We’ve been time-traveling. We went back and forth between January 20 and January 21 so many times, I have whiplash. OK, maybe I’m exaggerating, but still, it was weird. Then we got stuck on 21 January. It was reminiscent of the movie “Groundhog Day” here on board the ship. I was beyond confused about the International Date Line (IDL), so I looked into the matter. I will share what I found out in case you are not clear about it either.
As the countries of the world became increasingly interconnected in the second half of the nineteenth century with nascent technologies, commerce and communication between countries grew exponentially. World leaders became aware that there really needed to be a place where the new day began. Basically, the world needed to be, as we say, “on the same page” with respect to date and time. United States President Chester Arthur organized a conference in Washington to discuss the need to find common ground and set an internationally acknowledged and agreed upon world clock. Attendees included representatives from twenty six countries. The conference was expressly convened “for the purpose of fixing upon a meridian proper to be employed as a common zero longitude and standard of time-reckoning throughout the globe.” They met in 1884, and out of that meeting, seven resolutions were passed. Needless to say, with such a meeting of minds from so many countries, there is no formal international law, but an agreement was reached by the participating countries and it is up to each country to enforce the agreement.
Out of that conference, the prime meridian in Greenwich was recognized as the official prime meridian and the location of zero longitude. Oddly enough, before then, prime meridian status had been claimed in several cities such as Rome, Paris, Oslo, St.Petersburg, and Jerusalem, but two thirds of commercial steam ships were already using the prime meridian at Greenwich as the point of zero longitude or “initial meridian,” as it was called, so it made sense to choose Greenwich as “ground zero,” so to speak. The conference decided that all nautical and astronomical days would start at 12:00 a.m. It also decided to adopt a universal solar day beginning at midnight at Greenwich. A solar day is the time taken by the earth to make one complete rotation on its axis. As we know, it takes twenty four hours for this to happen. If the date line was not in a fixed position, a person traveling east around the globe would gain a day on someone who was staying in place. But the earth doesn’t go own indefinitely; at some point, you have to stop and start over. Therefore, assigning a fixed location where a new day begins was essential. Since our ship was traveling east, a day was added to our calendar, which is why we had two days called 21 January on our itinerary. Had we been traveling westerly, we would have subtracted a day, and we would have jumped to 22 January from 20 January.
If you look at the IDL, you will notice that it is not straight. It has actually changed several times over the years. Again, the line was not set by international law, so countries along the IDL are free to choose which side of the line they want to be on. For one thing, the line zigzags around national borders; take a look at how crooked it is between Russia and Alaska. Also, Samoa decided that it would be better off on the same side as Australia for trade reasons, but American Samoa stayed on the other side (same side as the USA). To put a personal spin on it, if we were on a cruise going west, the cruise would be one day shorter, but we are heading east, so we gained a day. And considering the weather reports we’ve heard from back home, we are grateful for the extra day in the sun!
Addendum 27 January 2024 – Let this sink in: Just before we crossed the IDL, we were sixteen hours ahead of our family back home. As soon as we crossed the IDL, we were five hours behind them.