June 24th Naked-Eye Asteroid Eclipse Seen in Australia & N.Z.
Updated: 2003 July 7
On Tuesday evening, June 24, the asteroid (124) Alkeste eclipsed (or "occulted" as astronomers call the event) the star Zavijava in the constellation Virgo (the Virgin) for up to 4 seconds in a path that crossed southern Australia and New Zealand's South Island. The path shifted about a quarter of a path-width south of its predicted location with the time about 4 seconds earlier than predicted, both close to the expected "1-sigma" errors. The sky was clear in New Zealand, contrary to the forecasts, but widespread high clouds plagued observers in Australia, especially in Victoria. Nine observers timed the occultation in Australia and another 9 observed it from New Zealand's South Island. Data for most of the observers, now including several of those from New Zealand, are available, although some timings are preliminary. Extensive information on observing the eclipse (occultation), including simple star charts to locate the star and methods for timing the event prepared for public use before the event can be found here.
Profile of Alkeste Determined from the Observations
Here is the profile of Alkeste plotted by David Herald with an older version without connecting lines here. He describes the plot:
Attached is a plot with all the observations included [Western Australia, South Australia, Victoria, and New Zealand]. There are 18 observed chords. See comments below. One initial comment: a PE of 0.2 secs is likely to be too small. I have appied PE's of at least 0.3s, and more usually 0.4 s. A longer PE was one of the results from the Pallas occultation many years ago. The biggest uncertainty now is the discordance between Farrell's observation and the NZ observations. However the site coordinates for Farrell are at best approximate. Hopefully the Sth Australian obervers can arrange for better site coordinates.
The other discrepancy is from the Mt Magnet obervation. Having regard to the observer's comments, I have increased the PE to 0.6 secs.
Note that most of the observations are visual. This means that the error associated with any one observation is quite large in the context of the asteroid's diameter. A 0.4 sec error is equivalent to 8km, or 10% of the asteroid's diameter. Against that context, most of the observations have a good correlation. Unfortunately, there are no observations from near the southern limit (including miss observations).
Two observers reported a miss when they should have seen an event. Commiserations to them (unless I have incorrect site coordinates for them.)
The changes have made the fit slightly less elliptic (74.0 x 58.2 km), with smaller rms errors. If Farrell's observation is excluded, the dimensions are a couple of km larger - 76.4 x 62.2 km.
The list of observers is: 2(C) Nth Limit - Predicted 3(M) P Skilton, Avenel, Vic, AU 4(M) J Eisner, Mansfield, Vic, AU 5(M) C Rowe/J Osbourne, Culverden, NZ 6(C) C Pratt, Kanumbra 7(C) Hills/Thurley/Price, Mangalore, Vic 8 J Hill, Aldgate, Sth Australia 9 S Buda, Heathcote, Vic, AU 10(M) J & L Grida, Unley, Sth Australia 11 G. Blow, Balmoral Forest, NZ 12 D Dunham, Tailem Bend, SA, AU 14 D Gault/B White, Sarsfield, Vic 15 J Blanksby, Warracknabeal, Vic, AU 16 D Herald, Lakes Entrance, Vic, AU 17(C) P Larkin, Heathcote, Vic 18 R Paramor, Mt Magnet, WA, AU 19 M Head, Hawarden, NZ 20 L Hussey/L Fairly, Waikari, NZ 21 P Gerbeaux, Hokitika, NZ 22 M Finn/C Laurence, Bairnsdale,Vic, AU 23 D Downing/O Petterson, Waipara, NZ 24 P & B Loader, Ram Paddock Rd, NZ 25 P Barker, Broomfield, NZ 26(C) P Nelson, Bairnsdale, Vic 27 F Farrell, Aldinga, Sth Australia 28 D Goodman, Grays Rd, NZ 29 E Mason/P Catton, Mount Grey Rd, NZ 30(C) Sth Limit - Predicted 31(C) G McLeod, Woodend, Vic 32(C) J Bailey, Daylesford 33(C) M Hickman, Horsham, Vic 34(C) T Richards, Eltham, Vic 35(C) G Dudley, Blackburn, Vic 36(C) Kruijshoop/Farr, Mount Waverley 37(C) Chandler/Skilton/Fowler, Frankston Dave H (M) are Miss events. (C) are Clouded Out events (dashed lines) or are used for S. Preston's predicted limits. Hopefully any uncertainties surrounding the observations can be resolved in the next week, before people lose their recollection of what happened. I have some comments/questions about the New Zealand observations: Anargyros/Perry were well north of the path, and are not included in the plot. _________________________________ Also, look at Alfred Kruijshoop's excellent site about the June 24th asteroid eclipse and how to observe it. Also of interest is the Web site of the Occultation Section of the Royal Astronomical Society of New Zealand. Both of these may have more reports of the occultation, and possibly later versions of the profile plot than the one above. Below is the first account of the event from Alfred Kruijshoop followed by my preliminary report. _________________________________ Sent: Tuesday, June 24, 2003 9:41 PM Subject: Alkeste VIC Reports #1 Preliminary Reports Received from Victoria until the date and time of this email. The first reports are from the field, i.e. before analysis of tapes and detailed advice on position. Many observers had to travel far from their 'planned' site in the last hours before the event. The list below is simply in order of telephone calls and emails received, not (yet) in order of time or location. 