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

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

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.

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

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.

Simple Functional Fit

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)

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