RASNZ OCCULTATION SECTION MEETING - 2004 JULY 3  06:00 UT

NZ International Campus, Upper Hutt, Wellington

 

(Compiled from notes taken by Bob Evans)

 

 

There were 34 people in attendance.

 

At the start of the meeting Graham Blow made available copies of the Section’s News and Minor Planet Circulars.

 

General Matters:

 

• Graham asked how many people had seen a total or grazing occultation.  About 50% indicated 'yes'.  He then asked how many had seen one in the last 2 years.  Only a very small number of people indicated so.  Graham noted that a few years ago Australia and NZ were, per capita, behind only the U.S. in the number of these events observed, but that was no longer the case.  Graham emphasized that observing total and grazing occultations was still valuable, with an additional reason now being that they provided good practice for reducing observers’ reaction times which are now the major factor limiting the accuracy of minor planet occultation results.

 

• Graham noted that occultation predictions are now easily available via OCCULT software written by David Herald.  This software will predict occultations for any site, perform on-line reductions, and supply graze profiles, etc.  Graham indicated that copies of OCCULT were available at the meeting and that updates would be posted to the Occultation Section website.

 

• Graham asked how many people used the ‘Upcoming Minor Planet Occultations’ page in the News Circulars and whether there was any value in retaining it.  No-one appeared to use the page and Graham indicated that it would be dropped in future.

 

• Graham noted that at present ~100 minor planet occultation predictions by Edwin Goffin are  published annually as hard copy, with many more events listed on the Section website.  Previously, members had asked to retain the hard copy MP Circulars.  However he noted that next year there would likely to be 200 to 250 events predicted by Edwin Goffin (because of fainter stars being used: down to 12th magnitude), which had cost implications for the Section.  Further, some of the fainter events would not be visible to those without larger telescopes.  Since there was some feeling to retain the MP Circulars, Graham suggested that hard copies of only bright events be published.  This will be discussed with other Section leaders.

 

• Graham asked whether the finder charts for MP events published on the website were being used.  Few people appeared to do so.  Some people mentioned that they produced their own charts in preference.

 

Timing Matters:

 

Shortwave Signals

 

• John Drummond mentioned that WWV was sometimes difficult to pick up, and he would like a more reliable timebase.  Graham noted that this was a problem also faced by a majority of Australian observers.  Further, it was difficult to source good quality shortwave receivers in NZ at a reasonable price.

 

Stephen Russell (from Australia) noted that the VNG User’s Consortium was planning to make available a device which would use GPS data to emulate VNG signals.  However the project had been under development for two years now and there was as yet no timeframe as to completion or commercial manufacture.

 

Gordon Hudson asked whether the Radio Shack WWV TimeKube receivers were still available.  Graham indicated that they were not.  Gordon undertook to investigate whether he, together with his son Rick, might be able to manufacture some for sale through the Section.

 

Graham then indicated that the GPS-based KIWI system developed in Christchurch would be an answer to the timebase problems and handed the meeting over to Brian and Pauline Loader.

 

KIWI System

 

• Brian explained that Geoff Hitchcox of Christchurch has produced software (“KIWI”) to generate a time signal to millisecond accuracy from GPS signals.  GPS signals can be obtained from surplus U.S. GPS chips, but KIWI requires a computer running pure DOS.  KIWI generates time pips similar to those produced by the now defunct VNG.  A KIWI device was demonstrated to the meeting.  Its features are:

 

• GPS position to about 0.1” accuracy.  Height accuracy to about 10 m.

 

• Time pips are produced and sound similar to VNG signals, but without voice announcements.  There is a higher tone pip every 10 seconds, the 56th, 57th and 58th second pips are shorter, the 59th pip is missing and the minute pip/tone is longer.  Time is read out on the computer screen.  John Drummond asked if this readout could be enlarged so that it would be more easily seen in the dark, but the answer was 'No'.  Brian also noted that an LED, which could be put down the end of a telescope tube, could be connected to the system. The LED would flash once a second and be recorded on a video camera connected to the telescope, thus providing a timebase for video observing.

 

• A facility to remind the observer that the occultation time is approaching.

 

• A 'stopwatch' facility.  Every time a button (on the end of a cable) is pressed, the time is recorded and saved to a text file along with positional data.  It was noted however that to save this file the program must be run from a hard disc, not from a bootable floppy.

 

• Reaction time programs for both disappearance and reappearance.

 

Some concern was expressed about having to rely on a computer running only DOS. (KIWI cannot be run from a DOS window in the Windows OS because Windows does not give enough CPU cycles for the application to meet spec). However it was noted that any PC would be suitable so long as it could be booted from a DOS floppy which also contained the KIWI software (subject to the restriction noted above that the text file of time and position data cannot be saved to the floppy).

 

Grant Christie declared that there was a way around Windows.  Bill Parkin said that FreeDOS, a substitute for Microsoft DOS, was being developed and was soon to be available.  He will keep Graham appraised of this.

