• International Date Line (IDL) at the 180th meridian and how the calendar date changes when crossing it • Direction of travel: what happens to the date when you cross the IDL westbound vs eastbound • Relationship between zone time (local civil time) and the change of date at the IDL

💭 Think About

• First, forget the multiple-choice answers and ask yourself: on 5 July at 1200 local time just before crossing westward over the 180th meridian, what date and time is it just across the line on the other side? • Are you gaining a day or losing a day when you go west across the International Date Line? How does that affect the calendar date, not the clock time? • Does crossing the IDL automatically change the clock time (hours and minutes), or does it primarily change the date attached to that same clock time?

✅ Before You Answer

• Be clear which side of the 180th meridian you started on: east longitude side or west longitude side and what date it is there. • Confirm whether traveling westward across the International Date Line means you move your calendar forward one day or back one day. • Make sure you separate the idea of time-of-day (1200) from the calendar date (4th, 5th, or 6th of July) when deciding your answer.