Update UT1 - UTC dec06
10dec06
UT1 - UTC (DUT1) is used to convert
from UTC to UT1. This is needed for pointing the telescope.
The Earth orientation dept. of the USNO publishes the measured and predicted
values for DUT1. A fit is done to the "future" values and then
used for the pointing. It is stored in the file : /home/online/vw/etc/Pnt/utcToUt1.dat
.
The last fit was done jan06 when the
leap second was installed. New data was loaded 07dec06 and refit. The plots
show the Dut1
fit error from the jan06 fit and the new fit (.ps) (.pdf):
-
Page 1 Err jun06-dec06: The top plot shows the actual dut1
value (black) and the value used for pointing (red) for jun06 to
dec06. The vertical scale in time in seconds. The bottom plot shows the
pointing error caused by this time difference. On 07dec06 it was about
2.7 arc seconds. The error is that same as tilting the platform in the
east/west direction. This would be a pointing error with a 1az dependence.
-
Page 2 shows the new fit using projected data 07dec06 to
01jul07. Top: Black is the data and red is the fit. Center and bottom plots
show the fit error in mjd and date. The rms fit error is 5.8 milliseconds.
After jul07 the fit diverges so we should redo the fit sometime in june.
We will probably redo it after the painting of the platform when the a
new pointing model is made.
The new fit was installed
10dec06 around 20:00 (after the x102)
processing: x101/061207/plotdut1.pro
page up
home ~phil