Gabor Horvath

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• Professor
• Professor (Full) at Eötvös Loránd University

Although plant stem cross-sections are most often circular, some are square, triangular or elliptic, but these are rare. The advantage of quadratic stems over cylindrical ones, if one exists, is unclear. Here we propose a (bio) mechanical advantage of square-stemmed plants. Our idea is based on the fact that the second moment of inertia I of a stem...

3rd, revised, extended edition. Springer Series in Vision Research, series editors: Michael Bok, Fabio Cortesi

In field experiments, the behavioural responses of Ephoron virgo and Caenis robusta mayflies were studied to lamps emitting horizontally and vertically polarized and unpolarized light. In both species, unpolarized light induced positive phototaxis, horizontally polarized light elicited positive photo- and polarotaxis, horizontally polarized light w...

During dawn and dusk, the sun is near the horizon, and when looking at the water perpendicular to the solar vertical near the Brewster’s angle 53° from the nadir (mirror point of the zenith), the Brewster’s dark patch (BDP) occurs on the water surface. The BDP exists only if the solar elevation angle θS above the horizon is smaller than 58°. Its ex...

Non-migratory female greater mouse-eared bats (Myotis myotis) use celestial polarization at sunset to calibrate their magnetic compass used for homing. Anatomical, physiological and behavioural investigations should elucidate how these bats perceive polarized light and how they use it for orientation. In choice experiments, migratory Nathusius’ bat...

Anomala corpulenta scarab beetles possess metallic green, left-circularly-polarizing exocuticle. In laboratory choice experiments, the mating behaviour of this species was not influenced by circular polarization (CP). Until now, no evidence has been found for behavioural responses to CP light in Anomala vitis, Anomala dubia, Anomala corpulenta (Rut...

In optomotor experiments, the larvae of Anax imperator dragonflies proved to be polarization sensitive. These larvae may use polarization to improve the perception of radiance contrast by selectively filtering partially linearly polarized light scattered by the turbid underwater optical environment. In double-choice field experiments, the polarotax...

In optomotor experiments, the post-larvae of the coral-reef fish Premnas biaculeatus proved to be polarization sensitive. Also in optomotor experiments, the polarization sensitivity of the planktivorous fishes Atherinomorus forskalii and Sparus aurata was studied. Atherinomorus forskalii was only polarization sensitive if UV light was available, wh...

In this chapter, we deal with Vikings and the hypothetical sky-polarimetric Viking navigation (SPVN), surveying the knowledge accumulated in the following related topics: Viking sun-compass and sunstones. Atmospheric optical prerequisites of SPVN. Error functions of the four main steps of SPVN. Error propagation in SPVN—navigation accuracy versus s...

In this chapter, we deal with the following sources and case studies of polarized light pollution (PLP): Tree resin as the most ancient PLP source: polarotactic aquatic insects fossilized in amber. Car surfaces and solar panels. How white orthogonal grid lines reduce PLP. PLP of lamplit bridges for night-swarming polarotactic mayflies. Asphalt road...

In this chapter, we deal with the following astropolarization studies: Sky-polarimetric corroboration of the resolution of the UV-sky-pol paradox of insect celestial polarization sensitivity; night sky polarization at super blue blood Moon during a total lunar eclipse; polarization of the sky, solar corona and lunar disc during total solar eclipses...

The anatomy, photoreceptive structure and optics of the two ocellar fields on the head of poduromorph springtails (Collembola) are here summarized. The water-surface-inhabiting Podura aquatica springtails have the ability to estimate both the degree and the angle of polarization. They are attracted to linearly polarized light, the polarization dire...

This chapter introduces to trilobites, extinct arthropods of the Palaeozoic and their diversity of morphological characteristics, lifestyles and visual systems. We explore the perspective to reveal something about the capability of perception and the relevance of linearly polarized light for these animals which became extinct about a quarter of a b...

In object discrimination and detection laboratory experiments, it turned out that harbour seals (Phoca vitulina) do not respond to linearly polarized test stimuli. Future work should elucidate whether these seals are polarization insensitive per se.

In optomotor experiments, Aedes aegypti female mosquitoes responded to rotating stripes of alternating orthogonal polarization directions. Future studies should reveal the possible regional differences in polarization sensitivity of the compound eyes, and which ommatidial retinula cells and in which spectral range are polarization sensitive.

