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PLANETARY OCCULTATIONS: 2001 RESULTS


This page is intended to provide a brief summary of observational attempts for certain important events only. Full details of all events are published in the Section's Circulars.

(48) Doris - 2001 November 28
(159) Aemilia - 2001 November 25
(14) Irene - 2001 November 21
(94) Aurora - 2001 October 12
(410) Chloris - 2001 October 6
(909) Ulla - 2001 October 5
(423) Diotima - 2001 August 22
(1240) Centenaria - 2001 July 7
(250) Bettina - 2001 May 16
(804) Hispania - 2001 May 2
(2920) Automedon - 2001 April 25

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Occultation of HIP 29126 by (48) Doris - 2001 November 28:

SUMMARY:

This event was predicted by Edwin Goffin to run from just south of Brisbane to just south of Perth. To see the Goffin prediction, click
here. Steve Preston's update moved the path slightly north to clip both metropolitan areas. To see the update posted to this website, click here.

At this stage, five observations of this event are known - two of them are positive and two are tightly constraining negative reports.

Ian Bacon (Bac), south of Bunbury, Western Australia, Australia:

Ian Bacon reports: "The original prediction for this minor planet put its occultation path close to Perth, encouraging me to observe it. The 22/11/01 update on the RASNZ site confirmed the likelihood of a positive event. I decided to travel south from Perth to observe the event. Unfortunately, the sky was not good. There were very high ground winds that shook my telescope making accurate measurements difficult as well as intermittent, light cloud moving across the field of view. The near full Moon also did not help. I also experienced some technical difficulties with my telescope.

My observation is definite in that the star did dim. I cannot be certain, however, of the precise times. They may be inaccurate by several seconds in either direction. The approximate length of the event remains 15 seconds."

Disappearance At : 18:05:23 UT (PE of 0.3 sec applied)
Reappearance At : 18:05:38 UT (PE of 0.3 sec applied)
Duration = 15 seconds
Monitored Period : 18:00 - 18:10 UT.

Stephen Hutcheon (Hut), Sheldon, Queensland, Australia:

A short informal report has been received from Peter Anderson of a positive observation by Steve Hutcheon.

Disappearance At : 17:59:20.5 UT
Reappearance At : 17:59:26.5 UT
Duration = 6 seconds

Peter Anderson (And), The Gap, Queensland, Australia:
Peter Anderson reports: "Observations were difficult because the images of the double were boiling and nearly merging at times in the poor seeing. However I am confident that no event took place. Dawn prevented observations of the separation. I was unable to assess the distance and direction of closest passage."

Monitored period - 17:52 - 18:04 UT - No occultatation observed.

Ralph Paramor (Par), Perth, Western Australia, Australia:

No occultation observed. No details available at the time of writing. Depending on Ralph's location within Perth, his observation will produce a chord close to those of Steve Hutcheon and Peter Anderson.

Alex Liu (Liu), Exmouth, Western Australia, Australia:

Monitored Period - 17:50 - 18:15 UT.
No occultations observed.

DISCUSSION:

The discussion below centres on the observations by Bacon, Hutcheon and Anderson as Paramor's position is not yet known precisely and Liu's location is well to the north of the observed occultation path.

On first presentation, these three observations do not seem to produce a consitant outline for (48) Doris. Click here to see a graphic comparing the three chords with a circular outline of diamter 219km as given on Goffin's prediction. (Occult gives a diamter of 221 km while Guide 7 agrees with the Asteroids II diamter of 225 km.) The ambiguity of this data set starts to make sense when the previous occultations involving (48) Doris are considered.

Three previous occultations involving (48) Doris have been observed:

The North American observation gives a diameter of 219 km +/- 25 km and is most probably the source of the data used by Goffin. The author is unaware of the length of the occultation observed by Charlie Smith. However, it is the South African observation that sheds the most light on the outline of (48) Doris. The four well spaced chords clearly indicate a very elongated object of dimensions 278 km (+/- 20 km) by 142 km (+/- 25 km). This result was noted in David Dunham's article in the February 2001 issue of Sky and Telescope - Vol 101. No. 2 p116-120. The outline derived in reproduced here. As Dunham notes in the text of the article, the fit to the ellipse is relatively loose and that the most significant result is that (48) Doris is an extremely irregular shaped object.

