Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Asteroid observing in light pollution with color camera

Astrometry Astrophotography Beginner Filters
  • Please log in to reply
14 replies to this topic

#1 martinrw

martinrw

    Lift Off

  • -----
  • topic starter
  • Posts: 4
  • Joined: 04 Dec 2021

Posted 05 December 2021 - 09:01 PM

I am a newbie and just now gathering equipment and software to do asteroid astrometry. I live in a light polluted area and need to find something to reduce effects of light pollution. I have read info on several light pollution filters but I know the filter will reduce the light from an asteroid also. What can I do?

 

Also I got a good deal from a friend on a nice astrocamera, the ZWO ASI294MC-Pro. Problem is it is a color camera and nothing I have read in Astrometrica software mentions any processing for color images. Is there some preprocessing that I must do?

 

I need any help.



#2 ted_barnes

ted_barnes

    Lift Off

  • -----
  • Posts: 16
  • Joined: 27 Sep 2014

Posted 05 December 2021 - 09:58 PM

Hello martinrw,

 

I have been pursuing faint asteroid astrophotography as a fun sideline for several years now, and will be interested in seeing what recommendations people have for this topic. I use the same model ZWO camera you mentioned, which I have had for over 3 years. In my experience, bringing out the faintest asteroids requires that you concentrate the light in the smallest possible area, like 2x2 pixels, so you need good optics, good seeing and sharp focus. I use a 190mm Orion Mak-Newt, which performs very well, and a CGX mount. Another problem is that with siderial tracking the asteroids trail visibly if the exposure is longer than a few minutes. So, my magnitude limit to date for main belt asteroids has been about 18.3. For "fixed" stars in comparison I have reached about 20.5. I use stacks for asteroids rather than single exposures because my guiding (PHD2) with long single exposures does not give me a tight enough image. Ideally one could use PHD2 comet tracking to follow an asteroid, but again I don't yet get tight enough images with this approach. I don't use any filters, I need all the photons I can get. I also find that my best faint images are a few days from new moon.

 

We are fortunate to have excellent databases, e.g. using TheSkyX and dnloading the Lowell Observatory file astorb.dat you get positions and predicted 24 hour paths of over a million asteroids, and can select the magnitude range of interest to you. The All Sky Plate Solver is very useful in finding the fainter ones.

 

As a random example I have attached a crop from an image of asteroid 4740 Veniamina, mag 16.3, d = 1.21 AU, just outside the orbit of Mars and currently in Orion left of Betelgeuse, near Monoceros. This is a stack of 240 4-sec frames (total exposure 16 mins), with gain 400 and the usual post processing, taken about 11 PM Eastern 3 Dec 2021; the trail center is at RA 06 12 51.1, Dec +09 13 05 (J2000.0), just as expected.

 

4740_Veniamina_240x4sG400_WDS_snip_crop_edit_jpg.JPG


Edited by ted_barnes, 05 December 2021 - 10:04 PM.

  • astropec and lonn like this

#3 martinrw

martinrw

    Lift Off

  • -----
  • topic starter
  • Posts: 4
  • Joined: 04 Dec 2021

Posted 06 December 2021 - 10:50 PM

Ted Barnes - Thank you for replying to my questions. I am glad to have found someone experienced who uses the same equipment as I do. I looked at TheSkyX and the Lowell Observatory file astorb.dat that you recommended. They look like they have a lot of benefits over the Minor Planet Center recommendations. I will soon try them out. I need to learn all about these new tools you have suggested.

In regard to the color output of our cameras (ASI294MC-P) is there any color processing you used since Astrometrica seems to only process B&W images. Does it read color files and do we pay a  penalty in light sensitivity for the color? I was thinking the magnitudes of color versus B&W may be different when compared to the reference stars in the catalogs where we are trying to make a match. Is this a problem?

I admired your image of asteroid 4740 Veniamina that you posted. You must have great equipment and experience. I know you have a great observing site as I was at ONRL several times attending meetings. Your sky is very dark. I was with the University of Dayton Research Institute for 37 years where my last couple of years we teamed with ORNL to solve a corrosion problem for the Navy at Naval Research in Virginia. 



#4 555aaa

555aaa

    Vendor (Xerxes Scientific)

  • *****
  • Vendors
  • Posts: 2,352
  • Joined: 09 Aug 2016
  • Loc: Ellensburg, WA, USA

Posted 07 December 2021 - 12:42 AM

You really want a mono camera. You lose too much light through the beyer matrix. It is also critical that you have time stamping accurate to better than one second because your best objects now are very fast moving, so your exposure times may be only a few seconds but you might stack 50 to 100 using a moving stack approach or synthetic tracking.