In this chapter, we deal with the following aspects of the polarotaxis in horseflies (Tabanidae): Seasonality and weather-dependent flight activity of polarotactic male and female horseflies monitored by polarization and canopy traps. Why do horseflies need polarization sensitivity for host detection? Striped bodypaintings protect against horseflie...

Mature inflorescences of sunflowers ( Helianthus annuus ) orient constantly on average to the geographical east. According to one of the explanations of this phenomenon, the eastward orientation of sunflower inflorescences increases the number of attracted insect pollinators. We tested this hypothesis in three field experiments performed in floweri...

Drone-based imaging polarimetry is a valuable new tool for the remote sensing of the polarization characteristics of the Earth’s surface. After briefly reviewing two earlier drone-polarimetric studies, we present here the results of our drone-polarimetric campaigns, in which we measured the reflection–polarization patterns of greenhouses. From the...

The Kordylewski dust clouds (KDCs) around the L5 and L4 Lagrange points of the Earth–Moon system have been first observed by imaging polarimetry in 2017 and 2022 in a Hungarian astronomical observatory. Due to the non-ideal (almost always hazy, aerosol-polluted) astroclimate of Hungary and the extremely low intensity of dust-scattered sunlight, the...

Specific polarized light pollution (PLP) means the adverse influences of strongly and horizontally polarized light reflected from smooth and dark artificial surfaces on polarotactic water-seeking aquatic insects. Typical PLP sources are photovoltaic panels. Using drone-based imaging polarimetry, in a solar panel farm, we measured the reflection-pol...

Viking sailors ruled the North Atlantic Ocean for about three hundred years. Their main sailing route was the 60° 21’ 55’’ latitude between Norway and Greenland. Although they did not have a magnetic compass, in sunshine they used a sun-compass to determine the geographical north (solar Viking navigation: SVN). It has been hypothesized that when th...

Dark artificial surfaces reflecting highly and horizontally polarized light usually have negative effects on polarotactic aquatic insects detecting their habitats by the horizontal polarization of water-reflected light. This ecologically disadvantageous phenomenon is called polarized light pollution. We have observed that the water between the conc...

The differences between the consecutive world-records of shot put and hammer throw tendentiously decrease. Therefore, nowadays it would be worth taking into account the influence of certain environmental factors on the range L, such as the latitude and release azimuth direction. Both factors exert influence on L by the centrifugal acceleration acen...

Aquatic insects detect water by the horizontal polarization of water-reflected light and thus are attracted to such light. Recently, in the Hungarian Lake Balaton we observed dark water patches forming between every autumn and spring because of the inflow of black suspended/dissolved organic matter into the bright lake water. Earlier, the polarizat...

In 1961, Kordylewski found two bright patches near the L5 Lagrange point of the Earth-Moon system. This referred to an accumulation of dust particles, later called as Kordylewski dust cloud (KDC). In spite of the photographic observation of the L5 KDC by Kordylewski and its visual (naked-eyed) or photometric confirmation by others, some astronomers...

Several hypotheses tried to explain the advantages of zebra stripes. According to the most recent explanation, since the borderlines of sunlit white and black stripes can hamper thermal vessel detection by blood-seeking female horseflies, striped host animals are unattractive to these parasites which prefer hosts with an homogeneous coat, on which...

Multiple hypotheses have been proposed for possible functions of zebra stripes. The most thoroughly experimentally supported advantage of zebra stripes is their visual unattractiveness to horseflies (tabanids) and tsetse flies. We propose here a plausible hypothesis why biting horseflies avoid host animals with striped pelages: in sunshine the temp...

After anthesis, the majority of mature sunflower (Helianthus annuus) inflorescences face constantly East, which direction ensures maximal light energy absorbed by the inflorescences in regions where afternoons are on average cloudier than mornings. Several theories have tried to explain the function(s) of this eastward orientation. Their common ass...

In the Northern Hemisphere, south is the conventional azimuth direction of fixed-tilt monofacial solar panels, because this orientation may maximize the received light energy. How does the morning-afternoon cloudiness asymmetry affect the energy-maximizing azimuth direction of such solar panels? Prompted by this question, we calculated the total li...

Mature sunflower (Helianthus annuus) inflorescences, which no longer follow the Sun, face the eastern celestial hemisphere. Whether they orient toward the azimuth of local sunrise or the geographical east? It was recently shown that they absorb maximum light energy if they face almost exactly the geographical east, and afternoons are usually cloudi...

