Lunar Observations Research Articles

Updated inflight calibration of Hayabusa2's optical navigation camera (ONC) for scientific observations during the cruise phase

The Optical Navigation Cameras (ONC-T, ONC-W1, ONC-W2) onboard Hayabusa2 are also being used for scientific observations of the mission target, C-complex asteroid 162173 Ryugu. Science observations and analyses require rigorous instrument calibrations. In order to meet this requirement, we have conducted extensive inflight observations during the 3.5 years of cruise after the launch of Hayabusa2 on 3 December 2014. In addition to the first inflight calibrations by Suzuki et al. (2018), we conducted an additional series of calibrations, including read-out smear, electronic-interference noise, bias, dark current, hot pixels, sensitivity, linearity, flat-field, and stray light measurements for the ONC. Moreover, the calibrations, especially flat-fields and sensitivities, of ONC-W1 and -W2 are updated for the analysis of the low-altitude (i.e., high-resolution) observations, such as the gravity measurement, touchdowns, and the descents for MASCOT and MINERVA-II payload releases. The radiometric calibration for ONC-T is also updated in this study based on star and Moon observations. Our updated inflight sensitivity measurements suggest the accuracy of the absolute radiometric calibration contains <1.8% error for the ul-, b-, v-, Na-, w-, and x-bands based on star calibration observations and ~5% for the p-band based on lunar calibration observations. The radiance spectra of the Moon, Jupiter, and Saturn from the ONC-T show good agreement with the spacecraft-based observations of the Moon from SP/SELENE and WAC/LROC and with ground-based telescopic observations for Jupiter and Saturn. Our calibration results suggest that the 0.7-μm absorption band typically observed on Ch and Cgh asteroids at the ~3–4% level can be detected with the ONC's signal-to-noise ratio (SNR) of ~2. We also demonstrate a decrease in SNR due to CCD temperature increases caused by radiant heat when the spacecraft is close to the surface, as the SNR is measured to be 150 at a CCD temperature of 20 °C (the worst case scenario). Since Ryugu may possess a significant amount of internal volatiles, a sodium atmosphere around Ryugu is considered to be highly plausible. We evaluated the upper limit of detectability of a sodium atmosphere around Jupiter using the Na-filter as 100 R with 100 images. This implies that the ONC-T can detect a sodium atmosphere of several 10s kR based on a single image set of v- and Na-bands and of several 100 s R based on 100 image sets. Finally, we report the first inflight observation of Ryugu by ONC-T from 1.3 × 106 km away on 26 February 2018. The ONC-T v-band photometric observation displays consistency with ground-based observation, which confirms the capability of ONC-T.

A Causal-Pluralist Metatheory of Observation

Abstract An extended definition of “observation” is developed in order to account for the usage in the physical sciences and in neuropsychology. An observation is initially defined as a perception that has a focus of attention and is guided by theoretical considerations. Since the focus may change, one adopts a pluralist position according to which the object of perception may involve any stage of the causal chain that leads to perception, such as the source of light or sound, the obstructions, the medium or even the receptor. The “neutral” observations of the empiricists are seen as involving only low-level or medium-level theorization. Examples are examined, such as a lunar eclipse, the rainbow, and observations mediated by instruments, whose “artifacts” are considered observations of the instrument itself. One also defines null-effect observations. Observations of photographs and drawings may be considered either the observation of a printed sheet of paper or the observation of the pictured object or people. This causal-pluralist metatheory of observation also accepts that one may “observe light”, observe the retina, and observe parts of the brain which are outside the region of the “sensorium”. Illusions and hallucinations are analyzed within this “observational materialism”, which considers that qualia are self-observations of the brain. Criticisms that the approach is too wide in scope are analyzed in the conclusion.

