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• Twilight phenomena occurs in the thermosphere. • An equation has been derived to calculate diurnal atmospheric height using the twilight images analysis. • The diurnal atmosphere has estimated height ∼304 km above sea level. • Lower wind speeds and temperatures resulted in a higher thickness of diurnal atmosphere. • Higher relative humidity and dew point resulted in a higher thickness of diurnal atmosphere. • The first appearance of dawn twilight is at dip = ∼15°. An equation has been derived through which the height of the diurnal atmospheric layer (lower atmosphere) can be calculated using ground base twilight image analysis. This equation relies on the angular altitude of the twilight with the dip at that moment. Based on the images, it was found that true twilight of dawn occurs at a dip of 14.90° ± 0.17° as detected by the camera or ∼15° by considering the elevation above sea level (while it may be delayed to ∼14.7–14° with the naked eye), which is accompanied by an average twilight angular altitude of 2.66° ± 0.23°. From these values, the twilight height is estimated to be 303.80 ± 5.69 km above sea level. It is shown that the twilight region is the peak zone of the thermosphere. Its height also varies with time according to changes in various atmospheric parameters. Lower wind speeds, higher relative humidity, higher dew point, and lower temperatures resulted in a higher altitudinal angle of the atmosphere and consequently a greater diurnal atmospheric layer's thickness. Image analysis shows that the thermosphere always has a maximum value of light brightness during the night even before the appearance of twilight. Additionally, It defined the light source, shapes, and stages of twilights that detected by images. This implies that sky image analysis is an inexpensive method for understanding the properties and various parameters of the atmosphere. [ABSTRACT FROM AUTHOR]

Abstract Zodiacal light (ZL) is sunlight scattered by interplanetary dust particles (IDPs) at optical wavelengths. The spatial distribution of IDPs in the Solar System may hold an important key to understanding the evolution of the Solar System and material transportation within it. The number density of IDPs can be expressed as $$n(r) \sim r^{-\alpha }$$ n ( r ) ∼ r - α , and the exponent $$\alpha \sim 1.3$$ α ∼ 1.3 was obtained by previous observations from interplanetary space by Helios 1/2 and Pioneer 10/11 in the 1970s and 1980s. However, no direct measurements of $$\alpha $$ α based on ZL observations from interplanetary space outside Earth’s orbit have been performed since then. Here, we introduce initial results for the radial profile of the ZL at optical wavelengths observed over the range 0.76 $$-$$ - 1.06 au by ONC-T aboard the Hayabusa2# mission in 2021-2022. The ZL brightness we obtained is well reproduced by a model brightness, although there is a small excess of the observed ZL brightness over the model brightness at around 0.9 au. The radial power-law index we obtained is $$\alpha = 1.30 \pm 0.08$$ α = 1.30 ± 0.08 , which is consistent with previous results based on ZL observations. The dominant source of uncertainty arises from the uncertainty in estimating the diffuse Galactic light (DGL). Graphical Abstract

Zodiacal light (ZL) is sunlight scattered by interplanetary dust particles (IDPs) at optical wavelengths. The spatial distribution of IDPs in the Solar System may hold an important key to understanding the evolution of the Solar System and material transportation within it. The number density of IDPs can be expressed as n (r) ∼ r - α , and the exponent α ∼ 1.3 was obtained by previous observations from interplanetary space by Helios 1/2 and Pioneer 10/11 in the 1970s and 1980s. However, no direct measurements of α based on ZL observations from interplanetary space outside Earth's orbit have been performed since then. Here, we introduce initial results for the radial profile of the ZL at optical wavelengths observed over the range 0.76 - 1.06 au by ONC-T aboard the Hayabusa2# mission in 2021-2022. The ZL brightness we obtained is well reproduced by a model brightness, although there is a small excess of the observed ZL brightness over the model brightness at around 0.9 au. The radial power-law index we obtained is α = 1.30 ± 0.08 , which is consistent with previous results based on ZL observations. The dominant source of uncertainty arises from the uncertainty in estimating the diffuse Galactic light (DGL). [ABSTRACT FROM AUTHOR]

