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.

All the seeing values shown here are for the zenith at wavelength of 0.73 ± 0.08 μm. The values have been converted from those sampled at various elevations mainly around 70 degrees with the auto guider camera. Overall median seeing from May 2000 through April 2008 is 0.639 arcsec.

Updates

Due down time of the telescope for recoating of the primary mirror and other tasks, statistics for August and September 2010 are not available. Statistics for October 2010 will be published in November 2010.

Updated plots will be published later.

Seeing statistics

Following table shows median seeing sizes for recent months.

MonthMedian(arcsec)Average* for 2000-10/11
January 20110.6540.720
February 20110.7610.679
March 20110.5850.741
April 20110.5790.661

*The values are average of the median for respective months within the years indicated.

**Statistics for July, August, and September are not available due to shutdown of the telescope for primary mirror recoating.

Clear sky ratios

Following table shows monthly clear sky ratios.

MonthClear sky ratio (%)Average* for 2000-
April 20137972
March 20135360
January 20116474
February 20116369
March 20116260

*The values are average of the ratio for respective months within the years indicated.

**Statistics for July, August, and September are not available due to shutdown of the telescope for primary mirror recoating.

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

Overall distribution of seeing

The plot below shows distribution of seeing from all the samples we have taken since May 2000.

Seeing size since January 1999

Monthly Average Seeing Size

Clear sky ratio since May 2000

Monthly Average Clear sky ratio

Change in assignment of engineers

As of January 2009, Subaru Telescope assigned a new engineer to make the statistics due to retirement of the engineer who has been making the statistics available for the past 10 years. Due to the new assignment, there might be a change in statistics because of possible difference in selection measurements into statistics. Please refer the results from November 2008 through February 2009 shown below to evaluate the possible change.

Seeing statistics

Overall median seeing from May 2000 through April 2008 is 0.639 arcsec. Following table shows median seeing sizes for recent months.

Calculated byFormer engineerNew engineer
MonthMedian(arcsec)Average* for 2000-2008/09 Median(arcsec)Average* for 2000-2008/09
November 20080.7450.6500.7380.637
December 20080.5740.7280.5830.729
January 20090.7940.7280.8220.639
February 20090.8570.7540.8210.658

*The values are average of the median for respective months within the years indicated.

Clear sky ratios

Following table shows monthly clear sky ratios.

Calculated byFormer engineerNew engineer
MonthClear sky ratio (%)Average* for 2000-2008 Clear sky ratio (%)Average* for 2000-2008
November 200861697470
December 200846694669

*The values are average of the ratio for respective months within the years indicated.


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