[time-nuts] June 30 2015 leap second

Mark Spencer mark at alignedsolutions.com
Sun Jan 11 10:15:36 EST 2015

I've often wondered why more systems don't use TAI or other similar time scales as their time source.   If needed the time displayed to end users or third parties could be converted to UTC just prior to presentation or transmittal.

For example a financial system that needs to time stamp individual transactions could sync their system clocks to TAI.   As the difference between TAI and UTC changed (or was scheduled to change) a lookup table could be updated that would provide the offset between UTC and TAI for given date ranges.

Sent from my iPad

On 2015-01-10, at 7:49 AM, Jim Lux <jimlux at earthlink.net> wrote:

> On 1/9/15 4:57 PM, Henry Hallam wrote:
>> Such slewing solutions are OK for Google.  They wouldn't work well for
>> one of the systems I work with, which uses system time to calculate
>> the position of a LEO satellite for purpose of pointing a 7.6 meter
>> X-band dish.  Half a second of error corresponds to a pointing error
>> of 0.5 degrees, well outside the main lobe of the antenna beam.
> Which is why we use TAI in the space business and don't fool with this "Greenwich Mean Time" or "Coordinated Universal Time" which is discontinuous and potentially non-monotonic.
> We DO need to compensate for the earth's varying rotational speed, though, but that's just handled as a separate model for deep space, or for LEO, where the coordinate system is Earth Centered, absorbed into the spacecraft orbital elements.. nobody is going to use 1 year old ephemerides)
> I do find myself explaining exactly WHY we can't just use PC system time, etc. and periodic leap seconds are an object lesson in why not.
> (or, you can arrange to not being doing any operations at the moment of leap...that's been done too)
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