Following Asteroids

[jrkirkham]

Has anyone spent much time tracking asteroids or Ceres? If so, what telescopes have worked best for you?

[dcrowson]

Rob,

the main issue is magnitude and speed. I have no issues getting 14-15 mag ones with my 90mm refractor. I can get down to 19 or so with my 12" AT12RCT. It is important to take into account the movement. One can go much deeper on static objects. I've made somewhat 'pretty pictures' - https://www.flickr.com/photos/dcrowson/ ... 2773671313 - as well as submitted observations to the MPC (I have an observatory code).

I tend to start by determining how long I can expose without seeing movement and go from there. I can document how I do this using TheSkyX which is great because you can load the whole database - close to 1M asteroids now - and then limit the results to a certain magnitude and brighter.

Dan

[helicon]

I have yet to try asteroid observing but I agree that watching these objects move from night to night is pretty intriguing.

[ARock]

Interesting discussion. So it looks like you can "timelapse" it moving across the FOV. It might be something I can do with my 80mm F/5 achromat and the EQ mount.

[mention]dcrowson[/mention] Are the individual frames in your videos, single shots, or some small number of stacked subs? I am guessing with 15 sec exposures single shots, I can image brighter than Mag 11 asteroids in my skies.

I have heard that astropy has some way to get the asteroid data from some JPL database. Maybe that can be used to calculate magnitude and speed and direction to select/filter asteroids based on exposure and timelapse duration.

[OzEclipse]

My TACOS BD video capturing 5 frames per sec through an 8" Cassegrain can detect magnitude 14. Field is very narrow (16' x 20'). Finding targets is quite challenging.

A 135mm f2 will get to around mag 11 with a much wider field 2.5 degrees x 3 degrees.

The Tacos BD is a pretty expensive mono analogue camera based on the board version of the Watec 910 HX camera. It has some operating advantages including the innovative arduino based software controller.
http://www.kuriwaobservatory.com/TACOS_BD-System.html

I also have a Lihmsec security starlight camera which is a colour camera and about 1 magnitude less sensitive eg magnitude 13 through 8" and mag 10 with 135mm f2 5fps but about 10 times cheaper. I purchased this from Ali express for USD59 2 years ago but can no longer find a supplier. Runcam make some similar low cost low light analogue videos. I generally do not make recordings with this cam. With the addition of a 5" car video screen and a 12V supply, it makes a very capable and compact realtime video finder.

All the described cameras are analogue.

Video can be easily recorded to computer from an analogue using a video frame grabber such as this one from Star Tech.
This is an Australian site and the $103 price tag is Australian Dollars - approximately USD70.
https://www.startech.com/en-au/audio-vi ... svid2usb23#

I have this equipment to record asteroid occultations.

Timelapses showing motion can be more easily captured by timelapse stills with a DSLR. Brighter close approach fast moving NEO's with a 50mm lens, slower moving or main belt asteroids motion can be captured night to night with a telephoto or prime focus.

One of the best NEO videos I've seen was of 2012 DA14 taken in Feb 2013 by my friend Colin Legg from Western Australia. This asteroid moved right across the sky S to N past the Coma cluster over a few hours. He writes," The scene was captured at 50 mm, iso 8000, f/2.2, 8 second shutter duration, 9 second intervals."
https://tinyurl.com/y56zq728

Cheers

Joe

[DEnc]

Reading Joe's post I'm reminded of the skill and technology that's brought to bear on occultations. There might be something in this field that's of interest. Here's a start:--

https://occultations.org/

[dcrowson]

@dcrowson Are the individual frames in your videos, single shots, or some small number of stacked subs? I am guessing with 15 sec exposures single shots, I can image brighter than Mag 11 asteroids in my skies.

They are single exposures. I can't stress enough that determining the speed is critical because you might find some where you see movement in 30 minutes and others that show it in a fraction of a second.

You can also attempt to track on an asteroid as well. Here's a good example - https://www.flickr.com/photos/dcrowson/48703116291/.

Dan

[OzEclipse]

The IOTA VTI (Video time inserter is an expensive GPS time engine that sits between camera and the frame grabber and inserts a very accurate time stamp on each frame.

