Tuesday, November 24, 2020

filtered comets in Stellarium

OK. Think I figured it out...

After delivering the webinar on the basic and intermediate features of Stellarium 0.20.3, a participant asked the following question:

How do you specify comet criteria to import?

I quickly accessed the Configuration settings, Plug-ins, and the Solar System Editor and conducted an Online Search for C/2020 S3, found it, loaded it, and located it in the sky.

The questioner reiterated her query which I had jumped the gun on.

She specifically wanted to know HOW to review a list of comets with the intention to ONLY importing those that were viable, doable, given her skies, instrument, etc. I.e. maybe filter by magnitude before importing.

Oh. I had not carefully read the question.

So I headed back into the Configuration, SSE. This time I showed the Lists tab. I selected the "MPC's list of observable comets" and hit the Get button. Right. Now we had a list.

The difficulty here is that list of dozens or hundreds of comets does not show any particulars such as absolute magnitude or coma size or surface brightness or distance from Earth...

The user is in a bit of a lurch here. In Stellarium, must one select all the comets and then assess each on a case by case basis? Are some of these "observable" comets going to be magnitude 18 or 20? Why import them? Likely there will be a bunch out of range.

I shared that I'm a dyed-in-the-wool SkyTools fanatic and over there, it's easy. I gave a quick demo. Start the app, go to the Current Comets list. Update manually, if using version 3. Sort by apparent magnitude or surface brightness. Note the size column. Apply horizon and time frame constraints, as necessary, considering one's location. Select interesting (bright) targets and add 'em to an observing or imaging campaign list. Nice (although, now that I think on it, that's quite a number of steps).

So, planning tools... well, it's in their DNA to apply criteria to gauge the viability of seeing celestial targets.

Told my participant that I'd get back to them.


This question kicked off a round of research...

It made me realise or consider that part of this is the LOADING of ALL possible or potential comets into an application or tool first then applying geographic and time-of-night constraints... Of course, Greg Crinklaw's algorithms are very sophisticated taking into account atmospheric conditions, local light pollution, observer age and experience.

True absolute magnitude needs to be distilled to apparent magnitude. So that raw list from the MPC must be loaded. Then the software can calculate the apparent values...

I looked in the Stellarium manual (for version 0.20.3). The PDF with 350 plus pages. And nothing obvious. Hrmm.

I wondered what the criteria was for MPC "visible comets." Visited IAU's Minor Planet Center web page for Observable Comets. It says "This page lists links to orbital elements and ephemerides of (potentially) observable comets." Nope. I could find an explicit answer to that.

I looked in the Stellarium wiki. Nope. Nothing. Sheesh.

I checked the Stellarium Google Groups. Huh. Only 6 convos total with "comet" in the content. 

I looked in Stellarium forum on the developer side. Dog's breakfast.

Hopped into the Stargazers Lounge discussion on Software. Didn't see anything after a few quick searches.

Similar outcome in the Cloudy Nights forum on Astronomy Software & Computers.

Like earlier Google searches, most threads were how to load a comet. Nothing about filtering or analysing before importing. Or getting a short list of good candidates by magnitude criteria. Nothing about the MPC's criteria. 

I returned to CN, logged in, and created a post. I apologised if the question had already been answered. I explained the situation. I asked if the "new" Astronomical Calculations Window came into play noting I did not a lot of experience with it. I asked pointed questions:

Do you have to load all "potentially" "observable" comets into Stellarium as a starting point?

Then is there a way to know which ones are seriously attainable for your location, light pollution, instrument, etc?

After about 60 minutes, there were 30 views of my question but no replies in CN.

I pinged Chris V for ideas.

Then I fired up Stellarium (version 0.18.0), with a hunch in mind... I did the following:

  1. Loaded cometary data.
    1. Accessed the Configuration window (F2).
    2. Clicked the Plug-ins tab.
    3. Selected the Solar System Editor option. Mine is already active, loading automatically at startup so I was ready to go.
    4. Clicked the Configure button to open the SSE. The Minor Solar System objects dialogue box appeared.
    5. Clicked the Solar System tab.
    6. Clicked the Import orbital elements in MPC format... button. The Import data dialogue appeared.
    7. Ensured the Lists tab was active.
    8. In the type options, I clicked Comets.
    9. In the source section, I chose MPC's list of observable comets from the list.
    10. I clicked the Get orbital elements button. The Import data box changed to show Objects found.
    11. I clicked the Mark all button to load every one of the "observable" MPC comets into Stellarium.
    12. I closed all the config boxes.
  2. Set up for good comet viewing conditions.
    1. Set the location to a dark-ish site. I used Collingwood, Ontario.
    2. Set the date and time to early November 2020. When that somewhat bright comet flew through Orion. C/2020 M3 (ATLAS).
  3. Tried the new-ish calculator tools.
    1. Accessed the ACW (Astronomical Calculations Window).
    2. Ensured the Position tab was active.
    3. Set the object filter (at the top-right) to Solar system objects: comets.
    4. Ticked the Use horizontal coordinates check box, so to get altitude values.
    5. Used the spinner to Show objects brighter than magnitude 14. I can see to about mag 14 in my 8-inch SCT.
    6. Hit the Update positions button at the bottom.

Look at that.

Astronomical Calculations Window - Positions - showing comets

I'm impressed.

I've dabbled with the ACW but it was really good to have a specific use-case.

This makes me consider the "observable" comets in Stellarium / the MPC is like the "current" comets feature in SkyTools (who knows, might be same source). So probably brighter than magnitude 16 or 18 or something like that.

Then Chris replied. He did similar things but went into the ACW's WUT. That's the What's Up Tonight tab.

  1. I clicked the WUT tab.
  2. Clicked comets in the category list.
  3. Adjusted the magnitude limit spinner.

There you go.

Astronomical Calculations Window - What's Up - showing comets

I actually think Chris's method is better. Mostly because it works for the entire evening; the Positions tab is sensitive to the specific hour and minute.

A little thing I don't like in the WUT is that you're restricted to one category at a time... Oh well.

Anyhoo, there's the answer.

Yes, sorta. While you cannot filter comets at the import stage, you can get Stellarium to filter "potential" comets based on magnitude. Load all current comets then use the Astronomical Calculations Window to make a short list by magnitude value. 

That's pretty good.

I'll list my webinar peeps know...

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