Ursa 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.

This study investigates the vibrational behavior of 15×15 cm rectangular metal and plastic plates using both finite element analysis (FEA) and experimental measurements. The research aims to compare simulation results with real-world experimental data to validate the accuracy of numerical models in predicting plate vibrations under excitation from a speaker. Initially, modal analysis is performed via FEA to determine the natural frequencies and mode shapes of the plates. The numerical simulations are conducted using appropriate boundary conditions and material properties to ensure realistic modeling. Subsequently, an experimental setup is designed to excite the plates using a modal hammer, modal shaker and sound exciter. Thus, the resulting vibrations are measured using accelerometers and acoustic microphone. The measured frequency response is then compared with the FEA predictions to assess discrepancies and potential sources of error. Results indicate that while the FEA models provide a good approximation of the experimental outcomes, differences arise due to material imperfections, boundary condition assumptions, and damping effects not fully captured in simulations. The findings contribute to a better understanding of plate vibration characteristics, with implications for applications in acoustics, structural engineering, and materials science.

Abstract. We report the first observations of continuum emission at the poleward boundary of the dayside auroral oval. Spectral measurements of high-latitude continuum emissions resemble those of Strong Thermal Emission Velocity Enhancement (STEVE), with light characterized by colours such as white, pale pink, or mauve. The emission enhancement spans the entire visible wavelength range. However, unlike STEVE, the high-latitude dayside continuum emission events tightly follow the auroral particle precipitation, often forming field-aligned rays and other dynamic shapes. Some dayside emissions appeared as wide arcs or cloud-like structures within the red-emission-dominated dayside aurora. Our spectral measurements further suggest that the broadband continuum emission may extend into the near-infrared (NIR) regime. Similar to the STEVE emission, low-Earth-orbit measurements of plasma flow in the region of continuum emission show a strong horizontal cross-track velocity shear. Ground-based radar and optical observations provide evidence of both plasma and neutral heating, as well as upwelling, in connection to the continuum emissions. We conclude that the interplay between different heating mechanisms may be an important factor in generating high-latitude continuum emissions.

<strong class="journal-contentHeaderColor">Abstract.</strong> We report the first observations of continuum emission at the poleward boundary of the dayside auroral oval. Spectral measurements of high-latitude continuum emissions resemble those of STEVE, with light characterised by colours such as white, pale pink or mauve. The emission enhancement spans the entire visible wavelength range. However, unlike STEVE, the high-latitude dayside continuum emission events tightly follow the auroral particle precipitation often forming field-aligned rays and other dynamic shapes. Some dayside emissions appeared as wide arcs or cloud-like structures within the red-emission dominated dayside aurora. Our spectral measurements further suggest that the broad band continuum emission may extend into the near-infrared regime. Similar to the STEVE emission, low-Earth orbit measurements of plasma flow in the region of continuum emission show a strong horizontal cross-track velocity shear. Ground-based radar and optical observations provide evidence of both plasma and neutral heating, as well as upwelling, in connection to the continuum emissions. We conclude that the interplay of different heating mechanisms may be an important factor in generating high-latitude continuum emissions.

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.

Observations and measurementsWe present some results of diminishing of Martian Southern Polar Cap (SPC) during the apparition 2020&amp;#8211;2021 by Finnish amateur data. We had ca 150 images taken by the members of the Lunar and Planetary group of Ursa Astronomical Association. Observations are made with 0.10-m up to 0.40-m telescopes with planet imaging cameras. Image data cover period from May 2020 to April 2021 [1].We have selected a sample of images and converted them into a polar projection using the WinJUPOS software [2]. We have measured the northernmost latitude of SPC from each image.Results of SPC dataFigure 1 shows the evolution of SPC northernmost latitude from May to December 2020. The polynomial fitting of the diminishing rate is consistent with to the data from earlier apparitions, e.g. by British Astronomical Association and American Lunar and Planetary Observers [3, 4]. The asymmetry of the polar cap cause some deviation to the measurements.&amp;#160; Secondly, there are some variation in the image quality of the observations.Due to poor weather conditions in midwinter 2020&amp;#8211;2021 the disappearance of the SPC is unsolved. In January 2021, the SPC is not detectable in Finnish data, albeit there are some reports of its visibility in British Astronomical Association observations [5].The SPC asymmetry is clearly visible. The center of SPC is misplaced from the Martian South Pole. The northern egde of the polar cap extends towards 0&amp;#8211;60&amp;#176; latitudes. Asymmetry have been already noticed by Hyugens in 1672 and Maraldi noticed the misplacement from the pole in 1719 [6]. Later this is confirmed by Mars Missions data [7]. The phenomenon is explained by topographic and climatic features in Martian western hemisphere near the southern polar region [8, 9].Novus Mons featureNovus Mons, aka &amp;#8220;Mountains of Mitchell&amp;#8221; area was observable as a separated icy fragment near the edge of the SPC during the period 15&amp;#8211;21 Aug 2020. The geographic location of this feature is 300&amp;#8211;330&amp;#176; W and 75&amp;#176; S. O. M. Mitchell discovered it in 1845 [4]. The mountain region keeps shortly its ice cover when the SPC is melting and the edge is shrinking southwards.Figure 2 is an example of observation with Novus Mons feature and figure 3 is the polar projected version of this image.

