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REVIEW 4 major objections 4 minor 4 references

Dangerous dust clouds above lunar surface

T0 review · 4 major / 4 minor · reviewed 2026-08-10 · deepseek-v4-flash

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Pith's one-line read The paper argues that dense, global circumlunar dust clouds appear intermittently, reach hundreds of kilometers, and can slow a lander on a low orbit enough to crash it within a day.

desk verdict A genuinely new statistical look at centuries of Earth-based lunar observations, but the crash-risk numbers rest on a circular calibration and need to be treated as illustrative, not quantitative. read the letter →

arxiv 2501.16402 v1 pith:R5RRZCC3 submitted 2025-01-27 physics.space-ph astro-ph.EP

Oleksiy V. Arkhypov , Maxim L. Khodachenko This is my paper · ORCID
classification physics.space-phastro-ph.EP
keywords lunardustcircumlunarcloudsannularMoonstellaroccultationsexospherespacecrafthazardsolartideslevitation
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

Drawing on Earth-based observations spanning three centuries, including dark bands on occulted planets, anomalously long stellar occultations, and the rarely seen annular Moon, this paper argues that dense global clouds of sub-micrometer lunar dust form from time to time and reach altitudes of hundreds of kilometers. If those historical sightings are real dust, modern spacecraft have simply not been observing long enough or low enough to catch them. The paper estimates that the densest of these clouds would give a low-orbiting lander less than a day before drag collapse at altitudes below 10 km, which the authors connect to the failures of Vikram, Beresheet, and Hakuto-R M1. It also finds a 14.77-day periodicity in dust appearance, implicating solar-tide-modulated lunar outgassing as a second dust source alongside meteoroid impacts. This matters because it changes the assumed risk environment for near-future landing and crewed missions.

What carries the argument

The central mechanism is the vertical dust-density profile $n_d(z) = n_0 \exp(-z/h)$, an exponential falloff with scale height $h$. The scale height is linked to grain mass through $h = C/m_d$, with $C = 1.52\times 10^{-13}$ kg m fixed by setting the finest grains (about 0.1 $\mu$m diameter) to the average annular-Moon altitude of 116 km. A visibility argument for the annular Moon, requiring the scattered column brightness to exceed the lunar ashen-glow brightness by a factor $K$ between 1.1 and 10, plus Mie cross-sections at wavelength 0.5 $\mu$m, fixes the column density and hence $n_H$ and $n_0$. Finally, spacecraft drag is computed with $T_c \approx g_M M_{sc} h / (m_d n_0 S V_M^3) \,(\exp(Z_0/h) - 1)$, which converts the inferred dust densities into crash times.

What would settle it

A direct dust-density measurement from a low orbiter during a confirmed annular Moon event would settle the claim: the model predicts $n_d$ rising smoothly to $n_0 \approx 10^8\,\mathrm{m}^{-3}$ at the surface for roughly 0.1 $\mu$m grains, whereas a thin-shell or much lower profile would show a sharp cutoff and far lower densities below the luminous layer. A dedicated high-cadence survey of stellar occultations over two or three years could independently test the predicted 14.77-day periodicity.

Watch

Extended reading notes

Core claim

The paper's central discovery claim is that dense circumlunar dust clouds have been observed from Earth for centuries but were misattributed to a lunar atmosphere, and that these clouds are a real, intermittent hazard. Using the annular Moon geometry, the authors infer that dust-scattering envelopes occupied altitudes from roughly 8 km up to 438 km in 23 documented cases. Combining those heights with Mie scattering and a brightness-matching condition for naked-eye visibility, they derive dust number densities of about $n_H \sim 10^7\,\mathrm{m}^{-3}$ at the 108 km shadow edge and $n_0 \sim 10^8\,\mathrm{m}^{-3}$ at the surface for grains smaller than about 0.16 $\mu$m. With an assumed exponential vertical profile and a scale height $h = 116$ km calibrated to the average annular-Moon altitude, the drag calculation gives crash times below 0.12 day for a lander entering a low ($<10$ km) orbit. The paper also claims that the appearance statistics show an annual peak during the Perseid meteor season and a second peak at 14.77 days, and that the reconstructed limb cloud has a two-lobed impact-plume shape, pointing to both meteoroid impacts and solar-tide-triggered outgassing as sources.