#5 Tapio

Tapio

    Fly Me to the Moon

  • -----
  • Posts: 5,353
  • Joined: 24 Sep 2006
  • Loc: Tampere, Finland

Posted 07 December 2021 - 01:07 AM

You really want a mono camera. You lose too much light through the beyer matrix. It is also critical that you have time stamping accurate to better than one second because your best objects now are very fast moving, so your exposure times may be only a few seconds but you might stack 50 to 100 using a moving stack approach or synthetic tracking.


Don't know what objects require few seconds because they move so fast. I understand the timing if you are doing occultation observing but asteroid astrometry or photometry doesn't require it.
With an color camera can't you use binning to mitigate the effects of bayer matrix?

#6 ted_barnes

ted_barnes

    Lift Off

  • -----
  • Posts: 16
  • Joined: 27 Sep 2014

Posted 07 December 2021 - 12:10 PM

Ted Barnes - Thank you for replying to my questions. I am glad to have found someone experienced who uses the same equipment as I do. I looked at TheSkyX and the Lowell Observatory file astorb.dat that you recommended. They look like they have a lot of benefits over the Minor Planet Center recommendations. I will soon try them out. I need to learn all about these new tools you have suggested.

In regard to the color output of our cameras (ASI294MC-P) is there any color processing you used since Astrometrica seems to only process B&W images. Does it read color files and do we pay a  penalty in light sensitivity for the color? I was thinking the magnitudes of color versus B&W may be different when compared to the reference stars in the catalogs where we are trying to make a match. Is this a problem?

I admired your image of asteroid 4740 Veniamina that you posted. You must have great equipment and experience. I know you have a great observing site as I was at ONRL several times attending meetings. Your sky is very dark. I was with the University of Dayton Research Institute for 37 years where my last couple of years we teamed with ORNL to solve a corrosion problem for the Navy at Naval Research in Virginia. 

Hello martinrw,

 

Asteroids is/are a great topic, I hope you will enjoy their pursuit as much as I do. Their qualities vary widely, and there are over a million known.

 

I mainly use a ZWO color camera because colored star and nebula images are attractive, and I post my images on fb for my old HS friends. I see other people here have recommended a mono camera for improved access to faint objects. That's an interesting suggestion. I just save the ZWO ASI294MC-P images in SharpCap as jpgs for no good reason except file size, and do extreme contrast stretching to pull out faint objects using a generic free program, "Windows Live Photo Gallery," my only excuse being that it works for me. I don't know if I lose much sensitivity that way. My impression is that sharp focus matters most.

 

I'm glad you liked 4740 Veniamina. 16th magnitude is not difficult at all. Since you mentioned astrometry, note you can plate solve these images, and pin down the start and stop locations of the trail quite accurately. Comparisons with jpl ephemerides on ssd.jpl.nasa.gov allow a nice check of results.

 

Also intriguing is pursuing outer asteroids like Jupiter Trojans (often moderately bright), and TNOs and dwarf planets, which come in starting at about 17th mag, and are very exciting.

 

My current frontier is improving my guiding, and learning how to guide on the asteroid's predicted path rather than just following field stars.

 

n.b. Skies here near Oak Ridge are not nearly as dark as when I moved here 30 yrs ago. Knoxville and its light pollution are spreading. Then we had a galaxy; now we only have a few hints of one. Still, you can work on your techniques in preparation for access to darker skies.

 

Please keep me informed of your progress!

 

Ted
 


Edited by ted_barnes, 07 December 2021 - 12:52 PM.


#7 ted_barnes

ted_barnes

    Lift Off

  • -----
  • Posts: 16
  • Joined: 27 Sep 2014

Posted 07 December 2021 - 12:40 PM

You really want a mono camera. You lose too much light through the beyer matrix. It is also critical that you have time stamping accurate to better than one second because your best objects now are very fast moving, so your exposure times may be only a few seconds but you might stack 50 to 100 using a moving stack approach or synthetic tracking.

Hello 555aaa,

 

What model mono cameras would you suggest, and what are their advantages and limitations?

 

Can you say more about moving stacks / synthetic tracking?

 

Thanks!

Ted Barnes



#8 martinrw

martinrw

    Lift Off

  • -----
  • topic starter
  • Posts: 4
  • Joined: 04 Dec 2021

Posted 07 December 2021 - 06:56 PM

Ted Barnes - Thank you for your additional suggestions and 555aaa suggestions also. I have a lot of learning to do. 

I have some wide field poor quality color star field images and I will try extreme contrast imaging on them very soon. Thanks again.

I will try to follow posts by both of you.



#9 ted_barnes

ted_barnes

    Lift Off

  • -----
  • Posts: 16
  • Joined: 27 Sep 2014

Posted 07 December 2021 - 08:11 PM

Ted Barnes - Thank you for your additional suggestions and 555aaa suggestions also. I have a lot of learning to do. 

