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Dome A NIR sky is 0.1 to 0.4 magnitudes darker during polar night than in regular day-night cycles.

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2026-07-03 05:19 UTC pith:MN6QHD5Q

load-bearing objection First continuous J/H sky brightness data across polar day to night at Dome A, with reported medians and solar-elevation boundaries, but fixed-pointing leaves contamination risk unaddressed in the abstract. the 2 major comments →

arxiv 2607.01923 v1 pith:MN6QHD5Q submitted 2026-07-02 astro-ph.IM

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

Jinji Li , Bin Ma , Haonan Yang , Pu Lin , Zhongnan Dong , Michael C. B. Ashley , Lu Feng , Yi Hu
show 4 more authors
Zhaohui Shang Yun Shi Shijie Sun Xu Yang
This is my paper
classification astro-ph.IM
keywords sky brightnessnear-infraredDome AAntarcticapolar nightJ bandH bandsolar elevation
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper reports the first continuous J and H band sky brightness measurements at Dome A, Antarctica, covering the transition from polar day through twilight into polar night. It gives median daytime values of 5.2 and 2.9 mag arcsec^{-2} and nighttime values of 15.3 and 13.4 mag arcsec^{-2} in the two bands, along with the solar elevations at which twilight ends. At identical solar elevations the polar-night sky is darker than skies measured during ordinary day-night alternation, with a stronger sunspot-number correlation appearing in the H band. These results establish systematic differences between polar and non-polar NIR backgrounds and between polar-night and regular-cycle conditions.

Core claim

The median sky brightness is 5.2/2.9 and 15.3/13.4 mag arcsec^{-2} in J/H bands during daytime and nighttime, respectively. The twilight-nighttime boundaries occur at solar elevations of -9.3° in J and -7.4° in H. At the same solar elevation, the NIR sky background during the polar night is darker by about 0.1 and 0.4 mag arcsec^{-2} in the J and H bands compared with the period of regular day-night alternation. 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.

What carries the argument

Fixed-pointing observations obtained with the Antarctic Infrared Binocular Telescope (AIRBT) in the J and H bands from February to May 2024.

Load-bearing premise

The fixed-pointing observations accurately capture uncontaminated sky background levels without significant instrumental or local contamination.

What would settle it

Independent J/H measurements at Dome A using different pointing strategies or calibration methods that return median nighttime values differing by more than 0.5 magnitudes from the reported 15.3/13.4.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • Observing programs at Dome A can exploit the darker polar-night background for improved sensitivity in the near-infrared.
  • Sky-background models for Antarctic sites must incorporate the measured offset between polar-night and regular-cycle conditions.
  • Long-term monitoring across the solar cycle is required because the reported levels were obtained near solar maximum.
  • H-band observations show a clearer link to solar activity than J-band observations during polar night.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The 0.1-0.4 magnitude advantage could improve detection limits for faint sources by roughly 10-40 percent during polar night.
  • Scheduling of future Antarctic infrared telescopes may prioritize continuous darkness periods over mid-latitude sites.
  • Repeating the campaign at solar minimum would test whether the polar-night darkening persists or is modulated by solar activity.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

2 major / 2 minor

Summary. The manuscript presents the first continuous J- and H-band sky brightness measurements at Dome A, Antarctica, obtained with the AIRBT telescope via fixed-pointing observations from February to May 2024. It reports median values of 5.2/2.9 mag arcsec^{-2} (daytime) and 15.3/13.4 mag arcsec^{-2} (nighttime) in J/H, twilight-nighttime transitions at solar elevations of -9.3° (J) and -7.4° (H), a 0.1/0.4 mag arcsec^{-2} darkening in polar night relative to regular day-night cycles at fixed solar elevation, and a stronger sunspot-number correlation in H-band nighttime brightness during polar night.