Load-bearing premise

The whole danger estimate rests on assuming the dust density falls off exponentially with altitude with a single scale height calibrated from the average altitude of annular-Moon sightings; if the luminous dust is actually a thin layer or shell, or the scale height is much larger near the surface, the inferred surface densities near $10^8\,\mathrm{m}^{-3}$ and crash times near 0.12 day do not follow.

Editorial extensions

If this is right

  • Global dust clouds capable of scattering sunlight have been seen repeatedly over 300 years, so their absence from modern in-situ data reflects limited sampling rather than absence of the phenomenon.
  • Low pre-landing orbits below about 10 km can become dangerous during dense fine-dust episodes, giving a lander less than a day before drag-induced crash; this offers an explanation for several recent lander failures.
  • The reconstructed cloud shape, with two lobes near 45 degrees incidence, matches an impact plume with a hollow cone, supporting meteoroid impacts as the dominant dust source.
  • The 14.77-day periodicity in dust sightings indicates a non-impact source, lunar outgassing modulated by solar tides, which should be included in future exosphere models.
  • Parking orbits near 100 km are comparatively safe for fine dust but not for larger grains above about 0.4 $\mu$m, so orbit selection and mission timing interact with the dust-cloud phase.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • A testable extension follows: if the solar-tide mechanism is right, dust-cloud sightings should cluster near the first and third quarters of the lunar month, a prediction a future optical monitor could check within one or two lunations.
  • If the inverse correlation with sunspot number really reflects solar-wind pickup and removal of dust, the hazard should be strongest around solar minimum, which overlaps with several scheduled near-Moon missions.
  • The same extinction and occultation method could be applied to other airless bodies in the Solar System, and to exoplanet transit anomalies, where dusty circumplanetary material may produce analogous signatures.
  • Because the calibration anchors surface density to a visible-brightness threshold, the crash-time numbers are effectively lower bounds: events too dim to produce an annular Moon could still fill low altitudes with drag-inducing dust.
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Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

4 major / 4 minor

Summary. The manuscript assembles historical reports from the 18th-20th centuries of lunar-limb phenomena (dark bands during planetary occultations, long-lasting stellar occultations, crescent-horn prolongations, and 'annular Moon' events) together with the modern Lunar Occultation Archive (LOA), and interprets them as evidence of dense circumlunar dust clouds. Using the geometry of Eqs. (1)-(2), it converts observed angular extents into cloud altitudes; using Mie theory and an assumed exponential vertical density profile, it estimates dust concentrations and derives spacecraft crash times. The central claim is that global clouds of sub-micron dust with surface concentrations around 1e8 m^-3 occur occasionally, reach altitudes of hundreds of km, and could crash a vehicle on low (<10 km) orbits, plausibly explaining the Vikram, Beresheet, and Hakuto-R M1 failures. The paper also reports annual (meteor-shower) and 14.77-day (solar-tide/outgassing) periodicities and an anti-correlation with solar activity.

Significance. If correct, this would overturn the current picture of a tenuous, locally confined lunar dust exosphere and would have direct engineering consequences for lunar landers and low orbiters. The paper's strengths are its broad compilation of otherwise-forgotten historical observations, its use of a large machine-readable occultation archive, and its explicit, testable formulas linking observable optical signatures to dust columns and crash times. The claimed 14.77-day periodicity and the association with outgassing regions are novel and would merit follow-up. However, the quantitative hazard estimate rests on a small number of visually reported annular-Moon events and on a vertical profile calibrated from the same events, so the numerical concentrations and crash times are not yet established; the qualitative warning may survive, but the specific numbers in Figs. 17-18 should be treated as scenario-dependent.

