Night Sky Quality Monitoring Report

Yosemite NP, California

Pothole Dome, September 1, 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: Monitoring site on north side of summit, away from a grove of trees to southwest. Definitely darker than Sentinel Dome. Broad glow evident to west and southwest, Fairview Dome and other peaks to the south obscure Fresno, also in the Milky Way. Pipe nebula visible but not distinct, possibly due to Fresno lights. Pretty clear, some smoke to south. Gegenschein visible in late evening. Seeing very good.
Site Name	Pothole Dome
Longitude	-119.39367
Latitude	37.88067
Elevation (m)	2692
Date (UT)	September 1, 2005
Time Start (UT)	4:18:22
Data Quality	Excellent
Equipment	SBIG 50mm f/2 6084
Observers	D.Duriscoe
Air Temp (°F)	52
Rel Humid (%)	44
Wind Sp (mph)	5
CCD Temp (°C)	-20
Exp (seconds)	15
Bortle Class	3
ZLM	6.8

SKY BRIGHTNESS DATA

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	4:18:22 4:39:18	0.175	0.041	21.97 21.84	-6.98	-6.41	20.03	22.19	PAN HEMI
2-Start End	5:18:29 5:39:22	0.171	0.042	21.42 21.14	-7.06	-6.51	20.02	22.01	PAN HEMI
3-Start End	6:18:33 6:39:21	0.167	0.040	21.39 21.40	-7.22	-6.68	20.01	21.72	PAN HEMI

LIGHT DOME DATA

City	Distance (km)	Azimuth	1st Data Set Brightness (mags)	Image
Fresno, CA	127	196.3	-0.11
Modesto, CA	143	260.6	-2.93
Stockton	168	274.0
Sacramento, CA	197	293.4
Reno, NV	188	348.7	0.67
Total			-3.12