The BVRcIc sky brightness of the Caucasian Mountain Observatory of MSU

TL;DR

This study analyzes the increase in night sky brightness at the Caucasian Mountain Observatory from 2014 to 2024, attributing the rise mainly to light pollution and solar activity, with implications for observational astronomy.

Contribution

It provides a comprehensive analysis of sky brightness changes over five years and identifies light pollution and solar activity as key factors influencing these changes.

Findings

Sky brightness increased by 0.7 mag in B and V bands over five years.

Light pollution from nearby cities accounts for up to 85% of brightness increase.

Growing role of LED lamps in light pollution observed.

Abstract

In this paper we analyse the measurements of the brightness of the night sky above the CMO SAI MSU in the visible and near-infrared range made in 2019-2014. In 2023-2024 the median zenith brightness of the moonless night sky was 21.31 mag in the B band, 20.63 mag in the V band, 20.15 mag in the Rc band, and 19.11 mag in the Ic band. In 5 years the sky brightness had increased by 0.7 mag in B and V, by 0.45 mag in Rc, and ~0.1 mag in Ic. We found that the brightness growth is mostly (up to ~85%) due to the increasing light pollution from nearby cities, while the remainder can be attributed to the increase of solar activity after the 2019 minimum. We discuss how the sky brightness is influenced by such factors as the airmass and the location of the Sun and the Moon in the sky. A qualitative analysis of the sky emission spectrum has demonstrated the growing role of LED lamps in light pollution. These changes in sky brightness which are only going to get harder favour observations that are less sensitive to the degree of light pollution - IR photometry and spectroscopy and high-resolution optical spectroscopy.