, U. hopp 5,6 , C. Haumea-one of the four known trans-Neptunian dwarf planetsis a very elongated and rapidly rotating body 1-3 . In contrast to other dwarf planets [4][5][6] , its size, shape, albedo and density are not well constrained. The Centaur Chariklo was the first body other than a giant planet known to have a ring system 7 , and the Centaur Chiron was later found to possess something similar to Chariklo's rings 8,9 . Here we report observations from multiple Earth-based observatories of Haumea passing in front of a distant star (a multichord stellar occultation). Secondary events observed around the main body of Haumea are consistent with the presence of a ring with an opacity of 0.5, width of 70 kilometres and radius of about 2,287 kilometres. The ring is coplanar with both Haumea's equator and the orbit of its satellite Hi'iaka. The radius of the ring places it close to the 3:1 mean-motion resonance with Haumea's spin period-that is, Haumea rotates three times on its axis in the time that a ring particle completes one revolution. The occultation by the main body provides an instantaneous elliptical projected shape with axes of about 1,704 kilometres and 1,138 kilometres. Combined with rotational light curves, the occultation constrains the three-dimensional orientation of Haumea and its triaxial shape, which is inconsistent with a homogeneous body in hydrostatic equilibrium. Haumea's largest axis is at least 2,322 kilometres, larger than previously thought, implying an upper limit for its density of 1,885 kilograms per cubic metre and a geometric albedo of 0.51, both smaller than previous estimates 1, 10,11 . In addition, this estimate of the density of Haumea is closer to that of Pluto than are previous estimates, in line with expectations. No global nitrogen-or methane-dominated atmosphere was detected.Within our programme of physical characterization of trans-Neptunian objects (TNOs), we predicted an occultation of the star URAT1 533− 182543 by the dwarf planet (136108) Haumea and arranged observations as explained in Methods. Positive occultation detections were obtained on 2017 January 21, from twelve telescopes at ten different observatories. The instruments and the main features of each station are listed in Table 1.As detailed in Methods (see also Fig. 1), the light curves (the normalized flux from the star plus Haumea versus time) show deep 1 2

Aims. The Antarctica Search for Transiting Extrasolar Planets (ASTEP), an automatized 400 mm telescope located at Concordia station in Antarctica, monitored β Pictoris continuously to detect any variability linked to the transit of the Hill sphere of its planet β Pictoris b. The long observation sequence, from March to September 2017, combined with the quality and high level duty cycle of our data, enables us to detect and analyse the δ Scuti pulsations of the star. Methods. Time series photometric data were obtained using aperture photometry by telescope defocussing. The 66 418 data points were analysed using the software package Period04. We only selected frequencies with amplitudes that exceed four times the local noise level in the amplitude spectrum. Results. We detect 31 δ Scuti pulsation frequencies, 28 of which are new detections. All the frequencies detected are in the interval 34.76−75.68 d −1 . We also find that β Pictoris exhibits at least one pulsation mode that varies in amplitude over our monitoring duration of seven months.

A general review of spider burrows and history of their research in eighteenth to nineteenth centuries are provided on the basis of the literature, which is dispersed and almost forgotten by majority of ichnologists. Moreover, burrows of the wolf spider Trochosa hispanica Simon, 1870 from a mountain meadow in Albania are presented. They are composed of an almost straight through gently curved to slightly winding vertical shafts (8.2-17.2 mm in diameter) with a basal, oval chamber, which is 14.5-30.6 mm wide. Above the ground level, some of them show a low, agglutinated chimney a cone composed of soil granules. The burrows are 83-235 mm long. They are comparable with the trace fossil Macanopsis Macsotay, 1967. Other spider burrows can form a simple shaft, which may be ascribed to the ichnogenus Skolithos Haldeman, 1840, or a shaft with the side oblique branches, which is is similar to the ichnogenus Psilonichnus Fürsich, 1981. Many spider burrows show one or more chambers. Their outlet may be closed with a trapdoor or show a chimney sticking above the ground. They may show scratch traces running parallel to the burrow. The burrows are domiciles in which spiders spend a part of, or even the whole life. They protect spiders against harsh environmental conditions, foremost against too low or to high temperature, sheet floods, or predators. Moreover, they can be also a place for copulation, oviposition, parental care, placement of cocoons, or shedding the exuvia. Burrowing spider are more common in in warmer climatic zones, in open space, above the water ground level, and less common in flooded. So far, very few examples of fossil spider burrows are recognised, mostly in Cenozoic sediments, even if spiders are known since the Carboniferous.

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The exoplanet revolution is well underway. The last decade has seen order-of-magnitude increases in the number of known planets beyond the Solar system. Detailed characterization of exoplanetary atmospheres provide the best means for distinguishing the makeup of their outer layers, and the only hope for understanding the interplay between initial composition chemistry, temperature-pressure atmospheric profiles, dynamics and circulation.While pioneering work on the observational side has produced the first important detections of atmospheric molecules for the class of transiting exoplanets, important limitations are still present due to the lack of systematic, repeated measurements with optimized instrumentation at both visible (VIS) and near-infrared (NIR) wavelengths. It is thus of fundamental importance to explore quantitatively possible avenues for improvements. In this paper we report initial results of a feasibility study for the prototype of a versatile multi-band imaging system for very high-precision differential photometry that exploits the choice of specifically selected narrow-band filters and novel ideas for the execution of simultaneous VIS and NIR measurements.Starting from the fundamental system requirements driven by the science case at hand, we describe a set of three opto-mechanical solutions for the instrument prototype: 1) a radial distribution of the optical flux using dichroic filters for the wavelength separation and narrow-band filters or liquid crystal filters for the observations; 2) a tree distribution of the optical flux (implying 2 separate foci), with the same technique used for the beam separation and filtering; 3) an 'exotic' solution consisting of the study of a complete optical system (i.e. a brand new telescope) that exploits the chromatic errors of a reflecting surface for directing the different wavelengths at different foci.In this paper we present the first results of the study phase for the three solutions, as well as the results of two laboratory prototypes (related to the first two options), that simulate the most critical aspects of the future instrument.