British Astronomical Association

Abstract We present a photometric study of the interstellar comet 3I/ATLAS based on observations obtained between 2025 July 3 and September 22 from two observatories in Spain (Z10 and Y71) using small-aperture telescopes. The comet was monitored in five photometric bands ( CV, C, R, G , and B ), revealing an apparent brightness range from 19.10 to 13.50 mag. The observed variability reflects differences in observing site and filter bandpass, as well as significant scatter caused by background stellar contamination in crowded fields. Throughout the observing interval, comet 3I/ATLAS exhibited weak activity, with only a faint tail detected. A consistent brightening trend was measured in all filters, with average rates ranging from 0.033 to 0.066 magnitudes per day, indicating a progressive increase in activity. Measurements of coma size, tail length, and tail position angle were obtained for selected epochs. Derived Af ρ values suggest that comet 3I/ATLAS was undergoing a phase of increasing activity associated with its approach to perihelion.

JunoCam images show a stable and approximately irrotational north polar cyclone, surrounded by eight circumpolar cyclones (CPCs) (Figure 1). The CPCs have been essentially stable over almost a decade since their discovery in 2016. They show only a minor zonal drift. Some of the CPCs develop and maintain a counter-rotating core that remains sustained over several months or longer. Those CPCs show a much stronger signature in MWR data than CPCs without a large embedded counter-rotating vortex. Between the north polar cyclone and the surrounding CPCs, up to about two additional large anti-cyclones occur that are not as stable or as long-lasting as the CPCs.Figure 1: North polar CPC cluster seen by MWR and JunoCam. The north polar cyclone is nearly invisible in MWR data. CPCs with counter-rotating core tend to be brighter in MWR.We have used a two-layer fluid dynamical model. In its first 2D layer we have assumed a steady flow with a north polar cyclone surrounded by CPCs with an optional counter-rotating core. A coupled second 2D layer behaves like an incompressible Euler flow, except for its coupling defined by a vorticity flux proportional to the vorticity difference between the two layers. This model develops almost no vertical vorticity flux for the north polar cyclone, but more vorticity flux for CPCs with a counter-rotating core than for those without such a feature, see Figure 2.Figure 2First row: Two-layer fluid model with an assumed steady 2D flow in layer 1 in the left panel, the simulated fluid layer 2 in the right panel, and the required vorticity flux at the center. Yellow means north anticylonic, blue means cyclonic vorticity.Second row: Simulated vorticity flux blurred with color scheme adjusted to that of MWR. The model vorticity flux resembles MWR data while the simulated fluid layer resembles JunoCam data. It is important to note that JunoCam is an optical imager and therefore sees the cloud tops, while MWR is a microwave radiometer whose 6 channels see thermal emission from about the 1-bar level to about the 100-bar level. Vertical vorticity flux between simulated layers might be interpreted as related to convection and induced heat transport between otherwise geostrophic fluid layers. This may then show up in temperature deviations in MWR data. Since the north polar cyclone and the CPCs without a counter-rotating core are closer to an equilibrium, and require less vorticity flux to remain stable, their geostrophic layer shows less temperature anomalies in MWR. However, this conceivable physical interpretation is beyond the limitations of the simplified empirical model. Once an approximate underlying steady flow is inferred from MWR and JunoCam data, another deeper layer can be proposed to enable that inferred and assumed steady flow pattern. Such a deeper flow might host a rotationally symmetrical zonal flow that is suggested by observations of Jupiter's lower latitudes. The three-layer extension of the model starts with members of the family of rotationally symmetrical zonal flows, and attempts to infer a member that is suitable to induce an overlying fluid layer that resembles the CPC cluster that was previously assumed as an underlying steady flow to explain MWR and JunoCam data, see Figure 3. Figure 3: A three-layer fluid-dynamical model with a rotationally symmetrical flow in layer 0 shown in the left panel. This layer induces a structure of CPCs (blue) with anticyclonic (orange) cores as shown in layer 2 in the right panel via an intermediate layer 1 as shown in the center panel. For stable CPCs to form from a rotationally symmetrical zonal flow, a cylonic annulus with anticyclonic borders is required. The induced overlying layer will develop a cluster of CPCs if the coupling is adjusted to a suitable range. The number of CPCs is related to the width of the annulus, and depends to some degree on its structure in detail.For a counter-rotating core to form and to be kept stable, the cyclonic annulus is best split into two with a suitable anticyclonic annulus inserted. Once the cyclones form in the overlying layer, they develop an anticyclonic core, if their centers happen to be located above the inserted anticylconic annulus. The modeled vorticity flux will accumulate anticyclonic vorticity in the core of the CPC from underneath.Anticyclones can form between the north polar cyclone and the CPCs, if the shielding of the polar cyclone is modeled in the bottom-most layer as an anticyclonic annulus that is separated from the polar vortex.The north polar cyclone needs to be shielded at some point within the polygon enclosed by the centers of the CPCs since otherwise the enclosed circulation would induce a net zonal CPC drift, see Figure 4a. Figure 4a: A cyclonic solid body vortex shielded by an anticyclonic annulus. Its radius can vary between that of the solid body vortex and that of the inner shielding of the cylconic annulus.b: Model with two to three anticyclones forming from an underlying anticyclonic ring inside the CPC cluster. The degree of freedom can be used to model an annulus that induces the formation of two or more large anticyclones, as shown in Figure 4b. Distinct morphological structures within the CPCs tend to develop from an annular structure more naturally if the annuli of cyclonic and anticyclonic vorticity are separated more distinctly than based on a Gaussian-like cross section of their stream function, see Figure 5a. Figure 5a: An underlying steady flow with sharply defined annuli induces distinct structures.b: An underlying steady flow that induces FFR-like flow. Simulated structures resembling folded filamentary regions (FFRs) tend to form if the underlying concentric annuli structure does not show a sufficiently clear excess of cyclonic vorticity together with a border of shielding anticyclonic vorticity as a function of radius, as illustrated in Figure 5b. In that case, local chaotic turbulence tends to form easier than a distinct filament roll-up into large vortices. This scenario appears to be present outside the polar CPC cluster.

