# around the world..and through it **URL:** \ **Category:** Factual Questions\ **Created:** [May 18, 2002, 5:23am UTC](https://boards.straightdope.com/t/around-the-world-and-through-it/109675 "2002-05-18T05:23:04Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![nobacon](https://avatars.discourse-cdn.com/v4/letter/n/3e96dc/32.png) [@nobacon](https://boards.straightdope.com/u/nobacon)\ **Post date:** [May 18, 2002, 5:23am UTC](https://boards.straightdope.com/t/around-the-world-and-through-it/109675/1 "2002-05-18T05:23:04Z")
Hi, This has been bugging me since i was very young… If one was to travel around the world, setting off say on monday about 12pm, with the sun directly above their head at all times, and each town they came to they asked what day and time it was. When they arrive back to their starting point and asked what day and time it was the answer would be tuesday 12pm…at what point did it become tuesday for the person travelling around the world? Surely, because they travelled with the sun directly above their head…it remained monday 12pm at all times… and another thing… If one was to dig a hole right through the earth, from one pole to the other… what would happen if they jumped into it? Would they eventually come to rest in the center or what? I have a few more, but i think even Cecil will struggle with these two 🙂 ---
**Author:** ![ShibbOleth](https://avatars.discourse-cdn.com/v4/letter/s/848f3c/32.png) [@ShibbOleth](https://boards.straightdope.com/u/ShibbOleth)\ **Post date:** [May 18, 2002, 6:10am UTC](https://boards.straightdope.com/t/around-the-world-and-through-it/109675/2 "2002-05-18T06:10:41Z")
Well, the sun goes around the world. It’s always noon when it goes around. But when you cross the International date line it’s noon the next day. ---
**Author:** ![JimOfAllTrades](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@JimOfAllTrades](https://boards.straightdope.com/u/JimOfAllTrades)\ **Post date:** [May 18, 2002, 6:13am UTC](https://boards.straightdope.com/t/around-the-world-and-through-it/109675/3 "2002-05-18T06:13:57Z")
> [@](#): > > at what point did it become tuesday for the person travelling around the world? Surely, because they travelled with the sun directly above their head…it remained monday 12pm at all times… The day and date changed when you crossed the International Date line. This is exactly why it exists. > [@](#): > > If one was to dig a hole right through the earth, from one pole to the other… what would happen if they jumped into it? Would they eventually come to rest in the center or what? Already been discussed here a few times. Check these threads: [http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=39750](http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=39750) [http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=54876](http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=54876) [http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=89300](http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=89300) and Cecil’s take on it: [http://www.straightdope.com/classics/a1\_165.html](http://www.straightdope.com/classics/a1_165.html) > [@](#): > > I have a few more, but i think even Cecil will struggle with these two Guess again. 🙂 And welcome to the boards. Your question about the date changing is the clearest expression of why we need the International Date Line I’ve come across. I’m going to have to remember it. Ugly ---
**Author:** ![SPOOFE](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@SPOOFE](https://boards.straightdope.com/u/SPOOFE)\ **Post date:** [May 18, 2002, 11:04am UTC](https://boards.straightdope.com/t/around-the-world-and-through-it/109675/4 "2002-05-18T11:04:44Z")
> [@](#): > > The day and date changed when you crossed the International Date line. This is exactly why it exists. Nuh-uh! If you go around the world fast enough, eventually you can make it stop rotating, and even start _travelling backwards in time!_ Superman’s done it. And, to be completely honest, I trust Superman more than I trust Cecil. ---
**Author:** ![stankow](https://avatars.discourse-cdn.com/v4/letter/s/cdc98d/32.png) [@stankow](https://boards.straightdope.com/u/stankow)\ **Post date:** [May 18, 2002, 11:18am UTC](https://boards.straightdope.com/t/around-the-world-and-through-it/109675/5 "2002-05-18T11:18:48Z")
> [@](#): > > \*Originally posted by SPOOFE \* > \*\*Nuh-uh! If you go around the world fast enough, eventually you can make it stop rotating, and even start _travelling backwards in time!_ Superman’s done it. And, to be completely honest, I trust Superman more than I trust Cecil. \*\* Come to think of it, has anyone ever seen Superman and Cecil at the same time? ---
