Short story: The human nature – A Fairy Tale?

A father lived deep in the woods in a small house with his two growing children, a daughter and a son. The mother did not love the woods and had therefore left her husband and children many years ago.

The father taught his children to be one with nature. And so the son knew all the birds that lived in the forest, not only the many species, but also each individual, which he could always recognize by the sound of its personal melody. The daughter loved the trees and she too knew all kinds and every single tree.

The father had once moved his family from the big city to the woods because he believed that it was the big cities that robbed people of their minds and natural instincts, thus inciting destruction and violence.

In seclusion, he wanted to allow himself and his family to become part of nature again, because he hoped that it would be his descendants who could survive the fate of the world. It quickly became too much for the woman. She missed the narrow streets, the crowded markets, the idleness and the noise of the busy city. And so she fled one dark night and never came back.

The man taught the children how to make fire with stones, and which berries, fruits, and mushrooms are edible. And for a while the father lived with the son and daughter in happy and calm harmony. Only the wind occasionally swept through the green treetops and became the accompanying music in the symphony of birdsongs and the whispering, greening and howling of the wild animals.

But the older the children got, the more they bothered about the seclusion in which they lived. Increasingly, they no longer saw the wild nature around them as an asset, but as a constant threat.

The birds shit on their heads, ate the berry bushes and fruit trees bare. At night the ominous cry of the owls robbed them of their sleep. And the trees, bushes and weeds grew closer and closer to the family’s small wooden house with the crooked chimney.

And it seemed to the children as if the forest wanted to slowly and cruelly suffocate them and their house. And so, estranged from the father, both son and daughter conspired, met secretly in the forest clearing near the river and discussed that the father was probably not in his right mind to just let nature happen. And they realized that only those who know how to subjugate nature would survive.

And when the father went out to get food and firewood, the children began to tame, to control, to clean up wild nature. The son showed the daughter how to make a bow out of wood fibers and thin branches. The daughter explained to the brother which flints could be used most efficiently to quickly start a fire.

And every day, punctually when father left the house, they would meet in the forest clearing and together they would plan to shoot as many birds as possible with the bow. And it was not long before the magnificent symphony of the birds over the great, wide forest fell silent forever.

And brother and sister worked hard to carry the many small dead bodies to the forest clearing by the river, where in the late afternoon, before their father returned, they kindled a huge campfire in which they burned the dead birds of the forest in droves. And they couldn’t resist the smell of the simmering, tender meat, so they ate a feast that prevented them developing any appetite later when their father was preparing supper.

But he wasn’t surprised because he firmly believed that modesty always comes when people have found their way back to their original nature.

When there were no more birds in the whole forest, brother and sister hunted mice and rabbits and everything that was small and rustled or squeaked and frightened the siblings. Here, too, they ate and became fuller and fuller every day. But the father, exhausted from his long excursions and almost blind to everything that contradicted his ideals, continued to ignore the changes in his children and the forest.

And now it was only the increased hunger that moved the siblings to kill all the deer and pigs. And at the feast in the clearing by the river, they filled their bellies almost to the point of bursting. But the father, who was getting older and more tired, still didn’t notice any of this. And now the weasels, foxes, and wolves died of their own accord, so that the brother and sister laid aside their bows, because they only had to collect the dead animals.

There were so many that the siblings slept into the afternoon for many weeks and then indulged in gluttony while the father progressively lost his sight and noticed nothing.

Like pigs, brother and sister had become so fat that they had great difficulty making their way through dense undergrowth and over gnarled tree roots to the clearing by the river. And so they decided to clean up the forest and once and for all to remove all vegetation between the house and the forest clearing.

To this end, both set fire to different places. But they completely underestimated the destructive power of the flames. At first only individual trees burned, but then the flames combined and became a raging and violent conflagration, which first completely burned down the house with unspeakable heat and breakneck speed and then took hold of the entire forest. Brother and sister had no choice but to throw themselves into the river and stay there, mostly completely submerged, for two days until the fire died out, until the forest was completely burned down.

