Topics

Comet tracking.

Aisling Lightworks
 

Are there any plans to add comet tracking? Punch in a comet's apparent motion in RA and DEC and have it track at that rate? 

Khalid Baheyeldin
 

On Thu, Nov 28, 2019 at 06:38 PM, Aisling Lightworks wrote:
Are there any plans to add comet tracking? Punch in a comet's apparent motion in RA and DEC and have it track at that rate? 
The RA and DEC are not sufficient to calculate an orbit for a solar system body.
Further parameters are needed, and there are some uncertainties (gravitational pull of Jupiter on the way in or out, ...etc.)

https://en.wikipedia.org/wiki/Comet#Orbital_characteristics

https://www.math.ubc.ca/~cass/courses/m308-05b/projects/lim/index.html

The data for any given comet are usually published here

https://minorplanetcenter.net/iau/info/CometOrbitFormat.html

Similar calculations go for asteriods, as well as artificial satellites (though they are much faster).

In the past we had a discussion on satellites, and it was an external program that did the calculations. Maybe because they are too daunting for OnStep's microcontroller to calculate in real time.

See this thread https://onstep.groups.io/g/main/topic/7725169#321

Not sure if Howard can add comets and asteroids, or it is too complicated to be worth the effort.

Aisling Lightworks
 

Well, I was envisioning something much simpler. Planetarium software gives us an objects apparent motion. So we'd just punch in how much it needs to move each axis per second to track whatever we need to track. It wouldn't work long term but for a few hours observing it would be handy. Like, if you hit the comet tracking mode, it brings up two fields, for the RA and DEC. And it just tracks in sidereal time + whatever you put into those fields per second. Basically like sending guiding pulses

Aisling Lightworks
 

Hell, I wouldn't mind doing the math myself and punching it in as steps per second or whatever Onstep's native variable is for the tracking rate

Khalid Baheyeldin
 

On Thu, Nov 28, 2019 at 09:20 PM, Aisling Lightworks wrote:
Well, I was envisioning something much simpler. Planetarium software gives us an objects apparent motion. So we'd just punch in how much it needs to move each axis per second to track whatever we need to track. It wouldn't work long term but for a few hours observing it would be handy. Like, if you hit the comet tracking mode, it brings up two fields, for the RA and DEC. And it just tracks in sidereal time + whatever you put into those fields per second. Basically like sending guiding pulses
From what I understand, comets do not work that way.
Apparent motion is basically: n arc seconds per year for RA, and m arc seconds per year for DEC.

Comets can move several arc seconds per minute, for example, see those time lapses that I did

https://www.youtube.com/watch?v=Z81LII36mbs

https://www.youtube.com/watch?v=ijzZcxpZT_A

For comets, no such information of "apparent motion" exists, and Stellarium, KStars and CdC all have to get the orbital parameters from the data that is published at the Minor Planet Center web site.
This data is not set in stone (like a star having a fixed RA/DEC and so much apparent motion for each axis).
It changes as small tugs in gravity from Jupiter and Saturn changes the orbital, ...etc.
That is why all the planetariums provide a download feature to update comet data, and they do the heavy lifting of calculating where the comet is.

Khalid Baheyeldin
 

On Thu, Nov 28, 2019 at 09:33 PM, Aisling Lightworks wrote:
Hell, I wouldn't mind doing the math myself and punching it in as steps per second or whatever Onstep's native variable is for the tracking rate
So it would basically be back to the satellite tracker scheme: an external program calculating pulse guides.

Aisling Lightworks
 

So this data in Sky Safari wouldn't be enough to punch into Onstep and get it to track a comet for a few hours?

Khalid Baheyeldin
 

On Thu, Nov 28, 2019 at 09:47 PM, Aisling Lightworks wrote:
So this data in Sky Safari wouldn't be enough to punch into Onstep and get it to track a comet for a few hours?
When I commented previously on Apparent Motion, I was mistaken on the term. My comment was about Proper Motion, which is known for most stars (measured by specialized sky surveys and satellites).
As I said before, it does not apply to comets, and all planetarium (that I am familiar with) calculate it from MPC published data.

I don't know whether the Sky Safari data is sufficient to generate guiding pulses or, or better yet, change the tracking rate for both axes.
Howard has to comment on all this.

James Lancaster
 

As of right now, (I'm not on current master, but I had a look.) You can set a custom RA tracking rate, but can't set a custom DEC rate. How the satellite tracker works (That I still haven't gotten fully working) is that it uses guiding, and the ability to set custom guide rates via:
//   :RAdd.d#   Set Axis1 Guide rate to dd.d degrees per second
//   :REdd.d#   Set Axis2 Guide rate to dd.d degrees per second

Note that I have started to dig into it, but haven't completely. If my understanding is correct, and I just looked at it, those are set, and will cause it to guide at those rates.

