(49) Pales occults 2UCAC 38788900

[Moon (James)]

This one is due Sat 01 Jan, 00:55 Local time.

Question is - how do I find 2UCAC 38788900 in TheSky6?

[Astroman (Andrew Wall)]

wow that looks very faint, good luck with it though... here are a few maps.. http://www.asteroidoccultation.com/2...1_49_25753.htm

[Moon (James)]

wow that looks very faint, good luck with it though...

It could be out of reach, but I'll see how I go.

There must be some way to search for the star in TheSky? No?

[Blue Skies (Jacquie)]

If you look at the detailed info it gives the RA and DEC down towards the bottom of the page, in data for the target star. 13th mag is a bit faint.

[mithrandir (Andrew)]

Originally Posted by Moon

This one is due Sat 01 Jan, 00:55 Local time.

Question is - how do I find 2UCAC 38788900 in TheSky6?

See this page at SB.

What are you using to compute your occultation? If it is Occult Watcher it can talk to C2A to plot the event.

C2A can use the UCAC2 catalog as well as the SAO, GSC, USNO-A, USNO-B, Tycho-2, Hipparcos, UCAC1, UCAC3, NOMAD, GCVS, WDC and Loneos catalogs.

Also C2A will drive various mounts, including anything supported by ASCOM.

Andrew

[Moon (James)]

Thanks Andrew, that's exactly what I was looking for.
I'm only using Occult Watcher at this stage, so I'll give C2A a try.
James

[Outbackmanyep]

Mag 13 star should be reachable with 8" aperture in good seeing, although my only worry is the 0.3 mag drop. This drop may not be detectable by eye but a video event should make it no worries!

The asteroid is brighter than the star, so keep in mind with your field that you take into account the extra "star". The mag drop will be unnoticeable visually in my opinion!
The star won't blink out at all, it will just dim slightly if you happen to be in the right place at the right time (ie: if the prediction favours you)

good luck!

[tonybarry (Tony)]

I set up for this occultation, more as a "can I do this?" than anything else. I have yet to analyse the video. I'll add a post if I find anything.

But the skies were wonderful! So long since we've had it like this.

Regards,
Tony Barry

[tonybarry (Tony)]

I put the video through LiMovie. No occultation from Penrith, Sydney. Thanks to Dave Gault for assistance beyond the call of duty.

Regards,
Tony Barry

[mithrandir (Andrew)]

Originally Posted by tonybarry

I put the video through LiMovie. No occultation from Penrith, Sydney.

Tony, OW has you and me on the edge of the 1 sigma. Did you expect to see anything? The edges of the shadow prediction went through Canberra and Melbourne.

Andrew

[tonybarry (Tony)]

Hi Andrew, the aim of the game is to observe and let the chips fall where they may. The 1 sigma bands represent an area of uncertainty in the known orbit of the asteroid, and perhaps the position of the star as well. A negative observation on the borders helps to narrow down those 1-sigma bands. Certainly a positive is worth "more" to the observer because it's fun and exciting. But to the calculations, it's all data.

Regards,
Tony Barry

[Blue Skies (Jacquie)]

My impression from the talk on the RASNZ list was that there were lots of misses and it appeared that the path had shifted to the south. So that in itself is a useful result.

[DaveGee (Dave Gault)]

The last tally was zero positives, 5 misses and many clouded or winded outs. This is one that got away.

On the uncertainty, 1-Sigma, 2-Sigma, should I observe or not. Tony is spot-on...

Originally Posted by tonybarry

the aim of the game is to observe and let the chips fall where they may

and the uncertainty zones are a reflection of the uncertainty in the position of the star and the orbit of the asteroid.

On the position of the star, this was a 2UCAC cataloge prediction and it is useful to have a look at the Catalogue Comparison plot that is available in Dave Herald's "Occult" and can be accessed through Hristo's Occult Watcher if you have the Add-In and Occult installed. See a screen-shot below...

DaveH's and Hristo's comments on the plot, that were posted on the RAZNZoccsec group were...
***************
Re: [RASNZoccultations] 49 Pales - Tonight

I fear the situation is even more complex....

The fact that PPMXL has not used the PPMX position is an indication of problems.
And as I state in the Help topic:
If the PPMXL position has been taken from PPMX, the 3rd flag will be set to 'P'. If the star is in both PPMXL and PPMX, and the 3rd flag in PPMX is 'O', the PPMXL position may be preferable.

Looking at the individual catalogues: UCAC2 and 3 have essentially the same position at imaging epoch. The differences are all proper motion. Comparing the other catalogue positions (incl. the CMC14 position) , I'm inclined to think that the old epoch position(s) for this star are bad, and that the proper motion is small. My inclination is that the PPMXL position may be the best guide (or certainly the PPMXL proper motions) - which means the the path will probably be a good path-width south of predicted.

Dave Herald
Canberra, Australia


----- Original Message -----
From: Hristo Pavlov
To: RASNZoccultations@yahoogroups.com
Sent: Friday, December 31, 2010 11:08 AM
Subject: Re: [RASNZoccultations] 49 Pales - Tonight


Hi DaveG,

I agree with you about the catalog comparison interpretation but I think the shift may be smaller. UCAC3 position doesn't have proper motion so if you use the UCAC2 or PPMX proper motion for the UCAC3 position you will end up somewhere between the 2U and PPMX predictions. So I recon 1/2 path width shift to the left/south. Which still means if you are in Melbourne you'll get central event. But I wont be surprised from a 1 path width shift for a central event over Wellington/Nelson.

Hristo.

*************
I'm 100% certain Dave and Hristo won't mind me reproducing their posts here.

The take-home message is that the true position of any star is uncertain. Sometimes the catalogue comparison plots show a 180 degree diagreement. If you are in the 1-Sigma zone - observe. if you are in the 2-Sigma zone - observe if you can.

And... An Asteroid Occultation is the toughest test there is of any star catalogue.

Observe more - worry less!

DaveGault