And when they emerged from the river, there was only a soot-blackened wasteland with gnarled skeletons crouching on the ground, the sad remnants of what was once the forest. A huge cloud of soot and water vapor covered the sky and the sun, everything was gray and dark and the smell of death and ash filled the air.

And the father? He was on his way back, with bundles of firewood hauling in a cart and bags full of fruit slung over his shoulder, when he saw the blaze racing toward him. He parked the cart and put his bags down. And in that moment he finally realized what had happened. He would never see his children growing adult, other people would never follow the example of his family and found a new dynasty of purer, nature-loving people with his children.

And just before the firestorm reached his body, shattering his head and evaporating his brain, just before his body thereafter completely crumbled to ashes, tears welled up in his eyes and he exclaimed in a hoarse voice, „So this isn’t a brain spectre, it’s indeed human nature, destruction and killing!“

Oh, if only brother and sister had known the way back to the city. But that was far away, and the path was completely burned and turned into a wasteland. The siblings had little strength left to anticipate and mourn the death of their father.

They laboriously built a small, shabby hut out of the burnt ruins of the house, in which they lived together in a very small space from then on. It wasn’t long before the brother knew every moss and lichen, while the sister knew every stone and every dry waterhole in this forest desert. And so they ate mosses and lichens, which they crushed to pulp with all kinds of suitable stones. And they drank the water from the shrunken river, which was more like thick, foul-smelling slime.

Both, brother and sister, grew thin as spindles, and days turned into months and months into years. Since we are in the year 2085 and cold winters have long since ceased to exist even far from the equator, the former forest slowly turned into a real desert of sand and stone. The rare rain filled the riverbed just enough for brother and sister to drink. Mosses had become rare. And so the siblings were eating lichens and the putrid bank mud of the river, when a dispute arose among the siblings over the privilege of eating.

So they divided the one shabby hut into two shabby huts, which they built along the river bank at a suitable distance from each other, so as to remain close to their feeding grounds but as far away from each other as possible. But occasional quarrels were not absent. Ultimately, the initial quarrel turned into deep anger, and then abysmal hatred. The brother, now a man, began throwing heavy stones at the sister whenever she tried to approach the succulent heap of putrid riverweed and filthy mud he had first spotted.

But the sun shone relentlessly and hot winds sanded the desert landscape more and more. The bed of the river shrank, and the huts of the quarreling scrawny siblings inevitably drew nearer and nearer to one another. In the end, the brother saw no other way out than to burn down the sister’s hut, whereupon she grabbed an old, rusty and long nail and drove it right into the brother’s skull.

She buried her dead brother where the forest clearing had once been, and yes, she shed a tear in the process. And more tears followed, day after day and month after month. After another year, the sister died, not of hunger, nor of thirst or a force of nature, but of loneliness. How can you go on living when there isn’t even someone to hate, she thought just before closing her eyes forever. Her body crumbled to dust that the wind carried up into the air. And the dust became one with the ashes of the forest and those of the father, and finally fell down on the brother’s grave. In the end there was nothing left but the desert.

© all copyrights (text, idea, drawings) by Stefan F Wirth, Berlin, 3 January 2023

Mate guarding of a juvenile female in mites of the Histiostomatidae (Astigmata, Acariformes)

Male of Histiostoma sp. guards a female tritonymph, copyrights Stefan F. Wirth 2005-2022

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A strategy to avoid male competition for females

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Some mites of the Histiostomatidae practice so-called mate guarding of subadult females in order to have an advantage in the intraspecific competition between males for adult females. My SEM image shows a male on top of a female, which is still inside its tritonymphal cuticle. Inside the tritonymphal cuticle, the adult female is already developed and shortly before hatching. Before hatching, the legs of the new instar are folded under the body side. The new second leg on the right side is visible in the SEM, because the weak cuticle of the old leg broke off. This strategy to avoid sexual competition is quite common with Histiostomatidae. Due to insufficient mite material and not longer available clear ecological data, I determine the long haired adults of my old SEM series with caution as Histiostoma sp., it seemingly was found around sap flux on a tree trunk in Berlin. The species is not identical with Seliea pulchrum (= Histiostoma pulchrum), typically known from sap flux. The distance between the male legs 1 and 2 in the photo is about 0.1 mm. These SEM objects were seemingly chemically dried for the scanning electron microscopic procedure. The photos were taken around 2005 with an older SEM at FU Berlin. © Stefan F. Wirth Berlin 2022