Construction of simulation models of lunar observations

The aim of the present paper is to establish optimal parameters for simulation models of the lunar telescope. Modelling of the observations taken from the surface of the Moon is carried out on the basis of dynamic algorithms describing diurnal motion of stars and specifically designed software modules. The first steps in the development of simulation models were made when planning the ILOM (In-Situ Lunar Orientation Measurement) mission which implied the installation of an optical telescope on one of the lunar Poles. The main task of the project was to observe physical libration of the Moon directly from its surface in order to reveal subtle effects related to the characteristics of internal structure of our natural satellite, including the refinement of the Lava elasticity coefficients, tidal dissipation and dissipation at the core-mantle boundary parameters, core’s size, ellipticity, and its chemical composition. The results obtained in this work allow for the development of lunar physical libration and dynamics theory in order to apply them in the future lunar observations taken with the automated optical telescope.

CASSINI'S 1679 MAP OF THE MOON AND FRENCH JESUIT OBSERVATIONS OF THE LUNAR ECLIPSE OF 11 DECEMBER 1685

On 18 February 1679 Paris Observatory astronomer Jean Dominique Cassini presented a new map of the Moon to the Academy of Sciences in Paris, and this then became the standard reference work for French astronomers who carried out selenographical observations. Among these was a contingent of Jesuit missionary-astronomers who sailed from Brest on 3 March 1685, bound for China. <italic>En route</italic> they were forced to spend some months in Siam (present-day Thailand) and used the map when they observed the lunar eclipse of 11 December 1685. In this paper we examine the creation of the 1679 Moon map and its use by the French Jesuit missionary-astronomers in Siam in 1685.

Measurements of the Quiet-Sun Level Brightness Temperature at 8 mm

Defining the solar brightness temperature accurately at millimeter wavelengths has always been challenging. One of the main reasons has been the lack of a proper calibration source. New Moon was used earlier as a calibration source. We carried out a new extensive set of observations at 8 mm using the New Moon for calibration. The solar and Moon observations were made using the 14-meter radiotelescope operated by the Aalto University Metsähovi Radio Observatory in Finland. In this article, we present our method for defining the brightness temperature of the quiet-Sun level (QSL). Based on these observations, we found 8100~mbox{K} pm 300~mbox{K} to be the mean value for the QSL temperature. This value is between the values that were reported in earlier studies.

Exploring the stability and residual response versus scan angle effects in SNPP VIIRS sensor data record reflectance products using deep convective clouds

The reflective solar bands (RSB) of the Visible and Infrared Imaging Radiometer Suite (VIIRS) on Suomi National Polar-orbiting Partnership satellite are calibrated using solar diffuser and lunar observations. To evaluate the performance of the VIIRS RSB calibration, the deep convective clouds (DCC) are utilized as invariant targets to assess the stability of NASA’s VIIRS sensor data record (SDR) reflectance product for 10 moderate resolution bands (M-bands, M1 to M5 and M7 to M11) and three imagery resolution bands (I-bands, I1 to I3). All the frames along with each scan are divided into six aggregation zones for the scan angle. An empirical bidirectional reflectance distribution function (BRDF) correction is performed to SDR reflectances over DCC to reduce the scattering anisotropy in view and solar angles. The BRDF-corrected reflectances are used to assess the stability and to explore the residual RVS effects for selected bands. Results of this study show that after more than 6 years of on-orbit operation, the use of the prelaunch-based RVS still meets the radiometric requirement for the VIIRS RSB. Examination of the small but noticeable RVS residuals indicates they occur in a few shortest wavelength bands based on a time-dependent quadratic fit of the reflectance trends obtained at all scan angle zones. As the mission continues, continuing monitoring of on-orbit RVS stability and its effects on VIIRS SDR reflectance products are necessary with the DCC technique in the future VIIRS calibrations to ensure the quality of the RSB SDR products.