Abstract We presented the first photometric light curve solutions of four W Ursae Majoris-type contact binary systems. This investigation utilized photometric data from the Transiting Exoplanet Survey Satellite and Gaia Data Release 3 (DR3). We used the PHysics Of Eclipsing BinariEs Python code and the Markov Chain Monte Carlo method for these light curve solutions. Only TIC 249064185 among the target systems needed a cold starspot to be included in the analysis. Based on the estimated mass ratios for these total eclipse systems, three of them are categorized as low mass ratio contact binary stars. The absolute parameters of the systems were estimated using the Gaia DR3 parallax method and the orbital period and semimajor axis (P–a) empirical relationship. We ascertained that the TIC 318015356 and TIC 55522736 systems are A-subtypes, while TIC 249064185 and TIC 397984843 are W-subtypes, depending on each component’s effective temperature and mass. We estimated the initial masses of the stars, the mass lost by the binary system, and the systems’ ages. We displayed star positions in the mass–radius, mass–luminosity, and total mass–orbital angular momentum diagrams. In addition, our findings indicate a good agreement with the mass-temperature empirical parameter relationship for the primary stars.

One of the earliest independent discoveries of the 1946 eruption of the recurrent nova T CrB was by British amateur variable star observer, N.F.H. Knight, on 1946 February 9 at 05.40 UT. Correspondence between Knight and W.M. Lindley, the Director of the British Astronomical Association Variable Star Section, reveals what might be the first prediction of a future eruption in 2026–27.

In the original version of article [Publ. Astron. Soc. Japan (2024) 76(2); https://doi.org/10.1093/pasj/psae010], the email address was incorrectly typed during the production process. The PDF and HTML versions of the original article are updated with the correct email address upon the publication of this erratum.