1. Peter Nelson (between Stratford and Bairnsdale, Vic): clouded out 2. David Gault (Nowa Nowa, Vic): timed 2.4 sec occultation 3. Friend of David Gault (Nowa Nowa, Vic): positive observation naked-eye 4. David Herald (Lakes Entrance): 3.2 sec occultation on video 5. Jim Blanksby (Warracknabeal, Vic): timed about 3 sec occultation - (NOTE: Jim had planned to observe from Broadford, but had to travel well over 300 km to the west in search of clear sky...) 6. Judith Bailey (Daylesford, Castlemaine, Ballarat): clouded out - (NOTE: Judith had planned to observe from Daylesford, but travelled both north and south in search of clear sky; still without success) 7. Stefan Buda (Heathcote): observed brief occultation of less than a second at 10:36:13-10:36:14, noticeably shorter than expected. (NOTE: Stefan had planned to observe from Kilmore, but travelled much further north in search of clear sky) 8. Clem Pratt (Kanumbra): clouded out (NOTE: in the period before the Clem travelled across the Alexandra - Kanumbra - Merton region in search of clear sky, but without success. 9. Alfred Kruijshoop (Mount Waverley North): clouded out 10. Tom Richards (Eltham): clouded out 11. Martin Swanson (South Gippsland): observed, but no occultation seen. 12. Maurice Valimberti (Viewbank): clouded out 14 Ian Grant (East Ringwood): observed, but no occultation seen 15. John Hills, David Thurley, Robert Price (Mangalore, Avenel): clouded out - (NOTE: they travelled around the area in search of clear sky without success. It cleared up 20 minutes later......) 16. Peter Skilton (near Euroa): observed, but no occultation seen - (NOTE: Peter travelled widely from Kilmore to Avenel an further in search of clear sky. In Euroa he must have ended up being just north of the final track) 17. Michelle Hickman (Horsham): clouded out 18. Roger Chandler (Frankston): clouded out 19. Rosalind Skilton (Frankston): clouded out 20. Gary and Trish Fowler (Frankston): clouded out 21. George and Thurley Fowler (Frankston): clouded out Many Thanks to all concerned for their hard work. Further overviews will follow. Please let me know if you see any mistakes. If I receive detailed reports I shall forward these to the regional coordinators. Best regards, Alfred ======================================================= Alfred Kruijshoop 31 Josephine Avenue, Mount Waverley, Victoria 3149 Australia ======================================================= _________________________________ From: David Dunham [dunham@erols.com] (Station 12 on D. Herald's plot) Sent: Friday, June 27, 2003 12:48 AM To: IOTAoccultations@egroups.com; planoccult@aula.com Subject: 16809 km to the edge of 124 Alkeste 16809 km (151.0 deg.) is the great-circle distance from my home in Greenbelt, Maryland to my observing site just south of Tailem Bend, South Australia, for my observation of the occultation of beta Virginis by (124) Alkeste on June 24. I'm now back in the USA, in California, and will be home in Maryland tomorrow night. After travelling all that distance (and even more; I drove a total of nearly 850 km on June 24th to find a reasonably good break in the cloud-cover, over 600 km of that wasted just driving from Adelaide north to Port Augusta (where the weather turned out to be worse) and back, and finally over 80 km southeast to Tailem Bend), I ended up just 2 or 3 km from the northern limit, fortunately on the south side, where I had an approximately 1.8-second occultation (Joe Grida was about 4 km north relative to the path and unfortunately was on the wrong side, having a miss). I video recorded it with a telephoto lens, and also looked up to see the event naked-eye (my calls of that were quite poor, with thin cirrus present, really need binoculars for a star that bright, mag. 3.6, at least with a little cloud). The video record shows obvious diffraction effects lasting about 0.3 second at the D and at least 0.5 second at the R - with some analysis, it will be possible to use that to trace the profile of the asteroid for a distance of several kilometers near the contact points near