Although Viking sailors did not have a magnetic compass, they could successfully navigate with a sun-compass under a sunny sky. Under cloudy/foggy conditions, they might have applied the sky-polarimetric Viking navigation (SPVN), the high success of which has been demonstrated with computer simulations using the following input data: sky polarizati...

In 1961, the Polish astronomer, Kazimierz Kordylewski found dust clouds around the triangular Lagrange points L4 and L5 of the Earth-Moon system. After this discovery, several astronomers observed the Kordylewski dust clouds (KDCs) with photometry or ground-based imaging polarimetry, altogether 21 times. Remarkably, the L5 KDC has been detected thr...

There is a long-lasting debate about the possible functions of zebra stripes. According to one hypothesis, periodical convective air eddies form over sunlit zebra stripes which cool the body. However, the formation of such eddies has not been experimentally studied. Using schlieren imaging in the laboratory, we found: downwelling air streams do not...

During the total solar eclipses on 11 August 1999 in Kecel (Hungary) and on 29 March 2006 in Side (Turkey), two Hungarian groups performed full-sky imaging polarimetric measurements of the eclipsed sky. They observed the spatiotemporal change of the celestial polarization pattern and detected three polarization neutral points as well as two points...

The moon illusion is a visual deception when people perceive the angular diameter of the Moon/Sun near the horizon larger than that of the one higher in the sky. Some theories have been proposed to explain this illusion, but not any is generally accepted. Although several psychophysical experiments have been performed to study different aspects of...

The mature inflorescence of sunflowers (Helianthus annuus) orients eastward after its anthesis (the flowering period, especially the maturing of the stamens), from which point it no longer tracks the Sun. Although several hypothetical explanations have been proposed for the ecological functions of this east facing, none have been tested. Here we pr...

Many insect species rely on the polarization properties of object-reflected light for vital tasks like water or host detection. Unfortunately, typical glass-encapsulated photovoltaic modules, which are expected to cover increasingly large surfaces in the coming years, inadvertently attract various species of water-seeking aquatic insects by the hor...

Tabanid flies (Diptera: Tabanidae) are attracted to shiny black targets, prefer warmer hosts against colder ones and generally attack them in sunshine. Horizontally polarised light reflected from surfaces means water for water-seeking male and female tabanids. A shiny black target above the ground, reflecting light with high degrees and various dir...

This book presents the current knowledge on arthropod vision and the results of successful manipulations of arthropods. It also suggests new methods for using optical manipulation to protect against arthropod pests and to improve the performance of beneficial arthropods. Due to the applied nature of this book, only brief overviews of the knowledge...

This book presents the current knowledge on arthropod vision and the results of successful manipulations of arthropods. It also suggests new methods for using optical manipulation to protect against arthropod pests and to improve the performance of beneficial arthropods. Due to the applied nature of this book, only brief overviews of the knowledge...

This book presents the current knowledge on arthropod vision and the results of successful manipulations of arthropods. It also suggests new methods for using optical manipulation to protect against arthropod pests and to improve the performance of beneficial arthropods. Due to the applied nature of this book, only brief overviews of the knowledge...

Blood-sucking horseflies (tabanids) prefer warmer (sunlit, darker) host animals and generally attack them in sunshine, the reason for which was unknown until now. Recently, it was hypothesized that blood-seeking female tabanids prefer elevated temperatures, because their wing muscles are quicker and their nervous system functions better at a warmer...

Space debris larger than 1 cm can damage space instruments and impact Earth. The low‐Earth orbits (at heights smaller than 2,000 km) and orbits near the geostationary‐Earth orbit (at 35,786 km height) are especially endangered because most satellites orbit at these latitudes. With current technology, space debris smaller than 10 cm cannot be tracke...

From a large distance tabanid flies may find their host animal by means of its shape, size, motion, odour, radiance and degree of polarization of host-reflected light. After alighting on the host, tabanids may use their mechano-, thermo-, hygro- and chemoreceptors to sense the substrate characteristics. Female tabanids prefer to attack sunlit again...

Amber contains numerous well-preserved adult aquatic insects (e.g., aquatic beetles – Coleoptera, water bugs – Heteroptera, dragonflies – Odonata, caddisflies – Trichoptera, mayflies – Ephemeroptera, stone flies – Plecoptera). Since amber is fossilised resin of terrestrial conifer trees, it is an enigma how aquatic insects have ended up in the resi...

Bodypainting is widespread in African, Australian and Papua New Guinean indigenous communities. Many bodypaintings use white or bright yellow/grey/beige stripes on brown skin. Where the majority of people using bodypainting presently live, blood-sucking horseflies are abundant, and they frequently attack the naked brown regions of the human body su...

