The Night Sky Spectrum of Xinglong Observatory: Changes from 2004 to 2015

TL;DR

This study analyzes 12 years of spectroscopic data from Xinglong Observatory, revealing light pollution effects and a slight increase in sky brightness, emphasizing the need for ongoing monitoring to support astronomical research.

Contribution

It provides a comprehensive long-term spectroscopic analysis of the night sky at Xinglong Observatory, highlighting changes in light pollution and sky brightness over a decade.

Findings

Sky brightness increased by about 0.5 mag arcsec^-2 from 2004 to 2015.

Light pollution from Beijing is more significant than from other directions.

Artificial emission lines from Hg I and Na I are present alongside atmospheric lines.

Abstract

We present spectroscopic measurements on the night sky of Xinglong Observatory for a period of 12 years from 2004 to 2015. The spectra were obtained on moonless clear nights using the OMR spectrograph mounted on a 2.16-m reflector with a wavelength coverage of 4000-7000A. The night sky spectrum shows the presence of emission lines from Hg I and Na I due to local artificial sources, along with the atmospheric emission lines, i.e., O I and OH molecules, indicating the existence of light pollution. We have monitored the night sky brightness during the whole night and found some decrement in the sky brightness with time, but the change is not significant. Also, we monitored the light pollution level in different azimuthal directions and found that the influence of light pollution from the direction of Beijing is stronger compared with that from the direction of Tangshan and other areas. An analysis of night sky spectra for the entire data set suggested that the zenith sky brightness of Xinglong Observatory has brightened by about 0.5 mag arcsec -2 in the V and B bands from 2004 to 2015. We recommend consecutive spectroscopic measurements of the night sky brightness at Xinglong Observatory in the future, not only for monitoring but also for scientific reference.