Rudimentary Geography Question 1

[No Bias FTW]

People who have taken basic history and geography classes should know the story dealing with one of the first exploratory circumnavigations. Apparently in one of the expeditions, officers were faithfully counting days spent on the ocean based on the sunrises and sunsets. However, once they arrived back in Spain, their logs were either a day ahead or a day behind the actual date of the country.

I am sure basic arithmetic can most easily demonstrate how one arrives at the correct fact. However, I would like to understand the phenomenon at an even more intuitive and sensational level with words. I hope that this would not prove to be too much a difficult task for experts here.

[StuM]

When you are sailing west, you are moving in the same direction that the sun is "apparently moving" which is opposite to the way the earth is rotating with respect to the sun.



Assume that you are at longitude x at noon on one day and sailing to the west. 24 hours later, it is noon again at longitude x, but you have moved further west and the sun is not yet overhead at your new location. So it takes more than 24 hours for the sun to be overhead again for you. So the time from "noon to noon" is more than 24 hours.



By the time you have gone around the earth, your count of longer "noon to noon days" is one less that the count of 24 hour periods (days in one location).


Taken to to the extreme, if you travel at the same speed as the "movement of the sun" (ie. at the speed of rotation of the surface of the earth at your latitude), you do the circumnavigation in 24 hours (one day), but the sun is always overhead to you so your count of "noon to noon" days is zero.



It doesn't matter fast you travel, the result is the same. The slower you move, the more days it takes, but the smaller the difference between "noon to noon days" and 24 hours periods.


The difference between 24 hours periods and "noon to noon" days is always such that a circumnavigation at that constant speed will take exactly 1 more 24 hour period than the count of "noon to noon days".


Obviously if you are traveling to the east, your noon to noon day is shorter than 24 hours. Again in the extreme case of a circumnavigation in 24 hours, you will actually have another noon ater 12 hours on the opposite side of the globe, so your count of "noon to noon" days is two.

[Lodesman]

I assume this happened before the creation of the International Date Line. When you sail east or west it is customary to adjust your clock occasionally, else you'd be having your noon meal in complete darkness, and watching the sunrise just as you are planning to go to bed. Contemporary time zones are 15º of longitude wide, consider that for the equivalent travel eastward you would have to advance the clock an hour, and conversely passing every 15º westward would cause you to retard the clock an hour. In the early days of navigation, I imagine the clock would be adjusted to bring the clock into rough agreement with apparent noon (that point at where the sun is highest in the sky above one). Presumably, circumnavigation means the continuous journey in the same direction around the earth - so if our intrepid navigator was to turn the clock back an hour every 1/24th of his westward journey, then by the time he returned home, he would be 24 hours behind - the lost day an artifice of observational error. These days, when we pass the middle (180ºE/W) the clock isn't changed by an hour - we advance or retard the date by 1.

[No Bias FTW]

Incredible details in the explanations, guys. Thank you.

[tkeithlu]

Wow, Stu. That's a beautifully clear explanation. Were you a teacher in another life? If so, your students were lucky to have you.

[The Perfessor]

Yeah, Stu, that was a great explanation! Thanks!

[waterman46]

A different explanation, perhaps more suited to the frequent flyer type.

Without getting into astronomy, lets say you fly from New York to Chicago. You would find your phone picks up the new time being one hour earlier than it is in NY. You have traveled one "time zone" West.

Now when you go around the world you are making a 360 degree circle. Each time zone you move through is 15 degrees of that circle, and there are 360/15 = 24 of these time zones to go through all the way around the world. Each time you go into a new time zone you have to set your clock 1 hour earlier. If you traveled all the way around the world, you would end up setting your clock 24 hours earlier. If you didn't do that, and your clock also had a calendar, you'd find your calender was 24 hours, or one day, later than where it should be.

[Lodesman]

Originally Posted by waterman46

A different explanation, perhaps more suited to the frequent flyer type.

Without getting into astronomy, lets say you fly from New York to Chicago. You would find your phone picks up the new time being one hour earlier than it is in NY. You have traveled one "time zone" West.

Now when you go around the world you are making a 360 degree circle. Each time zone you move through is 15 degrees of that circle, and there are 360/15 = 24 of these time zones to go through all the way around the world. Each time you go into a new time zone you have to set your clock 1 hour earlier. If you traveled all the way around the world, you would end up setting your clock 24 hours earlier. If you didn't do that, and your clock also had a calendar, you'd find your calender was 24 hours, or one day, later than where it should be.

If you didn't reset your clock it wouldn't be different than a local clock/calendar on arrival. If you reset your clock every time zone, then your calendar would be one day earlier than where it should be.

[StuM]

Originally Posted by waterman46

A different explanation,

Which, unfortunately is completely incorrect

perhaps more suited to the frequent flyer type.

Without getting into astronomy, lets say you fly from New York to Chicago. You would find your phone picks up the new time being one hour earlier than it is in NY. You have traveled one "time zone" West.

The early Spanish circumnavigators didn't have planes, "time zones" or phones.

Each time you go into a new time zone you have to set your clock 1 hour earlier. If you traveled all the way around the world, you would end up setting your clock 24 hours earlier. If you didn't do that, and your clock also had a calendar, you'd find your calender was 24 hours, or one day, later than where it should be.

Wrong! If you do nothing to your watch, it's calendar will be correct when you get back home.

If you keep putting your watch back by an hour it will end up with the wrong date when you get back home (which is in essence what the circumnavigators did)
That is unless you put it forward by one day (24 hours) when you cross the "international date line"
(They didn't have one of these either!)


Travel is not a time machine. UTC is UTC whether you are sitting in one location or moving around the world.

[Lodesman]

Originally Posted by No Bias FTW

People who have taken basic history and geography classes should know the story dealing with one of the first exploratory circumnavigations.

Fascinating read: https://en.wikipedia.org/wiki/Magell...rcumnavigation

It was when they arrived in Cape Verde, so not quite home in Spain that they discovered it was July 10th, not July 9th, 1522 as they calculated.
Took this guy to figure out what happened: https://en.wikipedia.org/wiki/Gasparo_Contarini

[kish]

Around the World in 80 Days, the novel [published 1872] by Jules Verne
https://en.wikipedia.org/wiki/Around...in_Eighty_Days
had its' denouement [https://www.google.com/search?client...tf-8&oe=utf-8]
the perfect explanation of the question posed by No Bias FTW

[StuM]

Originally Posted by Lodesman

Took this guy to figure out what happened: https://en.wikipedia.org/wiki/Gasparo_Contarini

"Contarini was the first European to give a correct explanation of this phenomenon"

Which implies that there was a "non-European" who worked it out before he did? Who? Enquiring minds want to know!

[sanibel sailor]

Which implies that there was a "non-European" who worked it out before he did? Who? Enquiring minds want to know!

The ancient astronauts who helped the Aztecs fly to Egypt.

[El Pinguino]

Originally Posted by StuM

"Contarini was the first European to give a correct explanation of this phenomenon"

Which implies that there was a "non-European" who worked it out before he did? Who? Enquiring minds want to know!

Possibly the very first person to circumnavigate the globe ....Manuel the Moluccan....

[waterman46]

Originally Posted by Lodesman

If you didn't reset your clock it wouldn't be different than a local clock/calendar on arrival. If you reset your clock every time zone, then your calendar would be one day earlier than where it should be.

Yeah, that's why I qualified it by saying "if your clock had a calendar". Showing one day earlier is correct, I thought I made that clear, but perhaps not.

I used to have a watch that showed not only time but date. I guess those have all gone the way of dinosaurs, or as some would have us believe, the same way as the CQR anchor!