[Aavso-photometry] Re: Atomic Clock Synchronization -

[Greg Crawford]

My understanding is that the longer the ping time, the less accurate your time
setting. Also, in Windows, the time progression may be altered by IRQ access, so
that frequent time setting before and after an image download is essential. The
inbuilt access in Windows XP may not be accurate enough for this.

The Minor Planet Centre requires time reported to 0.00001 of a day. I think that
works out at 0.864 0f a second. (See the Guide to Minor Planet Astrometry
http://cfa-www.harvard.edu/iau/info/Astrometry.html )

With all that in mind, the USNO time server may not be your best resource for
two possible reasons: 1) Like me, you live in another part of the world, and 2)
you have Internet delays in accessing it. I'd suggest you seek a time server
with the lowest ping time from your location.

Also, bear in mind that AboutTime attempts to calculate the ping time and make
adjustments for it.

Greg Crawford


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Bagnall Beach Observatory

http://www.nelsonbay.com/~gc/observatory.htm
 

> -----Original Message-----
> From: aavso-photometry-bounces at mira.aavso.org [mailto:aavso-photometry-
> bounces at mira.aavso.org] On Behalf Of Shankland, Paul D CDR U.S. Naval
> Observatory
> Sent: Thursday, 24 March 2005 6:36 AM
> To: aavso-photometry at mira.aavso.org
> Subject: [Aavso-photometry] Re: Atomic Clock Synchronization -
> 
> Yes - NTP is the baseline for precise time on the web, and NTP.org is a good
> start... but do be aware that, if you run WinXP, have a Router or a WiFi - any
> one of these - (and didn't mess with the NTP settings) you are already pinging
> our (USNO) or NIST's NTP servers so that yor PC clock is probably accurate to
> within multi-millisec's (unless there exists a bottleneck - another story
> itself)... See our clock at: http://tycho.usno.navy.mil/master.html. Also - if
> you can get 1PPS ticks off the GPS NMEA stream (IOTA does alot of that if you
> google for it) - we provide very (sub-microsecond) time to the constellation
> (see: http://tycho.usno.navy.mil/gps.html and
> http://tycho.usno.navy.mil/gpstt.html)
> 
> I also recommend using: http://tycho.usno.navy.mil/ctime.html
> - just note that our time is typically good to <10 nanoseconds, all NTP
> transmissions suffer varying delays... unless you wanny buy time on TWSTT
> (http://tycho.usno.navy.mil/twstt.html) <grin>
> 
> Hope that adds to the info-
> Best,
> Paul
> 
> ---
> CDR Paul "Happy" Shankland, USN
> Head, Plans & Requirements
> U.S. Naval Observatory
> Washington, D.C.
> 
> USNO... Oldest US Government Scientific institution - and a cutting-edge
> leader in.... Astrometry, The DoD & National Atomic Clock, The World's Precise
> Time/PTTI, Atomic Fountain Clock Design/RFC/Cesium/LITE, TWSTT, Loran Time,
> NTP, GPS Time and monitoring, IVS, TEM, the US Master Atomic Clock, Earth
> Orientation, VLBI, ICRF, IERS, NEOS, Astronomical Applications, MICA,
> SLAC/SLAP, NOVAS, RORF, QSO Reference framing, US Naval Correlator, Strategic
> & Space Navigation & Ephimerides, Celestial Navigation/ACN, Nautical Almanac
> Office, Celestial, Air and Nautical Almanacs, Naval Observatory Flagstaff, NP
> Optical Interferometer, Parallax Program, IR, Wide & Narrow Angle Astrometry,
> Sloan digital Sky Survey, other Catalogs, NOMAD, USNO-B, WDS, UCAC, URAT,
> Tycho-2, PMM, Photometry, Alt US Master Clock Colorado, OBSS, SIM Reference
> Tie Science Team, TPF Support/Science Team
> 
> Comm: 202-762-0108
> paul.shankland at navy.mil
> Work: http://www.usno.navy.mil/
> Exoplanet astrophysics/dynamics/observations/searches/research:
> http://www.ucolick.org/%7elaugh/GJ876____c.results.html
> Full Member: http://www.aas.org/: DPS, DDA, HAD; AIP, IAU C41, ICHA, IUHPS,
AL,
> IDA
> Carpe noctem!
> 
> 
> Consider using NTP, which is a continual adjustment of the rate of time
> and as such avoids discontinuities.
> 
> http://www.ntp.org/
> 
> Cheers,
> Michael
> 
> On Mar 22, 2005, at 4:41 PM, Keith Graham wrote:
> 
> > Hi,
> >
> >
> >
> > S
> 
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