...
There are three natural timescales involved: a day, a month and a year. At second order there is also the timescale for OH variability that determines NIR sky background.
Relationship between RA, DEC, HA and zenith angle (from Zombeck)
...
| lunar phase\filter | u | g | r | i | z | y4 |
|---|---|---|---|---|---|---|
| 0 | 42 | 89 | 111 | 159 | 218 | 238 |
| 3 | 53 | 107 | 113 | 159 | 218 | 238 |
| 7 | 81 | 160 | 140 | 174 | 224 | 238 |
| 11 | 143 | 280 | 205 | 215 | 242 | 242 |
| 14 | 240 | 474 | 305 | 269 | 263 | 254 |
| (bright/dark) ratio | 5.7 | 5.3 | 2.7 | 1.7 | 1.2 | 1.07 |
| SNR impact~sqrt(sky) | 2.4 | 2.3 | 1.6 | 1.3 | 1.1 | 1.03 |
SDSS cumulative DR1 sky brightness distribution (no bright time imaging...)
The 10% to 90% range in r is 20.6-21.1=0.5 mag=factor of 1.6. The 10% to 90% range in z (OH dominated) is 19.4-18.6=0.8 mag=factor of 2.
Merit Function Ingredients.
...