Amateur astronomy of the Solar System is living a golden age with major contributions to modern planetary science. These contributions cover a wide spectrum of topics that range from the discovery of impacts in Jupiter [1-2], to the observation of stellar occultations by minor bodies [3-4], the characterization of unexpected high-atmospheric events in Mars [5], or the characterization of giant storms on Jupiter [6] and Saturn [7-8]. Besides these examples of high-profile publications, there is an increasing number of amateur contributions to dozens of studies of planetary atmospheres and countless contributions to the study of minor bodies. While we focus here in the role of amateur astronomy observations of planetary atmospheres, we also recognize the varied and healthy professional and amateur collaborations in other areas of solar system astronomy.The reasons behind this golden age lie in the two sides of the collaboration: On the side of amateur astronomers, many of them use very efficient detectors and advanced software tools, and they are highly connected at an international level. Thus, they provide high-quality observations on a regular basis to professional astronomers, or have strong analysis teams like the JUPOS team as an example (http://jupos.privat.t-online.de/index.htm). These frequent amateur observations provide essential monitoring of the temporal evolution of planetary atmospheres. On the other side, professional astronomers are aware of the potential of these observations and actively seek the collaboration of amateur astronomers and citizen scientists. A key case in this regard is NASA’s Juno mission to the giant planet Jupiter, and its large-scale collaboration around the JunoCam instrument on the mission Juno website: https://www.missionjuno.swri.edu/. The mission has been recently extended until 2025 and details of the contribution of amateur observers to this new mission scenario are presented by Orton et al. in session ODAA5 in this meeting. Other examples of professionals seeking a global collaboration with amateurs are the various professional and amateur astronomy services and workshops organized by research projects like the Europlanet 2020 Research Infrastructure (2016-2019) and Europlanet 2024 Research Infrastructure (2020-2024).We anticipate that the trend of amateur astronomy playing an important role in providing additional data sets to space missions will continue to grow and we advocate for the early establishment of such collaborations.  We review some of the elements that have made the collaboration of amateur astronomers with the Juno mission so fruitful for both parties and how this collaboration has grown beyond Jupiter into enhanced collaborations in other fields through networking amateur astronomers and providing a successful example to other fields.We also discuss future ground-based high-resolution amateur observations of Solar System planets in support of future missions. These include the James Webb Space Telescope observations of planets (launch in October 2021), ESA’s Jupiter Icy moons Explorer (JUICE, launching in 2022) and NASA’s Europa Clipper missions to the Jupiter system in the early 2030s, the in situ exploration of Saturn’s moon Titan by the Dragonfly mission (NASA) in 2034, the Envision mission to Venus (if selected by ESA), and possible future missions to the Icy Giants Uranus and Neptune. Each of these ambitious missions will benefit from the strong partnership between amateur and professional planetary scientists. The first in this line is the JWST observations of Giant planets to be conducted in 2022 (see Fletcher et al. in session OPS3 in this conference).Finally, we also show some professional and amateur networking elements developed under the umbrella of the Europlanet projects, including the recently launched Europlanet Telescope Network (https://bit.ly/2Br5LDt), and we present possible scenarios for future pro-am collaborations beyond the end of the Europlanet 2024 project. AcknowledgementsPart of this research has been supported by Europlanet 2024 RI. Europlanet 2024 RI has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 871149.