Effects of Practicing Physical Activity During Ramadan Fasting on Health-Related Indices: An Updated Brief Review

Based on Moon observation, every year, adults healthy Muslims practiced Ramadan intermittent fasting (RIF) for 29 or 30 consecutive days. During RIF Muslims are allowed to food and fluid intake only during night (from sunset to sunrise). Thus, behavioral changes are observed during RIF (e.g., food and sleep habits). Despite these changes, many healthy Muslims maintain their normal habitual physical exercise practice during RIF. However, changes in blood lipids, metabolic markers, electrolytes and hematological parameters during RIF in practitioners of physical activity are yet poorly studied. Therefore, the present review article will summarize the health specific effects of RIF in subjects engaged in physical training during Ramadan.

Measuring the global 21-cm signal with the MWA-I: improved measurements of the Galactic synchrotron background using lunar occultation

We present early results from a project to measure the sky-averaged (global), redshifted $21\,$cm signal from the Epoch of Reionisation (EoR), using the Murchison Widefield Array (MWA) telescope. Because interferometers are not sensitive to a spatially-invariant global average, they cannot be used to detect this signal using standard techniques. However, lunar occultation of the radio sky imprints a spatial structure on the global signal, allowing us to measure the average brightness temperature of the patch of sky immediately surrounding the Moon. In this paper we present one night of Moon observations with the MWA between 72 - 230 MHz and verify our techniques to extract the background sky temperature from measurements of the Moon's flux density. We improve upon previous work using the lunar occultation technique by using a more sophisticated model for reflected `earthshine' and by employing image differencing to remove imaging artefacts. We leave the Moon's (constant) radio brightness temperature as a free parameter in our fit to the data and as a result, measure $T_{\rm{moon}} = 180 \pm 12 $ K and a Galactic synchrotron spectral index of $-2.64\pm0.14$, at the position of the Moon. Finally, we evaluate the prospects of the lunar occultation technique for a global EoR detection and map out a way forward for future work with the MWA.

Astrometric Observations of the Galilean Moons of Jupiter at the Pulkovo Normal Astrograph in 2016−2017

We present the results of observations of the Galilean moons of Jupiter carried out at the Normal Astrograph of the Pulkovo Observatory in 2016−2017. We obtained 761 positions of the Galilean moons of Jupiter in the system of the Gaia DR1 catalog (ICRF, J2000.0) and 854 differential coordinates of the satellites relative to each other. The mean errors in the satellites’ normal places and the corresponding root-mean-square deviations are eα = 0.0020′′, eδ = 0.0027′′, σα = 0.0546′′, and σδ = 0.0757′′. The equatorial coordinates of the moons are compared to the motion theories of planets and satellites. On average, the (O–C) residuals in the both coordinates relative to the motion theories are less than 0.031′′. The best agreement with observations is achieved by a combination of the EPM2015 and V. Lainey-V.2.0|V1.1 motion theories, which yields the average (O–C) residuals of approximately 0.02″. Peculiarities in the behavior of the (O–C) residuals and error values in Ganymede have been noticed.

Regressusand Empiricism in the Controversy about Galileo’s Lunar Observations

This paper defends a version of J. H. Randall’s thesis that modern empiricism is rooted in the Scholastic regressus method epitomized by Jacopo Zabarella in De Regressu (1578). Randall’s critics note that the empirical practice of Galileo and his contemporaries does not follow Zabarella. However, Zabarella’s account of the regressus is imprecise, which permitted an interpretation introducing empirical hypothesis testing into the framework. The discourse surrounding Galileo’s lunar observations in Sidereus Nuncius (1610) suggests that both Galileo and his interlocutors amended the regressus method in this way, such that a developmental narrative links Scholastic logic to Galilean science.

Earth and moon observations by thermal infrared imager on Hayabusa2 and the application to detectability of asteroid 162173 Ryugu

Thermal Infrared Imager TIR on Hayabusa2 has proven its in-flight performance to detect celestial bodies during the cruise phase, especially by the observations of the Earth and the Moon before and after the Earth swing-by on 3rd of December 2015. The result indicates that the target C-type asteroid 162173 Ryugu will be detected from the distance of 3000 km at the beginning of the approach phase, and that a C-type small moon larger than 1 m will be detected from the home position, 20 km from the asteroid, if it orbits around the asteroid.