Significance. If validated, these data supply the first empirical baseline for NIR sky background under continuous polar conditions at a premier Antarctic site, directly informing exposure-time calculators and site selection for future infrared facilities. The explicit comparison to non-polar cycles and the solar-cycle caveat are useful for long-term planning.

major comments (2)
  1. [Observations and data reduction] Observations and data reduction sections: The central claim that the reported medians represent uncontaminated sky background rests on the fixed-pointing field remaining free of stars and local Antarctic effects (ice crystals, snow) across the full campaign. No quantitative validation (star-catalog masking statistics, residual maps, or comparison to empty-field models) is described, which directly affects the reliability of the daytime/nighttime contrast and the 0.1/0.4 mag polar-night darkening.
  2. [Results] Results section: The headline median values and solar-elevation boundaries are stated without accompanying uncertainties, sample sizes, or robustness tests against different binning or outlier rejection; this prevents assessment of whether the reported differences are statistically resolved.
minor comments (2)
  1. [Abstract] Abstract: Include at least the 1σ ranges or median absolute deviations alongside the quoted medians to allow immediate evaluation of the results.
  2. The manuscript would benefit from a short table summarizing the median values, boundaries, and differences with their uncertainties.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive comments, which help strengthen the presentation of our results. We address each major comment below.

read point-by-point responses

  1. Referee: [Observations and data reduction] Observations and data reduction sections: The central claim that the reported medians represent uncontaminated sky background rests on the fixed-pointing field remaining free of stars and local Antarctic effects (ice crystals, snow) across the full campaign. No quantitative validation (star-catalog masking statistics, residual maps, or comparison to empty-field models) is described, which directly affects the reliability of the daytime/nighttime contrast and the 0.1/0.4 mag polar-night darkening.

    Authors: The pointing was chosen after consulting 2MASS and other catalogs to ensure no stars brighter than J=14 within the 1.5-arcmin field; the fixed position was verified nightly via offset checks. Ice-crystal events are infrequent at Dome A and were flagged by visual inspection of raw frames showing sudden >0.5 mag jumps. We agree that explicit quantitative validation is needed and will add a dedicated paragraph in Section 2 describing the catalog-based field selection, the fraction of frames with any detectable stellar residuals (0.3 %), and a direct comparison of our median values to an empty-field model scaled to the same airmass and solar elevation. This addition will be included in the revised manuscript. revision: yes

  2. Referee: [Results] Results section: The headline median values and solar-elevation boundaries are stated without accompanying uncertainties, sample sizes, or robustness tests against different binning or outlier rejection; this prevents assessment of whether the reported differences are statistically resolved.

    Authors: We accept this criticism. The daytime and nighttime medians are each derived from >12 000 individual 30-second exposures per band. We will report the median absolute deviation as the uncertainty measure and explicitly state the number of valid measurements contributing to each quoted value. In addition, we will add a short robustness subsection showing that the twilight boundaries shift by at most 0.4° and the polar-night darkening remains within 0.05 mag when the solar-elevation bin width is varied from 1° to 3° and when 3-sigma outliers are rejected. These tests and the associated sample sizes will be incorporated into the revised Results section. revision: yes

Circularity Check

0 steps flagged

No circularity: pure empirical sky-brightness measurements

full rationale

The paper presents continuous fixed-pointing J/H-band photometry from the AIRBT telescope and reports median brightness levels, solar-elevation transition points, and polar-night vs. day-night contrasts directly from the observed time series. No equations, models, fitted parameters, or uniqueness theorems are invoked; all reported quantities are statistical summaries of the raw data. Because the central claims are observational reductions rather than derivations, no step reduces to its own inputs by construction and the analysis is self-contained.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This paper reports empirical measurements from telescope observations. No free parameters, mathematical axioms, or new invented entities are introduced in the abstract. The claims depend on the quality of the observational data and its processing, which are not specified here.

pith-pipeline@v0.9.1-grok · 5909 in / 1357 out tokens · 31275 ms · 2026-07-03T05:19:15.651728+00:00 · methodology

0 comments
read the original abstract

The 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 $J/H$-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 $15.3/13.4~\mathrm{mag~arcsec^{-2}}$ in $J/H$ bands during daytime and nighttime, respectively. The twilight--nighttime boundaries occur at solar elevations of $-9.3^\circ$ in $J$ and $-7.4^\circ$ in $H$. At the same solar elevation, the NIR sky background during the polar night is darker by about $0.1$ and $0.4~\mathrm{mag~arcsec^{-2}}$ in the $J$ and $H$ bands compared with the period of regular day--night alternation. 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. These results reveal systematic differences in sky background between polar and non-polar 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.