major comments (4)
  1. [Section 4.1, Eqs. (3), (8), (9), (14)] The scale-height calibration is circular. The constant C in Eq. (9) is fixed by adopting h_max = 116 km, which in turn is identified with the average altitude <H> = 108 km of the annular-Moon events in Table 4 and with a 1-arcmin naked-eye resolution limit. However, H from Eq. (1) is a geometric visibility threshold (the minimum altitude at which scattering dust closes the crescent along a tangential line of sight), not an e-folding scale height of n_d(z). Using H to calibrate h and then using Eq. (8) to infer n_H at the same H makes n_0 = n_H exp(H/h) and the crash time T_c in Eq. (14) depend on the very events they are supposed to explain. The authors should obtain h from an independent constraint (e.g., LADEE/Apollo vertical profiles or plume-expansion modeling) or present a sensitivity analysis over plausible h(z), including non-exponential and detached-shell profiles.
  2. [Section 2.1.2, Figs. 4-5] The claim that 418 long-lasting occultations with 0.1 < tau <= 8.6 s are caused by lunar dust is not uniquely supported. Unresolved close double stars can produce blended occultation events with durations of seconds, and the paper's statement that 'the duration of event does not include to the time between the occultations of each companion' is not sufficient, because a close binary below the resolution limit can appear as a single prolonged fade. The O-C residual test in Fig. 5 excludes a dominant role of terrestrial clouds, but it does not discriminate between stellar duplicity and circumlunar dust. Please quantify the expected number of unresolved binaries among the 418 events and, if possible, redo the analysis using only events with known single-star status or with consistent multi-station observations.
  3. [Section 3.4, Fig. 13c] The 14.77-day periodicity, central to the proposed solar-tide/outgassing source, is based on a histogram of inter-event intervals for long-lasting occultations, without any formal significance test. The one-day sampling peak and the annual modulation are strong confounders, and a peak at half the synodic month could arise from the window function or from harmonics of the 29.53-day lunar illumination cycle. A Lomb-Scargle or bootstrap periodogram with false-alarm probabilities, applied to the individual event times rather than to interval histograms, is needed before this periodicity can be used as evidence for a non-impact dust source.
  4. [Section 5 and Figs. 17-18] The conclusion that the modeled dust clouds 'could crash a space-vehicle at the low (<10) km orbits, similar to the incidents with landers Vikram, Beresheet and Hakuto-R M1' goes beyond what the analysis demonstrates. No contemporaneous dust observations or forensic data tie those specific lander failures to dust impacts; the paper only notes their malfunction altitudes. The association should be framed as an illustrative scenario, not as a demonstrated cause, and the crash-time curves should be recomputed with a range of independent vertical profiles, as requested above.
minor comments (4)
  1. [Section 3.1] The phrase 'this information limits the timescale of an annual Moon between ~2 and 24 hours' should read 'annular Moon'.
  2. [Section 4.1] In the discussion of the low-altitude crash time, the text refers to 'Figure 9b'; the intended reference appears to be Fig. 18b.
  3. [Eq. (14)] The notation M_sc = rho_sc S^{3/2} with S = 1 m^2 should state explicitly that the plotted crash times apply to a vehicle with an areal density of 100 kg/m^2 and that scaling to other cross-sections uses the quoted sqrt(S/1 m^2) factor.
  4. [Tables 1-4] Many entries have reconstructed times and observer locations (e.g., 1882/-/- in Table 4); it would help to mark reconstructed entries with a flag or superscript and to state the estimated uncertainty in H arising from the time and location reconstruction.

Circularity Check

1 steps flagged · score 5.0 of 10

Low-altitude dust density and crash time are extrapolated from an exponential profile whose scale height is calibrated to the same annular-Moon altitude the model explains; the quantitative danger claim is partly constructed from that identification.

  1. fitted input called prediction [Section 4.1, Eqs. (3), (4), (8), (9), (14); Fig. 17]
    "averaging the listed in Table 4 minimal heights H of the illuminated dust, estimated with Eq. (1), which enable the light ring closure around dark side of the lunar limb, providing γ = 90o, gives ⟨H⟩ = 108 km. On the other hand, the fact of visibility of an annular Moon in the sky with a naked eye gives approximately the same height of 116 km... Therefore... we finally adopt as an average scale height of a global circumlunar dust cloud, the value h = hmax = 116 km and obtain from Eq. (9) the constant C = m_min h_max = 1.52×10−13 kg m."

    Scale height h is not independently measured; it is set equal to the annular-Moon visibility threshold H from the same Table 4 events. Eq. (1) defines H as a geometric minimum altitude for closing the crescent, not an exponential e-folding length. The model then uses this h in Eq. (8) to compute n_H at H and converts to n_o = n_H exp(H/h); with h≈H this gives n_o≈e n_H, i.e., the surface density is the visibility column density rescaled by the same threshold. Eq. (14) then uses n_o and h for the crash time. The low-altitude dust density and T_c therefore reduce to the choice h=H rather than to independent profile data; using the paper's own smaller h=14.5 km changes n_o and T_c by orders of magnitude.