Telescopes mounted with polarizers can study the neutral points of the Earth's atmosphere, the solar corona, the surface of planets/moons of the Solar system, distant stars, galaxies, and nebulae. These examples demonstrate well that polarimetry is a useful technique to gather astronomical information from spatially extended phenomena. There are tw...

Since the discovery in 1772 of the triangular Lagrange points L4 and L5 in the gravitational field of two bodies moving under the sole influence of mutual gravitational forces, astronomers have found a large number of minor celestial bodies around these points of the Sun-Jupiter, Sun-Earth, Sun-Mars and Sun-Neptune systems. The L4 and L5 points of...

Evolutionary traps are scenarios in which animals are fooled by rapidly changing conditions into preferring poor‐quality resources over those that better improve survival and reproductive success. The maladaptive attraction of aquatic insects to artificial sources of horizontally polarized light (e.g. glass buildings, asphalt roads) has become a fi...

Researchers studying the polarization characteristics of the optical environment prefer to use sequential imaging polarimetry, because it is inexpensive and simple. This technique takes polarization pictures through polarizers in succession. Its main drawback is, however, that during sequential exposure of the polarization pictures, the target must...

There are as many as 18 theories for the possible functions of the stripes of zebras, one of which is to cool the animal. We performed field experiments and thermographic measurements to investigate whether thermoregulation might work for zebra-striped bodies. A zebra body was modelled by water-filled metal barrels covered with horse, cattle and ze...

Inspired by the pioneer work of the nineteenth century photographer, William Nicholson Jennings, we studied quantitatively how realistic painted lightnings are. In order to answer this question, we examined 100 paintings and 400 photographs of lightnings. We used our software package to process and evaluate the morphology of lightnings. Three morph...

According to a famous hypothesis, Viking sailors could navigate along the latitude between Norway and Greenland by means of sky polarization in cloudy weather using a sun compass and sunstone crystals. Using data measured in earlier atmospheric optical and psychophysical experiments, here we determine the success rate of this sky-polarimetric Vikin...

Ecological traps are maladaptive behavioural scenarios in which animals prefer to settle in habitats with the lowest survival and/or reproductive success. Aquatic insect species, for example, are attracted to sources of horizontally polarized light associated with natural water bodies, but today they commonly prefer to lay their eggs upon asphalt r...

Artificial shiny dark objects reflecting horizontally polarized light (e.g. asphalt roads, black cars, solar panels) can attract polarotactic aquatic insects in mass. Glass buildings on the riverside also lure swarming caddisflies emerging from the river. These caddisfly swarms are a temporary rich food source for certain bird species, such as whit...

Numerous negative ecological effects of urban lighting have been identified during the last decades. In spite of the development of lighting technologies, the detrimental effect of this form of light pollution has not declined. Several insect species are affected including the night-swarming mayfly Ephoron virgo: when encountering bridges during th...

Horseflies (Tabanidae) are polarotactic, being attracted to linearly polarized light when searching for water or host animals. Although it is well known that horseflies prefer sunlit dark and strongly polarizing hosts, the reason for this preference is unknown. According to our hypothesis, horseflies use their polarization sensitivity to look for t...

When the sun is near the horizon, a circular band with approximately vertically polarized skylight is formed at 90° from the sun, and this skylight is only weakly reflected from the region of the water surface around the Brewster’s angle (53° from the nadir). Thus, at low solar heights under a clear sky, an extended dark patch is visible on the wat...

According to Thorkild Ramskou's theory proposed in 1967, under overcast and foggy skies, Viking seafarers might have used skylight polarization analysed with special crystals called sunstones to determine the position of the invisible Sun. After finding the occluded Sun with sunstones, its elevation angle had to be measured and its shadow had to be...

Ecological traps occur when rapid environmental change causes animals to actually prefer inferior habitats. Traps increase the likelihood of species extinction, but our understanding of how evolved behavioral algorithms interface with increasingly novel ecosystems to trigger them remains limited. Both polarized and unpolarized light are increasingl...

When an artificial surface (e.g. an asphalt road) reflects strongly and horizontally polarized light as water bodies do in the nature, polarotactic aquatic insects, like the creek-dwelling Ephemera danica mayflies easily become deceived. After swarming above the creek surface, E. danica females begin their upstream compensatory flight and can be de...