And so, despite Ian Bacon's reservations about the quality of his observation, the results presented here are in quite good agreement with what is known about (48) Doris. Presented here are the observed chords with an ellipse of the dimensions derived from the South African data - the curve fit is almost respectable. Of course it is very unlikely that the same profile of (48) Doris was observed in this instance as that seen from South Africa 25 months earlier but this observation does go some way of confirming the earlier conclusion.

All of the observers are to be congratulated for their efforts. In particular, Ian Bacon's move south from Perth to allow the spacing between his chord and the other three Brisbane and Perth chords. Without this spacing, the important confirmation of the South African observation would not have been possible. Presented here is a plot of Steve Preston's updated path showing the locations of the four observers in its vicinity (Ralph Paramor's position is marked as per Perth). Comparing the observations with the update show that error in the path location and timing is a small fraction of a path width and much smaller than the error in path width given the irregular outline !!

There may be further updates to this page as the two outstanding formal reports are received.

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Occultation of TYC 0676-00413-1 by (159) Aemilia - 2001 November 25:

SUMMARY:

This event was predicted by Edwin Goffin to cross the far southern end of the South Island of New Zealand and to pass just south of Tasmania. To see the Goffin prediction, click
here.

Brian Loader of Darfield on the South Island reports a positive occultation as detailed below.

Brian Loader (Loa), Darfield, South Island, New Zealand:

Brian Loader reports: "In the event an 11 second occultation occurred here, just about the maximum length expected. Assuming I was more or less central, the northern edge of the path should have been from somewhere like Kaikoura to Greymouth, with the Southern edge at Timaru and including Mount John."

Disappearance At : 15:18:14.8 UT +/- 0.3 sec (PE of 1 sec applied)
Reappearance At : 15:18:25.9 UT +/- 0.3 sec (PE of 1 sec applied)
Duration = 11.1 seconds
Monitored Period : 15:11:30 - 15:26 UT.

DISCUSSION:

Congratulations to Brian on this positive observation. As he notes above, it would appear that he has observed a fairly central chord implying a path sift to the north of around one path width and around 50 seconds later. This is illustrated in a close up view of the Goffin prediction marking Brian's location. This drawing may be seen by clicking here. The path would then have crossed much of the central parts of the South Island as well as the southern half of Tasmania but at the time or writing no further reports have been received.

As of May 2001, no previous occultations involving (159) Aemilia have been reported. This observation can only indicate that (159) Aemilia has at least one dimension as large as (or larger than) the diameter of 131 km associated with the 11.1 seconds expected for this event.

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Occultation of HIP 93339 by (14) Irene - 2001 November 21:

SUMMARY:

This event was identified in Occult and updated by Steve Preston. The update was posted on this website and can be viewed by clicking
here. David Gault of Hawkesbury Heights northwest of Sydney has observed an occultation while Albert Brakel in Downer (Canberra) reports a negative observation. These two observations combine to show that Steve Preston's update was correct in location to a small fraction of a path width and only around five seconds late.

David Gault (Gad), Hawkesbury Heights, New South Wales, Australia:

David Gault reports: "This is my second mp occ'n and my timinge should not be relied on. I intend to purchase a tape recorder and download software and somehow get it to work on my Mac. I realy enjoy these occultations and fully intend to improve accuracy."

Disappearance At : 10:25:10 UT (No PE applied or given)
Reappearance At : 10:25:13 UT (No PE applied or given)
Duration = 3 seconds
Monitored Period : 10:10 - 10:35 UT.

