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Mars Comet Encounter Observations, C/2013 A1 Siding Spring, 19 Oct 2014
jmknapp
post Oct 19 2014, 12:17 PM
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I think the sol 782 images taken around 4:08am, elevation 70 degrees, azimuth 100 degrees are the ones with SS in frame, if visible, e.g.,

http://mars.jpl.nasa.gov/msl-raw-images/ms...149C00_DXXX.jpg
http://mars.jpl.nasa.gov/msl-raw-images/ms...148C00_DXXX.jpg
http://mars.jpl.nasa.gov/msl-raw-images/ms...344C00_DXXX.jpg

Based on the ML shots, seems there was quite a bit of sky brightness in the east around 4:10am, a little over an hour before sunrise:

http://curiosityrover.com/synth/?camera=ML&station=246


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Gerald
post Oct 19 2014, 12:46 PM
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A preliminary stitch of three of the Sol 782 ML images:

The shape of the comet begins to become more apparent. (Wishful thinking, see next post.)
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mhoward
post Oct 19 2014, 12:59 PM
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QUOTE (Gerald @ Oct 19 2014, 06:46 AM) *
The shape of the comet begins to become more apparent.


Uh... no. That's got to be just pre-dawn illumination of the sky.

Those pictures have been on the ground over 24 hours. If that were the comet, that image would right now be plastered all over media around the world.
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Cosmic Penguin
post Oct 19 2014, 04:02 PM
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Sorry if I sounds like an orbital mechanics rookie, but what are the closest approach distances of the 5 Mars orbiters to the comet? smile.gif


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Adam Hurcewicz
post Oct 19 2014, 04:36 PM
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QUOTE (Cosmic Penguin @ Oct 19 2014, 06:02 PM) *
Sorry if I sounds like an orbital mechanics rookie, but what are the closest approach distances of the 5 Mars orbiters to the comet? smile.gif


comet - MOM - 88 222 km at 18:14 UTC
comet - MRO - 135 750 km at 18:28 UTC
comet - MEX - 136 890 km at 18:26 UTC
comet - Odyssey - 141 140 km at 18:26 UTC
comet - MAVEN - 143 290 km at 18:26 UTC


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Deimos
post Oct 19 2014, 08:10 PM
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As Joe said, the comet was up at 70 deg when the twilight images happened. The sky was brighter than any comet has ever been at 1.5 AU from the Sun.

The latest predictions (i.e., what I see in Starry Night - 2 magnitudes, per http://cometcampaign.org/current-status) suggest the comet may total 100X as bright as M31, outside of twilight, at a time when its coma has >5X the angular extent: so the light is diluted to <20X M31. If you've seen previous attempts to image M31 (here and here) in less dusty conditions, then you have an appropriate sense of how bright the comet may appear.

Opportunity's night is done, but it is a long wait for a relay pass. Curiosity should get to work soon, but again it will be a long wait.
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nprev
post Oct 19 2014, 08:18 PM
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Thanks very much for the update, Deimos.

I've seen unconfirmed reports that the coma is greater in extent than anticipated (though no means for determining that was specified; presuming it was via Earth-based telescopes, but I'd think that the glare from Mars would complicate that). Does anyone have any reliable information regarding this, or anything else of interest for that matter?

EDIT: Found a NASA site for US orbiter status post-passage. Not particularly informative at the moment; all statuses are 'pending'.


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scalbers
post Oct 19 2014, 08:26 PM
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Just to shuffle these numbers a bit, current magnitude would be about 11.5 from Earth, translating to -4.7 from Mars at closest approach. If M31 is 3.5 magnitude, then SS is about 2000 times as bright. If SS has 5 times the angular diameter as M31, then the areal extent is 25x. Thus the surface brightness would be 80x that of M31.

Seen from Earth, an image 8hrs before closest approach from comets-ml is here where it looks pretty well condensed in an area smaller than 1 arcminute, with the overall coma being around 1 arcminute: http://www.dpreview.com/galleries/45945840...?inalbum=comets

Via Twitter today is this pretty neat color image: http://cf.tzecmaun.org/2014/10/mars-and-co...-siding-spring/

An Oct 17th visual description is here: https://groups.yahoo.com/neo/groups/CometOb...ons/topics/5852


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fredk
post Oct 19 2014, 08:50 PM
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QUOTE (Deimos @ Oct 19 2014, 03:11 AM) *
Opportunity also imaged Pi Ceti during a test run a few sols ago. In addition to increased extinction, the distant dust storms make for an annoyingly bright twilight.

Thanks for identifying the field. This image shows the stars I identified in the two frames:
http://mars.nasa.gov/mer/gallery/all/1/p/3...YOP2664L1M1.JPG
http://mars.nasa.gov/mer/gallery/all/1/p/3...YOP2664L1M1.JPG
Noise subtraction doesn't help very much with these frames, probably due to the high sky brightness. But it's pretty easy to ID the stars by flipping between the two frames and matching the faint streaks in the longer exposure with the points in the shorter exposure. Here's the result, with identified stars circled:
Attached Image

I've superimposed a star map, slightly shifted to the right, so you can see that the identifications are good. There's nothing unexpected here, except the uppermost circled point, which I'm guessing is a star just below the magnitude limit of my map (though someone should check this). It would be nice to know the location of SS when these images were taken, though...

On the (slightly) plus side, tau was 1.19 on 3812, when these images were taken. The latest values are slightly better, 1.07 for 3815.

Edit: The faintest identifiable stars in my image are about 6th magnitude, at least in the darker part of the frame.
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Explorer1
post Oct 19 2014, 08:58 PM
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According to DSN Now everything went well Maven, MRO, Mars Express, and Odyssey. Communications going on just fine...
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nprev
post Oct 19 2014, 09:14 PM
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As expected. It'll be interesting to see if there have been any effects at all on any of the spacecraft.


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Gerald
post Oct 19 2014, 10:04 PM
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QUOTE (fredk @ Oct 19 2014, 10:50 PM) *
There's nothing unexpected here, except the uppermost circled point, which I'm guessing is a star just below the magnitude limit of my map (though someone should check this)...

That's probably the variable star Z Eri, mag. 6.79, according to Redshift 7 software, as far as this can be said for variable stars.
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nprev
post Oct 19 2014, 10:41 PM
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Now reporting MRO's fine & successfully maneuvered for all planned observations.


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JohnVV
post Oct 19 2014, 11:43 PM
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QUOTE
Noise subtraction doesn't help very much with these frames, probably due to the high sky brightness

for image
http://mars.nasa.gov/mer/gallery/all/1/p/3...YOP2664L1M1.JPG
and image
http://mars.nasa.gov/mer/gallery/all/1/p/3...YOP2664L1M1.JPG
[attachment=34022:386EFFCH...2664L1M1.jpg] [attachment=34023:4406EFFC...2664L1M1.jpg]
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jmknapp
post Oct 20 2014, 12:16 AM
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QUOTE (fredk @ Oct 19 2014, 04:50 PM) *
It would be nice to know the location of SS when these images were taken, though...


I get RA 02:44:15, dec -15.25 for SS at the time of those images--can you place it on your diagram from that?


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