1. LSST Sky Brightness Model Peter Yoachim University of Washington LSST All Hands 2016

2. Components of the night sky
Twilight (sunlight scattered by the atmosphere)
Zodiacal (sunlight scattered by solar system dust)
Moon (lunar light scattered by atmosphere)
Airglow (atmosphere continuum)
Upper and lower atmosphere (line emission)
Scattered starlight
Function of airmass only (mostly)
Included in ESO sky brightness model
LSST sky model takes and RA, Dec, MJD (and optionally stellar activity), and returns either an optical-IR spectra or 6 LSST mag/sq arcsec values

3. Components
What the resulting components look like at one time snap shot
Sun is low enough that there is no twilight. This is R-band, lower atmosphere is only in IR.
Model is mostly geared for optimizing the scheduler.

4. 30 second exposures through the night in R,G,B Bayer filters
Canon All-Sky Camera
off-the-shelf Canon camera with an equal-area-projection fisheye lens operating at the LSST site. Operating for ~1.5 years
30 second exposures through the night in R,G,B Bayer filters
SExtractor on each clear frame returns ~2,000 stellar magnitudes and sky background values
42,000 images, generating 91 million sky brightness observations
All-sky camera installed and operated by Michael Coughlin and Chris Stubbs

5. Sun setting
Select frames with the moon down, and median sky brightness values in healpixels to eliminate clouds.
Note, this probably leaves a little bit of zodical light at low sun altitudes.

6. Simple Functional Fit

7. 4 parameter fit to the twilight! (per filter)
Simple Functional Fit
12-degree twilight
brightness
Linear in sun alt
Linear in airmass
Cos and airmass-term in
direction of sun
4 parameter fit to the twilight! (per filter)

8. In the Future
Would like to have an all-sky camera that can generate a full transparency map
Need to verify model in y-band, especially off zenith
Predict motions of clouds
Do we need to include additional parameters in sky model (temperature, pressure, season, time-of-night)?
Gemini is looking at their archival data to get sky brightness data