Software Development

When does AEST not mean AEST?

Only in Australia could we have two identical time-zone abbreviations that mean different things.

Every couple of years or so, I forget about a quirk in the Olsen time-zone data that removes Australian Eastern/Central/Western Daylight time zone, or so I think.

For over 20 years, the battle has raged: is the hour shift that results from daylight savings Australian Daylight Time or Australian Summer Time?

Here's the quote from John Mackin circa 1991 in the Australiasian zone info that still holds sway:

From John Mackin (1991-03-06): We in Australia have never referred to DST as "daylight" time. It is called "summer" time. Now, by a happy coincidence, "summer" and "standard" happen to start with the same letter; hence, the abbreviation does not change ... The legislation does not actually define abbreviations, at least in this state, but the abbreviation is just commonly taken to be the initials of the phrase, and the legislation here uniformly uses the phrase "summer time" and does not use the phrase "daylight time".

And so it has been.

If time zones were referenced with their full name, there wouldn't be an issue, but on *NIX systems, an abbreviation is returned.

Currently, the date command returns:
Fri Oct 12 14:52:43 EST 2012

This is correct, but is that abbreviation Eastern Standard Time or Eastern Summer Time? In Sydney, it would be Summer Time, but in Brisbane it is Standard Time. If you were arranging a phone call between those two cities and stated that it would happen at 10am EST, whose EST is it?

To get a more informative answer, use an -R flag to return a date that confirms the RFC 2822 format.

Now the output becomes:
Fri, 12 Oct 2012 14:55:47 +1100
To get a date that shows both the time-zone abbreivation and offset from universal time, you can use the following command:
date +%c" "%z
This outputs:
Fri 12 Oct 2012 15:02:03 EST +1100

From this result, we can see that the computer is in an eastern Australian locale that has shifted its time in line with daylight saving.

It's a lot of work, and I think it would be much easier to change the abbreviation to EDT for daylight savings.

Do you agree? Tell us your opinion in the poll below.

And then there is that other question: should we add an A to the front of our time-zone abbreviations to differenciate ourselves from American eastern timezones?


Some would say that it is a long way from software engineering to journalism, others would correctly argue that it is a mere 10 metres according to the floor plan.During his first five years with CBS Interactive, Chris started his journalistic advent...


The US state of Indiana used to follow different Daylight Saving Time rules from the rest of the US Eastern Time zone. I say 'used to' because in 2005 they changed to match the rest of the eastern US. So why do Windows operating systems developed and released since then (definitely Vista and W7, not sure about W8) still have separate time zone settings for Indiana?

Deadly Ernest
Deadly Ernest

I live in NSW and always have, born in 1954. It's always been called Daylight Saving Time by the media and government people I've seen and heard. The same for Victoria too. Here is a quote from the official NSW gov't site on the issue: "For future summers, daylight saving in New South Wales begins at 2:00 am, Eastern Standard Time, on the first Sunday in October and ends at 3:00 am Eastern Daylight Saving Time on the first Sunday in April." Please note they call it Eastern Daylight Saving Time. Chris, what part of Australia did you grow up in, and where do you now live - as calling it Summer time might be just a local regional thing. I do know the people from Queensland hate it as they don't use it and it messes up a lot of things for them and always has since it was introduced, so they may be calling it all sorts of things. Also, I've never heard of this John Mackin, and having trouble finding out much about him. I assume he's the one who was active on a few newsgroup and not known for anything else at all, as there's nothing else on Google about him, unless he's the UK footballer.


According to the Australian Government web site at we have AEST (Australian Eastern Standard Time) and when daylight savings kicks in, it becomes AEDT. Of course, how official this web site is anyones guess. I think the National Measurement Institute (part of the Federal Government Industry, Innovation, Science, Research and Tertiary Education Portfolio) is responsible for measuring/defining "time", specifically the "second". Not sure who sets time zones and associated abbreviations though.

Deadly Ernest
Deadly Ernest

the rest of the industry, but it's more likely they haven't yet become aware they need to steal a new version of the software that manages this.

Chris Duckett
Chris Duckett

But my "feeling" is that it has fallen away quite a bit in recent years. I've even heard Eastern Daylight Summer Time used a few times, resulting in AEDST. For reference sake: I'm NSW now, and always (when in Australia).

Deadly Ernest
Deadly Ernest

in Sydney and left there in the mid 1980s to live in the Queanbeyan area until 2003 and now live in the Riverina. I checked around with a few people I know and none of them had heard the term Summer Time in relation to daylight savings, but a few had heard it used in relation to the summer school holidays, especially for January.

Deadly Ernest
Deadly Ernest

that it is mentioned in several places and all seem to flow back to either the John Mackin text in the UTC Time code page or a couple of media people from the same sector of Victoria, maybe from the same uni or something. It's clearly NOT widespread not has been. I suspect it comes under the same heading as the outback Queensland reference to DST as A$$h0le time - ie a local dialectic use which probably got a wider issue due to the work a few of the people did. I've not heard it in any of the ABC broadcasts or Vic broadcasts I've seen over the years. However, it's only in recent years that I started listening to the ABC radio broadcasts although I did used to watch all the ABC TV cricket broadcasts up to the early 1990s. There are a lot of references to the use of DST during the 'Summer Time' (meaning the summer period) and thus not really relevant to the discussion.

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