NGC7023

Weather

The QSO Team records weather conditions every night of the year. Our logs indicate that:

  • Averaged over the last 5 years (semesters 19A to 23B), each instrument lost between 24% and 30% of the time to weather. The loss was generally due to high extinction (clouds), high humidity or fog, or high winds. The loss for a given run can be as low as 0% or as high as 40-50%.
  • Over the last 5 years, between 18% and 37% of the time was lost each semester for all instruments.
  • Averaged over the last 5 years, for all instruments, 26% of the time was lost to weather.

The graph below shows that there can be significant variations from year to year.

Hours per night

Taking into account the average time lost to weather and time used by overheads (e.g. slewing the telescope and initiating the guiding), the effective average number of hours per night for each instrument is:

  • MegaCam: 5.0 hours/night
  • Wenaokeao: approximately 7.0 hours/night

Image quality

The following plot compares the Image Quality (seeing) as measured by MegaCam in the r and the u band with the seeing measured by the Mauna Kea Atmospheric Monitor (MKAM) located on a tower between the CFHT and Gemini osbervatories. MegaCam measurements were corrected for the airmass and wavelength. The wavelength corrected applied follows a lambda^0.6 relationship. The seeing is generally well below 1 arcsec but does vary over time.

In the plot below, the u band data has been offset by 0.25", which represents the offset measured with MegaCam between the r and the u bands. The r band and u band data now overlap.