However, there are also cheap phone apps for iPhone(Astrotimer) and Android (Occult Flash Tag ) that use the phone GPS to precisely generate a flash of a set length. The App generates a text file with the start time of the flash and duration. Record one flash at the start, one at the end and just make sure the video runs continuously between the flashes. Also, don't point the camera down the telescope. These cameras are very sensitive and you'll saturate the CCD and the start and end time of the flash won't record cleanly - the signal will persist. I use a small piece of black card to catch and reflect a small part of the flash.

[OzEclipse]

@dcrowson Are the individual frames in your videos, single shots, or some small number of stacked subs? I am guessing with 15 sec exposures single shots, I can image brighter than Mag 11 asteroids in my skies.

They are single exposures. I can't stress enough that determining the speed is critical because you might find some where you see movement in 30 minutes and others that show it in a fraction of a second.

You can also attempt to track on an asteroid as well. Here's a good example - https://www.flickr.com/photos/dcrowson/48703116291/.

Dan

Dan is correct. The asteroid looks just like a star and only its motion will allow you to identify it.

To work out speeds/intervals before capture:

Using a planetarium program like Starry Night, you can either find the asteroid in the database or go to the Minor Planet & Comet Ephemeris Service
https://minorplanetcenter.net/iau/MPEph/MPEph.html

You can then check the box for the program you use and it will spit out a file with the orbital elements so that you can create the object in your program. Then set up a field of view indicator and step through it in 1 minute intervals, or 1 hr intervals etc and see the motion of the object. You can work out the cadence of the time lapse from there.

Main belt asteroids like Ceres only need 1 exposure per hour. NEO's can pass very close to Earth and exhibit motions of tens of degrees per hour.

Cheers

Joe

[jrkirkham]

This is one of the things I like about this hobby. There is so much to learn and others who are helpful along the journey. It just keeps stretching you more and more. This is a fascinating discussion.

Let's say I wanted to start with something like Ceres. Could a person use a DSLR and point to the location where Ceres should be, then take an exposure of that area as long as one can take without stars trailing? Depending on the telescope and tracking ability that might be 5 seconds or 50 seconds. From here it would be similar to taking a DSO shot through a DSLR, except instead of one exposure every few seconds, it might be one exposure every hour for Ceres or every 30 seconds for another object.

Assuming the object is fairly bright, such as Ceres, would it make much difference what telescope was used? If I used my C11 with a .63x focal reducer would that offer a wide enough field of view to easily locate and photograph the starfield surrounding the object, or would something wider, like the ED80 be a better choice?

[ARock]

Assuming the object is fairly bright, such as Ceres, would it make much difference what telescope was used? If I used my C11 with a .63x focal reducer would that offer a wide enough field of view to easily locate and photograph the starfield surrounding the object, or would something wider, like the ED80 be a better choice?

I just looked at Ceres in Stellarium in my DSLR FOV with the 80mm F/5 and increased time. I have it for about 3 hours in my visible sky and it does cross the meridian. The relative movement would show up on my wide angle shot but not by much. A smaller FOV (pixel scale) might be better in showing a larger movement on Ceres. I could of course crop the pictures before I combine them into a video. Ceres might be better as a multi night target.

[mention]dcrowson[/mention] How do you process the individual shots? Do you shoot RAW and calibrate each of them with darks, bias, flats? Or just shoot jpeg and combine them into a video.

[OzEclipse]

Hi Rob,
This is illustrative. It is a plot of Ceres shown at 24 hr intervals at 16:00 UT each day from Nov 3-11.

I have scaled the FOV [blue box] to simulate a full frame DSLR on a C11 with a 0.63x reducer. Ticks are 24 hr intervals.

Cheers

Joe

[jrkirkham]

Wow, I am going to have to learn how to do that. Thank you for showing me how it is done.

[jrkirkham]

Thanks for showing me that screen, Joe. I learn something new every day. I've been playing around with simulations like that. I think I am going to switch from my big scope to my ED 80 to hunt for Ceres. That should pick it up and the wider the starfield the better. I think I'll try to get a view of it once a day for several days to follow its motion. Even with a focal reducer on the C11 there wouldn't be much of a starfield to compare and I think I would get lost trying to follow it. Astronomy magazine also had a little section on chasing asteroids. It backed up what you all have been saying on here. I probably won't get much done with this weekend's full moon.

