Protecting the Night Sky Resource of Cherry Springs Dark Sky Park

Stan Stubbe and Gary Honis, P.E.

Pennsylvania Outdoor Lighting Council

1. Purpose of Document:

This document was prepared by the Pennsylvania Outdoor Lighting Council (POLC) as a guide and reference for the Pennsylvania Department of Conservation and Natural Resources (DCNR) for use in the protection of the night sky resource of the Cherry Springs Dark Sky Park (CSDSP). In particular, the document addresses environmental considerations in regard to the mitigation of light pollution from the proposed Potter County windfarm.

Details of the proposed windfarm such as location and elevation of wind turbines, type and amount of lighting proposed, and other specifics of the windfarm's design and planned construction activities and support facilities were not made available to the POLC. Lacking technical details of the proposed project, this document was prepared to address all potential impacts to the nighttime environment of CSDSP.

2. Threatened Night Sky Resource of Park

Cherry Springs State Park was designated by DCNR as the first Dark Sky Preserve in the Commonwealth. In 2001, PA House Bill 300, "Outdoor Lighting Control Act", was unanimously passed in the House by a vote of 195-0. The following language was contained in the Bill: "The Department of Conservation and Natural Resources shall identify and designate Cherry Springs State Park in Potter County as a Dark Sky Preserve. The Department of Conservation and Natural Resources shall manage Cherry Springs State Park in a manner to eliminate or prevent light pollution and preserve the exceptional conditions necessary for astronomical observations."

The actions taken by the Commonwealth to protect the night sky resource have been predicated on the realization that this small area of the Commonwealth is the last area remaining in the Commonwealth with a natural night sky. In addition, it is one of only a few areas remaining in the Eastern United States free of light pollution.

The light pollution map of Pennsylvania below is based on nighttime images obtained from the Defense Meteorological Satellite Program and is taken from the map of North America by the Light Pollution Science and Technology Institute:

The small single black spot located in Potter County in the above image represents the skies of Cherry Springs Dark Sky Park and the only area remaining in the Commonwealth of Pennsylvania with a natural night sky free of light pollution and classified at a Level of 2 on the Bortle Scale as described below:

Color	Artificial / Natural Sky Brightness	Sky Brightness mags / sq arcsec V Band	Bortle Scale approx	Description (Descriptions are approximate. Your sky may vary.)
	< 0.01	22.00 to 21.99	1	Gegenschein visible. Zodiacal light annoyingly bright. Rising milkyway confuses some into thinking it's dawn. Limiting magnitude 7.6 to 8.0 for people with exceptional vision. Users of large dobsonian telescopes are very happy.
	0.01 to 0.11	21.99 to 21.89	2	Faint shadows cast by milkyway visible on white objects. Clouds are black holes in the sky. No light domes. The milky way has faint extensions making it 50 degrees thick. Limiting magnitude 7.1 to 7.5.
	0.11 to 0.33	21.89 to 21.69	3	Low light domes (10 to 15 degrees) on horizon. M33 easy with averted vision. M15 is naked eye. Milky way shows bulge into Ophiuchus. Limiting magnitude 6.6 to 7.0.
	0.33 to 1.0	21.69 to 21.25	4	Zodiacal light seen on best nights. Milkyway shows much dark lane structure with beginnings of faint bulge into Ophiuchus. M33 difficult even when above 50 degrees. Limiting magnitude about 6.2 to 6.5.
	1.0 to 3.0	21.25 to 20.49	4.5	Some dark lanes in milkyway but no bulge into Ophiuchus. Washed out milkyway visible near horizon. Zodiacal light very rare. Light domes up to 45 degrees. Limiting magnitude about 5.9 to 6.2.
	3.0 to 9.0	20.49 to 19.50	5	Milkyway washed out at zenith and invisible at horizon. Many light domes. Clouds are brighter than sky. M31 easily visible. Limiting magnitude about 5.6 to 5.9.
	9.0 to 27.0	19.50 to 18.38	6 or 7	Milkyway at best very faint at zenith. M31 difficult and indistinct. Sky is gray up to 35 degrees. Limiting magnitude 5.0 to 5.5.
	>27.0	<18.38	8 or 9	Entire sky is grayish or brighter. Familiar constellations are missing stars. Fainter constellations are absent. Less than 20 stars visible over 30 degrees elevation in brighter areas. Limiting magnitude from 3 to 4. Most people don't look up. CCD imaging is still possible. But telescopic visual observation is usually limited to the moon, planets, double stars and variable stars.

The night sky over CSDSP is one of only a few areas remaining in the Eastern United States that is free of light pollution as shown in the image below. The night skies of CSDSP are depicted in the image as a small black spot.