IntroductionThe polygons of cyclones at Jupiter’s poles – a pentagon at the south pole and an octagon at the north pole, each centred on another cyclone – were discovered at Juno’s first few perijoves by the JunoCam and JIRAM instruments [ref.1].  JunoCam images showed that the configurations remained stable for the next two years, up to perijove (PJ) 15 [ref.2].  Here we summarise their behaviour up to PJ33 in 2021 April; with the orbital period of 53 days, this covers 4½ years.The data are polar projection maps produced from JunoCam images as described in [ref.2].South polar clusterThe five southern circumpolar cyclones (CPCs) surround the central South Polar Cyclone (SPC).  However, the SPC is not at the pole, but displaced by 1°-3° latitude, always into the same quadrant of longitude; and there is a gap between two of the CPCs (CPC-1 & 2), in the same quadrant [ref.2].This asymmetry of the pentagon has persisted until now (Figures 1&2).  At PJ23 a smaller, compact cyclone was present in the gap, suggesting that the pentagon might be turning into a hexagon, but at PJ24 it was replaced by a chaotic cyclonic region and the asymmetric pentagonal structure was then restored.We proposed [ref.2] that the cluster is a ‘vortex crystal’ whose configuration could be explained geometrically, if we adopt two conjectures: that the cyclones have a maximum size that prevents them growing larger or merging, and that the central cyclone must be smaller than the mean size of the others (as observed).  In this case, tight packing of the cyclones  produces a pentagon with a gap; and to pack the cyclones as close as possible to the pole, the cluster must be displaced towards the side of the gap, with the largest cyclone on the opposite side, as observed. Consistent with this model, as the cluster wanders somewhat, the gap tends to be widest when the SPC is furthest from the pole (Figure 3).  However, when the SPC longitude is greatest, it lies alongside CPCs-2 & 3 rather than CPCs-1 & 2; and at these times a gap opens up between CPCs-2 & 3, supplementing or replacing the gap between CPCs-1 & 2, as the model would predict.  We noted [ref.2] that the wandering of the SPC appeared to be cyclic.  The record over 4½ years confirms this, showing that it performs loops with a period of 11.5 (±1) months (Figure 4).  The loops are of varying sizes, but show a progressive drift in one direction.  The rate of this drift of cycles has been very uneven, but if it were interpreted as precession of the cycles around the pole, the rate would be ~8° (±8°) per year.Independently of this cyclic motion, the whole pentagon shows a very slow rotation about the SPC, which is stable in the long term: we estimated +1.5°/PJ from PJ1 to PJ15 [ref.2].  Up to PJ32, the average rotation is  +1.21 (±0.07) °/PJ, i.e. 8.3 (±0.5) °/yr.Figures 1 & 2.  Maps of the south polar cluster, down to 75°S at the edges.  CPCs are numbered.  The red cross marks the south pole, grey crosses 80°S; L3=0 to left.Figure 3 (left).  Width of the gap in the pentagon. The angle between CPCs-1 & 2 as measured from the SPC, at each PJ, is plotted against the distance of the SPC from the pole (measurements of the cyclone centres). Brown points represent PJs when there was also a gap between CPCs-2 & 3, i.e. the angle between them was >76° (it is normally ~70°).Figure 4 (right).  Position of the centre of the SPC (colour-coded by PJ) with respect to the south pole (white cross).  PJs in the first and latest cycles are numbered (except PJ1 & PJ31).  The SPC has been cycling anticlockwise throughout.  Background image from PJ25. North polar clusterThe north polar octagon originally consisted of 8 CPCs of alternating morphology (‘filled’ and more diverse types), so it was best described as a ditetragon, centred on the North Polar Cyclone (NPC) [refs.1 & 2].  JunoCam has less complete coverage of the north polar region than of the south.  Nevertheless, about half the cluster is imaged at each PJ and over four PJs a high-quality map can be assembled (Figure 5).  And as the sun rose on the north pole, the NPC (previously observed only by JIRAM in 5-µm thermal emission) has become visible to JunoCam.In 2017, the polygon was a ditetragon with one anticyclonic oval (AO) north of CPC-7.  In 2018, one of the diverse CPCs gradually turned into a fifth ‘filled’ CPC; meanwhile, CPC-7 was increasingly displaced to lower latitude, away from the NPC, by the AO just north of it. By 2020, another AO had appeared on the opposite side, north of CPC-3.In 2021 (from PJ32 onwards), the AO north of CPC-7 disappeared and CPCs-6 & 8 closed up together. So we discuss whether the cluster is still a (distorted) octagon, or now a heptagon, with CPC-7 excluded from it, joining several smaller ‘filled’-type cyclones as satellites of the polygon (Figure 5).  Moreover, the NPC is displaced by ~0.6-1.2° from the pole – possibly a response to the new asymmetry, comparable to the displacement of the SPC.These rearrangements could be random, or temporary, or seasonal in response to the sun rising over the north pole.  JunoCam will continue to monitor the polar clusters during the extended mission.Figure 5:  Composite map of the north polar cluster, PJ30-PJ33, down to 75°N at the edges.  The PJ33 sector was rotated 7° and translated slightly.  CPCs are numbered.  Unnumbered arrows indicate smaller peripheral cyclones (yellow) and anticyclonic ovals (red). Acknowledgements:Some of this research was funded by NASA. A portion of this was distributed to the Jet Propulsion Laboratory, California Institute of Technology.