Albert Brakel (Brk), Downer (Canberra), Australian Capitol Territory, Australia:

Albert Brakel reports: "Star only visible from one spot in my backyard, and it disappeared behind a tree only a minute after the observation ended." Albert monitored over the period 10:19:04 UT to 10:31 UT without seeing an occultation.

DISCUSSION:

A plot of these two observations can be seen by clicking here. With only the one positive chord, little can be said about the physical size or shape of (14) Irene so for this diagram the outline is assumed to be circular and of 182 km in diameter as given in Occult. Albert's negative observation clearly constrains David's chord to the southern limb of (14) Irene - entirely consistant with the update calculated by Steve Preston. To see a close-up view of the updated path with the locations of the observers marked, click here.

This is the fourth occultation involving (14) Irene. The three previous events are:

This observation does not conflilct with any of these.

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Occultation of TYC 6910-01938-1 by (94) Aurora - 2001 October 12:

SUMMARY:

Steve Preston updated this event to produce a path crossing Melbourne, Canberra, western Sydney and Brisbane. While the weather was uncooperative in Victoria, nine seperate chords have been timed across the ACT, New South Wales and Queensland to produce the most spectacular observation set yet produced by the RASNZ Occultation Section.

To view a plot of the updated path along with the locations of the successful observers, click here.

THE OBSERVATIONS:

Briefly outlined below are the basic observations made. Further details will be given in the CN circular.

Peter Anderson (And) , The Gap (Brisbane), Queensland, Australia:
Disappearance At : 13:56:14.2 UT (PE of 1.03 s applied)
Reappearance At : 13:56:27.7 UT (PE of 0.3 s applied)
Duration = 13.5 seconds

Tamas Zalezsak (Zal) , Kenmore Hills (Brisbane), Queensland, Australia:
Disappearance At : 13:56:14.1 UT (PE of 1 s applied)
Reappearance At : 13:56:27.5 UT (PE of 0.3 s applied)
Duration = 13.4 seconds

Charlie Smith (Smc) , Woodridge (Brisbane), Queensland, Australia:
Disappearance At : 13:56:12.0 UT (PE of 0.6 s applied)
Reappearance At : 13:56:26.8 UT (PE of 0.5 s applied)
Duration = 14.8 seconds

Steve Hutcheon (Hut) , Sheldon (Brisbane), Queensland, Australia:
Disappearance At : 13:56:14.3 UT (PE of 0.9 s applied)
Reappearance At : 13:56:28.3 UT (PE of 0.45 s applied)
Duration = 14.0 seconds

Colin Bembrick (Bem) , Bathurst, New South Wales, Australia:
Disappearance At : 13:55:21.5 UT (PE of 0.5 s NOT applied)
Reappearance At : 13:55:36.4 UT (PE of 0.5 s NOT applied)
Duration = 14.9 seconds

Case Bosloper/Ray Pickard (Boc/Pir) , Bathurst, New South Wales, Australia:
Disappearance At : 13:55:22.01 UT (PE of 0.8 s applied)
Reappearance At : 13:55:39.01 UT (PE of 0.8 s applied)
Duration = 17.0 seconds

David Wheeler (Whd), Wollongong, New South Wales, Australia:
Disappearance At : 13:55:19.08 UT (PE of 0.7 s NOT applied)
Reappearance At : 13:55:20.18 UT (PE of 0.3 s NOT applied)
Duration = 1.5 seconds

Michael Nelmes (Nem) , Spence (Canberra), Australian Capitol Territory, Australia:
Disappearance At : 13:55:03.8 UT (PE of 0.8 s NOT applied)
Reappearance At : 13:55:19.3 UT (PE of 0.4 s NOT applied)
Duration = 15.9 seconds

Mike Dower (Dom) , Spence (Canberra), Australian Capitol Territory, Australia:
Disappearance At : ?
Reappearance At : 13:55:19.6 UT (PE ?)
Duration = 2 seconds ?

DISCUSSION:

Congratulations to all observers on their efforts !!!

