What Time Is It on the International Space Station? (2013) | Hacker News Reader

What Time Is It on the International Space Station? (2013)

astronautabby.com

49 pointsvinnyglennon41 comments

It's weird that the author chooses Iceland as an example of a GMT+0 country, rather than Britain which is where Greenwich is.

Unlike Britain, Iceland does not have Daylight Saving Time, and therefore is GMT+0 throughout the year.

Precisely. GMT does not change with Summer time, though the time in Greenwich (and teh rest of the UK) does. [0]

[0] https://greenwichmeantime.com/uk/time/british-summer-time/

The usual mismatch between "London is in GMT+0" and "...in BST"

Am I the only programmer who is suddenly super duper envious of Iceland?

DST should not be the only reason to use UTC. It's probably just what makes it obvious once a year that someone uses timestamps wrong.

i read somewhere that some people may not like referring to britain as the default 'reference point' for timezones due to political/cultural reasons of their country. personally i dont have an issue with it, and i'm not saying that's the case here, maybe the author just likes iceland?

The UK developed the first portable timepiece good enough to accurately tell longitude. It's theirs.

The French didn't like it, but were outvoted. See:

https://en.wikipedia.org/wiki/International_Meridian_Confere...

To be slightly more accurate: in the 1880s, the British Empire had the preeminent navy and thus the preeminent naval charts. While other countries (including the US) maintained more local meridians for doing geodetic surveys of their own countries, it was the Greenwich Meridian that tended to dominate naval charts, which meant that it was more or less a de facto standard anyways by the Meridian Conference.

This is an old article since iOS has added UTC time zone to system settings and clock app.

Android still doesn’t support UTC time zone, and need to use Iceland as hack. Which depends on Iceland not changing their time zone.

Had anyone here tried to live life with their iPhone on UTC?

yes. it makes reading logs easier.

I don't have a phone, boss wants me to get one, & I'll be setting it to UTC if I end up with one

I've had my own devices set to UTC for the past few years. It made sense for coordinating when my friends are in whichever places of time, especially for online PvP gaming. It worked well when I was working remotely

UTC as a world clock is a happy medium, and works well. You get it in the notifications tray.

There are probably better choices than Iceland, if Android supports them. Iceland doesn't do DST now, but has in the past (1917-1918, and 1939-1968). The farther North a place is, the stronger the case for DST, so I wouldn't count on Iceland changing not their mind someday.

I'd pick someplace reasonably close to the equator. Then there is little difference in sunrise and sunset times throughout the year, and there is pretty much no case to be made for DST on sunlight grounds.

Some good choices, if whatever you are trying to set supports any of them:

• Liberia. City of Monrovia if you have to specify by city. There's only 0:43 difference between the longest and shortest daylight periods of the year there.

• Guinea, city of Conakry.

• Togo, city of Lomé.

There are a few other countries in the general area of these three that are on UTC+0 but these three have never had DST so are probably more likely to stay that way.

> The farther North a place is, the stronger the case for DST

I disagree. If you get to the north pole or anywhere near the Arctic Circle (where Iceland is), it can still be dark at noon in the winter and light at midnight in the summer. You can't nearly compensate for that with a mere hour change, so why bother?

I think they actually have a separate time called OBT (maybe it stands for Orbit).

I was at the Johnson Space Center in Houston recently, where we got a tour of the live Mission Control room for the International Space Station. I noticed two clocks at the top of one of the screens. One was GMT, the other was "OBT", and the OBT clock was around 17 seconds ahead of GMT. I think it has to do with relativity, and the fact that the space station is moving relatively faster than the earth. Maybe someone can confirm.

I got a photo of this mission control monitor if anyone is interested.

If you know the clock drift, won't you be able to calibrate the space station clock back to GMT+0, thus eliminating the need for an OBT?

GMT is already corrected back to earth GMT. But if you’re doing a time sensitive measurement and went to measure real seconds, you look at OBT.

+17s would not be due to time dilation, neither in magnitude nor sign; references I could find show that time on the ISS is slower than on Earth by around 14ms per year, and the ISS has been on orbit for less than 20 years.