We present a review of the observations of the solar F-corona from space with a special emphasis of the 25 years of continuous monitoring achieved by the LASCO-C2 and C3 coronagraphs. Our work includes images obtained by the navigation cameras of the Clementine spacecraft, the SECCHI/HI-1A heliospheric imager onboard STEREO-A, and the Wide Field Imager for Solar Probe onboard the Parker Solar Probe. The connection to the zodiacal light is considered based on ground- and space-based observations, prominently from the past Helios, IRAS, COBE, and IRAKI missions. The characteristic radiance profiles along the two symmetry axis of the "elliptically" shaped F-corona (aka equatorial and polar directions) follow power laws in the 5 ∘ – 50 ∘ range of elongation, with constant power exponents of −2.33 and −2.55. Both profiles connect extremely well to the corresponding standard profiles of the zodiacal light. The LASCO equatorial profile exhibits a shoulder implying a ≈ 17 % decrease of the radiance within ≈ 10 R ⊙ that may be explained by the disappearance of organic materials within 0.3 AU. LASCO detected for the first time a secular variation of the F-corona, an increase at a rate of 0.46% per year of the integrated radiance in the LASCO-C3 field of view. This is likely the first observational evidence of the role of collisions in the inner zodiacal cloud. The temporal evolution of the integrated radiance in the LASCO-C2 field of view is more complex suggesting possible additional processes. Whereas it is well established that the F-corona is slightly redder than the Sun, the spectral variation of its color index is not yet well established. A composite of C2 and C3 images produced the LASCO reference map of the radiance of the F-corona from 2 to 30 R ⊙ and, by combining with ground-based measurements, the LASCO extended map from 1 to 6 R ⊙ . An upper limit of 0.03 R ⊙ is obtained for the offset between the center of the Sun and that of the F-corona with a most likely value of zero. The flattening index of the F-corona starts from zero at an elongation of 0.5 ∘ ± 0.01 ∘ (1.9 R ⊙ ) and increases linearly with the logarithm of the elongation to connect to that of the zodiacal light with however a small hump related to the shoulder in the equatorial profile. The shape of the isophotes is best described by super-ellipses with an exponent linked to the flattening index. An ellipsoid model of the spatial density of interplanetary dust is solely capable of reproducing this shape, thus rejecting other classical models such as fan, and cosine. The plane of symmetry of the inner zodiacal cloud is strongly warped, its inclination increasing towards the planes of the inner planets and ultimately the solar equator. In contrast, its longitude of ascending node is found to be constant and equal to 87.6 ∘ . LASCO did not detect any small scale structures such as putative rings occasionally reported during solar eclipses. The outer border of the depletion zone where interplanetary dust particles start to be affected by sublimation appears well constrained at ≈ 19 R ⊙ . This zone extends down to ≈ 5 R ⊙ , thus defining the boundary of the dust-free zone where the most refractory materials – likely moderately absorbing silicates – disappear. [ABSTRACT FROM AUTHOR]