If a human looks at the clear blue sky from which light with high enough degree of polarization d originates, an 8-shaped bowtie-like figure, the yellow Haidinger's brush can be perceived, the long axis of which points towards the sun. A band of high d arcs across the sky at 90° from the sun. A person can pick two points on that band, observe the y...

Photovoltaic solar panels represent one of the most promising renewable energy sources, but are strong reflectors of horizontally polarized light. Polarized light pollution (PLP) associated with solar panels causes aquatic insects to prefer to oviposit on panels over natural water bodies, with potential to negatively impact their global populations...

The theory of sky-polarimetric Viking navigation has been widely accepted for decades without any information about the accuracy of this method. Previously, we have measured the accuracy of the first and second steps of this navigation method in psychophysical laboratory and planetarium experiments. Now, we have tested the accuracy of the third ste...

The 6-ommatidium ventral eye of the water-surface-inhabiting springtail Poduara aquatica has horizontal and vertical microvilli and perceives light from the ventral, frontal and frontodorsal regions, while the 2-ommatidium dorsal eye possesses two upward-looking ommatidia with vertical microvilli. The ventral eye may serve water detection by its po...

Like other aquatic insects, mayflies are positively polarotactic and locate water surfaces by means of the horizontal polarization of water-reflected light. However, may vertically polarized light also have implications for the swarming behaviour of mayflies? To answer this question, we studied in four field experiments the behavioural responses of...

According to an old but still unproven theory, Viking navigators analysed the skylight polarization with dichroic cordierite or tourmaline, or birefringent calcite sunstones in cloudy/foggy weather. Combining these sunstones with their sun-dial, they could determine the position of the occluded sun, from which the geographical northern direction co...

Electronic Supplemetary Material for Adjustment errors of sunstones in the first step of sky-polarimetric Viking navigation: Studies with dichroic cordierite/tourmaline and birefringent calcite crystals

The calcitic lenses in the eyes of Palaeozoic trilobites are unique in the animal kingdom, although the use of calcite would have conveyed great advantages for vision in aquatic systems. Calcite lenses are transparent, and due to their high refractive index they would facilitate the focusing of light. In some respects, however, calcite lenses bear...

Ecological photopollution created by artificial night lighting can alter animal behavior and lead to population declines and biodiversity loss. Polarized light pollution is a second type of photopollution that triggers water-seeking insects to ovisposit on smooth and dark man-made objects, because they simulate the polarization signatures of natura...

Cloud cover estimation is an important part of routine meteorological observations. Cloudiness measurements are used in climate model evaluation, nowcasting solar radiation, parameterizing the fluctuations of sea surface insolation, and building energy transfer models of the atmosphere. Currently, the most widespread ground-based method to measure...

Although the tabanid species and populations occurring in eastern central Europe (Carpathian Basin) are thoroughly studied, there are only sporadic data about the influence of weather conditions on the abundance and activity of horseflies. To fill in this lack, in Hungary, we performed a 3-month summer survey of horsefly catches registering the wea...

Cue-conflict experiments were performed to study the compass calibration of one predominantly diurnal migrant, the dunnock (Prunella modularis), and two species of nocturnal passerine migrants, the sedge warbler (Acrocephalus schoenobaenus), and the European robin (Erithacus rubecula) during autumn migration in South Sweden. The birds' orientation...

In this chapter the occurrence of circularly polarized (CP) light in nature (both in the abiotic and biotic optical environment) is surveyed. We deal with the reason and the possible adaptive significance of CP light reflected from the exocuticle of many beetle species belonging to the Scarabaeoidea. This unique feature of the insect exocuticle see...

In this chapter we show that primary aquatic insects fly predominantly in mid-morning, and/or around noon and/or at nightfall. We describe the different types of their diurnal flight activity rhythm characterised by peaks at low and/or high solar elevations. We present here experimental evidence that the polarization visibility Q(θ) of water surfac...

Blood-sucking female tabanid flies cause serious problems for animals and humans. For the control of tabanids, the knowledge about their seasonality and daily activity is of great importance. Earlier, only traditional traps capturing exclusively female tabanids have been used to survey tabanid activity. The data of such temporal trapping do not ref...

Using full-sky imaging polarimetry, we measured the celestial distribution of polarization during sunset and sunrise at partial (78% and 72%) and full (100%) moon in the red (650 nm), green (550 nm), and blue (450 nm) parts of the spectrum. We investigated the temporal change of the patterns of degree p and angle α of linear polarization of sunlit...