full rationale

Most of the paper is a compilation of historical reports and statistical analyses (LOA occultation durations, annual and 14.77-day periodicities, limb distribution), which are independent of the fitted model. The Mie-scattering brightness estimate, the periodicities, and the impact-plume shape reconstruction are not circular. However, the quantitative risk estimate in Section 4.1 has a structural circular component: the scale-height constant C is calibrated by equating h_max to the average H from the same annular-Moon events, and the same H/h ratio then enters n_o = n_H exp(H/h) and Eq. (14). The cited Apollo (100-120 km) and LADEE detections provide some independent support for high-altitude dust, and the visibility factor range 1.1<K<10 is explicitly acknowledged, but these do not independently constrain the low-altitude exponential extrapolation. No load-bearing self-citation was found; the Arkhypov et al. references are only contextual. The qualitative existence of high-altitude dust is supported, but the specific <10 km crash-time claim is substantially fixed by the assumed h=H identification, so a partial circularity score of 5 is appropriate.

Assumptions & free parameters 4 free parameters · 7 assumptions · 0 invented entities

The central risk estimate rests on several unverified domain assumptions: historical reports are genuine lunar dust, LOA long-duration occultations are dust rather than binaries or Fresnel effects, and an exponential, mass-dependent vertical profile is calibrated to the same annular-Moon dataset used for concentrations. The paper notes some of these uncertainties but does not benchmark the assumptions against independent measurements.

free parameters (4)
  • visibility factor K = 1.1 to 10 (dimensionless)
    In Eq. (8), K sets the minimum brightness of an annular Moon relative to ashen light and linearly controls n_H and all derived concentrations and crash times; it is chosen as a reasonable excess factor rather than measured.
  • scale-height calibration constant C = 1.52e-13 kg m
    Defined by C=m_min*h_max in Eq. (9), where h_max=116 km is adopted from the average annular-Moon altitude in Table 4 and from eye resolution, Apollo, and LADEE reports. This constant sets h(d) for all grain sizes and therefore the exponential dust profile used in crash-time estimates.
  • dust grain minimum diameter and density = d_min=0.1 micron, rho=2500 kg/m^3
    Sets m_min=1.3e-18 kg and all grain-size-dependent densities and drag times. The grains are assumed to be spherical, transparent glass with refractive index 1.5 in the Mie calculations.
  • plume optical depth tau = 0.1 to 1
    In Eq. (17), an assumed detectability range converts the long-occultation extinction into plume dust concentration n_d, which then sets the single-flyby altitude loss in Eq. (18).
assumptions (7)
  • domain assumption Long-duration stellar occultations (tau>0.1 s) in the Lunar Occultation Archive are caused by circumlunar dust extinction, not by unresolved double stars, Fresnel diffraction, or recording artifacts.
    Invoked throughout Section 2.1.2 and Figures 4-5. The paper tests and rejects terrestrial clouds via O-C residuals, but it does not quantify double-star or Fresnel contributions.
  • domain assumption Historical visual reports (hazy Saturn, dark bands, cusp prolongations, annular Moon) are genuine observations of lunar dust rather than optical illusions, atmospheric effects, or misprints.
    Used to build Tables 1-4. Some dates and locations are corrected post hoc, such as the Gruithuisen 1838 to 1839 correction, and many reports are anecdotal.
  • domain assumption The vertical dust concentration follows an exponential/Boltzmann profile n_d(z)=n_0 exp(-z/h), with h inversely proportional to grain mass.
    Equations (3) and (9) in Section 4.1. This profile is adopted from earlier lunar dust models and extrapolated to derive surface density and crash time.
  • domain assumption Mie scattering by transparent glass spheres with refractive index 1.5 at lambda=0.5 micron represents lunar dust scattering.
    Used for sigma_s and Phi(theta) in Eq. (8). Lunar dust is irregular and absorbing, so this is an idealized scattering model.
  • standard math The lunar orbital speed V_M=1.022 km/s converts occultation duration into geometric cloud thickness L.
    Used in Section 3.2. This assumes the dust cloud is stationary relative to the Moon and that the line of sight is perpendicular to the occultation trajectory.
  • domain assumption Lunar outgassing sites correspond to ancient volcanic regions such as Mare Orientale, Mare Smythii, and Mare Marginis.
    Section 3.4 and Figure 15. This assumption supports the non-impact source interpretation of the 14.77-day periodicity.
  • domain assumption The 14.77-day periodicity in occultation intervals reflects solar tidal modulation of lunar outgassing.
    Section 3.4 and Figure 13c. This is an interpretation not independently tested against observing-window sampling or a null model.