The above image is testament to why CSDSP is known both nationally and internationally for its pristine night sky resource and why it has been the subject of many news and magazine articles published worldwide. One such 2006 Associated Press article by Dan Nephin, AP writer, has had a circulation of 2.4 Million and impressions of nearly 50 Million over a two-month period:

Date	Media Outlet	Circulation	Impressions
	Associated Press Cherry Springs article
8/12/2006	PhillyBurbs.com (Philadelphia, PA)	N/A	377,786
8/13/2006	Eagle (Reading, PA)	90,856	218,054
8/13/2006	Sunday Times (Scranton, PA)	74,275	178,260
8/13/2006	Altoona Mirror (Altoona, PA)	39,109	93,861
8/13/2006	Mercury (Pottstown, PA)	24,539	58,893
8/13/2006	Sunday Pocono Record (Stroudsburg, PA)	25,830	61,992
8/13/2006	Reporter Sunday (Lansdale, PA)	18,659	44,781
8/13/2006	CentreDaily.com (State College, PA)	N/A	33,782
8/14/2006	Sentinel (Carlisle, PA)	15,072	36,172
8/14/2006	Beford Gazette (Bedford, PA)	10,500	25,200
8/14/2006	Beaver County Times (Beaver, PA)	41,950	100,680
8/20/2006	Tri-County Sunday (DuBois, PA)	12,200	29,280
8/20/2006	Times Herald (Norristown, PA)	16,391	39,338
8/20/2006	Post-Gazette Online (Pittsburgh, PA)	N/A	1,499,184
8/31/2006	The Record Online (Parsippany, NJ)	N/A	42,590
9/11/2006	Yahoo! News	N/A	8,383,046
9/11/2006	Canadian Press	N/A	2,056
9/11/2006	KTVZ-TV Online (Portland, OR)	N/A	N/A
9/12/2006	DenverPost.com (Denver, CO)	N/A	891,720
9/13/2006	ABC News Online	N/A	4,362,505
9/13/2006	Philly.com (Philadelphia, PA)	N/A	1,254,721
9/15/2006	Cecil Whig (Elkton, MD)	17,500	42,000
9/15/2006	Telegram.com (Worchester, MA)	N/A	77,657
9/15/2006	DallasNews.com (Dallas, TX)	N/A	1,169,123
9/15/2006	Post-Gazette.com (Pittsburgh, PA)	N/A	1,499,184
9/16/2006	Free Lance Star (Fredericksburg, VA)	47,925	115,020
9/16/2006	Daily Record (Baltimore, MD)	18,000	43,200
9/16/2006	Canada.com	N/A	1,083,835
9/17/2006	Sunday Voice (Wilkes-Barre, PA)	29,608	71,059
9/17/2006	Sunday Review (Towanda, PA)	10,200	24,480
9/17/2006	Valley News Dispatch (Tarentum, PA)	34,000	81,600
9/17/2006	Centre Daily Times (State College, PA)	33,782	81,760
9/17/2006	Sunday Recorder (Amsterdam, NY)	9,506	22,814
9/17/2006	Sunday Tribune-Review (Greensburg, PA)	107,139	257,133
9/17/2006	Sierra Vista Herald (Sierra Vista, AZ)	12,516	30,038
9/17/2006	Bisbee Daily Review (Bisbee, AZ)	1,205	2,892
9/17/2006	Sun (Yuma, AZ)	25,061	60,146
9/17/2006	High Point Enterprise (High Point, NC)	30,573	73,375
9/17/2006	Paragould Daily Press (Paragould, AR)	6,500	15,600
9/17/2006	Times Daily (Florence, AL)	34,126	81,902
9/17/2006	Beaufort Gazette (Beaufort, SC)	12,036	28,886
9/17/2006	Index-Journal (Greenwood, SC)	14,384	34,521
9/17/2006	Rapid City Journal (Rapid City, SD)	33,599	80,637
9/17/2006	Columbus Dispatch (Columbus, OH)	361,304	867,129
9/17/2006	Sunday Observer (Dunkirk, NY)	15,000	36,000
9/17/2006	Northwest Herald (Crystal Lake, IL)	37,964	91,113
9/17/2006	Herald-Tribune Online (Cincinnati, OH)	N/A	4,000
9/17/2006	Lansing State Journal Online (Lansing, MI)	N/A	N/A
9/18/2006	Herald-Standard Online (Uniontown, PA)	28,765	69,036
9/18/2006	Delaware Online	N/A	287,347
9/18/2006	CNN.com	N/A	20,624,395
9/19/2006	Wilmington Star Online (Wilmington, DE)	N/A	N/A
9/23/2006	Review Times (Fostoria, OH)	42,060	100,944
9/24/2006	Intelligencer (Doylestown, PA)	45,000	108,000
9/24/2006	Burlington County Times (Willingboro, NJ)	44,711	107,306
9/24/2006	Eagle (Reading, PA)	90,856	218,054
9/24/2006	Bucks County Courier Times (Levittown, PA)	73,249	175,797
9/24/2006	Erie Times-News (Erie, PA)	88,622	212,692
9/24/2006	Idaho Press-Tribune (Nampa, ID)	17,816	42,758
9/25/2006	Evening Sun (Hanover, PA)	19,767	47,440
9/25/2006	Eagle Online (Reading, PA)	N/A	64,600
9/25/2006	Courier Post Online (	N/A	80,635
9/29/2006	Staten Island Advance (Staten Island, NY)	67,033	160,879
10/1/2006	Sun (Baltimore, MD)	467,911	1,122,986
10/1/2006	New Haven Register (New Haven, CT)	99,532	238,876
10/1/2006	Scottsdale Tribune (Scottsdale, AZ)	18,429	44,229
10/1/2006	The Providence Journal Online (Providence, RI)	N/A	279,509
10/1/2006	Baltimore Sun Online (Baltimore, MD)	N/A	888,282
10/6/2006	Daily News (McKeesport, PA)	25,000	60,000
10/8/2006	Cleveland Plain Dealer Online (Cleveland, OH)	N/A	463,482
10/8/2006	Asbury Park Press (Asbury Park, NJ)	N/A	310,390
	Total	2,390,060	49,416,642

