Night Sky Quality Monitoring Report

Yellowstone NP, Wyoming

Old Faithful Water Tank, September 15, 2004

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	YELL	Narrative: NOTE: THIS SITE IS CLOSED TO THE PUBLIC. Very damp, frost forming on filter requires heating between data sets. First data set 40% clouds, decreasing to 20% for second and third, low clouds moving fast. Very dark, virtually no light domes seen, only very subtle reflections against clouds. When clear, great detail in Milky Way. Lights of Old Faithful very annoying, ruin night vision. Site at water tank (closed to public), will eventually become obsolete as lodgepole pines grow up blocking horizon. Seeing very good, transparency very good when clouds part. Would be excellent site if not for glare of unshielded lights, occasionally reflecting off clouds.
Site Name	OLD FAITHFUL
Longitude	-110.83207
Latitude	44.45205
Elevation (m)	2308
Date (UT)	September 15, 2004
Time Start (UT)	3:33:59
Data Quality	Fair
Equipment	SBIG 50mm f/2 6084
Observers	D.Duriscoe, C.Duriscoe
Air Temp (°F)	33
Rel Humid (%)	80
Wind Sp (mph)	1
CCD Temp (°C)	-20
Exp (seconds)	15
Bortle Class	4
ZLM	6.9

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	3:33:59 3:54:36			21.53 21.32	-7.27	-6.71	19.61	21.81	PAN HEMI
2-Start End	4:07:43 4:28:20	0.133	0.053	21.12 21.17	-7.25	-6.72	19.49	21.72	PAN HEMI
3-Start End	4:41:27 5:02:06	0.135	0.062	21.34 21.35	-7.22	-6.66	20.41	21.73	PAN HEMI

LIGHT DOME DATA

City	Distance (km)	Azimuth	1st Data Set Brightness (mags)	Image
Total			-3.99