I'm looking at the timezones and trying to figure out abbreviations. I'm using list of timezones and offsets to display them on my website.
Client asked to add abbreviation for each timezone. Once I listed abbreviations I realised that there are the same timezone names for different abbreviations such as:
'edt'
'offset' = -14400
'timezone_id' = 'America/New_York'
'ept'
'offset' = -14400
'timezone_id' = 'America/New_York'
'est'
'offset' = -18000
'timezone_id' = 'America/New_York'
'ewt'
'offset' = -14400
'timezone_id' = 'America/New_York'
Can someone please explain what is that exactly and how do I know which abbreviation to display?
US Timezones
If you're working with US Timezones they are broken down into 4 Timezones that cover the Mainland US (Except Alaska and Hawaii)
EST EASTERN STANDARD TIME UTC - 5
EDT EASTERN DAYLIGHT TIME UTC - 4
CST CENTRAL STANDARD TIME UTC - 6
CDT CENTRAL DAYLIGHT TIME UTC - 5
MST MOUNTAIN STANDARD TIME UTC - 7
MDT MOUNTAIN DAYLIGHT TIME UTC - 6
PST PACIFIC STANDARD TIME UTC - 8
PDT PACIFIC DAYLIGHT TIME UTC - 7
So you'd be using EST,CST,MST and PST for the Mainland US anyway. Hawaii and Alaska have different Timezones and off the top of my head am not sure exactly what they are
Related
I have an integer that represents a unix epoch time in millisecond precision and a time zone string. I need to create a TimeWithZone object with them.
epoch_ms_integer = 1586653140000
time_zone = "America/Los_Angeles"
Trying to convert to:
Sat, 11 Apr 2020 20:59:00 PDT -07:00
I was able to accomplish this by doing:
Time.at(epoch_ms_integer/1000).asctime.in_time_zone("America/Los_Angeles")
but was wondering if this is the best way to achieve this. The app I'm working on is configured to EST/EDT time zone so Time.at(epoch_ms_integer/1000) returns 2020-04-11 20:59:00 -0400.
I was able to find the asctime solution in one of the answers here Ruby / Rails - Change the timezone of a Time, without changing the value
the same question was asked here but no answer converting epoch time with milliseconds to datetime.
Assuming that the timestamp is in milliseconds, then 1586653140000 is
Epoch: 1586653140
GMT: Sunday, April 12, 2020 12:59:00 AM
PDT: Saturday, April 11, 2020 17:59:00 PM -in time zone America/Los Angeles
These are just 3 different ways to refer to a specific point in time around the world.
Sat, 11 Apr 2020 20:59:00 PDT -07:00 and 2020-04-11 20:59:00 -0400 each refer to different points in time and not the same as epoch(1586653140)
Since the Unix epoch (or Unix time or POSIX time or Unix timestamp) is the number of seconds that have elapsed since January 1, 1970 (midnight UTC/GMT), it wouldn't make sense to take 1586653140 and only change the time zone without adding the zone's offset because now you are talking about another point in time.
To get the right "translation" from the epoch to any time zone you could just do
Time.zone = "GMT"
Time.zone.at(1586653140)
=> Sun, 12 Apr 2020 00:59:00 GMT +00:00
Time.zone = "America/Los_Angeles"
Time.zone.at(1586653140)
=> Sat, 11 Apr 2020 17:59:00 PDT -07:00
When working with dates in time zones in rails it is important to only use functions that take the set time zone into account:
DON’T USE
Time.now
Date.today
Date.today.to_time
Time.parse("2015-07-04 17:05:37")
Time.strptime(string, "%Y-%m-%dT%H:%M:%S%z")
DO USE
Time.current
2.hours.ago
Time.zone.today
Date.current
1.day.from_now
Time.zone.parse("2015-07-04 17:05:37")
Time.strptime(string, "%Y-%m-%dT%H:%M:%S%z").in_time_zone
Also keep in mind that in a Rails app, we have three different time zones:
system time,
application time, and
database time.
This post by thoughtbot explains things clearly.
I have a Date Time(Friday, 27 October 2017 4:00:00 AM) in US Central Time zone (CDT). I want to convert this Date Time into different time zones. These are time zones i wanted to convert.
Eastern Time (EDT)
Pacific Time (PDT)
New Delhi, India (IST)
Central Europian Time (CET)
Riyadh, Saudi Arabia (AST)
Pakistan Standard Time (PKT)
Lagos, Nigeria (WAT)
Australian Standard Time (AET)
Greenwich Mean Time (GMT)
Moscow, Russia (MSK)
China Standard Time (CST)
This is how i am doing
var dateTime = moment.tz("2017-10-27 4:00:00 AM", "America/Chicago");
var IST = dateTime.tz('Asia/Calcutta').format('MMMM Do YYYY, h:mm:ss a');
console.log(IST) // October 27th 2017, 9:30:00 am
The returned Date Time is wrong. Because Indian Standard Time is 10 hours and 30 minutes ahead of Central Time.
It should be Friday, 27 October 2017 2:30 PM (IST)
Thanks!
The problem isn't with the conversion to the Indian time zone - it's the original parsing of the Chicago time.
This:
var dateTime = moment.tz("2017-10-27 4:00:00 AM", "America/Chicago");
... is treated as 4am UTC, and then converted to America/Chicago, so it ends up representing 11pm local time (on October 26th) in Chicago. You can see that by just logging the value of dateTime.
If you change the code to:
var dateTime = moment.tz("2017-10-27 04:00:00", "America/Chicago");
... then it's treated as 4am local time on the 27th, which is what I believe you expected. The result of the conversion to Asia/Calcutta is then 2:30pm as you expected.
