Seeing

We appreciate the cooperation by the observers in performing the "AG Focus Check" three times during a night. It takes from 5 to 10 minutes to complete each AG Focus Check. This procedure provides the best focus as well as a historical record of image quality of the telescope and atmosphere above Mauna Kea.

Updates

Seeing statistics

Following table shows median seeing sizes.

Month	Median(arcsec)	Average for 2000-2008
January 2008	0.780	0.719
February 2008	0.816	0.741
March 2008	0.731	0.744
April 2008	0.750	0.659

Clear sky ratios

Following table shows monthly clear sky ratios.

Month	Clear sky ratio(%)	Average for 2000-2008
January 2008	68	72
February 2008	62	69
March 2008	63	60
April 2008	62	74

Distribution of seeing

The seeing FWHM measured from the Auto Guider during focus checks has been compiled for the period of May 2000-October 2006. Measurements were made three times ( before 21:00; Orange, 21:00-26:00; Green, after 26:00; Blue ) each night.

There is a trend that the seeing improves during the night. There are several possible explanations for this behavior:

1. Some heat from the daytime remains inside the enclosure
2. Instabilities in the upper atmosphere after sunset
3. The primary mirror temperature control is optimized for 26:00 and it might be over-cooled in the early evening

Seeing size since January 1999

Monthly Average Seeing Size

Clear sky ratio since May 2000

Monthly Average Clear sky ratio