# The Naked Scientists Forum

### Author Topic: How are time zones calculated?  (Read 4998 times)

#### Matthew

• Guest
##### How are time zones calculated?
« on: 28/10/2009 12:30:04 »
Matthew asked the Naked Scientists:

My friend went to Japan for 3 weeks over the summer (lucky) and there was, I think, a 14 hour time difference between us (in the future).

HOWEVER, his flight was 16 hours long; so what was the time difference ?

thanks alot and if this stumps you do i get a prize?

matthew katzenstein summit, NJ - USA

What do you think?

#### DoctorBeaver

• Naked Science Forum GOD!
• Posts: 12656
• Thanked: 3 times
• A stitch in time would have confused Einstein.
##### How are time zones calculated?
« Reply #1 on: 28/10/2009 13:44:33 »
No matter how long it takes to get there, the difference is 14 hours. Think about it - if you have 2 places in the same time zone & it takes 2 hours to drive from 1 to the other, there isn't suddenly a 2-hour time difference between them.

But here's a little something for you to think about. If 2 people set off on the same journey, 1 on foot, the other on a very fast motorcycle and they both follow exactly the same route, by the time they arrive 1 will have travelled further than the other due to relativistic effects. At mundane, Earthly speeds the difference is negligible but it's real. That means the Earth is a different size depending how fast you travel.

There's the adage about the world shrinking. Well, with transport getting faster & faster, it really is. I'm sure 1 of our resident physics whizzos can tell you all about this this but, in the meantime, have a look at http://www.fourmilab.ch/cship/lorentz.html where this phenomenon is explained in greater detail with some animations.

#### chris

• Neilep Level Member
• Posts: 5337
• Thanked: 65 times
• The Naked Scientist
##### How are time zones calculated?
« Reply #2 on: 30/10/2009 11:56:10 »
What a wonderful point; thanks Eth.

#### LeeE

• Neilep Level Member
• Posts: 3382
##### How are time zones calculated?
« Reply #3 on: 30/10/2009 18:14:29 »
Time zones are calculated according to how far around the Earth (in an East-West direction) they are.  There are 360 degrees in the East-West direction and 24 hours to a day, so for every 15 degrees East or West the time changes by one hour.  However, if we strictly stuck to using these 15 degree sections then we'd have problems with having half of one country, or even a state/county/town in one time zone and the other half in another, so the actual lines that separate the different time zones zig-zag around a bit so that most sub-continental sized countries are in a single time zone.  With large continental sized countries, such as the U.S.A. this isn't really possible and there's a three hour difference between the East and West coasts.

#### Mr. Scientist

• Neilep Level Member
• Posts: 1451
• Thanked: 2 times
• http://www.facebook.com/#/profile.php?ref=profile&
##### How are time zones calculated?
« Reply #4 on: 31/10/2009 02:38:48 »
No matter how long it takes to get there, the difference is 14 hours. Think about it - if you have 2 places in the same time zone & it takes 2 hours to drive from 1 to the other, there isn't suddenly a 2-hour time difference between them.

But here's a little something for you to think about. If 2 people set off on the same journey, 1 on foot, the other on a very fast motorcycle and they both follow exactly the same route, by the time they arrive 1 will have travelled further than the other due to relativistic effects. At mundane, Earthly speeds the difference is negligible but it's real. That means the Earth is a different size depending how fast you travel.

There's the adage about the world shrinking. Well, with transport getting faster & faster, it really is. I'm sure 1 of our resident physics whizzos can tell you all about this this but, in the meantime, have a look at http://www.fourmilab.ch/cship/lorentz.html where this phenomenon is explained in greater detail with some animations.

Then what is the difference when taking into consideration the rotation of the earth (which would add) to the time required if rotating against the route of travel? Is it a noticible difference?

#### LeeE

• Neilep Level Member
• Posts: 3382
##### How are time zones calculated?
« Reply #5 on: 31/10/2009 21:12:00 »
A typical flight from London Heathrow to New York JFK takes about 8 hours to make but when you arrive at JFK there will only be a 3 hour time difference between when you took off and when you landed.  Of course when Concorde was flying, your local landing time would be earlier than your local departure time.

Flying the other way, from JFK to LHR takes about 7 hours but when you arrive at LHR there will be an 11 hour time difference.  I believe the shorter time from JFK to LHR is due to being able to use the Jetstream.

Apart from that, the rotation of the Earth doesn't make any difference to the duration of the journey because you are rotating with it.

#### Mr. Scientist

• Neilep Level Member
• Posts: 1451
• Thanked: 2 times
• http://www.facebook.com/#/profile.php?ref=profile&
##### How are time zones calculated?
« Reply #6 on: 01/11/2009 15:49:11 »
Interesting, thank.

#### Nizzle

• Hero Member
• Posts: 964
• Thanked: 1 times
• Extropian by choice!
##### How are time zones calculated?
« Reply #7 on: 12/11/2009 08:12:00 »
Sid Vicious was right.

There IS anarchy in the UK!

Check google maps satellite: 50.086253,-5.254555

#### The Naked Scientists Forum

##### How are time zones calculated?
« Reply #7 on: 12/11/2009 08:12:00 »

Login
Login with username, password and session length