Asteroid 176-Iduna

[Orion]

I thought it was time to bag another asteroid.  176-Iduna is currently in Aquila, which is an easy constellation to find at this time.  The asteroid is a few degrees to the right of the bright star Altair.  It was a little more challenging  around 13th magnitude.  I found it with a DSLR camera and 70-300 mm zoom lens set at 300 mm, with a 15s exposure at ISO 6400. I'm getting close to the capability of recording Pluto with the same equipment. The camera was mounted on a Star Adventurer mount driven at sidereal rate.  A series of images were taken over about an hour, which might be enough to show movement if zoomed in but I've not checked to see how much it moves.  I'll have to wait and see when I get round to stacking or video making.  It was interesting that a very faint satellite or space junk wandered by and pointed to where Iduna was, but I didn't know if it would transit it.  Line of sight, looks like it possibly would have been a close encounter but I didn't get that shot because of the delay I made to trigger the shutter.  23:35 UT, 19 Aug 2018.

 

Main belt asteroid.

Size ~121 km.

Orbital period 5.69 years.

 

 

 

 

 

 

 

 

 

 

[Tweedledee]

Nice capture Derek. ?

 

Will be interested to see the track over an hour if you get chance to sort it. 

[Orion]

Thanks Pete.  I'll give it a go.  If I upload files, you could have a go. 

[Tweedledee]

If you show me the first and the last capture, and the timings, I'll tell you how far it went. 

 

In the bottom two pics, the 4 brighter stars in the trapezium surrounding the asteroid are 8th to 9th magnitude.

[Orion]

I understand the asteroid is brighter than expected

[Orion]

Pete.  Looking at the images when zoomed in, it doesn't look much relative movement between 00:27:28 and 00:52:26 20/8/2018. You'd probably have to zoom in very close to get the resolution needed to generate the precision for co-ordinate measurement and hence delta RA or delta Dec.  The images may need to be processed a bit to maximise the asteroid position with more certainty.

 

https://we.tl/t-dOxouCqnXe

 

Cropped areas, enhanced.  Movement very subtle.

https://we.tl/t-wemFallIYP

 

[BAZ]

That's an impressive capture Derek.

[Tweedledee]

20 hours ago, Orion said:

Pete.  Looking at the images when zoomed in, it doesn't look much relative movement between 00:27:28 and 00:52:26 20/8/2018. You'd probably have to zoom in very close to get the resolution needed to generate the precision for co-ordinate measurement and hence delta RA or delta Dec.  The images may need to be processed a bit to maximise the asteroid position with more certainty.

 

https://we.tl/t-dOxouCqnXe

 

Cropped areas, enhanced.  Movement very subtle.

https://we.tl/t-wemFallIYP

 

Sorry but I can't make out any movement between the images either.

 

Working from Stellarium, in the time period, the asteroid moved roughly 15 arc seconds.

 

So it is currently moving across the sky at very roughly 30 arc seconds per hour, 12 arc minutes per day.

[Orion]

Thanks for examining the images Pete.  I think your comments on movement in the time period in arc seconds, remind me of a need for me to learn more about resolution, pixel size and quantitatively, by calculation, whether or not it is possible to sense check whether or not a movement can be seen in a given chosen time period, or whether a longer period is needed - e.g. the minimum separation time period needed in order to detect motion. Then add a little longer and I'd know definitely, we'd see motion.

 

Last night, I had another go at Iduna.  Unfortunately the moon was up and there was a lot of illuminated haze. This limited the minimum magnitude (though not looked at the images except at the camera last night).  The images I took showed a pattern of stars around where the asteroid should be, and it was, I'd say, hit or miss whether the asteroid could be seen. There was something there, but it might have been a star.  I won't know until I examine in detail, and stack batches to see if that might improve S/N ratio. 