While the altitude of this event was quite low at the time of the event from most observing sites (20 to 25 degrees), most observers were confident of correctly sighting the event. The exception is the final time made by Mike Dower. He reports that he was not aware of the dissappearence but timed a reappearence at a time virtually the same as that given by Michael Nelmes from his very nearby location. Dower reports that the could see the star/asteroid at all time but was not so confident of the observation on hearing of Nelmes'.

The inconsistancy of this single chord is apparent when viewing the projected outline of (94) Aurora as derived from these observations. To see the outline, click here. This ellipse has been hand fitted with a bias to the more reliable reappearence times - disappearances end of the chords is the upper right end.

From the chord derived ellipse, it is apparent that (94) Aurora is not circular. Rather an outline of 225km X 173 km is derived. This does not greatly conflict with the diameter of 204 km as given by Occult.

A negative observation was also reported by Stephen Kerr in Rockhampton about 1 path width to the west.

No previous occultations involving (94) Aurora have been reported.

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Occultation of TYC 6870-00551-1 by (410) Chloris - 2001 October 6:

SUMMARY:

An email notice was distributed to New Zealand observers for this event to occur at low altitude in the west. Due to time constraints and a lapse on the part of the webmaster, an update was not prepared until the day after the event and this was not posted to the website. In the end though, the vast majority of New Zealand was under cloud at the time preventing widespread observation. However, at Gore in the far south of the South Island, Ross Dickie scored clear conditions and has recorded an occultation

To see the Win Occult generated update using the UCAC star position and 27 USNO positions for the asteroid plotted with Ross' location, click here.

Ross Dickie, Gore, South Island, New Zealand:
Ross Dickie reports: "Three and a half minutes after I began my monitoring, I suddenly noticed that the target star was missing. I did not see its actual disappearance, but I pressed the lap-timer on my stopwatch. Both the magnitude 9.0 SAO star and the 10.8 GSC star, plus each of its sprinkling of five 11th and 12th magnitude stars ALL REMAINS VISIBLE and were unaffected during that missing period. The target star reappeared instantaneously to my eye, 3.2 seconds later. Subtracting my P.E.s of 1.0 and 0.5 to my D and R, respectively, my timings are at 12:34:46.2 and 12:34:49.9 UT, which makes it an occultation duration of 3.7 seconds by Chloris. "

Disappearance At : 12:34:46.2 UT (P.E. of 1.0 seconds applied)
Reappearance At : 12:34:49.9 UT(P.E. of 0.5 seconds applied)
Duration = 3.7 seconds

DISCUSSION:

Congratulations to Ross on his fourth positive for this year. Comparing this observation with the update gives good agreement in the expected time although the error margins for the path location calculation are small enough that Ross can consider himself very lucky. The observed duration of 3.7 seconds is less than the expected maximum of 5.2 seconds. Presumably this represents the northern limb of (410) Chloris.

No previous occultations involving (410) Chloris had been reported as of June 2001.

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Occultation of TYC 5061-00070-1 by (909) Ulla - 2001 October 5:

SUMMARY:

Alex Liu of Exmouth in Western Australia has observed an occultation of TYC 5061-00070-1 by (909) Ulla from his home observatory. His observation indicates a shift in the path of around 0.25" to the south and around 70 seconds later as compared with the prediction prepared by Occult.

To see the Occult prediction, click here.

Alex Liu, Exmouth, Western Australia, Australia:
Alex Liu reports: "A brief occultation was observed - but, because of the stop watch button failed, some 4 to 5 seconds elapsed before I could activate the second stop watch. I estimated the uncertainty of the disappearance was around plus/minus 2 seconds centered at 12:14:17 UT. The duration of the occultation was less than 1 second - my estimate was about 0.7 second. The occultation was real and I am certain that it was not due to cloud obscuration or atmospheric, etc. "

Disappearance At : 12:14:17 UT
Reappearance At : 12:14:17.7 UT
Duration = 0.7 seconds

DISCUSSION:

Congratulations to Alex on his second positive for this year and his fourth so far. Not withstanding the uncertainties associated the timing, it is quite clear that this occultation represents an edge chord - ie. the duration of 0.7 seconds is significantly less than the maximum expected of 3.7 seconds. No previous occultations of Ulla have been reported. No other reports of this appulse have been received.