Two different forms of cryptic species-complexes in mites of the Histiostomatidae (Astigmata) from bank mud and bark beetle-galleries and their significance for applied biodiversity research

Biologe ISSN 2750-4158

Stefan F. Wirth, acarologist, freelancer, Berlin, Germany

Citation: WIRTH S. F. (2021): Two different forms of cryptic species-complexes in mites of the Histiostomatidae (Astigmata) from bank mud and bark beetle-galleries and their significance for applied biodiversity research. Biologe (ed. Stefan F. Wirth), category : original scientific papers volume 1 (2021; 2022) , 1-7. URL: https://biologe.wordpress.com/2021/12/31/two-different-forms-of-cryptic-species-complexes-in-mites-of-the-histiostomatidae-astigmata-from-bank-mud-and-bark-beetle-galleries-and-their-significance-for-applied-biodiversity-research

Abstract

In biodiversity research, knowledge of species numbers is the basis for planning environmental protection and climate research. However, the taxonomic work is made more difficult by cryptic species complexes in the world of organisms. Careless determinations of similar species must be prevented. For a beter understanding, examples from different animal groups are given. Using two species complexes of the mite taxon Histiostomatidae (Astigmata), two different forms of cryptic species complexes are presented in detail. Based on three species from a group associated with bark beetles, an example of a species complex is presented in detail, in which all stages of development look confusingly similar to one another. On the other hand, four species of mites from the bank mud of standing waters can only be confused with one another on the basis of their phoretic dispersal stage (deutonymph), while the adults differ distinctly. The meaning of such species complexes is discussed in the evolutionary and applied context. It is critically pointed out that too few specialists are funded worldwide and few taxonomists have to work too quickly, so that there is a risk of cryptic groups of species not being taken into account in surveys.


Keywords: cryptic species groups, evolution, biodiversity research, Acariformes, Histiostomatidae, Astigmata, phoresy, Histiostoma piceae, Histiostoma Scheucherae, Histiostoma piceae, Histiostoma ulmi, Histiostoma palustre, Histiostoma litorale, male morphology, SEM, Histiostoma maritimum, Scolytinae, Carabidae, sapropel

Introduction

Biodiversity research is an essential fundament for disciplines like climate research and climate changes and thus contributes to an understanding about, how we humans need to treat our own environments. A main aspect of biodiversity research besides species monitoring is the evaluation of how many species we have. Specialists need to recognize and scientifically describe new species, especially, when it for example comes out that a complex of very similiar species contains more species than expected before (e.g. Laska et al. 2018). In tendency researchers in the field of biodiversity focus most on vertebrates in temperate regions and generally less in invertebrates (Titley et al. (2017).

The number of recently existing species in numerous cases is still unknown, especially in taxa of small organisms, such as mites. Due to a lack of specialists and due to a lack of fundamental research fundings, relatively much is known about direct pests of human sources, such as Varroa or Tetranychidae mites. But within the major clade Acariformes, ecological contexts and numbers and distribution of species of some free living taxa of Prostigmata and Oribatida/Astigmata are still an open field, even in Central Europe, e. g. Germany (Wirth, 2004).

This is despite the fact that for example phoretic mites, which use other arthropods as carriers for dispersal, can have highly complex relationships with their phoretic hosts, thus being of interest from the evolutionary, the ecological and even an applied point of view. The latter is discussed for example in context with different bark beetles, which their mites might affect by acting as vectors for fungus spores (Klimov & Khaustov, 2018).

Cryptic species complexes are a topic that is currently being widely dealt with in science. Such species complexes are characterized by the fact that they are difficult or impossible to distinguish morphologically. However, they can be clearly differentiated from one another using barcoding (e.g. Kameda et al, 2007), behavioral or ecological studies. Crossing experiments are a frequently used ecological method. Because according to the biological species concept, individuals of different species either cannot be crossed with one another or the offspring of such a hybridization is not fertile (e.g. Sudhaus & Kiontke, 2007).

