Night Sky and Lightscape Monitoring in the Golden Gate National Recreation Area

Night skies over the San Francisco Bay, showing the illuminated bay bridge and Alcatraz.
While Golden Gate may be affected by artificial light from nearby urban population centers, it still serves as a harbor of dark skies for nocturnal wildlife and park visitors alike.

NPS / Alison Taggart-Barone

Why is the Night Sky Environment Important?

Light pollution, the brightness in the night sky due to artificial light, hides natural light at night, such as the stars and the Milky Way. Artificial light from park facilities, nearby development, and visitors can all contribute to light pollution. The nighttime lightscape affects visitor experience and preservation of historic and cultural landscapes.

Also, darkness levels and the availability of natural nighttime light also impact ecosystems. Having artificial light present at night can affect animal behavior and physiology. Lighting can influence foraging, reproduction, communication, orientation, and navigation*. This is especially true for nocturnal wildlife and insects. These changes can offer advantages to some species and not others. Ultimately, this disrupts the normal balance of ecosystem food webs.

What Do We Monitor?

The National Park Service has developed a system for measuring sky brightness to quantify light pollution. This system, developed with help from professional astronomers and the International Dark‐Sky Association, uses a research‐grade digital camera to capture the entire sky with a series of images (see figure 1 for an example). This enables researchers to compare current lighting conditions with estimates of natural levels. The first baseline data for Golden Gate was collected in 2008.

Panoramic image of all (natural and anthropogenic) sources of light as observed from Panorama Hwy at Golden Gate NRA in 2008.
Figure 1. Panoramic image of estimated artificial light as seen from Golden Gate's Panorama Highway in 2008. Researchers used highly sensitive photographic equipment to identify sky glow from human light sources. White and red represent higher levels of artificial light, while blues and black represent lower levels. Images with less anthropogenic light may display celestial objects like stars or the span of the Milky Way.

NPS

Why Do We Monitor Night Skies?

  • To detect changes and trends in levels of light pollution at Golden Gate

  • To compare Golden Gate's dark sky resources with those of surrounding areas

  • To assess dark sky resources across different areas within Golden Gate

How Do We Use the Monitoring Data?

  • To inform strategic park-wide lighting plans aimed at improving dark sky resources
  • To inform coordination with neighbors and partners for reducing artificial light
Regional view of artificial light near Golden Gate National Recreation Area.
Figure 2. Regional view of artificial light near Golden Gate National Recreation Area. White and red represent higher levels of artificial light, while blues and black represent lower levels. While Golden Gate may be affected by artificial light, it still maintains more natural darkness than surrounding areas.

NPS

What Have We Learned?

Data show that no parks, however remote, are immune to stray artificial light. Golden Gate's night sky quality is heavily impacted by light from neighboring cities and towns. At average light levels across the park, the Milky Way is only visible when it is directly overhead. The nighttime sky generally appears discolored, and shadows from lights in the sky or along the horizon are obvious. Generally, these effects are more severe in areas of the park with more artificial light and less clear in areas with less artificial light. Areas that retain unperturbed nighttime darkness are rare.

Still, Golden Gate provides important coastal habitat for nocturnal wildlife, and a unique opportunity for millions of people to learn about night sky resources. The park protects these nocturnal habitats and viewing opportunities through continued monitoring. It also offers overnight camping and lodging and guided night sky programs to help visitors experience a taste of the awe that night skies can offer.

Last updated: July 23, 2018