While comets eject mass mostly at cm-sizes and larger, that size range of particles is mostly absent from the interplanetary medium. Such particles are thought to be lost from the solar system by grain-grain collisions. Here, we investigate the lifetime of cm-sized meteoroids from their abundance in meteoroid streams of different age. For 487 streams, we measured the orbital element dispersions, the magnitude size distribution index, the ratio of fluffy and dense materials in the stream and their bulk densities, and the meteor light curve shape-parameter. We find that older long-period comet meteoroid streams tend to be more dispersed and evolve towards smaller semi-major axis, higher magnitude size distribution index, and contain relatively more high-density material. Meteoroids that approach the Sun closer than 0.2–0.3 AU are mostly young and composed of denser materials poor in sodium. We compare the observed properties of the streams to age estimates from the literature and to a set of new age estimates for long-period comet streams based on observed dispersions. We find that streams broaden with age inversely proportional to the perihelion distance (q). By selecting narrow ranges of age, we find that their magnitude distribution index changes proportional to 1/√q, less steep than expected from meteoroid destruction by collisions. Instead, this shallow dependence suggests a lifetime inversely proportional to the peak grain temperature along its orbit, with the lifetime limited by thermal stresses if 0.3 < q < 1.02 AU and by sublimation if q < 0.2 AU. • Long-period comet streams disperse with inverse perihelion distance and linear in time. • Meteoroid streams lose cm-sized grains faster than mm-sized grains. • Streams contain both low- and high-density materials, dense materials survive longer. • Streams with q < 0.2 AU are young and their meteoroids are often physically altered. • Peak grain temperature limits the lifetime of cm-sized grains in orbits with q < 1.02 AU. • Thermal stresses are important for 0.3 < q < 1.02 AU, while sublimation is for q < 0.2 AU. [ABSTRACT FROM AUTHOR]

The problematic identity of the deity Savitṛ in early Vedic religion has sparked more than a century of discussion. Harry Falk, for instance, argued that this god, whose name literally means “Impeller”, can be identified with the Milky Way and associated with the rainy season. Others have suggested that he becomes visible in the zodiacal light or crepuscular rays. The aims of this paper are to review the most important theories about Savitṛ’s manifestations in nature in Ṛgvedic times and to reassess whether and in what ways different natural phenomena and celestial luminaries may have been associated with this deity. In discussing the theories proposed so far, I not only consider the Vedic sources but re-evaluate the archaeoastronomical arguments with modern software. As it turns out, there is no conclusive evidence that Savitṛ was associated with any single phenomenon or luminary at all. Rather, he was an anthropomorphic deification of what was perceived as a certain “cosmic” or “natural” force.

The Solar System is home to a cloud of dust that orbits the Sun and makes its presence known by virtue of scattered light (Zodiacal Light) that can be seen after dusk and before dawn. Within this cloud are bands of dust orbiting near the ecliptic plane, evidenced by an excess of scattered light at discrete ecliptic latitudes. Dedicated dust detectors borne by spacecraft in transit of the solar system have detected few such particles of the appropriate size owing to limited detector aperture and sparsity of the population. Thus, the distribution, origin, and orbital evolution of the dust in these bands remains a mystery. A star camera aboard the Juno spacecraft traveling from Earth to Jupiter recorded interplanetary dust impacts on the spacecraft in numbers sufficient to characterize the spatial distribution of such particles for the first time. The observed distribution is consistent with a primary source of dust particles sharing the Mars orbit plane between Earth and the 4:1 resonance with Jupiter. We propose that the primary distribution is scattered by orbital resonances with Jupiter via the Kozai‐Lidov (KL) effect into a secondary population at higher inclination to the ecliptic. The measured dust distribution, occupying a volume uniquely determined by the orbital elements of Mars and KL scattering, accounts for the observed variation of the Zodiacal Light with ecliptic latitude. Our results provide a compelling alternative to the prevailing theory of the origin and evolution of interplanetary dust observed at low ecliptic latitudes. Plain Language Summary: The Zodiacal light is sunlight reflected by dust in the inner solar system. Variations in the Zodiacal light with ecliptic latitude reveal discrete bands of dust orbiting near the ecliptic plane. The Juno spacecraft, in transit from earth to Jupiter, recorded a sufficient number of impacts with this dust to characterize their distribution in space for the first time. The radial distribution of the dust suggests a primary source of dust with the orbital elements (inclination and eccentricity) of Mars, scattered into a secondary population at higher inclination to the ecliptic. The resulting population accounts for the observed variation of Zodiacal light with ecliptic latitude. Key Points: The Juno spacecraft, in transit from Earth to Jupiter, recorded the impact of interplanetary dust particles on its solar arrays in large numbersThe distribution of dust near the ecliptic reveals the influence of mean motion resonances with Jupiter, providing clues to its originsThe modeled dust distribution accounts for the variation in Zodiacal light with ecliptic latitude, scattered by the Zodiacal dust bands [ABSTRACT FROM AUTHOR]