 

Meanwhile, I attempted asteroids Urania, Athamantis and Hygiea, and in that dreadful haze, an attempt for 13-14th magnitude comet Forbes in Pisces. There were asteroids near the pentagle, and Forbes was conveniently located between two of the main stars on one of the five sides of the pentagle.  I couldn't not take some images whilst I was in that local, and the comet being so well placed for location purposes by star hopping to the area to image.  In the garden, at the camera back, I could pick off stars that were probably 12th magnitude, and a hint of fainter in the region of the comet - on single images.  This requires stacking and all sorts of post processing (that I don't know how) to improve image quality to maximise the chance of detection, or not.  Had there been no illuminated haze, this would have been an excellent opportunity.  I even took some exposures with the lower ISO 400 (for better resolution) but for the equivalent longer time of 2 mins 40 seconds each.  I thought that might have been pushing the unguided driven platform for a 300mm lens, so there may be trailing.  But even if trailed, if the magnitude can be detected down to the comet magnitude or fainter, a trail would still be enough to show detection anyway, if nothing else.

[Tweedledee]

Not knowing the specs of your DSLR, here are a few very rough calculations. I don't think they will be too far out...

 

Your 300mm lens will produce an image scale of 5.24mm per degree. 

 

If the sensor is 22mm wide then the width of your FOV is about 4.2 degrees or 15120 arc seconds. When I compared it to Stellarium I measured it very roughly and got 4.3 degrees.

 

If you have 3900 pixels across those 15120 arc seconds then your resolution is 3.9 arc seconds per pixel.

 

So, if Iduna moved 15 arc seconds from first to last capture, its trail will be less than 4 pixels long.

 

Some of the brighter stars in your image are probably substantially more than 4 pixels across. I suspect with a bit of fuzzyness to the image Iduna could be more than a couple of pixel across. So the trail is going to be difficult to discern.

 

So I'd say you could benefit from a longer focal length to provide greater resolution and longer trails on slow moving objects like this.

Edited August 22, 2018 by Tweedledee

[Orion]

This is excellent Pete.  I can look up the specification of the camera (Canon 1100d) for the sensor and will attempt to follow your calculations.  I am extremely grateful you did this.  

 

I will be able to see how far Iduna moved from the first night imaged (over the period), to last night. I need to check exact dates and times for the second imaging session, which was last night or and early morning today.  Once I sort images from the second session, I can let you have some, and first, see if I had a detection, before then seeing how far it moved. In doing so, I'd learn about the pixel size and resolution.

[Orion]

I do have a GT81 (unsure of it's focal length, I'm guessing about 740 mm, but it has a focal reducer, so that probably reduces the FL when its altogether attached). An 102 mm Ostara f7 refractor. And a 8.75" f5.6 NR - it's not used that often due to the permanent pier too far south at the bottom of the garden, plus, it's too high and I once fell off steps and nearly killed myself). It has a FL of 1297 mm I think.  If conveniently positioned for an given asteroid, I think that would certainly give better resolution used in prime focus mode.  It's on a Fullerscope mount, so not very user friendly compared with today's GOTO like my HEQ5 Pro has.  When I get round to having another go at polar alignment of the Fullerscope, if I could get 30s exposures without trailing, that would probably be all I need.  But I think I'd be more productive with eventually using in a routine fashion, the GT81 (or and Ostara) on the HEQ5 Pro, which would allow guiding to allow digging deeper.

Edited August 22, 2018 by Orion
spelling mistakes

[Tweedledee]

Last night, I spent 3/4 hour on a garden lounger with my binoculars, but as you say, the moon was illuminating haze that blotted out the fainter stuff making it a disappointing observing session. I had intended to get my new 80mm scope out on the AZ8, but didn't bother as the conditions wouldn't have done it justice.

 

Sent you a PM Derek with a spreadsheet showing your FOVs and resolutions using the 1100d with your various scopes and lenses.

Edited August 22, 2018 by Tweedledee

[Orion]

Oh marvelous Pete.  Thanks very much. I'll look forward to using that.

 

[+Derbyshire Dave]

Fantastic capture Derek, really impressive. Hope you are feeling better now..