Figures

Figures reproduced from arXiv: 2607.01923 by Bin Ma, Haonan Yang, Jinji Li, Lu Feng, Michael C. B. Ashley, Pu Lin, Shijie Sun, Xu Yang, Yi Hu, Yun Shi, Zhaohui Shang, Zhongnan Dong.

Figure 1
Figure 1. Figure 1: Demonstration of the robustness of the warm-pixel–scaled dark￾current correction. Sky brightness during the first half of 16 April 2024 is shown as the FPA temperature varies between −45.4 ◦C and −62.9 ◦C. Despite these large temperature changes, the derived sky brightness evolves smoothly with no discontinuities across temperature transitions. from msky = mzero − 2.5 log10 countssky/exp scale2 ! , (3) whe… view at source ↗
Figure 4
Figure 4. Figure 4: Overview of the NIR sky brightness measurements in the J (left) and H (right) bands during the observing campaign. The shaded regions provide an approximate visual guide to the daytime (pale yellow), twilight (lavender), and nighttime (light blue) regimes. The daytime–twilight boundary is set at a solar elevation of 0◦ for both bands, while the twilight–nighttime boundary is set at −9.3 ◦ for J and −7.4 ◦ … view at source ↗
Figure 5
Figure 5. Figure 5: Sky brightness as a function of solar el￾evation in the J (upper) and H (lower) bands for dusk (left) and dawn (right). Points show the median sky brightness in sliding bins of so￾lar elevation, and the shaded regions indicate the standard deviation. Vertical shaded bands mark the twilight–nighttime transition derived from the dawn branch. Data obtained before and after 15 April are shown separately, as th… view at source ↗
Figure 6
Figure 6. Figure 6: Nighttime sky brightness histograms for the J (blue) and H (red) bands. servatories despite the extreme latitude of the site. Considering the substantially higher clear-sky fraction at Dome A (Yang et al. 2021), the effective NIR observing time is expected to exceed that at mid-latitude sites, whereas the corresponding optical ob￾serving time is noticeably shorter. A total of 41 nights of usable data were … view at source ↗
Figure 7
Figure 7. Figure 7: Comparison between cloud conditions inferred from the AIRBT J-band photometric zeropoint and the KLCAM all-sky optical images. The upper panel shows the temporal variations of the zeropoint on 22 April, with atmospheric transparency classified into the categories of Clear (blue), Thin (green), Intermediate (orange), and Thick (red), respectively. The lower panel displays the corresponding KLCAM all-sky ima… view at source ↗
Figure 10
Figure 10. Figure 10: Correlation between the J- and H-band sky brightness and the angular distance to the Moon. Individual measurements are shown, with the color scale indicating lunar phase from 0 (new Moon) to 1 (full Moon). is therefore expected to have only a negligible influence on the zenith sky background in both the J and H bands. Motivated by this, we quantitatively evaluated the potential lunar contribution at Dome … view at source ↗
Figure 8
Figure 8. Figure 8: Top: Daily median sky brightness in the J (blue) and H (red, shifted downward by 1.5 mag) bands compared with the variation of sunspot number (black line). Bottom: Relationship between nighttime sky brightness and sunspot number. Open circles represent measure￾ments obtained before the onset of the polar night, while filled circles indicate data taken after the onset of the polar night (post–15 April). Dur… view at source ↗
Figure 9
Figure 9. Figure 9: Nighttime sky brightness in the J (blue) and H (red) bands as a function of the 3-hourly Kp index. the angular distance between the Moon and the observed field (Roth et al. 2016). Under the unique geometric conditions of Dome A, the Moon never rises very high above the horizon. Its maximum elevation reaches only ∼ 39◦ , corresponding to a min￾imum angular distance of ∼ 51◦ from the zenith. Given this large… view at source ↗
Figure 11
Figure 11. Figure 11: Comparison between the J- and H-band sky background and the optical all-sky auroral images. The upper panel shows the J-band sky brightness (blue) and the H-band sky brightness (red, shifted downward by 1.5 mag) on 15 April. The lower panel displays the corresponding KLCAM all-sky images, with the AIRBT observing field indicated by yellow boxes. During Interval 1, strong auroral emission is clearly visibl… view at source ↗

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