set Time.zone to current user time zone

I want to set the Time.zone to the user's current time zone, I don't
want to store the timezone in user profile like many other solutions.
How to do that?

Thanks

Correct me if i am wrong, but current_user.time_zone will require you
store the time_zone under user profile.

I believe this has been discussed a number of times and my
understanding is that the only way to achieve it is via javascript and
pass the data back to to the server (or better just use it in the
browser if possible). Google will provide various suggestions such as
http://www.onlineaspect.com/2007/06/08/auto-detect-a-time-zone-with-javascript

Colin