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Occultation of TYC 4973-00537-1 by (423) Diotima - 2001 August 22:

SUMMARY:

Ross Dickie of Gore on the South Island of New Zealand has observed an occultation of TYC 4973-00537-1 by (423) Diotima from a location near Gore. His observation compares well with the astrometric update prepared by Steve Preston and presented on this website.

View the astrometric update here.

Ross Dickie (Dik), Gore, South Island, New Zealand:

Ross Dickie reports that he made the observation as a guest at a friends house. "I find that both magnitude 12.1 stars were reasonably easy to see through my 15mm RKE eyepiece, without any difficulty. Then precisely at 7:09:11.6 UT the target star suddenly and instantaneously disappeared, and I said "OFF" to my tape-recorder. It reappeared instantaneously at 7:09:17.2 UT, and I said "ON". (My P.E.s of 0.7 and 0.4 of a second has been subtracted to both D and R.) Between those timings, the right-hand magnitude 12.1 star clearly remains in view in my 15mm eyepiece and was unaffected during the occultation. I ended my monitoring much sooner than I normally would (at approximately three minutes after my occultation), as the three family members were waiting patiently just two metres behind me."

Disappearance At : 7:09:11.6 UT (PE of 0.7 s applied)
Reappearance At : 7:09:17.2 UT (PE of 0.4 s applied)
Duration = 5.6 seconds

Alan Gilmore (Gil), Mt. John Observatory, Lake Tekapo, South Island, New Zealand:

Alan monitored the event photometrically using 200 ms integrations on the 60cm telescope. Observations were made over two intervals - 7:06:14 to 7:08:30 and then again from 7:08:45 to 9:13:30 (All times UT). No fading events were noted.

Alan Thomas (Tho), Alexandra, New Zealand:

Alan intended to monitor this event but the twilight hampered his ability to find the field with a new 21" telescope.

DISCUSSION:

Congratulations to Ross on this his third positive observation for 2001 and his ninth positive overall. Particularly unusual is the fact that this is the second positive observation Ross has made involving (423) Diotima - the previous observation was on the 13 June 1991 under unusual circumstances.

The observed duration of 5.6 seconds is close to the maximum expected of 6.3 seconds associated with a diameter of 208 km for (423) Diotima. Assuming that this makes Ross' location near the centre line of the true occultation path, it would indicate that the updated path calculated by Steve Preston was only in error by around 0.5 of a path width to the north and virtually correct in time.

Diotima Path Map As can be seen in the plot to the left, Alan Thomas' site at Alexandra lay almost exactly half a path width to the north of Ross' location and a short occultation or a tightly constraining negative observation would have been possible. But things like that happen .....

As of 21 May 2001, this observation is the fourth involving (423) Diotima. In addition to Ross' earlier observation on the 13 June 1991, three visually timed chords were recorded across Switzerland and Italy on 17 January 2000 inferring an oval outline around 240km by 166km. And then on 15 March 2001, a total of 19 chords were recorded across southern France, Greece and India. As yet few details of this observation are available.





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Occultation of HIP 62211 by (1240) Centenaria - 2001 July 7:

SUMMARY:

Ross Dickie of Gore on the South Island of New Zealand has observed an occultation of HIP 62211 by (1240) Centenaria from a remote location near Gore. His observation confirms the astrometric update prepared by Steve Preston and presented on this website.

View the astrometric update here.