I have some wide field poor quality color star field images and I will try extreme contrast imaging on them very soon. Thanks again.

I will try to follow posts by both of you.

I usually post my astroimages on fb, at www.facebook.com/ted.barnes2 with open permission.


  • martinrw likes this

#10 jgraham

jgraham

    ISS

  • *****
  • Posts: 22,620
  • Joined: 02 Dec 2004
  • Loc: Miami Valley Astronomical Society

Posted 07 December 2021 - 08:52 PM

I have been using color cameras for photometry of variable stars for many years with excellent results. My camera set includes the ASI294MC Pro and it works fine. Color should have no effect on astrometry unless you are close to under sampling. If the color bothers the software all you need to do is to desaturate the image. Easy peasy.


  • martinrw likes this

#11 martinrw

martinrw

    Lift Off

  • -----
  • topic starter
  • Posts: 4
  • Joined: 04 Dec 2021

Posted 08 December 2021 - 02:13 PM

jgraham I thank you for your post. Do you use photoshop to desaturate an image? Did you try using a light pollution filter? I am told that a filter wastes too much light? By the way I was a member of MVAS for 3 years but then I moved south to the Mason area 5 years ago where there is a lot of light in the sky. I wish now that I could do this at John Bryan.

Clear skies to you.



#12 555aaa

555aaa

    Vendor (Xerxes Scientific)

  • *****
  • Vendors
  • Posts: 2,352
  • Joined: 09 Aug 2016
  • Loc: Ellensburg, WA, USA

Posted 09 December 2021 - 11:21 AM

Don't know what objects require few seconds because they move so fast. I understand the timing if you are doing occultation observing but asteroid astrometry or photometry doesn't require it.
With an color camera can't you use binning to mitigate the effects of bayer matrix?

Go to this page

 

https://www.minorpla...rm_tabular.html

 

This is the list of recently discovered asteroids which need immediate follow-up astrometry so that they won't be lost.

 

Now select the objects that are brighter than say 19th magnitude, and generate ephemeris for them.

 

When I did this, I get one object moving at 41 arc seconds per minute at 17.7 mag and one at 18th mag moving at about 300 arc seconds per minute (!).  Most objects on this list are pretty fast moving, several arc seconds per minute. And since you need to get a position accurate to a fraction of an arc second, it means very short exposures.



#13 555aaa

555aaa

    Vendor (Xerxes Scientific)

  • *****
  • Vendors
  • Posts: 2,352
  • Joined: 09 Aug 2016
  • Loc: Ellensburg, WA, USA

Posted 09 December 2021 - 11:44 AM

Hello 555aaa,

 

What model mono cameras would you suggest, and what are their advantages and limitations?

 

Can you say more about moving stacks / synthetic tracking?

 

Thanks!

Ted Barnes

The most common software package for producing research-grade astrometry for asteroids is called Astrometrica. It has a feature called "track and stack" where you load a whole series of images (your stack) and if you know the position angle (PA) and speed of the asteroid (from earlier observations), then when Astrometrica stacks the images, it offsets each one based on the image time stamp and the PA and speed you entered into the program.

 

The other popular program is called Tycho tracker. It is a synthetic tracking program, meaning it can do a blind search for moving objects by generating a large number of postulated PA and speeds, performing the stack, and then looking for objects which are stationary in the stack. This is a common method used by professional observatories also. Tycho can also stack based on a manually entered PA and speed as I understand it. It was written by a fellow here who's handle is asmcoder8088.

 

I don't have a specific camera recommendation other than it needs these criteria (IMHO)

  • mono only (because it produces a more accurate centroid than a OSC camera)
  • CMOS (because they are fast)
  • Needs precise timestamp (which is usually a SW issue).

The reason I would avoid OSC is that you are trying to get a measurement accurate to a small fraction of an arc second. If you are imaging "normal" and reasonably bright asteroids, the residual fit to your positions should be around 0.3 arc seconds, which is much less than the size of your pixels typically. A good plate solve with a polynomial fit can have a RMS error as low as 0.07 arc seconds, with a mono camera. If you are producing images with residuals as large as an arc second, they are pretty much useless.  You can check your obit fit residuals by taking a set of same-night measurements of a known asteroid and pasting them into an orbit calculating program e.g. find_orb, which will calculate a set of possible orbits, pick the best one, and then tell you what is the error of your observation set to that orbit.