The unique factors of CSDSP for astronomical use are as follows:

1. Elevation of 2400 feet with 360 degree horizonal views.

2. Located in the only remaining area of the Commonwealth free of light pollution with a night sky rated at a Bortle value of two, on a scale of one to nine.

3. The park is used by members of the astronomical community nationwide with occasional use by international visitors.

3. Visual Astronomy

CSDSP is used throughout the year by amateur astronomers and the general public at night to view celestial objects with the naked eye, telescopes and binoculars. The park is known for its panoramic views of the sky at night and the expanse of the Milky Way stretching across the sky from horizon to horizon. Such views are not available anywhere else in the Commonwealth. Under favorable weather conditions, the night sky of the park is known to provide naked eye views of the stars to the horizon in all directions on the observing field. Use of telescopes and binoculars are used as well to magnify the view of celestial objects near the horizon. Some astronomical events such as the Aurora Borealis (Northern Lights), make appearances close to the horizon. The Aurora Borealis is a celestial event that is most affected by even low levels of light pollution and because of the absence of artificial light, produces spectacular views in the Northern sky from CSDSP.

Light pollution is the most serious hazard to visual observation of faint sources of light from celestial objects. The absence of man-made light visible from CSDSP facilitates excellent dark adaptation. Although the human eye can expand its pupil size within a few seconds of dark, in order for the eye to become dark adapted, chemical changes in the retina involving the eye's rods and cones, need to take place in an area free of ambient light sources. The eye can detect light when certain precursor chemicals are transformed by light to other chemicals. These chemicals in turn cause signals to be sent to the brain representing the image seen by the eyes. The sensitivity of our eyes is directly related to the concentration of precursor chemicals. Even low level ambient light conditions can retard chemical adaptation, and a sudden burst of direct light can break down practically all of the precursor chemicals and ruin the dark adaptation, requiring another period of time for the eyes to dark adapt. For complete dark adaptation there must be no man-made ambient light within the field of view. The human eye may need 30 minutes or longer to dark-adapt, depending on the age of the observer. During the first minute of observing in dark sky conditions, the eye's sensitivity increases ten fold. In 20 minutes it increases 6000 fold and after forty minutes of dark adaptation, the eye's sensitivity increases 25,000 times.

4. Public Programs and Astronomy Education

Astronomy programs are offered to the general public on a regular basis at CSDSP that include nighttime observations and include the following:

1. Telescopic views of the Moon, planets, galaxies, star clusters and nebulae.

2. Tours of the star constellations.

3. Observation of special astronomy events such as meteor showers and comet appearances.

4. Observation in the northern sky of the Aurora Borealis (Northern Lights).

5. Observation of satellite passes.

6. Monthly Stars-N-Parks programs for the public sponsored by the National Public Observatory in New Mexico.

7. Major astronomy events held in June by the Astronomical Society of Harrisburg and in September by Central Pennsylvania Observers.

The park is used throughout the year by amateur astronomers who use telescope and camera equipment to observe and photograph the planets and deep sky celestial objects such as galaxies and nebulae. Long exposure film photographs and images taken by astronomical CCD imaging devices are taken at the park. Such film and CCD exposures can exceed a few hours in length and are extremely susceptible to the effects of light pollution.

5. Astrophotography and CCD Imaging

Light pollution can affect astrophotography and CCD imaging in a number of ways including:

1. Light Pollution causes sky glow, which creates sky fogging of the image that reduces the possible length of the exposure time that can be used to capture the image. Since the resulting maximum exposure time is shortened, this results in a poorer quality image with less detail captured. Sky glow can be severe to the level of causing fainter deep sky objects to be undetectable visually and undesirable to image with film or CCD imaging equipment.

2. Light pollution from a source in one direction can cause a sky fog gradient that appears across the frame of the photograph or image. Such gradients can result in poor or unusable images.

3. CCD imaging devices are highly sensitive to light and combined with lenses and telescopes can capture images of the faintest celestial deep sky objects. Amateur astronomers at CSDSP can now capture images and conduct astronomical studies using CCD imaging devices, o