Seasonal and Yearly Variations of Atmospheric Extinction Coefficient at Campus Station of Chungbuk National University Observatory from 2005 to 2007

Abstract

Systematic CCD observations of times of minimum lights for eclipsing binaries has been carried out from 2002 to 2007 at Campus Station of Chungbuk National University Observatory which is located in Cheongju city, Korea. As a by-product of our observations, photometric data for stars in CCD images taken from 2005 to 2007 were used to determine 1st order atmospheric extinction coefficient (hereafter AEC) and seasonal and yearly variations of the AECs were studied. Total nights used for determination of AECs were 57 days in 2005, 51 days in 2006, and 63 days in 2007. As a result the annual mean value of the AECs per air mass is calculated as 0.34m ± 0.18m for 2005, 0.38m ± 0.19m for 2006, and 0.45m ± 0.20m for 2007. These values show that the AECs and their standard deviations are two and four times, respectively, larger than those of normal observatories which are not located near large cities. Annual comparison between concentration of atmospheric fine dust and coefficient of atmospheric extinction show strong correlation between two quantities of which time variations show similar patterns. The AECs for the east sky show larger than those for the west sky. It can be easily understood by the reasonable possibility that air pollutants remain more in the east sky than in the west because the east area of Cheongju city has been more developed than the west one. In conclusion the atmospheric extinction of the night sky of Cheongju city has an annual trend of increase of 0.06m airmass^{-1} year^{-1} implying that it may take only about 13 years for Cheongju city to have 2 times brighter night sky than the present one. Our study highlights that variations of AEC can be used as an important indicator of air pollution to monitor night skies.

Keywords

• CCD observations
• atmospheric extinction coefficient
• atmospheric fine dust