Crossing experiments are particularly suitable for the investigation of cryptic species complexes in species that have a rapid life cycle and, due to their small size, can be accommodated well in standardized conditions. Such organisms are, for example, free-living nematodes of the Rhabditidae (e. g. Sudhaus & Kiontke, 2007) or mites of the Histiostomatidae (e.g. Wirth, 2004).

The cryptospecies phenomenon, which means that closer investigations show that animals once attributed to the same species actually represent several species, can in principle occur in the entire animal kingdom and in plants and fungi too (Shneyer & Kotseruba, 2015). Previously known subspecies are often given their own species status as a result. One example are the two monitor lizard species Varanus niloticus and V. ornatus (e. g. Böhme & Ziegler, 2004).

In this monitor lizard research mainly ecological differences to V. niloticus have been studied. As one of the results, V. ornatus does not have a diapause in summer, which is a distinct difference to V. niloticus (Böhme & Ziegler, 2004).
As an unusual phenomenon, a case of parthenogenesis was even observed in V. ornatus, but not in V. niloticus (Hennessy, 2010) so far. However, morphological differences between these two monitor lizards were known even before, for example relating to aspects of the dorsal drawing. But the authors named above were able to provide evidence that these morphological differences do not occur gradually, as orgininally assumed, but rather distinctly.

Another example of two sibling species (the most simple form of cryptic groups) that have been identified as different species by molecular biological studies are Homo sapiens and H. neanderthalensis (e.g. Prüfer et al., 2014). Originally it was assumed that H. neanderthalensis was a subspecies of H. sapiens. This is for example supported by the proven cultural exchange between the two species and the great morphological similarity. In the meantime, however, morphological findings such as the morphology of the nasal duct of the Neanderthal man have also supported the genetic findings (Márquez et al., 2014). However, very recent studies show that Neanderthal genetics have entered the lines of H. sapiens (Hajdinjak er al., 2021). As a result, both forms have crossed and produced fertile offspring. It remains to be seen whether this will possibly dismiss the concept of two species again.

Since the aim of all studies of cryptic species complexes is to find distinctive differences in the areas of morphology, ecology or barcoding (or all approaches together) that distinguish one species from all others, ultimately clearly definable, very closely related species remain in case of successful studies.

If the cryptic organisms are members of an organism-socialization, such as parasites and their hosts, the idea that a proven host specificity can be an indicator for a certain species of a cryptic complex is obvious. In fact, Wirth et al. (2016) for example postulated a host specificity for the phoretic mite Histiostoma piceae and its hosts, the bark beetles Ips typographus and I. cembrae. Nevertheless, relationships between associated species are usually not studied extensively enough to be able to unequivocally identify certain species on the basis of for example their hosts (Wirth, 2004).

Since cryptic species represent nevertheless separate species despite their extraordinary similarity, they are subject to the species concepts. As a result, they form different niches and can therefore appear sympatric in the same living space (e. g. McBride et al., 2009). This makes it difficult for biodiversity researchers and systematics to investigate the real numbers of species in such habitats.

If, instead, cryptic species are not sympatric, but distributed in adjacent areas, this can for example indicate that an allopatric species formation has either not been completed for a long time or is even still in the process of speciation (e. g. Gollmann, 1984).

Animal species that have different developmental stages can appear cryptic, i.e.  being morphologically confusingly similar, with regard to all these developmental stages, such as for example certain phoretic free-living nematodes, which then additionally have to be studied ecologically or genetically (e. g. Derycke et al. 2008).

Other species can hardly be distinguished morphologically with regard to a certain developmental stage, which is particularly common, but differ distinctly in other developmental stages, which are more difficult to find. Very similar looking lepidopteran caterpillars of sibling species (e. g. Scheffers et al. 2012) can be more commonly available than their adults, which might be easier to distinguish.