Abstract The Beagle family is a C-type subgroup of the Themis family, in the outer main belt. Previous works suggested that it could be younger than 20 Myr and a possible source for the dust in the i ≃ 1.4 ∘ α zodiacal dust band. Here we took advantage of a much larger database for Beagle family members to revisit previous age estimates of this group. Standard dating techniques based on the family V-shape or on Monte Carlo methods of Yarkovsky and YORP mobility suggest that i) there might be a dichotomy for the inner and outer part of the Beagle family, which may be either two separate families or the product of an anisotropic ejection velocity field and that ii) the age of the possibly younger outer part of the Beagle family should be 35 − 35 + 65 Myr. The past convergence of Beagle longitude of the node is compatible with a family age of ≃ 14 Myr, when (1678) Glarona is used as a reference orbit. Without further information on Beagle members spin states, however, only very lower limits on the family age can be currently obtained when the Yarkovksy force is accounted for. Highlights • The Beagle family is a sub-family of the larger Themis asteroid group. • It is a possible source for the dust in the i ∼ 1.4° α zodiacal dust band. • Here we obtained improved age estimates of this group. • There might be a dichotomy for the inner and outer part of the Beagle family. • The past convergence of Beagle longitude of the node suggests an age of ∼14 Myr. [ABSTRACT FROM AUTHOR]

Nicolae Donitch gave a special role to Romania's membership of the IAU, even though it had basically adhered to it in 1922, but only on the 12th of July 1928 was Romania's membership in the IAU recognized. He was a passionate observer of eclipses, of the zodiacal light, and a good instrument builder. His tortuous destiny was somehow similar to the destiny of many Romanians from Eastern Moldova: he was born in Chişinău, the capital of Bessarabia at that time; he studied in Odessa; after the first revolution in February 1917 he left Russia and remained in Odessa until the arrival of the Bolsheviks in 1920, who would completely destroy his laboratory. He then moved to his private Astrophysics Observatory in Dubăsarii Vechi, which he had set up in 1908, and stayed until 1940, when Bessarabia was once again torn away from Romania. He relocated to Bucharest, but soon after, when communists came to power, he had to leave the country on a permanent basis. As he severed all the ties with people from the country that had fallen into the red zone of communism, we completely lost track of him. It was only recently that, after thorough research, we could discover his traces, and learn of his last years of life. [ABSTRACT FROM AUTHOR]

Synoptic images obtained from the HI-2 instrument on STEREO-A and -B between 2007 and 2014 have been used to further investigate the circumsolar dust ring at the orbit of Venus that was reported by Jones et al. (2013). The analysis is based on high signal-to-noise ratio photometry of the zodiacal light, using data acquired over 10-day intervals, followed by a process of extracting spatial variability on scales up to about 6.5°. The resulting images provide information about the structure of the ring at the location where it is viewed tangentially. We identify 65 usable data sets that comprise about 11% of the available HI-2 data. Analysis of these images show that the orientation of the ring appears to be different to that of the orbit of Venus, with an inclination of 2.1° and longitude of ascending node of 68.5°. We map the variation of ring density parameters in a frame of reference that is co-rotating with Venus and find a pattern suggestive of dust in a 3: 2 orbital resonance. However, the location of the maxima of dust densities is not as expected from theoretical models, and there is some evidence that the dust density distribution in the ring has a pattern speed that differs from the mean motion of Venus. [ABSTRACT FROM AUTHOR]