&amp;lt;p&amp;gt;In this work we present the main results of the project named &amp;amp;#8216;Meteor mathematical modelling of dark flight&amp;amp;#8217; (MeMATH), and current state and future work related to our project. The MeMATH project started in September 2020.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The main objectives of the MeMATH project are:&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;i) numerical simulation of the dark-flight trajectory;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;ii) determining the search area for meteorite fragments;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;iii) the study of the ablation of large bodies.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;In the first stage of the project, we developed a mathematical model for the dark flight trajectory of a meteoroid. The novelty of our model is that it considers the ellipsoidal shape of the Earth, the Coriolis effect and the centrifugal force.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;In the current stage of the project, we are determining the ballistic coefficient &amp;amp;#945; and the mass loss parameter &amp;amp;#946;&amp;amp;#160;based on the meteoroid height and deceleration.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The &amp;amp;#945; and &amp;amp;#946;&amp;amp;#160;parameters have a great impact in the study of meteoroids from the identification of the parent body to determining the initial and final mass and finding out weather the remnant matter after ablation could result in a meteorite on the ground.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Acknowledgement.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The work of IB and MB was supported by a grant of the Romanian Ministry of Education and Research, CNCS-UEFISCDI, project number PN-III-P1-1.1-PD-2019-0784, within PNCDI III.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;

ABSTRACTWhen an object enters the atmosphere it may be detected as a meteor. A bright meteor, called a fireball, may be a sign of a meteorite fall. Instrumentally observed meteorite falls provide unique opportunities to recover and analyse unweathered planetary samples supplemented with the knowledge on the Solar system orbit they had. To recover a meteorite from a fireball event, it is essential that recovery teams can be directed to a well-defined search area. Until recently, simulations showing the realistic mapping of a strewn field were difficult, in particular due to the large number of unknowns not directly retrieved from the fireball observations. These unknowns include the number of fragments and their aerodynamic properties, for which the masses of the fragments need to be assumed in a traditional approach. Here, we describe a new Monte Carlo model, which has already successfully assisted in several meteorite recoveries. The model is the first of its kind as it provides an adequate representation of the processes occurring during the luminous trajectory coupled together with the dark flight. In particular, the model comprises a novel approach to fragmentation modelling that leads to a realistic fragment mass distribution on the ground. We present strewn field simulations for the well-documented Košice and Neuschwanstein meteorite falls, which demonstrate good matches to the observations. We foresee that our model can be used to revise the flux of extra-terrestrial matter onto the Earth, as it provides a possibility of estimating the terminal mass of meteorite fragments reaching the ground.

&amp;lt;p&amp;gt;Auroral forms are like fingerprints linking optical features to physical phenomena in the near-Earth space. While discovering new forms is rare, recently scientists reported of citizens' observations of STEVE, a pinkish optical manifestation of subauroral ionospheric drifts that were not thought to be visible to the naked eye. Here, we present a new auroral form named &amp;quot;the dunes&amp;quot;. On Oct 7, 2018, citizen observers took multiple digital photographs of the same dunes simultaneously from different locations in Finland and Sweden. We develop a triangulation method to analyse the photographs, and conclude that the dunes are a monochromatic wave field with a wavelength of about 45 km within a thin layer at 100 km altitude. Supporting data suggest that the dunes manifest atmospheric waves, possibly mesospheric bores, which are rarely detected, and have not previously been observed via diffuse aurora, nor at auroral latitudes and altitudes. The dunes present a new opportunity to investigate the coupling of the lower/middle atmosphere to the thermosphere and ionosphere. We conclude that the the dunes may provide new insights into the structure of the mesopause as a response to driving by ionospheric energy deposition via Joule heating and electron precipitation.&amp;amp;#160;Further, our paper adds to the growing body of work that illustrates the value of citizen scientist images in carrying out quantitative analysis of optical phenomena, especially at small scales at subauroral latitudes. The dune project presents means to create general interest towards physics, emphasising that citizens can take part in scientific work by helping to uncover new phenomena.&amp;lt;/p&amp;gt;