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Cite this review

Pith. "Pith review of Dangerous dust clouds above lunar surface." pith.science (2026). https://pith.science/paper/R5RRZCC3

@misc{pith2026250116402,
  author       = {Pith},
  title        = {Pith review of: Dangerous dust clouds above lunar surface},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/R5RRZCC3}},
  note         = {Machine review of arXiv:2501.16402}
}
read the original abstract

Time-limited space missions may miss rare occurrences of very dense clouds of lunar dust. At the same time, the information provided by the Earth-based monitoring of the Moon during at least the last three centuries still remains unused. In the present study, we fill this data analysis gap. The survey of historical reports of the 18-19 centuries about supposed lunar atmosphere manifestations, as well as the available data on too long-lasting stellar occultations by the lunar limb, enable us revealing numerous evidences of the lunar dust phenomena. By modeling of the conditions of such observations, we determine the geometrical parameters of the dust clouds, which scattered the sunlight during the particular events. Using this information, as well as the Mie scattering theory, we estimate the concentration of dust and its damaging effect at different orbits of a possible spacecraft. It was found that the some observed dust clouds of sub-micron grains could crash a space-vehicle at the low (<10 km) altitudes, similar to the incidents with landers Vikram, Beresheet, Hakuto-R M1, Luna-25, etc. The statistics of dust clouds' appearance enabled a reconstruction of a typical shape of a local dust cloud which resembles the shape of an impact plume. This, together with the revealed seasonal periodicity of observational manifestations of the dust phenomena, confirms a hypothesis on the meteoroid impact nature of the majority of the circumlunar dust clouds. At the same time, the discovered additional periodicity of the dust cloud appearance at half of synodic lunar month argue for an additional non-impact source of the circumlunar dust, connected with the lunar outgassing events, controlled by the solar tidal effects, completely unstudied. Moreover, the tendency of dust clouds to be observed during the low-level solar activity raises a question on possible dust pick up by the solar wind flow.

Figures

Figures reproduced from arXiv: 2501.16402 by the authors.