**Author:** ![Angua](https://avatars.discourse-cdn.com/v4/letter/a/8baadc/32.png) [@Angua](https://boards.straightdope.com/u/Angua)\ **Post date:** [May 18, 2002, 1:02pm UTC](https://boards.straightdope.com/t/around-the-world-and-through-it/109675/6 "2002-05-18T13:02:24Z")
> [@](#): > > \*Originally posted by nobacon \* > \*\* > If one was to dig a hole right through the earth, from one pole to the other… what would happen if they jumped into it? Would they eventually come to rest in the center or what? > > \*\* I take it we’re ignoring the fact that you’d probably melt before you get to the centre 😉 What would happen is that you’d oscillate aroound the centre of the Earh. The reason for this is (here comes the maths!) that the gravitational force, which is what pulls you to the centre of the Earth is proportional to the mass of the Earth which is directely below you, and inversely proportional to how far you are from the centre of the Earth. So, as you hurtle towards the centre of the Earth, the force acting on you decreases, until you get to the centre, where there’s zero force acting on you. But, you’ve still got momentum, so you don’t stop. Instead you carry on through the centre of the Earth, slowing down, until Earth’s gravity stops you. But then, there’s a force acting on you trying to drag you down to the centre of the Earth again, so you go throough the entire thing all over again. Ignoring air resistance (stupid thing to do, but hey, it makes the maths easier!), you’ll carry on doing this ad infinitum… ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [May 18, 2002, 2:00pm UTC](https://boards.straightdope.com/t/around-the-world-and-through-it/109675/7 "2002-05-18T14:00:28Z")
Right and IIRC the period of your motion is approximately 90 minutes, which, not coincidentally, is the time it takes a geosynchronos satelite to do one orbit. ---
**Author:** ![Angua](https://avatars.discourse-cdn.com/v4/letter/a/8baadc/32.png) [@Angua](https://boards.straightdope.com/u/Angua)\ **Post date:** [May 18, 2002, 3:18pm UTC](https://boards.straightdope.com/t/around-the-world-and-through-it/109675/8 "2002-05-18T15:18:52Z")
> [@](#): > > \*Originally posted by Hari Seldon \* > \*\*Right and IIRC the period of your motion is approximately 90 minutes, which, not coincidentally, is the time it takes a geosynchronos satelite to do one orbit. \*\* Yeah, I think that’s right, though I can’t remember off the top of my head, and I’m too lazy to either sit down and do the calculation, or look it up. 🙂 ---
**Author:** ![rowrrbazzle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rowrrbazzle/32/414_2.png) [@rowrrbazzle](https://boards.straightdope.com/u/rowrrbazzle)\ **Post date:** [May 18, 2002, 6:45pm UTC](https://boards.straightdope.com/t/around-the-world-and-through-it/109675/9 "2002-05-18T18:45:20Z")
> [@](#): > > \*Originally posted by Hari Seldon \* > Right and IIRC the period of your motion is approximately 90 minutes, which, not coincidentally, is the time it takes a geosynchronos satelite to do one orbit. Um, no. Anything in low earth orbit, like the ISS or Hubble, takes about 90 minutes. To be geosynchonous, i.e., have a period of 24 hours, your orbit has to be 22,300 miles above the earth. If this orbit is above the equator, the satellite appears to stay in the same place and the orbit can be called geostationary. ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [May 18, 2002, 8:39pm UTC](https://boards.straightdope.com/t/around-the-world-and-through-it/109675/10 "2002-05-18T20:39:07Z")
> [@](#): > > \*Originally posted by rowrrbazzle \* > \*\*Um, no. Anything in low earth orbit, like the ISS or Hubble, takes about 90 minutes. To be geosynchonous, i.e., have a period of 24 hours, your orbit has to be 22,300 miles above the earth. If this orbit is above the equator, the satellite appears to stay in the same place and the orbit can be called geostationary. \*\* Urp! Of course you are right. I cringe in shame. I can’t even spell. The period is the same as if it were in orbit at earth’s surface and there were no air resistance. And of course, the motion through the center also depends on that. ---
**Author:** ![mangeorge](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@mangeorge](https://boards.straightdope.com/u/mangeorge)\ **Post date:** [May 18, 2002, 8:49pm UTC](https://boards.straightdope.com/t/around-the-world-and-through-it/109675/11 "2002-05-18T20:49:59Z")
Snagged from **RJKUgly** ’s first reply; > [@](#): > > The day and date changed when you crossed the International Date line. This is exactly why it exists. So if the IDL didn’t exist, you could get back at exactly the same moment you left. Which means the line costs me a day of my life. Bummer. Who went and put that thing there, anyway? Peace, mangeorge