Astrometry Residuals

Introduction

Residuals are a means of measuring performance and accuracy.  There are various types of residuals.  For Astrometric purposes there are Plate Solve Residuals, Object Pre Fit Residuals and Object Post Fit Residuals.  Put VERY simply;

Plate Solve Residual is a measure of 'best fit' in RA and Dec of an image.  It is the average error of the measure of all reference stars used to 'solve' the image.

Pre Fit Residuals relate to the position and orbit solution fit to a set of measured points from two or more images for a given object in those images. (ie ones own measured positions fit to an orbit solution based on ones own data)

Post Fit Residuals relate to the measured position's fit to an orbit solution determined for the object from all measured position sources. (ie ones own measured positions fit to the MPC's orbit solution)

Typically my optical train is setup to image at 1.69"/pixel resolution (the 0.25m scope was setup at 2.02"/pixel resolution).  Given the nature of the optics used my images suffer from a certain amount of spherical aberration which affects the plate solution.  However, that said, on an average night (seeing around 4", little wind) I expect to get +0.09" RA and Dec on the 0.35m scope.   (The 0.25m scope suffered adversely from spherical aberration and the best I could average was +0.15" RA and +0.25" Dec plate solve residuals).

My Post fit residuals (the ones that really count) are measured by CFA at Harvard and can be seen in the table below.  Benchmark comparisons are also provided.  704 is LINEAR, a professional automated survey scope and J95 is Greater Sheffield Observatory, an amateur run observatory similar to mine.  The residuals are measured in Arc Seconds. 

What this all means is that I would expect that the precision of my observations will continue to improve.  As you can see, they have continued to improve each year.

COD  Year     Tot   <1"   <2"   <3"   <4"  >=4"   R.A.             Decl.
E14  2005     31    30     1    0     0    0    -0.08 +/- 0.35   -0.00 +/- 0.21
E14  2004    552   494    53    4     1    0    -0.10 +/- 0.44   -0.09 +/- 0.46
E14  2003    931   795   125   11     0    0    +0.07 +/- 0.52   -0.01 +/- 0.52
E14  2002     94    65    18    5     6    0    -0.18 +/- 0.74   +0.08 +/- 1.08

704 2004/07 110586 81661 25897 2536 492    0    -0.09 +/- 0.60   +0.31 +/- 0.63
704 2003/09  50908 36749 12837 1163 159    0    -0.14 +/- 0.59   +0.38 +/- 0.62

J95  2004   1492  1242   224   20     6    0    -0.04 +/- 0.55   -0.08 +/- 0.54
J95  2003   1858  1586   251   18     3    0    -0.04 +/- 0.53   +0.04 +/- 0.51
J95  2002    884   664   178   34     8    0    -0.02 +/- 0.75   +0.01 +/- 0.64

● Email Me: higginsdj at bigpond dot com ●