So if you want to test this, make sure that GUIDE_TIME_LIMIT is set to 0 (if you want it to keep going, unless you've got it recalculating/resending) first issue a guide (at whatever speed (the subsequent command does not set the direction, send :R0# to have the move be the smallest, before engaging the tracking/guiding))

:Me# (or :Mw#)
:Mn# (or :Ms#)

Then convert those to degrees per second, so (assuming it means non-sidereal days, and my unit conversion is right... it seems a bit off, can someone check it?) your values would be:
>>> 127.5204/24/60/60
0.0014759305555555556
>>> 1398.714/360/60/60
0.0010792546296296294

(It does have a low cutoff of 1/60/60 = 0.0002777777777777778 degrees per second, and high of the max speed)
Send the following:

:RA0.0014759305555555556#
:RE0.0010792546296296294#

May work, may not. Get ready with the shutdown, just in case. (Also someone want to check my unit conversion?)

Couple of notes:

I don't think you can use it with other guiding/pulse guiding/ST4 guiding, but I could be wrong. It seems to call enableGuideRate with currentGuideRate, which I don't believe gets set in any of the functions called by the :RA...# commands, so it'd drop back to normal rates, and kill the rate set with the above commands. (If set to -1, it should work, but only at the rate you'd already be moving.)

:RA may need +1 (I need to look again to be sure if it would include the existing tracking or replace it, and I spent way too much time on it.)

Anyway, I hope that gives you a way to test it.


On Thu, Nov 28, 2019 at 9:03 PM Khalid Baheyeldin <kbahey@...> wrote:
On Thu, Nov 28, 2019 at 09:47 PM, Aisling Lightworks wrote:
So this data in Sky Safari wouldn't be enough to punch into Onstep and get it to track a comet for a few hours?
When I commented previously on Apparent Motion, I was mistaken on the term. My comment was about Proper Motion, which is known for most stars (measured by specialized sky surveys and satellites).
As I said before, it does not apply to comets, and all planetarium (that I am familiar with) calculate it from MPC published data.

I don't know whether the Sky Safari data is sufficient to generate guiding pulses or, or better yet, change the tracking rate for both axes.
Howard has to comment on all this.

Howard Dutton
 

On Thu, Nov 28, 2019 at 09:49 PM, James Lancaster wrote:
I don't think you can use it with other guiding/pulse guiding/ST4 guiding, but I could be wrong. It seems to call enableGuideRate with currentGuideRate, which I don't believe gets set in any of the functions called by the :RA...# commands, so it'd drop back to normal rates, and kill the rate set with the above commands. (If set to -1, it should work, but only at the rate you'd already be moving.)
That's right.

 
:RA may need +1 (I need to look again to be sure if it would include the existing tracking or replace it, and I spent way too much time on it.)
The guide rate gets superimposed on the current tracking rate (both axes,) that includes refraction compensation/etc.

Howard Dutton
 

On Thu, Nov 28, 2019 at 09:49 PM, James Lancaster wrote:
(It does have a low cutoff of 1/60/60 = 0.0002777777777777778 degrees per second, and high of the max speed)
 
I lowered that limit to 0.001"/s in the latest master.

Howard Dutton
 

On Thu, Nov 28, 2019 at 09:49 PM, James Lancaster wrote:
Then convert those to degrees per second, so (assuming it means non-sidereal days, and my unit conversion is right... it seems a bit off, can someone check it?) your values would be:
>>> 127.5204/24/60/60
0.0014759305555555556
>>> 1398.714/360/60/60
0.0010792546296296294
For Dec, 1398.714:

arc-sec_per_second = arc-sec_per_day/24/60/60
0.0161"/s

deg_per_second = arc-sec_per_second/60/60
0.00000449 deg/s

RA works the same way but *15 first.

Howard Dutton
 

On Fri, Nov 29, 2019 at 08:46 AM, Howard Dutton wrote:
assuming it means non-sidereal days
No idea for Sky Safari but on the OnStep side the units are in degrees per sidereal second.

Aisling Lightworks
 

Hey it looks like PHD2 can track comets and send that info to the mount as guide pulses. Very cool. Going to try it out this weekend.

Khalid Baheyeldin
 

On Mon, Dec 2, 2019 at 10:55 AM, Aisling Lightworks wrote:
Hey it looks like PHD2 can track comets and send that info to the mount as guide pulses. Very cool. Going to try it out this weekend.
That is great info.
Let us know how it goes ...