Night Sky Quality Monitoring Report
Yosemite NP, California
Sentinel Dome, September 9, 2005
To effectively manage any resource, we need to know what we have and what we've lost. "Light Pollution", the brightness in the nighttime sky due to artificial light, can be seen from almost every park. The NPS has developed a system for measuring sky brightness to quantify the source and severity of light pollution. This system, developed with the assistance from professional astronomers and the International Dark-sky Association, utilizes a research-grade digital camera to capture the entire sky with a series of images. Data clearly shows that even remote national parks are not immune from stray artificial light. Sky brightness is measured in astronomical magnitudes in the V-band, abbreviated as "mags". The V-band measures mostly green light, omitting purple through ultraviolet and orange through infrared. The magnitude scale is a logarithmic scale. A difference of 5 magnitudes corresponds to a 100x difference in brightness. Lower values (smaller or more negative) are brighter. Further information on astronomical magnitudes can be found on this Sky and Telescope webpage. Data images are shown in false color, with yellow, red, and white corresponding to brighter sky and blue, purple and black corresponding to darker sky.A more detailed explanation is available.
| Category | Details | Image |
|---|---|---|
| Park | YOSE |
 Narrative: Sky appears brighter than on 9/7/2005 from airglow or higher light pollution levels, gegenschein not visible, sky to south looks bright to 45 degrees above the horizon. Very clear, steady, but with occasional smoke episodes in early evening, settling later to below summit. Milky Way to south washed out significantly by Fresno light dome. Very steady, faint stars near zenith easy to detect. A wonderful site for Astronomy because of the excellent seeing conditions, night after night.
|
| Site Name | Sentinel Dome | |
| Longitude | -119.58426 | |
| Latitude | 37.72316 | |
| Elevation (m) | 2478 | |
| Date (UT) | September 9, 2005 | |
| Time Start (UT) | 5:18:22 | |
| Data Quality | Excellent | |
| Equipment | SBIG 50mm f/2 6084 | |
| Observers | D.Duriscoe, N. Nicholas | |
| Air Temp (°F) | 48 | |
| Rel Humid (%) | 41 | |
| Wind Sp (mph) | 17 | |
| CCD Temp (°C) | -20 | |
| Exp (seconds) | 15 | |
| Bortle Class | 4 | |
| ZLM | 6.8 |
| Data Set Number | Time (UT) | Extinction Coefficient (mag/air-mass) |
Std Err Y Extinction Stars (mags) |
Zenith (mag/sq arc-sec) |
Whole Sky (mags) |
Sky Above 20° Altitude (mags) |
Brightest (mag/sq arc-sec) |
Darkest (mag/sq arc-sec) |
Links to Sky Maps |
|---|---|---|---|---|---|---|---|---|---|
| 1-Start End |
5:18:22 5:39:18 |
0.146 |
0.041 |
20.96 21.20 |
-7.63 |
-6.96 |
19.47 |
21.54 |
PAN HEMI |
| 2-Start End |
6:18:31 6:39:25 |
0.189 |
0.046 |
21.13 21.16 |
-7.66 |
-7.06 |
19.85 |
21.39 |
PAN HEMI |
| 3-Start End |
7:18:38 7:39:38 |
0.158 |
0.046 |
21.34 21.50 |
-7.60 |
-6.92 |
19.37 |
21.62 |
PAN HEMI |
| 4-Start End |
8:18:49 8:39:52 |
0.159 |
0.042 |
21.63 21.68 |
-7.42 |
-6.71 |
19.38 |
21.78 |
PAN HEMI |
| City | Distance (km) |
Azimuth | 1st Data Set Brightness (mags) |
Image |
|---|---|---|---|---|
| Fresno | 106 | 190.1 | -4.74 |
 |
| Merced | 93 | 239.5 | -3.24 | |
| Modesto | 125 | 267.2 | -3.79 | |
| Stockton | 154 | 280.8 | ||
| Sacramento | 190 | 300.1 | -2.78 | |
| Reno | 203 | 354.2 | 1.05 | |
| Total | -5.45 |