Exploring the Antarctic sky: Dome A’s astronomical endeavors in 2024 and beyond
The atmosphere at Dome A is characterized by extreme cold and aridity. Temperatures during the polar night often drop below −70°C, accompanied by negligible wind speeds. Stable atmospheric conditions ensured continuous sky observations for 3 months.
The astronomical seeing parameter refers to the blurring of stellar images caused by the Earth’s atmospheric turbulence. The typical values at the best mid-latitude sites, such as Mauna Kea, Hawaii, are around 0.6–0.8". Dome A exhibits a minimum seeing value of 0.13" at an elevation of 8 m above ice-cold ground, with a median value of 0.31". When positioned at a height of 14 m above the ice ground, values of less than 0.3" were observed approximately 49% of the time. Moreover, Dome A offers stable atmospheric inversions and prolonged clear polar nights that persist up to 83% of the time, accompanied by low average wind speeds measuring just 3.8 m/s.1 These characteristics collectively indicate that Dome A offers exceptional observing conditions within the optical band called "quasi-space." This can be attributed to its frozen tenuous atmosphere and tranquil polar nights.
Water vapor renders the terrestrial atmosphere opaque within frequency bands in the range 0.3–15 THz. The global average precipitable water vapor (PWV) value is approximately 25 mm; however, in Dome A, during winter months, this value plummets to a mere 0.1 mm, with potential daily averages dropping as low as 0.025 mm—one-fifth the typical winter PWV observed at the Atacama Large Millimeter/Submillimeter Array site.2 Consequently, Dome A presents an exceptional opportunity for conducting conventional terahertz far-infrared astronomical and atmospheric observations on Earth.
The average annual temperature of Dome A is −56°C, which significantly reduces the atmospheric background heat radiation and enhances the detection depth of astronomical observations in the infrared band. The sky-brightness measurements in J, H, and Ks bands at Dome A are 600–1,100, 1,100 and 2,600, and 200–900 μJy arcsec−2, respectively.3 Compared to other observation stations in low-latitude and high-altitude areas, the sky brightness at Dome A exhibits a significant reduction in the Ks band. This finding suggests that Dome A is an exceptional site for conducting Ks-band astronomical observations.
On polar days, the atmosphere in this region is tenuous and pristine, with a dim daylight background luminosity. Utilizing a newly installed J-band infrared telescope, we quantified that the zenith noontime J-band background brightness decreased below six magnitudes per square arcsecond in January. This enabled us to observe bright targets even during polar days.