Ross Dickie, Gore, South Island, New Zealand:

Ross Dickie reports; "So at 7:38pm, with the sky over Gore unexpectedly clouded over by low cloud, I immediately drove my car with my C8 and gear, away out of Gore to the northwest. Only a couple of kilometres out of Gore,I drove out of the cloud and back into the clear moonlit sky. I drove onto a public side road,7km out of Gore and parked my car by a cattle yard (Croydon's Siding). The cloud over Gore was at 10 above my southeastern horizon after my arrival, has since became closer and gaining altitude to beyond my zenith. Then I was also struggling to put on my (tight) cardboard dewcap over the front lens of my C8, which used up four minutes of my valuable time. Finally, I located Eta Corvi with my C8's 8x50mm finderscope, and I then moved my C8 eastward by 6 degrees to some sixth and seventh magnitude stars in my finderscope, which were almost about to be obscured by the ever-increasingly "past-zenith" low cloud. With no other obvious stars westward beyond this solitary star, and I knew time was getting quite short, I started monitoring this solitary star through my 26mm eyepiece,regardless of my slight doubts if this was really the correct target star I am monitoring. Just thirty seconds after I pressed my 10-lap memorised stopwatch to began my monitoring, I suddenly saw a blank eyepiece field with no solitary star, in my eyepiece. I did not even see its actual disappearance,so it appears that I must have blinked my eye during that actual time of disappearance. I then pressed the lap-timer on my stopwatch. Then exactly three seconds later, I suddenly saw the star instantaneously reappeared,and again,I pressed the lap-timer on my stopwatch."

Disappearance At : 8:13:02 UT (PE of 1.0 s not applied)
Reappearance At : 8:13:05.1 UT (PE of 0.4 s not applied)
Duration = 3.7 seconds

DISCUSSION:

Congratulations to Ross on this "just-in-time" observation. His observed time comes just 15 seconds prior to the time predicted by Steve Preston's update. The observed duration of 3.7 seconds is only slightly shorter than Occults expected maximum duration of 4.2 seconds indicating that Ross' chord was a fairly central one (assuming that (1240) Centenaria is a roughly spherical object of the expected 58 km diameter). Croydon's Siding lies near the centre line of the updated path suggesting that the error in this update is only a small fraction of a path width !!

No previous occultations involving (1240) Centenaria have been reported as of May 2001.

Other observers were not so lucky in their attempts. Bob Evans in Invercargill was clouded out while Alan Thomas at Alexandra scored fog. Further afield, this event was monitored by Brian Loader at Darfield with a negative result.

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Occultation of TYC 7899-06866-1 by (250) Bettina - 2001 May 16:

SUMMARY:

Alex Liu at Exmouth in Western Australia has observed an occultation of TYC 7899-06866-1 by (250) Bettina using his image intensification/video setup. His observation suggests a shift to the northwest of at least 100 km relative to the updated path.

View the astrometric update here.

Alex Liu, Exmouth, Western Australia, Australia:

Alex reports: " I am happy to say that early this morning I timed a 4.2 second event for 250 Bettina - TYC 7899-06899-1. I hadn't really expected to see an event as your latest update indicated a path some 140 km to the south of me. The sky was clear and still and the image intensifier/video display on the 12" monitor worked well. As this was a first event occurrence with my present setup, I didn't know what a drop in magnitude would look like on the screen. What actually happened was the target star, which was twice the diameter of Bettina, very suddenly fluttered momentarily and immediately shrank to about a third of its diameter. The recovery was just as sudden, but without any flutter."

Disappearance At : 20:25:44.4 UT
Reappearance At : 20:25:48.6 UT
Duration = 4.2 seconds

At the time of writing, no other observation reports have been received.

DISCUSSION:

The observed duration of 4.2 seconds is well within the expected maximum of 8.0 seconds implying a non-central chord. The fluttering mentioned by Alex during the inital disappearence would be consistant with the star entering the limb of the asteroid at a shallow angle. Alex has also supplied some astrometry of the asteroid together with the target star. This will be analysed shortly and included in the next circular.

This observation is the fourth know occultation involving (250) Bettina. Earlier observations were made by Danie Overbeek and Tim Cooper in South Africa on 9 July 1988, a number of French observers including A. Maury on 6 January 1999 and by RASNZ Occultation Section members Charlie Smith and Tamas Zalezsak in Brisbane, Queensland, Australia on 30 May 2000. Details of this final observation can be seen by clicking here.