We present an analysis of the blank-sky spectra observed with the Faint Object Spectrograph on board the Hubble Space Telescope. We study the diffuse sky emission from ultraviolet to optical wavelengths, which is composed of zodiacal light (ZL), diffuse Galactic light (DGL), and residual emission. The observations were performed towards 54 fields distributed widely over the sky, with spectral coverage from 0.2 to 0.7μm. In order to avoid contaminating light from earthshine, we use the data collected only in orbital nighttime. The observed intensity is decomposed into the ZL, DGL, and residual emission, in eight photometric bands spanning our spectral coverage. We found that the derived ZL reflectance spectrum is flat in the optical, which indicates major contribution of C-type asteroids to the interplanetary dust (IPD). In addition, the ZL reflectance spectrum has an absorption feature at ∼0.3μm. The shape of the DGL spectrum is consistent with those found in earlier measurements and model predictions. While the residual emission contains a contribution from the extragalactic background light, we found that the spectral shape of the residual looks similar to the ZL spectrum. Moreover, its optical intensity ismuch higher than thatmeasured from beyond the IPD cloud by Pioneer 10/11, and also than that of the integrated galaxy light. These findings may indicate the presence of an isotropic ZL component, which is missed in the conventional ZL models. [ABSTRACT FROM AUTHOR]

We describe a 'super-Earth'-size (2.30 ± 0.16 R⊕) planet transiting an early K-type dwarf star in the Campaign 4 field observed by the K2 mission. The host star, EPIC 210363145, was identified as a candidate member of the approximately 120 Myr-old Pleiades cluster based on its kinematics and photometric distance. It is rotationally variable and exhibits near-ultraviolet emission consistent with a Pleiades age, but its rotational period is ≈20 d and its spectrum contains no Hα emission nor the Li I absorption expected of Pleiades K dwarfs. Instead, the star is probably an interloper that is unaffiliated with the cluster, but younger (≲1.3 Gyr) than the typical field dwarf. We ruled out a false positive transit signal produced by confusion with a background eclipsing binary by adaptive optics imaging and a statistical calculation. Doppler radial velocity measurements limit the companion mass to <2 times that of Jupiter. Screening of the light curves of 1014 potential Pleiades candidate stars uncovered no additional planets. An injection-and-recovery experiment using the K2 Pleiades light curves with simulated planets, assuming a planet population like that in the Kepler prime field, predicts only 0.8-1.8 detections (versus ~20 in an equivalent Kepler sample). The absence of Pleiades planet detections can be attributed to the much shorter monitoring time of K2 (80 d versus 4 yr), increased measurement noise due to spacecraft motion, and the intrinsic noisiness of the stars. [ABSTRACT FROM AUTHOR]

An observing campaign was conducted in the Southern Hemisphere using low-light video camera triangulation to measure the trajectories and orbits of meteoroids with a possible origin at asteroid Bennu. New CAMS (Camera for Allsky Meteor Surveillance) video camera networks were established in Australia, Chile, and Namibia, and networks in New Zealand and South Africa were expanded. During observing periods in September 2019, 2020, and 2021, we measured 7672, 4936, and 5890 orbits, respectively. Based on the non-detection of predicted meteoroid trail encounters, Bennu's meteoroid production rate was <1.5 kg/s during 1500–1800 CE. Indeed, the current production rate is many orders of magnitude lower. Bennu may have an associated annual meteoroid stream of much older ejecta at a particle flux density of ≤1.3 × 10−6 km−2 h−1, based on seven Bennu-like orbits detected during the first three years of observations. • A search was conducted for possible meteors at Earth from debris ejected by asteroid Bennu in the past. • New networks of low-light video cameras were established in the southern hemisphere to measure meteoroid orbits from the predicted radiant in late September. • Only a handful of meteoroids in orbits similar to asteroid Bennu were detected, consistent with the low flux density expected form the present rate of meteoroid ejection. [ABSTRACT FROM AUTHOR]

Although Plato states that the perceptible god that he describes in Timaeus is visible to the human eye, the reflection of the Cosmic Soul in the heavens has largely been explained away or forgotten in the Western mind. But Roman texts, early Christian testimony, and Imperial coins illustrate that Plato’s intersection in the heavens played a major role in Hellenistic cosmology and soteriology.