OBT (I'm guessing onboard time actually), is probably using GPS time (https://en.wikipedia.org/wiki/Global_Positioning_System#Time...) which is now 18 seconds ahead of UTC due to additional leap seconds inserted into UTC since GPS time started.

Technically, UTC is a time standard, and GMT is a time zone, so the two, although equal, are not really the same thing. Also, you can set your iPhone to UTC in the World Clock, which I do as an amateur astronomer.

I thought UTC the same, doesn't that mean that GMT+0 is essentially wrong? I thought GMT was essentially UTC+0, and all other time zones (ignoring DST) are defined as offsets to UTC, not GMT.

Think of it as two pointers referencing the same data:

    Time* UTC = Time(0);
    Time* GMT = *UTC;

    *UTC == *GMT; // True
    UTC == GMT; // False

Your example with pointers actually wouldn't compile, and I think the analogy you are trying to make is not accurate. On the second line you are assigning the target address of `GMT` to be the value pointed to by UTC. In other words you are trying to assign a value of type "Time" to an object to type "Pointer-to-Time".

If, however you meant for that line to be: Time *GMT = UTC;

it would compile fine, but then your second comparison would evaluate to true, and the whole analogy be rather pointless.

What I meant was to have them both point to the same data, but be different objects.

Sure, C wouldn't work that way, but it's just supposed to be pseudocode anyway.

Tom Scott on timezones:

https://www.youtube.com/watch?v=-5wpm-gesOY

We spent a lot of time at Yeshiva discussing when a Jew in space, or on Mars, or on a planet orbiting Alpha Centauri (for example) would have to light Shabbos candles or celebrate Yom Kippur.

This issue has already come up with Jewish astronauts on the Space Station.

...is it even allowed to set things on fire inside of ISS?

This kind of makes me want to make a site that will show the current solar time of the ISS. i.e. when the ISS is between the Earth and Sun it's 12:00, on the opposite side it's midnight. And show what time sunrise and sunset are. The minutes would obviously be much shorter (as a day is only ~90 minutes long), but it'd be interesting to see.

I find it somewhat interesting that when SpaceX's streams switch to views with burned-in timecode it is always in UTC.

Edit: and usually in ISO8601-ish format

If you are going to design something using a time code the most obvious solution is probably to choose your own zone. When you realize that doesn't apply to anyone else, UTC is the next option. Especially because it means you don't need to deal with user configuration.

As for ISO8601, that probably results from people looking for some standard to help with compatibility. If you just mean YYYY-DD-MM HH:MM that is just nicely ordered. Actual ISO8601 would yield something like: 2018-03-11T22:53:40+00:00 I personally really hate that T in ISO8601, but it is actually a standard aimed at being both human and machine readable.

All that aside, I think we can all agree that MM-DD-YYYY is just incongruous and stupid.

It’s yyyy-mm-dd not yyyy-dd-mm....

You are totally right, I got that wrong :( sadly it's to late to either edit or delete my shame.

Well, the T can be omitted if reading and writing parties agree: »NOTE: By mutual agreement of the partners in information interchange, the character [T] may be omitted in applications where there is no risk of confusing a date and time of day representation with others defined in this International Standard.«

And I think SpaceX wouldn't even have the obvious option of using their own time zone. AFAIK mission control and launch are in different time zones anyway, so UTC is really the only sane option to make sure everyone refers to the same time.

I work in the space industry and UTC is the only things we use for anything operational. Most also use it for meeting coordination. Many missions also use a Mission Elapsed Time which is based on launch time. Usually only used during launch and early phase in case there are launch delays.

> Unfortunately the built-in iPhone clock application does not recognize the International Space Station in its search.

But it does do UTC.

Do their clocks take into account time dilation?

Article claims that Houston is GMT-5, but isn’t Houston GMT-6 as part of central standard time? (Although not CDT is GMT-5).

It's not just the ISS -- GMT (aka Zulu) is the standard for aviation and the US military in general.

Reply on news.ycombinator.com