So either change the format of your input, or specify that format. For example, this works fine too:
var dateTime = moment.tz("2017-10-27 4:00:00 AM", "YYYY-MM-DD h:mm:ss a", "America/Chicago");
Using the tz() function from moment-timezone as follow:
moment.tz('2017-10-15 13:53:43','Asia/Hong_Kong').format()
//returns '2017-10-15T13:53:43+08:00'
moment.tz('2017-10-15 13:53:43','Asia/Hong_Kong').format('h:m A')
//I expect to return '9:53 PM' but it returns '1:53 PM'
Ultimately, I want to apply the fromNow() function to format the result. But when I apply it, it uses the initial timestamp and ignore the timezone applied.
moment.tz('2017-10-15 13:53:43','Asia/Hong_Kong').fromNow()
//I expect to return '1 min ago' when actual time is 13:54 UTC (21:54 in HK) but it returns '8 hours ago'
What am I doing wrong here?
When you do:
moment.tz('2017-10-15 13:53:43','Asia/Hong_Kong');
You're creating a date/time that corresponds to October 15th 2017, at 1:53 PM in Hong Kong - which, in turn, corresponds to 2017-10-15T05:53:43Z (5:53 AM in UTC).
When you call the format() function:
moment.tz('2017-10-15 13:53:43','Asia/Hong_Kong').format();
It returns:
2017-10-15T13:53:43+08:00
The +08:00 part is just the UTC offset - it just tells that Hong Kong is 8 hours ahead UTC. But 2017-10-15T13:53:43+08:00 (1:53 PM in Hong Kong) is exactly the same instant as 2017-10-15T05:53:43Z (5:53 AM in UTC). That's why fromNow(), when the current time is 13:54 UTC, returns 8 hours.
If you want the date/time that corresponds to 1:53 PM in UTC, you should use the utc() function:
// October 15th 2017, 1:53 PM in UTC
moment.utc('2017-10-15 13:53:43');
Now, when the current time is 13:54 UTC, fromNow() will return 1 minute (because the date/time represents 1:53 PM in UTC).
To convert this to Hong Kong timezone, just use the tz() function:
// convert 1:53 PM UTC to Hong Kong timezone (9:53 PM)
moment.utc('2017-10-15 13:53:43').tz('Asia/Hong_Kong').format('h:m A');
This will convert 1:53 PM UTC to Hong Kong timezone (resulting in 9:53 PM):
I'm having a frustrating issue that I can't seem to narrow down. I have searched many similar articles but they are not close enough to my issue to resolve. I am trying to pull a time from the database and display it in more than one time zone. My Rails app is using UTC as default. Here is what I'm doing:
On the create action I take the string of time which will be saved in the time column in my DB:
params[:schedule][:start] = "09:00"
Time.zone = "Central Time (US & Canada)"
#schedule.start = Time.zone.parse(params[:schedule][:start])
The above formats the time as it is supposed to:
2016-04-12 09:00:00 -0500
This is saved in the DB as:
2000-01-01 14:00:00
This has no time offset which is fine since I know it's in UTC. The problem happens when I go to display the time:
#schedule.start.in_time_zone("Central Time (US & Canada)")
This returns:
Sat, 01 Jan 2000 08:00:00 CST -06:00
Now, since this is a time column, I don't care about the date. I plan on formatting the value to only show the time. However, it is showing CST when it is currently CDT.
I can't figure out why this is happening. As I said I am not setting the Time Zone anywhere in my application.rb or anywhere else and I only set the Time zone on the create action which should be fine when moving to a new action.
Any help on clarifying this would be awesome!
This seems to be because when the time is stored it is stored with the date in the year 2000-01-01 which seems to be why it is using CST. How can I ignore the date when converting it to a particular timezone or will I need to change the column type to DateTime to get this to work properly?
It is showing CST simply because the time is read from the database including the stored date, i.e. it's read as 09:00 of Jan 1st 2000.
I guess you'd have to parse the time upon reading the attribute back. You can use a helper method in your model, for example:
# schedule model
def start_in_zone(zone)
self.start.strftime("%H:%M").in_time_zone(zone)
end
This will take only the hours and minutes part of the stored time and parse it in the given time zone with the date set to today. See this example:
"Sat, 01 Jan 2000 08:00:00".to_time.
strftime("%H:%M").
in_time_zone("Central Time (US & Canada)")
# => Tue, 12 Apr 2016 08:00:00 CDT -05:00
The fact that it matters whether it's CST or CDT means you do, on some level, care about the date. While I'm not familiar with the exact rules of Daylight Savings in that region, I do know that Jan 1 is the middle of winter and will definitely not be on Daylight Savings time.
Add the relevant date into your #schedule before putting it into a time zone, and it should fix the problem.
Time.zone = 'Asia/Kolkata'
Time.zone
=> (GMT+05:30) Asia/Kolkata
Time.zone has been set properly.
Time.zone.parse('0000-01-01 03:00:00 UTC').strftime('%l:%M %p')
=> " 8:53 AM"
Incorrect offset being applied (+05:33 vs +05:30)
Why does this happen? Is there a better way?
The time zone in Calcutta before 1941 seems to have been 5 hours, 53 minutes ahead of UTC.
If you use a year later than that (for example year 2000) instead of year 0, you should get the result you expect.
Due to daylight savings time, you can't really convert a UTC time to a local time, 8:00UTC can convert to different local times in summer and winter. For automatic conversion to give the correct result, you need a full date, not just a time.