COMS Visible Channel Calibration Using Moon Observation Data

COMS (Communication, Ocean, and Meteorological Satellite) has been in operation since April 2011. The COMS MI (Meteorological Imager) has one visible and four infrared channels. Through the use of the GSICS (Global Space-based Inter-Calibration System), the KMA (Korea Meteorological Administration) has monitored the radiometric performance of the COMS visible channel through its own calibration system and the use of four different earth targets: ocean, desert, water cloud, and DCC (Deep Convective Cloud). To use the invariant target of the Moon, the KMA adopted GIRO (GSICS Implementation of the ROLO (Robotic Lunar Observatory) model), which was released by EUMETSAT. In this study, a total of 146 lunar observation data (Level 1A) with various phase angles obtained between April 2011 and December 2017 are analyzed. A degradation rate of approximately −1.52 ± 0.10% per year occurred using the GIRO method, which was a degradation of approximately 12% over the eight years (from 2011 to 2018) during COMS MI’s operational period. The lunar calibration result was in good agreement with results provided by other calibration methods such as the DCC using the RTM (Radiative Transfer Model), which was approximately −1.43 ± 0.13% per year. Selection of on-Moon pixels provided an uncertainty of approximately 0.01% per year, while that related to the phase angle (Sun-Moon-Satellite) was approximately 0.06% per year.

Sources and Databases for the Study of the Dynamics of Moons of Asteroids

A new database of all astrometric observations of moons of asteroids is offered. It has a simple structure and is accessible through the Internet. Regular database updating is provided when new observational results occur in publications. The database is located at the sites of the Natural Satellites Data Center created as a result of collaboration between the Sternberg Astronomical Institute of Moscow State University and the Institut de Mecanique Celeste et de Calcul des Ephemerides (IMCCE). The database addresses in the Internet are https://doi.org/www.sai.msu.ru/neb/nss/indexr.htm and https://doi.org/nsdb.imcce.fr/obspos respectively. On entering these sites, we need to select one of three languages, the Observation item, and the Astrometric positions of asteroids with moons item. The observational data are provided here with explanations and hyperlinks to the publications in the bibliographic database SAO/NASA Astrophysics Data System (ADS) Abstract Service.

THE RESEARCH ON LUCALIBRATION OF GF-4 SATELLITE

Abstract. Starting from the lunar observation requirements of the GF-4 satellite, the main index such as the resolution, the imaging field, the reflect radiance and the imaging integration time are analyzed combined with the imaging features and parameters of this camera. The analysis results show that the lunar observation of GF-4 satellite has high resolution, wide field which can image the whole moon, the radiance of the pupil which is reflected by the moon is within the dynamic range of the camera, and the lunar image quality can be guaranteed better by setting up a reasonable integration time. At the same time, the radiation transmission model of the lunar radiation calibration is trace and the radiation degree is evaluated.

Improvements in the On-Orbit Response Versus Scan Angle Characterization of the Aqua MODIS Reflective Solar Bands

The Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) has been chosen by the Global Space-based Inter-Calibration System operational community as the reference sensor in cross-sensor calibration. A number of geostationary orbit and low-earth orbit sensors use the 0.64- $\mu \text{m}$ band from Aqua MODIS as a calibration reference. After over 15 years on-orbit, the performance characteristics of the MODIS instrument have changed, with effects evident at short wavelengths. MODIS employs a reflectance-based calibration using the solar diffuser measurements with the monthly lunar observations facilitating a response versus scan angle characterization on-orbit. As the instrument continues to operate beyond its design lifetime of 6 years, the on-board calibrators alone are insufficient to accurately characterize the instrument’s response at all scan angles. This results in a long-term reflectance drift, particularly observed in the 0.64- and 0.85- $\mu \text{m}$ bands, while observing the temporally invariant desert sites. Long-term reflectance drifts of up to 2% and 3% are observed at the beginning of scan for the 0.64- and 0.85- $\mu \text{m}$ bands, respectively. An approach using earth-view response to supplement the on-board calibrator measurements has been shown to overcome these inadequacies and is now implemented for the 0.64-, 0.85-, 0.46-, and 0.55- $\mu \text{m}$ land bands of Aqua MODIS. This paper presents the details related to the algorithm implementation and an independent evaluation using the Dome Concordia site and deep-convective clouds. This approach has been reviewed, tested, and approved by the MODIS science team and has been implemented in the forward production of the MODIS L1B Collection 6 starting July 9, 2016. This enhanced approach has also been adopted in the MODIS L1B Collection 6.1 reprocess for the entire mission to facilitate an improved quality of downstream science products. The results with the enhanced approach reduce the reflectance drifts to within 0.5% for most cases.

Stability Monitoring of the VIIRS Day/Night Band over Dome C with a Lunar Irradiance Model and BRDF Correction

The unique feature of the Visible Infrared Imager Radiometer Suite (VIIRS) day/night band (DNB) is its ability to take quantitative measurements of low-light scenes at night. In order to monitor the stability of the high gain stage (HGS) of the DNB, nighttime observations over the Dome C site under moonlight are analyzed in this study. The Miller and Turner 2009 (MT2009) lunar irradiance model has been used to simulate lunar illumination over Dome C. However, the MT2009 model does not differentiate the waxing and waning lunar phases. In this paper, the MT-SWC (SeaWiFS Corrected) lunar irradiance model differentiating the waxing and waning lunar phases is derived by correcting the MT2009 model using lunar observations made by the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS). In addition, a top of atmosphere (TOA) bi-directional reflectance distribution function (BRDF) model during nighttime over Dome C is developed to remove the angular dependence from the nighttime TOA reflectance. The long-term stability monitoring of the DNB high-gain stage (HGS) reveals a lower reflectance factor in 2012 in comparison to the following years, which can be traced back to the change in relative spectral response (RSR) of National Oceanic &amp; Atmospheric Administration’s (NOAA’s) Interface Data Processing Segment (IDPS) VIIRS DNB in April 2013. It also shows the radiometric stability of DNB data, with long-term stability of less than 1.58% over the periods from 2013 to 2016. This method can be used to monitor the radiometric stability of other low-light observing sensors using vicarious calibration sites under moonlight illumination.

Calibration of the DSCOVR EPIC visible and NIR channels using MODIS Terra and Aqua data and EPIC lunar observations.

The unique position of the Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) at the Lagrange 1 point makes an important addition to the data from currently operating low orbit Earth observing instruments. EPIC instrument does not have an onboard calibration facility. One approach to its calibration is to compare EPIC observations to the measurements from polar orbiting radiometers. Moderate Resolution Imaging Spectroradiometer (MODIS) is a natural choice for such comparison due to its well-established calibration record and wide use in remote sensing. We use MODIS Aqua and Terra L1B 1km reflectances to infer calibration coefficients for four EPIC visible and NIR channels: 443 nm, 551 nm, 680 nm and 780 nm. MODIS and EPIC measurements made between June 2015 and June 2016 are employed for comparison. We first identify favorable MODIS pixels with scattering angle matching temporarily collocated EPIC observations. Each EPIC pixel is then spatially collocated to a subset of the favorable MODIS pixels within 25 km radius. Standard deviation of the selected MODIS pixels as well as of the adjacent EPIC pixels is used to find the most homogeneous scenes. These scenes are then used to determine calibration coefficients using a linear regression between EPIC counts/sec and reflectances in the close MODIS spectral channels. We present thus inferred EPIC calibration coefficients and discuss sources of uncertainties. The Lunar EPIC observations are used to calibrate EPIC O2 absorbing channels (688 nm and 764 nm) assuming that there is a small difference between moon reflectances separated by ~10 nm in wavelength provided the calibration factors of the red (680 nm) and near-IR (780 nm) are known from comparison between EPIC and MODIS.

