To contact us:      Phone: 612 9653 3395 | Mob:  0419 243 715  | E-mail: andras@arcadiaobservatory.org


Accurate time source for the observatory is provided by a Garmin model GPS 18x LVC  OEM style GPS receiver.  The receiver continuously outputs standard NEMA 0183 ‘sentences’ on a configurable RS232 link connected to the observatory computer.

 The sentences contain, apart from the coordinates (Latitude/Longitude),  speed, altitude etc  of its location,  an extremely accurate Coordinated UTC time and date to the precision of 0.1 second.  In addition this model of the sensor also outputs on a separate line, a short pulse, the leading edge of which is accurate to one microsecond of the current UTC second. This feature is not used currently in the observatory.

High precision timing is essential for all scientific observations involving transient phenomena such as occultations,  asteroids positions and variable star light curves.  This is especially true for fast moving asteroids as some Near Earth Objects (NEO) can move across the sky at more then 10 arc seconds per second of time.  A timing error of only 0.1 sec in the time stamp reported by the imaging software will produce an error of 1 second of arc in the position reported for the object.  The current setup at the observatory produces image timing no better than +-1 second relative to Universal Time Coordinated (UTC).  This is due mainly to the unknown and variable time offset from the time read by the imaging software  and the actual time the software opens the camera shutter.  The time used by the software is the computer clock which is updated by the GPS receiver once a minute using the GPS Time  applet. Another hurdle to improving on the 1 second precision is that the camera software (CCDOps) for SBIG only reports time of exposure to the 1 second precision.  Improving this to say 0.1  sec  would require either dedicated hardware and/or a different CCD camera that reports time to higher precision and a constant and deducible offset between reported time stamp and actual shutter opening time.