As a specialist for mites of the family Histiostomatidae (Astigmata, Acariformes) I will in my further argumentation refer to my biodiversity studies on these mites and explain the difficult situation for describers of new species based on several specific histiostomatid species, some being phoretically associated with bark beetles and others associated with different coleopterans from muddy sapropel-habitats around ponds in Berlin/Germany.
In connection with these cryptic groups of species, reference should be made to the applied difficulties in connection with biodiversity research. I am referring to the fact that, for a variety of reasons, often only a certain juvenile stage (deutonymph) is used for species descriptions (e. g. Klimov & Khaustov, 2018 B), although cryptic species can occur sympatricly in the same habitat and in many cases not be sufficiently differentiated from one another on the basis of just this one stage.

In Histiostomatidae as in most Astigmata taxa, the deutonymph (in older publications hypopus) represents the phoront, being adapted morphologically and behaviorally in getting dispersed by insects or other arthropods. This instar has no functional mouth, possesses a ventral suckerplate to attach to its carriers and a thicker sclerotization against dehydration. The deutonymph is often collected together with its phoretic host. Bark beetle traps are for example a common source, where dead deutonymphs still on their hosts come from and are subsequently forwarded to acarologists, who then are of course unable to create a mite culture in order to have also adult instars available for species descriptions  (e. g. Klimov & Khaustov, 2018 B) and other taxonomic purposes. This paper shall clarify, why it is instead necessary for a clear species determination to have the deutonymph and additionally at least adults available.

In this publication two cryptic species complexes from the taxon Histiostomatidae (Astigmata) are presented as result of my original scientific work. On the one hand morphologically very similar representatives of the Histiostoma piceae-group, which are originally associated with bark beetles (Scolytinae), on the other hand similar looking representatives, which are bound to insects in the area of ​​the banks of ponds with digested sludge (sapropel). It needs to be emphasized in that context that those herewith introduced two cryptic clades are phylogenetically not closer related to each other.

The presented bark beetle mites (chapter 1 in results) can only be distinguished morphologically by very gradual characteristics, in terms of phoretic deutonymphs as well as in terms of adults. However, there is a tendency towards host specificity (e.g. Scheucher, 1957), which is why there could be a permanent spatial separation of the species despite common occurrence in the same region.

The mites from the sapropel in the area of ​​the pond banks (chapter 2 in results) are presented on the basis of a certain area in Berlin (Germany), where they appeared sympatric. Unlike the bark beetle mites, they are morphologically clearly distinguishable with regard to the adults, but have morphologically very similar deutonymphs, which essentially only differ from one another in degrees.

Based on the representatives of two different cryptic species groups presented in this work, it should be shown that a sufficient range of morphological features for systematic and taxonomic differentiation and characterization of species can only be available if at least two developmental stages of a population can be studied. It is also pointed out that high-resolution optical methods can uncover a possibly systematically relevant variety of morphological features that would otherwise remain hidden. It is suggested that a suspected host specificity cannot always be used to differentiate between very similar species and that cryptic species can be found sympatricly on the same host as well as in the same habitat. The main aim is to show that there is a risk of confusion and a risk of underestimating the existing biodiversity if only the deutonymph is used for taxonomic purposes, just because it is for example easily available, when the host is captured. Nevertheless species descriptions based only on the deutonymphs are unfortunately still surprisingly common.

Due to the lack of sufficient research fundings and a corresponding decrease of experienced specialists, trends to remarkably simplify determinations and species descriptions are about to manifest themselves. Non specialists or less experienced acarologists increasingly try to recognize or describe new species based on the availability of deutonymphs only, because these phoronts are often easily accessible as bycatch of entomological material. It is mistakenly assumed that faster procedures could accelerate the level of scientific knowledge about the biodiversity of astigmatid mites (Wirth, 2004).

