Standard star position errors (Skillman)

From my catalog, I took the celestial ra/dec errors and calculated the average position error (on-the-sky) and the one sigma variation about that average.

Group mean error (arcmin) sigma (arcmin) number of stars

1 1.53 0.64 4

2 2.04 0.69 5

3 1.43 0.93 12

4 1.50 0.74 75

5 1.34 0.83 638

I used an iterative technique that, over just two iterations, was able to bring many more standard stars into comparison with each other. This produced a much more even error distribution. As an example, and as shown on an earlier page, I was able to tie one standard star (deltaLeo) to 14 other standard stars, thus significantly improving my confidence in its position.

Groups 1 through 4 are the 100 standard ('primary') stars, Group 5 is the remainder of the catalog. On my earlier pages I refer to the Group 5 stars as my 'secondary' stars.

I was able to perform this iterative approach because I had modern computer spreadsheets that could bring much more computational power and accuracy to my data. Tycho had no such tools at his disposal. I'm sure he would have used such an approach if the task had not been so hand-computationally intensive.

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