Abstract In the first 20 orbits of the Juno mission, over 150 waves and wave-like features have been detected by the JunoCam public-outreach camera. A wide variety of wave morphologies were detected over a wide latitude range, but the great majority were found near Jupiter’s equator.  By analogy with previous studies of waves in Jupiter’s atmosphere, most of the waves detected are likely to be inertia-gravity waves.The Juno mission’s JunoCam instrument [1], has detected very small-scale waves. Our survey of JunoCam images revealed a surprising variety of features with wave-like morphologies.  They are presented in terms of differences in visual morphology, without implication that this differentiation arises from the associated responsible dynamics.Long wave packets with short, dark wave fronts represent 79% of the types of waves in our inventory, especially in the Equatorial Zone (EZ) that were also detected in previous studies.  These include wave trains with orthogonal wave crests.  Even more commonly, we detected wave packets with tilted fronts that are not oriented orthogonally to the wave packet direction. Both the meridional extent and wavelength of these waves are much shorter than the Rossby deformation radius, so it is logical to assume that they are formed by and interact with small-scale turbulence, and thereby propagate the waves in all directions (Fig. 1). Sometimes the short wavefronts are aligned in curved wave packets, all associated with larger features, and located outside the EZ. Short wave packets with wide wave fronts were also detected.   In the Earth’s atmosphere, such waves are often associated with thunderstorms producing a brief impulse period with radiating waves.Wave packets with bright features appear bright on a dark background rather than dark on a lighter background, like the waves described above.   Differences between darker and brighter wave crests could be the composition of the material affected.Lee waves, stationary waves generated by the vertical deflection of winds over an obstacle, were also detected. Jupiter’s atmosphere no doubt possesses the dynamical equivalent of an obstacle (Fig. 2).Waves associated with large vortices include compact cyclonic and anticyclonic features with extended radial wavefronts, resembling structures in terrestrial cyclonic hurricanes (Fig. 3). Long, parallel dark streaks are seen both with a non-uniform patterns and  in regularly spaced parallel bands.  Their orientation suggests that they are tracing out the direction of flow on streamlines. Figure 4 plots the distribution of mean wavelengths for different types of waves and wave-like features as a function of latitude, co-plotted with mean zonal wind velocity.  The minimum distance between crests is 29.1 km. The variability of wavelengths within a single packet is typically no greater than 20-30%.  The equatorial waves with long packets and short crests in the EZ have wavelengths that are clustered between 30 km and 320 km, with most between 80 and 230 km in size.  No waves are found at latitudes associated with retrograde zonal flow unless associated with a larger atmospheric feature.JunoCam, detected 157 waves or wave-like features in its first 20 perijove passes. Of these, 100 are waves with long, linear packets and short crests. Another 25were detected with short packets and long crests.  They are all likely to be truly propagating waves, which  form the vast majority of features detected, concentrated in a latitude range between 5ºS and 7ºN. Few of these appear to be associated with other features except for waves that appear to be oriented in lines of local flow. There were fewer waves in the EZ between the equator and 1ºN than there were immediately north and south of this band, which was different from the waves detected by Voyager imaging in 1979 that were more equally distributed.  Other waves outside the EZ are influenced by other features.  These include waves associated with an anticyclonic or cyclonic eddies, lee waves some 10 km above the surrounding cloud deck. Several features appeared within or emanating from vortices. Two sets of extremely long, curved features were detected near the edges of a southwestern extension of a region associated with high 5-µm radiances at the southern edge of the NEB.   No waves were detected south of 7ºS that were not associated with larger vortices, such as the GRS.  No waves or wave-like features were detected in regions of retrograde mean zonal flow that were not associated with larger features, similar to the waves detected by Voyager imaging.AcknowledgementsThe primary support for this research was provided by NASA, a portion of which was distributed to the Jet Propulsion Laboratory, California Institute of Technology. References [1] Hansen et al. Junocam: Juno’s outreach camera. Space Sci. Rev. 217, 475-506.  2017.[2] Wong et al. High-resolution UV/optical/IR imaging of Jupiter in 2016–2019. Space Sci. Rev. 247, 58. 2020. 

During the 2020 Mars opposition, we observe from Earth the occurrence of a non-typical large-scale high-altitude clouds system, extending over thousands of km from the equator to 50°S. Over 3 hours, they emerge from the night side at an altitude of 90 (-15/+30) km and progressively dissipate in the dayside. They occur at a solar longitude of 316°, west of the magnetic anomaly and concomitantly to a regional dust storm. Despite their high altitude, they are composed of relatively large particles, suggesting a probable CO2 ice composition, although H2O cannot be totally excluded. Such ice clouds were not reported previously. We discuss the formation of this new type of clouds and suggest a possible nucleation from cosmic particle precipitation.

ABSTRACT We present the results of a multiwavelength Professional–Amateur campaign to study the behaviour of flares from the active M1.5V star binary CR Draconis. CR Dra was observed with Transiting Exoplanet Survey Satellite (TESS) 20-s photometry, Swift near-ultraviolet (NUV) grism spectroscopy and with ground-based optical photometry and spectroscopy from a global collaboration of amateur astronomers. We detected 14 flares with TESS and Swift simultaneously, one of which also had simultaneous ground-based photometry and spectroscopy. We used the simultaneous two-colour optical and NUV observations to characterize the temperature evolution of the flare and test the accuracy of using optical data to predict NUV emission. We measured a peak temperature of $7100^{+150}_{-130}$ K for this flare, cooler than the typically assumed 9000 K blackbody model used by flare studies. We also found that the 9000 K blackbody overestimated the NUV flux for other flares in our sample, which we attributed to our Swift observations occurring during flare decays, highlighting the phase-dependence for the accuracy of flare models.