Figure 1
Figure 1. Sketch of a hazy view of the Saturn during its emergence from behind the dark side of the Moon on 17 June, 1762 (Dunn 1762) [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Examples of old reports on the dark band, seen above the lunar limb in the Jupiter background: (a) the jovian occultation on January 2, 1857 (Simms 1857); (b) the immersion of the Jupiter on August 7, 1889, as it was seen by W. Wickham at Radcliffe Observatory in Oxford, using 3.25 inch Marlborough telescope (Stone 1889); (c) and (d) the Jupiter appearance (emergence) on August 7, 1889, as it was seen by W.H. Robins… view at source ↗
Figure 5
Figure 5. [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗
Figures from the paper (14 more)
Figure 4
Figure 4. Figure 4: Duration time 𝜏 of the stellar occultations, extracted from the Lunar Occultation Archive (Herald et al. 2022): (a) the total histogram of log(𝜏); (b) the distribution of log(𝜏) estimates versus the occultation axis angle 𝜙, counted eastwards in the terrestrial sky fro…
Figure 7
Figure 7. Figure 7 [PITH_FULL_IMAGE:figures/full_fig_p009_7.png]
Figure 6
Figure 6. Figure 6: Lunar horizon glow seen from the Earth: (a) the prolongations of the lunar crescent horns on June 17, 1912 (Stolyarenko 1912); (b) the short ledges near the cusps of the solar crescent during the eclipse on September 29, 1875 (Noble 1875);(c)the long ledges near the cu…
Figure 8
Figure 8. Figure 8: Reconstruction of the lunar zodiacal light seen on April 3, 1874, at 22:15 UT in Cambridge (Massachusetts) according to the report of observer; L. Trouvelot (Corliss 1985). The virtual planetarium software Stellarium 1.2 was used for the reconstruction. MNRAS 000, 1–??…
Figure 9
Figure 9. Figure 9: shows the lunar projection onto the Sun-Moon￾observer plane. The point O is the lunar center, which is projected onto lunar cusps, i.e., the intersections of the terminator and the limb line (i.e., of the visibility horizon). Let us to find the altitude of the edge of …
Figure 10
Figure 10. Figure 10: a shows the distribution of the value ⟨𝜏⟩, versus the incidence angle 𝑖, averaged over a sliding window of 𝛿𝑖 = 20o width. This diagram is constructed only for the anomalously long￾lasting (𝜏 > 0.1 s) occultations, which are associated with the lunar dust clouds. One …
Figure 11
Figure 11. Figure 11: ""Supposed volcanic eruption on the Moon" on November 13, 1878, as it was presented by the U.S. Naval Observatory (Rodgers & Hammer 1878; No. 208 in Cameron 1978). In particular, a "light fountain" of 162 km height in the Aristarchus region at terminator has been phot…
Figure 13
Figure 13. Figure 13: Histograms of time intervals Δ𝑡 between successive stellar occul￾tation events available in LOA: (a) for all occultations, including also those with the measured 𝜏; (b) for the long-lasting occultations with 𝜏 ⩾ 0.1 s only; (c) same as in panel (b), but with a higher …
Figure 15
Figure 15. Figure 15: Regions (red ellipses) of an increased occurrence probability of the listed in the LOA long-lasting occultation events seen in Fig. 14c. The top and bottom panels show the eastern and western hemispheres of the Moon, respectively. In both cases, North pole is at the t…
Figure 14
Figure 14. Figure 14: Distribution of the long-lasting stellar occultation events from the LOA with 𝜏 ⩾ 0.1 s, averaged in a sliding window of 𝛿 𝜙 = 20o width, versus the occultation axis angle 𝜙: (a) the number of long-lasting occultations 𝑛 in the sliding window; (b) the occurrence proba…
Figure 16
Figure 16. Figure 16: Distributions of the observed dust clouds’ manifestations versus the daily total sunspot number 𝑊: (a) the histogram of all available mani￾festations in Tables 1-4 (the duplicates of the same dates are excluded); (b) the distribution of occurrence probability 𝑃 for th…
Figure 17
Figure 17. Figure 17: shows the parameters of dust cloud revealed with the above described model. As it can be seen in Fig. 17b, the annular Moon phenomenon requires at a typical height 𝐻 ≡ ⟨𝐻⟩ = 108 km of the lowest visible level of the dust cloud (according [PITH_FULL_IMAGE:figures/full…
Figure 18
Figure 18. Figure 18: A spacecraft crash time 𝑇𝑐, according to Eq. (14), for the initial altitudes 𝑍0 = 100 km (green) and for 𝑍0 = 10 km (red). The colored ranges correspond to the confidence intervals between the curves calculated with the adopted minimal and maximal values of the visibi…
Figure 19
Figure 19. Figure 19: Effect of a typical impact plume with 𝐿 = 1 km, manifested in the long stellar occultations: (a) an average value of dust concentration 𝑛𝑑 in the plume for an assumed reasonable range of its optical thickness 0.1 ≲ 𝜏˜ ≲ 1 providing detectability of the phenomenon; (b)…

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Works this paper leans on

4 extracted references · 4 canonical work pages

  1. [2]

    ThedarklineIthoughtatfirstarosefromthe intervention of a fine rim of the dark body of the Moon, but this couldhardlybethecasetowardstheterminationoftheoccultation

    in parallel with the lunar limb on the Jupiter background during the grazing occultation on November 7, 1856. One of the observersexplained:" ThedarklineIthoughtatfirstarosefromthe intervention of a fine rim of the dark body of the Moon, but this couldhardlybethecasetowardstheterminationoftheoccultation " (Grove 1856). During the next jovian occultation o...

    work page 2023

  2. [4]

    Correspondingly, the surfacevaluesofdustconcentrationforthegrainsize 𝑑 ≲ 0.16𝜇m (log 0.16≈− 0.79) appear𝑛o∼ 108 m−3, as shown in Fig

    the concentration of dust𝑛H∼ 107m−3. Correspondingly, the surfacevaluesofdustconcentrationforthegrainsize 𝑑 ≲ 0.16𝜇m (log 0.16≈− 0.79) appear𝑛o∼ 108 m−3, as shown in Fig. 17c. This is∼ 103 times higher than an estimate based on the Apollo measurements (McCoy 1976). However, such a great difference between the estimates of surface dust concentration does n...

    work page 2023

  3. [1839]

    9" as "8

    Moreover, quite indicative is that F.P. Gruithuisen began his systematic search for the lunar twilights only in 1840, i.e., two years after his, mentioned above, first observation of the horns prolongation in 1838. Therefore, it is highly likely that the actual date of the lunar twilight observation reported by F.P. Gruithuisen was April 16, 1839, whereas...

    work page 2023

  4. [1856]

    a dark line was plainly perceptible

    was seen, or "a dark line was plainly perceptible" (Grove

    work page

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