Finding longitude: The Investigator expedition, 1801–1803

This article analyses the methods deployed for finding longitude on the Investigator’s expedition to circumnavigate Australia, made under the command of Matthew Flinders in the period 1801–1803. Timekeeping and astronomy were complementary methods for ascertaining longitude; they were carried out using chronometers and by taking lunar observations. The article explains who was responsible for handling the astronomical readings on the expedition; the performance of the chronometers used; Flinders’s comparisons of the longitudinal readings with the work of previous navigators; and the reasons why dissemination of the longitudes taken during the voyage was delayed. The article shows how the combined use of chronometers and lunar observations helped Flinders to achieve scientific accuracy in his charting of coastal Australia in the atlas to his major work entitled A Voyage to Terra Australis.

Observations of the New Moon using Optical Telescopes and Radio Telescope from the Perspective of Islam

Observations of the moon were done by Islamic scholars since hundreds of years ago. It has been studied many researchers in various fields such as planetary motion, circumference of the earth, moon, eclipse and new moon (hilal). This study is proven by history that shows a variety of equipment to help process the observation of the new moon as astrophysic using scientific tools such as optical telescope. Technological advancements today have transformed in many area. Including in astronomy, various techniques are employed as possible to facilitate a way to see the new moon. However, it must be consistent with the requirements of Islam. The objective of this study is to investigate and identify appropriate alternative methods to overcome the problems weather (cloudy, rainy and fog) in hilal observation. In this study, the comparison method based on Optical Telescope and Radio Telescope has been use to point raised in its assessment of current observations and alternative technique are proposed to the Islamic astronomer in Malaysia. Base on this study, the use of optical telescopes and radio telescopes are very helpful to researchers in observing the moon with more accurate and more reliable and conform to Islamic rules'. The technology optical telescopes, radio telescopes and religion should be in line in every action.

Initial inflight calibration for Hayabusa2 optical navigation camera (ONC) for science observations of asteroid Ryugu

Hayabusa2, the first sample return mission to a C-type asteroid was launched by the Japan Aerospace Exploration Agency (JAXA) on December 3, 2014 and will arrive at the asteroid in the middle of 2018 to collect samples from its surface, which may contain both hydrated minerals and organics. The optical navigation camera (ONC) system on board the Hayabusa2 consists of three individual framing CCD cameras, ONC-T for a telescopic nadir view, ONC-W1 for a wide-angle nadir view, and ONC-W2 for a wide-angle slant view will be used to observe the surface of Ryugu. The cameras will be used to measure the global asteroid shape, local morphologies, and visible spectroscopic properties. Thus, image data obtained by ONC will provide essential information to select landing (sampling) sites on the asteroid. This study reports the results of initial inflight calibration based on observations of Earth, Mars, Moon, and stars to verify and characterize the optical performance of the ONC, such as flat-field sensitivity, spectral sensitivity, point-spread function (PSF), distortion, and stray light of ONC-T, and distortion for ONC-W1 and W2. We found some potential problems that may influence our science observations. This includes changes in sensitivity of flat fields for all bands from those that were measured in the pre-flight calibration and existence of a stray light that arises under certain conditions of spacecraft attitude with respect to the sun. The countermeasures for these problems were evaluated by using data obtained during initial in-flight calibration. The results of our inflight calibration indicate that the error of spectroscopic measurements around 0.7 µm using 0.55, 0.70, and 0.86 µm bands of the ONC-T can be lower than 0.7% after these countermeasures and pixel binning. This result suggests that our ONC-T would be able to detect typical strength (∼3%) of the serpentine absorption band often found on CM chondrites and low albedo asteroids with ≥ 4σ confidence.