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N00b Q yet again: Who's correct about 46P/Wirtanen's location?

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#1 fewayne

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Posted 06 December 2018 - 02:24 PM

So if I run KStars for my location and, say 7 PM Dec 8, it thinks 46P/Wirtanen is 3h 39m 17s, +6° 16' 00". Easy-peasy. Since that's what I usually use to point my scope, I'm ready to go...right?

 

Except if I ask, say, the SkyLive Blog or JPL's Horizons ephemeris, translating local to UTC, I get significantly different answers. (Can't get the table formatted, so doing a screen shot -- sorry!)

 

Is there that much of a difference between the J2000 and J2018 epochs? Or is something else going on here? Should be something like 15' discrepancy, right, not 9 degrees!

 

Screen Shot 2018-12-06 at 1.25.50 PM.png


Edited by fewayne, 06 December 2018 - 02:26 PM.


#2 RyanSem

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Posted 06 December 2018 - 02:45 PM

I ran into this problem with SkySafari vs. Stellarium. Luckily they were both close enough to be within a couple FOVs so I just went from one to another I see which was accurate. In the end, SkySafari was correct. 

 

SkyLive is the same as my SkySafari, so I would go with that. 

 

Edit: Incidentally, tonight would be a very easy night to find it, being that it's right next to the star Azha (which is bright enough that I can see it in a border red/white zone)


Edited by RyanSem, 06 December 2018 - 02:46 PM.


#3 sg6

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Posted 06 December 2018 - 02:51 PM

There is a reasonable difference. Skysafari uses 2018, university I visit uses the 2000 - big old catalogue of stars and objects. If you are inputting the RA+Dec then I would expect the 2018 to be the more accurate at this time.

 

If reading what a handset says, you do not really get a choice.

 

Guess it is caused by our movement and precession of the earth about its axis. May also be something from the elliptical orbit we have



#4 beggarly

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Posted 06 December 2018 - 04:05 PM

I think you need to update the comet orbital elements in KStars.
 
I used C2A to calculate an ephemeris using the latest orbital elements. Set location to 43°4′N 89°24′W time zone UTC-6.
(I still may have overlooked something.)

Attached Files


Edited by beggarly, 06 December 2018 - 04:24 PM.

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#5 fewayne

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Posted 06 December 2018 - 05:45 PM

A-HA! That was the key! Actually all I had to do was go to Data | Updates | Update Comets Orbital Elements and KStars was right with the others. But thanks for the link, too, with that I was able to update Stellarium too (which, oddly, didn't have 46P/Wirtanen at all).

 

Now I just have to switch my Raspberry Pi running StellarMate over to WiFi (instead of being a WiFi hotspot), do the same, and I ought to be able to do a GOTO Saturday night.

 

Sadly, I have commitments tonight and tomorrow both which will preclude astro, at least from a dark site. But I'm rubbing my hands for Saturday. (Will have to rub them a LOT on Saturday night, as it's expected to be 20° F / -7° C.)

 

Thanks!




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