 

Information about the KIWI system is available from Geoff Hitchcox’s website at:

http://www.geocities.com/kiwi_36_nz/kiwi/kiwi.htm

 

Pauline Loader’s “Beeper Box”

 

• Pauline Loader then demonstrated her portable “Beeper Box” which can be synchronised automatically with UT from KIWI, or synchronised manually from another time source.  The box produces VNG style time-pips, is small and portable, and costs about $20 in parts.  It is designed to be synchronised with a timebase and then be taken into the field for a grazing or minor planet occultation.  It is essentially a replacement for a shortwave radio and can be used in conjunction with a tape recorder to visually time events.  (The beeps can be muted during transport to and from a remote site).

 

Pauline noted that every 10th second pip is longer, the 56th, 57th and 58th second pips are shorter, and the 59th second is muted.  The minute is a long beep where the beginning of the beep marks the minute. As with the KIWI system, an LED can be attached. 

 

The box automatically synchronises itself once it is plugged into the KIWI System.  Accuracy is better than 0.01 seconds. As long as it hasn't been turned off, it can be rechecked afterwards against KIWI to determine any drift.  The box can also be synchronised (manually) with a radio time pip. The 4 x AA batteries powering the unit last about 20 hours.  When organizing a grazing occultation expedition a number of boxes could be synchronised from one KIWI or radio and then distributed to party members.

 

The box’s 10 MHz chip is temperature sensitive but can be calibrated for a particular temperature.  Pauline Loader is happy to supply the circuit and to program the main chip.  More information is available at: http://www.occsec.wellington.net.nz/videotime/beeper.htm

 

[Subsequent to the meeting Bill Parkin of Wellington indicated that he would be happy to investigate building a trial run of ~20 beeper boxes].

 

 

Video Observing:

 

• Brian Loader then described the use of his video camera for timing occultations.  He uses a 0.0003 lux Supercircuits PC-164C camera (www.supercircuits.com) which fits into the eyepiece holder of his scope.  It has a ¼” CCD chip, runs on 12 V, and he can reach to about magnitude 11.5 on his 10" Meade.  The field of view is 5 arcmin.  Brian felt that a C8 would probably have only a half magnitude brighter limit.  A cable from the camera is connected to a small black and white monitor and a VCR, and Brian plugs a small microphone and amplifier into the audio input of the VCR so he can record voice comments.  He uses a KIWI-based flashing LED inside the telescope tube to provide the timebase. He noted that each flash lasts for about 2 frames.  However as the camera is NTSC (not PAL), the VCR must be able to record in NTSC. 

 

Brian’s system (with photos) is described at:

http://www.occsec.wellington.net.nz/videotime/loadervideo.htm

 

• Graham mentioned that the Watec 902H camera (www.watec.net) is also very suitable.  The advantages of the Watec camera are that it has higher resolution than the PC-164, it is a PAL camera so an NTSC VCR and TV are not required, and the chip is larger at 1/3” (so there is a larger field of view).  The cost of the camera is about $NZ420 and it is available through Hill’s Industries in Lower Hutt.

 

Graham asked those who might be interested in a bulk order of Watec 902H cameras to put their names on a list.  Eleven people did so.

 

• In reply to a suggestion about using a Philips ToUcam webcam, it was stated that the sensitivity of this camera was much lower which would limit observation to only bright stars.

 

• Graham suggested that if people were concerned about spending several hundred dollars on a system suitable only for MP occultation work, it is possible that the system could be made much more versatile by installing a frame-grabber card in a computer and then using the camera and computer to grab and stack frames as is done with traditional CCDs. (No-one has yet tried out this option to our knowledge).

 

• It was noted that for observing other than MP events (e.g. lunar grazing occultations, where there can be a considerable difference in brightness across the CCD) it might be desirable to override the automatic gain control in both the PC-164 and Watec 902H cameras.  Such modifications can be made for the PC-164 by Sandy Baumgartner in the US.  [Subsequent to the meeting it was determined that the Watec camera does indeed appear to have a manual gain control within its housing and that in the simplest case, a hole could be drilled in the case to allow access to this].

 

• Graham mentioned that Geoff Hitchcox has recently developed an On-Screen Display (OSD) unit which overlays each frame of the video with millisecond accurate time plus positional information.  Although there are already commercial units which do this, the advantage of Geoff’s system is that the circuit is very simple, it is extremely cheap to make, and the system includes considerable error-checking and redundancy which commercial systems do not possess.  A prerequisite is that the observer has a small GPS unit and Graham mentioned that Deluo Electronics  (http://www.deluoelectronics.com/customer/home.php)  make such a unit for $US80.  Brian said that he was hoping to see Geoff’s OSD next week.  Geoff’s OSD is described at: http://www.geocities.com/kiwi_36_nz/kiwi_osd/kiwi_osd.htm

 

 

The meeting closed at 7:10 pm.