J- and H-band sky brightness measurements from polar day to polar night at Dome A, Antarctica

Near-infrared (NIR) sky brightness is a fundamental parameter for evaluating the performance of ground-based infrared observatories. Dome A on the Antarctic plateau offers exceptional atmospheric conditions, yet its NIR sky background has not been continuously monitored. We present the first continuous J- and H-band measurements of the sky background at Dome A from polar day to polar night and characterize their median levels and temporal variability. The Antarctic Infrared Binocular Telescope (AIRBT), operating in the J and H bands, obtained continuous fixed-pointing observations from February to May 2024, which were used to measure the NIR sky background. The median sky brightness is 5.2/2.9 and 15.3/13.4 in the J and H bands during daytime and nighttime, respectively. The twilight--nighttime boundaries occur at solar elevations of -9.3^̧irc in J and -7.4^̧irc in H. At the same solar elevation, the NIR sky background during the polar night is darker by about 0.1 and 0.4 in the J and H bands compared to the regular day--night alternation period. During the polar-night period, the nighttime sky brightness in the H band shows a more evident association with the sunspot number, while the corresponding trend in the J band is weaker. mag arcsec^ -2 mag arcsec^ -2 These results reveal systematic differences in the sky background between the polar and nonpolar environments and between polar night and regular day--night cycles. The measured sky brightness may be elevated, as the observations were conducted near solar maximum, highlighting the importance of long-term monitoring across the solar cycle.