HPWREN Cameras Used to Demonstrate the Effects of Light Pollution

By Robert Quimby

Director, Mount Laguna Observatory

Professor of Astronomy

San Diego State University

September 28, 2021

I have created a short video comparing the views of the stars from the HPWREN cameras on Mt. San Miguel (overlooking the San Diego–Tijuana metropolitan area) and at the Mount Laguna Observatory (44 miles east of downtown San Diego). The videos are intended to show that while the same stars shine over both sites, the sky glow from city lights strongly obscure the stars above Mt. San Miguel. The night sky is much darker at Mount Laguna Observatory, but the city sky glow is still quite noticeable to the eye on the horizon. Its effects are also detected by the observatory's sensitive instruments even at zenith.

Click on the image to watch the video.

The panning effect employed in the video was created by combining images from the four wide-angle cameras at each site, which together cover a full circle. Using the known positions of stars above the horizon, I was able to create a mapping function to convert between (x, y) coordinates in the image plane and (azimuth, altitude) angles. I used this mapping to re-project the HPWREN images onto new views centered on any azimuth and altitude angles I chose. The panning effect was then made by combining images from the cameras in different cardinal directions and changing the central azimuth for the new view in each video frame.

Separately, I have also added a video to my time-lapse astronomy collection with a focus on the Moon. This video also features the HPWREN cameras at the Mount Laguna Observatory.

Click on the image to watch the video.