the north edge. Once we get a procedure for that in place, other asteroidal grazing occultation recordings, like the one near the north limit of last September's 345 Tercidina occultation, can be analyzed the same way. I thank David Herald and Joe Grida for their help with my travels, and for others, especially Alfred Kruijshoop, Graham Blow, and Brian Loader, who did so much work organizing for this rare event. I had wanted to set up a couple of remote telephoto video stations as well, but with all the driving, I arrived at Tailem Bend only a little more than an hour before the event, and losing about a magnitude to the thin cirrus, I wasn't able to figure out the star fields with the smaller lenses in time to do that. A better pointing system is needed to use them more effectively, and I have ideas on how to do that which I will use for my next telephoto opportunity, Varsavia in California on July 17/18. But I was content with the long trip for Alkeste, seeing my first naked-eye asteroidal occultation and my first recording of prolonged diffraction effects with an asteroidal grazing occultation. The path shifted about 22 km southwest from Steve Preston's prediction (just over 1 sigma), judging from the n. limit observation, and the time was about 4 seconds early. At least 20 other observers in Australia and New Zealand timed the occultation; the results will be posted later on my Web site that, with the Alkeste item at the top, has links to Alfred Kruijshoop's and the RASNZ Occultation Section's Web sites where results are likely to be posted sooner. This is not the first asteroidal occultation to be seen without optical aid. I believe the first was the occultation of 3.6-mag. gamma Ceti A by (6) Hebe on 1977 March 5, by several astronomers at UNAM in Mexico City, and at least one observer (I think Dr. Mitsuru Soma) observed the occultation of Alhena (gamma Geminorum) by (381) Myrrha by naked eye on 1991 Jan. 13. There was a rather bright gibbous Moon on 1983 May 29 for the occultation of 1 Vulpeculae (about a mag. fainter than beta Vir) by (2) Pallas, and most observers had some cirrus for that event, so it was not observed by naked eye, as far as I know. My very preliminary report (visual timing of the video) is below. David _________________________________ IOTA ASTEROIDAL OCCULTATION REPORT FORM Asteroid (or other object):_(124)_Alkeste_____ Star:_beta_Virginis=Zavijava Date (U.T.):__2003_June_24____________ Predicted Time (U.T.):_10:36________ Observer Name:__David_W._Dunham____________ Telephone:_+1-301-474-4722_____ Postal Address:___7006_Megan_Ln._/_Greenbelt,_MD_20770-3012_USA_____________ E-mail Address:__dunham@erols.com_______________ Fax:__+1-240-228-0355_____ TELESCOPE: Aperture:_50_mm_ Focal length:__1.4_ Type:_telephoto_lens_____ Eyepiece Power:__N/A___ Observing site name: _Tailem_Bend,_S._Australia Longitude:_139d_27'_27.8"_E.______ Latitude:_35d_16'_41.5"_S.__________ Height above sealevel:_59_ft. How determined?:_GPS_-_WGS84_datum_______ Sky Transparency (Circle one, or delete two): Fair Star Image Stability ("seeing"; as above): Fair Other Conditions: (Wind, Clouds, Lights, etc.):_thin_cirrus_in_Virgo_______ EVENT TIMINGS: (All times in Universal Time) image intensifier with Time Source:___WWVH______ Recording method:_Panosonic_video_camera/camcorder Was the Asteroid Visible in your Scope? _no___ Approx. Limiting Mag.:__7___ ** Preliminary times ** Universal Time Estimated Accuracy, Remarks to be refined later h m s Reaction Time, Started Observing: _10:_33:_00.___ (sec.) _____30_sec_________ Star and Object Merged: ___:___:___.___ ____________________ preliminary Disappearance: _10:_35:_54.3__ _N/A?_ _0.3s_vis._reduction Estimated Closest Approach: ___:___:___.___ ____________________ (if no D/R) preliminary Reappearance: _10:_35:_56.1__ _N/A?_ _0.3s_vis._reduction Star and Object Separated: ___:___:___.___ ____________________ Stopped Observing: _10:_36:_40.___ ______10_sec________ Was your reaction time applied to the above timings? _N/A?____ If you could tell, did the object pass NORTH, SOUTH, EAST, or WEST of the star (cicle one, or delete three)? If possible, estimate the distance of closest approach in arc seconds: _______ List all Interruptions in Observing: Reason From ___:___:___ to ___:___:___ __________________________________ From ___:___:___ to ___:___:___ __________________________________ Additional comments: _D_gradual,_about_0.3s;_R_gradual_or_stepped,_0.5_sec.? Send Jan Manek Fax: +420-2-61216822 report to: Stefanik Observatory E-mail: jmanek@mbox.vol.cz Petrin 205 If an occultation is timed, copy to: 118 46 Praha 1 dunham@erols.com Czech Republic __________________________________ David Dunham