 

I have some ASI ZWO cameras which are very nice but when you use the ASIimg program, at least the version I have, the image time stamp can be off by six or seven seconds which is terrible. The way I found this out was by creating a high speed clock image on my display, and then attaching a video camera lens to the astro camera and taking fast images of the computer screen. Other image capture code that uses the ZWO camera driver doesn't have this problem, apparently. But in any case you have to verify that the capture time is accurate, and also in your computer you need to absolutely be sure you have precise timekeeping, which is easy with a GPS synchronizer or at minimum a time sync service, and you probably want to double check using shortwave radio.

 

An example of what can be done from light polluted skies, check out the Northolt branch observatories team

https://www.facebook...BObservatories/

 

I also recommend the Roger Dymock book "asteroids and how to observe them" ISBN-13 9781441964380

 

You can also do asteroid light curves using MPO Canopus or AstroimageJ but that is a different discipline.


Edited by 555aaa, 09 December 2021 - 11:56 AM.

  • PrestonE, FuriousRabbit and ted_barnes like this

#14 jgraham

jgraham

    ISS

  • *****
  • Posts: 22,620
  • Joined: 02 Dec 2004
  • Loc: Miami Valley Astronomical Society

Posted 09 December 2021 - 04:11 PM

Yes, I would use Photoshop to desaturate a color image since that is what I have. Many utilities can convert a color image to gray scale.

I use a light pollution for general imaging, but not photometry as it clips the green filter. I have also noticed a reduction in the effectiveness of my light pollution filter as we shift over to LED street lights. I'm going to stop using it. A light pollution filter shouldn't be all that useful for astrometry.

Yep, JB is still there, though I haven't used it in 30 years. I do all of my work from my Bortle 8 backyard. It's not dark, but it's home. :)

#15 ted_barnes

ted_barnes

    Lift Off

  • -----
  • Posts: 16
  • Joined: 27 Sep 2014

Posted 12 December 2021 - 02:12 AM

The most common software package for producing research-grade astrometry for asteroids is called Astrometrica. It has a feature called "track and stack" where you load a whole series of images (your stack) and if you know the position angle (PA) and speed of the asteroid (from earlier observations), then when Astrometrica stacks the images, it offsets each one based on the image time stamp and the PA and speed you entered into the program.

 

The other popular program is called Tycho tracker. It is a synthetic tracking program, meaning it can do a blind search for moving objects by generating a large number of postulated PA and speeds, performing the stack, and then looking for objects which are stationary in the stack. This is a common method used by professional observatories also. Tycho can also stack based on a manually entered PA and speed as I understand it. It was written by a fellow here who's handle is asmcoder8088.

 

I don't have a specific camera recommendation other than it needs these criteria (IMHO)

  • mono only (because it produces a more accurate centroid than a OSC camera)
  • CMOS (because they are fast)
  • Needs precise timestamp (which is usually a SW issue).

The reason I would avoid OSC is that you are trying to get a measurement accurate to a small fraction of an arc second. If you are imaging "normal" and reasonably bright asteroids, the residual fit to your positions should be around 0.3 arc seconds, which is much less than the size of your pixels typically. A good plate solve with a polynomial fit can have a RMS error as low as 0.07 arc seconds, with a mono camera. If you are producing images with residuals as large as an arc second, they are pretty much useless.  You can check your obit fit residuals by taking a set of same-night measurements of a known asteroid and pasting them into an orbit calculating program e.g. find_orb, which will calculate a set of possible orbits, pick the best one, and then tell you what is the error of your observation set to that orbit.

 

I have some ASI ZWO cameras which are very nice but when you use the ASIimg program, at least the version I have, the image time stamp can be off by six or seven seconds which is terrible. The way I found this out was by creating a high speed clock image on my display, and then attaching a video camera lens to the astro camera and taking fast images of the computer screen. Other image capture code that uses the ZWO camera driver doesn't have this problem, apparently. But in any case you have to verify that the capture time is accurate, and also in your computer you need to absolutely be sure you have precise timekeeping, which is easy with a GPS synchronizer or at minimum a time sync service, and you probably want to double check using shortwave radio.

 

An example of what can be done from light polluted skies, check out the Northolt branch observatories team

https://www.facebook...BObservatories/

 

I also recommend the Roger Dymock book "asteroids and how to observe them" ISBN-13 9781441964380

 

You can also do asteroid light curves using MPO Canopus or AstroimageJ but that is a different discipline.

Hello 555aaa,

 

Astrometrica's "track and stack" option sounds like my dream program. Thanks, I will look into it. I have either been stacking (w/o tracking the asteroid), so I get a trail, or using Comet Tracking on PHD2, but that requires long single exposures which have light pollution problems.

 

I recalled that I also like color because light pollution tends to produce highly colored backgrounds, which can be ignored. Asteroids are usually a recognizable flesh-colored dot.

 

Ted Barnes




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: Astrometry, Astrophotography, Beginner, Filters



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics