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Old 18-11-2011, 05:52 PM
astrospotter (Mark)
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astrospotter is offline
Join Date: Jan 2010
Location: San Jose, CA, USA
Posts: 146
On simple drawings and tiny object size estimation

First of all Hello SteveG and I think I know who you are ...

I am only now transcribing some field recordings of Abell Planetaries
and assorted Herschel 2 list objects and ran across a case where I
wish I had drawn a crude drawing (yet again). I was trying to describe in words the position of 5 stars in and around Abell 75 so that if one of them were the central star I could then say that it had been noted. I have no idea if one of them was it or not.

Well due to not having a drawing and perhaps poor DSS image back home
I for the life of me cannot figure out what the heck I was talking about.
The observation was from 3am on the 3rd day of a big star party (CalStar in California, USA) so perhaps fatigue caused the description to 'suffer' as well.

Some of my Australia trip from a year and a half ago were also rather difficult to follow. Ever try to verbally describe with some detail the area around the keyhole nebula? Or the whole Eta Car nebula for that matter. Difficult to do with words, very complex but amazing just the same and I hope I get back there again in a year or two.

Anyway, a little drawing sure would prove useful when the description takes more than 20 words or so.

I have heard SteveG in the past discuss the trick of mentioning size relative to nearby stars in the field for tiny objects and that was a nice tip to be sure.

Besides that great set of tips Steve mentions I'll add a tiny bit about one way to increase accuracy on length measurements I tend to use. I'll often bring an object to the edge of the field keeping in mind where I felt it's edge was when it was in the center. I bring it to the side of the view so it's main axis (if elongatted) is radial towards the center then a measurement that is a fraction of the half-field-of-view is noted. This method breaks down when the object is really small. I favor a 7mmNagler or 5mmNagler and the 7 gives about an 18' diameter of fov. So down to 1' is about where it breaks down in accuracy.

Another thing is I have stopped doing the math in my head on fov (too many 3am stupid math errors) and instead I now always note fraction of field of view in my field descriptions to recorder. Then I have a chart (got tired of calculator/head) and this chart is a spreadsheet with eyepieces along the left and across the top I write 1 2 3 ... 20 for the fraction (denominator) So for 7mm 1/8fov I later when transcribing say just that but use square braces and in those place the calculated value which for me I find 7 on the left and 8 on the top and drop down and get 2.21'. Of course before I got lazy I would run the math for 17.7'/8 but I find the spreadsheet printed on a paper at my desk is far more easy to lookup than fumbling with a calculator as I transcribe my recordings.

Anyway, I am sure it is the SteveG I am thinking of, rest assured that he knows basically all 'of the tricks' (or at least 10x more than I will every know).
Mark (Hint to SteveG: I am Marko)

Last edited by astrospotter; 19-11-2011 at 03:15 AM. Reason: Adding a small tip on measuring object length
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