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Occultation of CMC 505874 by (804) Hispania - 2001 May 2:

SUMMARY:

An occultation of the star CMC 505874 by (804) Hispania has been observed by Stephen Kerr in Rockhampton, Queensland. Rockhampton lies within the predicted path for this event as given by Occult although the observation was just over a minute later than expected.

View the original prediction here.

Stephen Kerr, Rockhampton, Queensland, Australia:

This was an extremely difficult observation to make as the target star was magnitude 12.4 and there was a 70% moon only 8 from the field. The target star was visible by averted vision with some effort using an 8mm Plossl eyepiece (ie. uncomfortably short eye relief) with some problems due to fogging. These issues combine to give the unusually large PE values shown here. However, as the event duration was much longer, the certainty of the event is quite good.


Disappearance At : 9:47:54.2 UT (P.E. 2 sec NOT applied)
Reappearance At : 9:48:27.9 UT (P.E. 2 sec NOT applied)
Duration = 34 seconds

DISCUSSION:

The long duration of this event is within the predicted maximum of 48 seconds. Given the above observation, it is probable that the occultation path crossed some parts of the Melbourne metropolitan area but at the time of writing, no further observations had been received.

As far as the author is aware, this is only the second occultation involving (804) Hispania observed to date. The previous observations were made by RASNZ Occultation Section members Jeff Byron in Sydney, Australia and Keith Vincent at Havelock North in New Zealand on the 5th of May, 1992.

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Occultation of PPM 152444 by (2940) Automedon - 2001April 25:

SUMMARY:

Ross Dickie of Gore on the South Island of New Zealand has observed an occultation of PPM 152444 by (2940) Automedon.

View a Win Occult generated prediction using the Tycho-1 star position here.

Ross Dickie, Gore, South Island, New Zealand:

Ross Dickie reports; "This Automedon occultation event occurred in POOR transparency, with fair stability. Unluckily,the target star's disappearance occurred when I looked away from the target star onto the Hipparcos star (HIP 35533) for "a break". Upon returning my eye to the target star's I noticed it was missing. So I later pressed my 10-lap stopwatch, which was later determined against VNG's 12.984MHz, as 8:00:12.65 UT. Very shortly afterward, the target star reappeared to my eye. Unfortunately I didn't press my stopwatch again, as the reappearance was too quick after I pressed my stopwatch, and that I was "startled" by the missing target star. The actual disappearance of the target star by Automedon would have occurred sometime between the 8.4 and 10.7 second UT. The target star was finally obscured by dense high cloud, 3.5 minutes after the occultation."

Disappearance At : 8:00:10.7 UT
Reappearance At : 8:00:13.6 UT (P.E. applied)
Duration = 2.6 seconds

DISCUSSION:

In the considerable amount of correspondence following the reporting of this event, it is clear that Ross was quite unsure of the reality of this event. He was particularly concerned that the observation may have been the action of the `blind spot' in the eye due to the optic nerve. To that end, Ross revisited the field to re-enact the observation and also to refine the PE values. At the conclusion of this exercise, Ross was not able to reproduce the observed effect using the `blind spot' and since he was reasonably confident that the disappearance was not due to cloud (the other stars were still visible), he is of the opinion that an occultation did occur. The times have been slightly adjusted between his comments quoted above and the final values given at the top of this report.

From the re-enactment studies, Ross indicates that he probably looked away from the target star to HIP 35533 around 8:00:08.4. As such, the start time of the occultation would have occurred between then and the 8:00:10.7 reported as being when the star was noticed missing. As such, there is considerable uncertainty in the duration of the event ranging between 2.6 and 5.2 seconds. Given the uncertainties of this event, it would be unrealistic to expect to be able to draw any more precise conclusions.

The expected maximum duration for this event was 5.3 seconds associated with a diameter of 111 km. As such, this observation would appear to be a fairly central one.


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