Quote:
Originally Posted by mithrandir
What does "In the 1-sigma zone" mean?
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Hi Andrew,
All predictions have a have a degree of uncertainity due to the position of the occulting body and the star. The first zone of uncertainity is called the 1-Sigma, the next 2-Sigma and so on.
For this event, the star position is not actually derived from UCAC2 or 3 or whatever, it is defined by "The Rio Group" as coordinated by Bruno and is considered to be better than UCAC? because the astrometry is more recent. Also the position of Nix is based on offsets from Pluto that is also determined by Bruno. However for observational purposes we can use the UCAC2 number stated.
The predictions of Bruno have a higher accuracy than those determined via the latest Pluto ephemeris and UCAC?. This is shown by the Pluto positive observed in New Zealand earlier in the month. Using the standard methods, the shadow path was not predicted to cross the earth, but the observed positive was within the stated uncertainty of Bruno's prediction.
Anyway... below is a plot from Occult Watcher that shows the 1-Sigma.