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Old 20-07-2019, 11:25 AM
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38degsouth (Dean)
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Join Date: Jul 2013
Location: Melbourne, Australia
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Sat 20/7: Asteroid to occult 11.5mag star, Melbourne and southern VIC

For those that may be interested in watching a minor planet in motion, 56km wide main-belt asteroid (1071) Brita is predicted to occult (block the light from) an 11.5 magnitude star at 21:50:44 this evening (Sat 20/7).

This is for people that have equipment that can clearly see down to 11.5 magnitude stars. Those with GoTo scopes can simply enter the target RA/Dec, then confirm the target star with the attached plot. Remember, the orientation of the attached finder chart may be rotated or inverted compared to your view! There is no need to be able to see the asteroid (it's magnitude 15.1), just the target star. The star will instantly disappear and reappear if the asteroid passes in front!

I'm a member of the Royal Astronomical Society of New Zealand (RASNZ) Occultation Section. I (along with Jacquie M) will be video recording and accurately timing this event using sensitive video camera's and GPS time insertion. The results of my and Jacquie's observations will help to accurately define the position and size of this minor planetary body. You can add your results too!

Time: 21:50:44 +/- 4 seconds
Duration: up to a maximum of 5.4 seconds, depending on which part of the asteroid 'shadow' that passes over your location.
RA 18 03 12.2534
DEC -29 03 07.309
please confirm using attached details!
Local altitude is 77 degrees, Local azimuth is 47 degrees.
Very high in the north east sky, as seen from Melbourne.

The shadow path also passes over southern Victoria (see map).
Mt Gambier, Hamilton, Ballarat, Geelong, Warragul, Traralgon, Sale, Lakes Entrance. All details and times will be within 30 seconds of those stated above. Earlier in Gippsland, later in Western districts.

The shadow also passes over Southern WA, but I see that cloud is forecast there for this evening. Note that the times will be different in WA.

For those that have never observed an occultation like this, then I encourage you to watch this event, it's quite spectacular when an occultation occurs! If you are not concerned with timing the event, then that's OK -enjoy! If you would like to time the event, a stopwatch would be the most rudimentary method. There are timing apps available, I'll let you look into those. A positive result is great, a negative result is good too! All collated positive results (ie an occultation occurs) will help define where the shadow passed, and all negative results (no disappearance) will help constrain the northern and southern limits of the shadow.


The red rectangle on the attached finder chart is 15' x 13', showing stars down to mag 13.
The predicted shadow is between the blue lines on the attached map.
The telescopes shown on the map are my and Jacquie M's locations.

As with all predictions of this nature, there is a chance that the shadow may deviate from the prediction. This event is ranked 98, which means there is a 98% chance that one of two observers, each being 1/5th of the way inside the prediction shadow edge will see an occultation. My predicted chance here in Parkdale is 78%.

Good luck!

Regards, Dean
Attached Thumbnails
Click for full-size image (brita 1.jpg)
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Click for full-size image (brita 2.jpg)
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Click for full-size image (brita 3 IOTA.jpg)
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Click for full-size image (brita 4.jpg)
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Click for full-size image (brita 5.jpg)
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Last edited by 38degsouth; 20-07-2019 at 12:15 PM.
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