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Observation by Alex Pratt: (940) Kordula occults UCAC4 577-017001

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Alex Pratt


Alex Pratt


2020 Nov 27 - 23:46


2020 Nov 29 - 12:01



  • C11 f/10 and f/3.3 focal reducer
  • Watec 910 video camera
  • IOTA-VTI GPS time inserter
  • OccuRec (recording)
  • Tangra and AOTA (reduction)




Target name

(940) Kordula occults UCAC4 577-017001


(940) Kordula occults UCAC4 577-017001

About this image

Mag 14.1 outer main-belt asteroid (940) Kordula, 80 km in diameter, was predicted to occult a mag 14.4 star in Taurus on the night of 2020 November 27. Observers within the 96 km wide shadow track could see them merge with a combined mag. of 13.5, then drop in brightness by 0.6 mag. for up to 6.7s.

My site was inside the predicted shadow zone, with 43% probability of success. I had to use a high gain setting for this magnitude, which combined with the strong Moonlight produced a noisy recording capturing the brief disappearance of the target star, for 4.8s. The attached screenshot shows the analysis of the light curve using Tangra and AOTA. Thanks to Eric Frappa (European occultations coordinator) for improving my provisional analysis, giving timings of:

    D  - 23 46 48.51 ± 0.40
    R  - 23 46 53.31 ± 0.24

Other observers were clouded out, but a single chord adds to information on the asteroid's diameter and the mid-time of the occultation is used for an astrometric measurement of its position.

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