[ARock]

If you want to keep a log, you can sketch it over a couple of days. In the past I have found the easiest way to do this was to take a screenshot from Stellarium/Sky Safari with a larger FOV, and then mark on it over time either through some picture editing application, or by a pen on a printout of the screenshot. Here is one for Asteroid Florence from a few years ago.

[OzEclipse]

[mention]jrkirkham[/mention], [mention]ARock[/mention] , [mention]dcrowson[/mention]

Rob, Dan, ARock

Rather than centring on the asteroid and have all the field stars moving, I suggest find an observing window when it passes near an easily identified star and photograph the same star field day after day. Then you can animate the asteroid motion through the same registered starfield.

Ceres is quite bright - mag 7. You could pick in up with a short lens in a few seconds exposure.

For example late next year, Ceres undergoes its retrograde inflexion in early October and loops right past Aldebaran and through the horns of Taurus. The attached screen shot shows the path through Taurus from August to December with the field of a 135mm lens framing the shot centred on Omega Tauri.

This image shows Ceres with a 300mm lens field and centred on Aldebaran.

Ceres at around mag 7 will record within a few seconds in a 135 f2.8 or even f4 lens, even from a suburban sky. So this is something that could be done on a fixed tripod but the camera angle and field alignment is more easily handled on an EQ mount.
The problems I foresee would be:-

• Bad weather interfering with sequences of nightly imaging.

• Varying background lighting levels from varying lunar phases

Cheers

Joe

[jrkirkham]

The November issue of Astronomy Magazine mentions that Ceres will be within 1 degree of the Helix Nebula from November 18 to 24. That is a 4-10 day moon. If the weather allows I thought that might be a good time to make a try. That also gives me some time to swap my OTA and take some practice runs.

[ARock]

Thats a neat idea to capture the retograde motion by careful framing. I think I can do some of it using my 400mm ST80 clone and a DSLR. Does take some commitment to go through with it over 3 months, but might be well worth it

I was thinking of a quicker setup. Take the top 10 brightest asteroids/dwarf planets currently. FIgure out the RA/Dec on a particular night, call it Night 1. For each of the 10, center on their RA/Dec for night 1, and take a couple of 15 sec shots for each asteroid. Repeat on subsequent nights still centering on the RA/Dec for night 1. I believe I can set up a sequence of Goto and Capture on my DIY mount so I can automate the whole process for all asteroids once I am polar aligned. A few shots taken in case of imperfect shots. Same camera angle position for each asteroid for minimum change. The FOV is about 3x5 degrees. Even if centered for 1st night , the asteroids should be in frame for 3-5 nights no matter the camera angle and their direction of motion. Process and combine the pics for each asteroid into an animation to see the asteroids move. At the end of the week you have images for all 10.

[jrkirkham]

I like the idea of using the RA/Dec from the first night for all the shots. It will take good polar alignment. I am terrible at polar alignment.

[OzEclipse]

I like the idea of using the RA/Dec from the first night for all the shots. It will take good polar alignment. I am terrible at polar alignment.

Rob,
I use a bright green pointing laser mounted in a very smooth altaz jig at the top of the pole facing tripod leg. Using a pair of 7x35mm binoculars, I point the laser at the pole. There are two stars 7th & 8th mag and if you point the laser between them and a little to the side to make a very squat isosceles triangle, the laser is pointing within a couple of minutes of the pole.




Next I lower the polar axis below my latitude. I eyeball the side of the mount so it is pointing roughly the same direction as the laser. I get on the polar finder and scan across until I see the beam then wind the altitude up until the centre cross of the finder is pointing at the end of the beam.

Voila! Near perfect alignment. After the mount is assembled, it only takes 4-5minutes to get the jig and binos from the car, attach to the mount, point the laser and complete alignment of the mount. I built the laser jig 2 years ago and it never fails if the scope is set up on solid ground. If on soft ground, it can slowly sink in after alignment. But this sinking problem applies to any type of polar alignment.

There is an article on my web site about it.
https://joe-cali.com/astronomy/astropho ... index.html

Unfortunately, there are no suitable bright stars to use near the pole in the northern hemisphere. Stars near the north celestial pole are mags 9.5-11. You will need to use bigger binoculars or a small spotting scope to point the laser but in principle, the technique could still work. The advantage of my 7x35 binos is they are light enough to hold in one hand while I point the laser with the other.

Cheers

Joe