Material and Methods

Chapter 1 is an illustration of the current state of my research about a cryptic bark beetle-associated group of species. Problems and questions are additionally shown both on the basis of existing, in part own, literature. Chapter 2 is about four species of Histiostomatidae that were recorded from an old gavelpit area in the urban Berlin forest Grunewald, named „Im Jagen 86“, located 52° 29′ N, 13° 14′ E. This chapter focuses specifically on Histiostoma maritimum, collected between 2002 and 2012 (and also between 1999 and 2000 during my diploma thesis). Besides H. maritimum three other species were found in the same area and habitat: Histiostoma palustre, collected once via deutonymphs from a beetle of Genus Cercyon in 2002 and reared in culture over about two years on moist decomposing potato pieces, Histiostoma litorale, isolated as adults from sapropel mud once in 2002 and Histiostoma n. sp., reared only one generation long from adults to adults in 2019, inside sapropel-mud samples with moss growth and moist decomposing potato pieces.

Mites of H. maritimum were collected as deutonymphs on the beetles Heterocerus fenestratus (rarer on Heterocerus fusculus) and Elaphrus cupreus from sapropel around two ponds in the named area. After different experiments, mites developed successfully on beetle cadavers on 1.5 % water agar in Petri dishes (diameter 5 cm) at room temperature (ca 20°C, summer 2002). Three cultures (one cadaver of C. elaphrus and twice each time two cadavers of H. fenestratus) were observed over a period of about three weeks (additionally small pieces of beef heart were added to all these cultures to maintain suitable food sources). Adult mites were stored in 80 % ethanol for about 5 days and then critical point dried for SEM studies. Photos were taken by an analogous medium size camera via a Philips SEM 515 and later developed. Still unpublished copies from 2002 were scanned in a high 600 dpi solution and as tiffs via a CanoScan Lide 2010 in 2021. Restauration and picture quality improvement were performed via Adobe Lightroom. The areal panorama of the former multiple pond area was captured in September 2018 via a Dji Mavic Pro drone at a height between 30 and 50 m and subsequently modified into black and white.

Setal nomenclature follows Griffiths et al. (1990).

Results:

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RAW Berlin as a cultural center in Germany’s capital

The RAW

An inspiring composition of terrace, window, gate, trashcan and graffiti, copyrights for photo Stefan F. Wirth, June 2021

The RAW (Reichsbahnausbesserungswerk) extends between Warschauer Strasse, Revaler Strasse and Modersonstrasse in the Berlin district of Friedrichshain. The former railway area, which was closed in 1995, is considered to be the largest contiguous and culturally used fallow area in Germany.

Graffiti art giving the old architecture an own kind of dynamics, copyrights for photo Stefan F. Wirth, June 2021

Today the ruins are used culturally in a variety of ways. In addition to several clubs and art galleries, there are sports facilities, art studios and various take-out stands.

Self-government and graffiti art

The area is under grassroots self-government.

Atmosphere during a summer day, copyrights of photo Stefan F. Wirth, June 2021

You can already see art without having to enter galleries, namely in the form of graffiti art, which blends harmoniously and inspiringly into the partly crumbling terrain.

Skate hall and mosaic of architecture, daily life remnants and graffiti

Sports activities are also revealed to the visitor very quickly when entering the area. For example, the skate hall, which opened in 2004/2005, is the only indoor skating facility in Berlin and is internationally well known in that sports scene.

But during my short visit on a summer day afternoon in end of June 2021, I was most impressed by the mosaic of architecture elements, Graffiti and signs of daily life.

A corner close to the entrance from Revaler Straße, copyrights of photo Stefan F. Wirth, June 2021.

All copyrights Stefan F. Wirth, 27 June 2021

Reawakening at very early spring

Morning mist

Forest in the morning, tree stems covered by a foggy most, borderless steam wraps slowly rising in the air and disappearing there tracelessly.

Forests as moisture reservoir, being released in the morning due to the awakening warmth. Morning mist is nothing else than a fog, only some meters over the ground. Consisting like each fog of numerous water bodies in gas conditions, which condensate due to the cold night and seem to have springled all plants and even insects and other sleeping animals with tiny water drops.

Especially in arid environments, that morning mist watering is most wanted and essential for surviving.

With the rising sun, warmth moves the misty clouds up, where they cover the forests in a mysterious light, before the fog disappears.

Sunlight

Consisting of all rainbow colors, each color of the spectrum being defined by a specific wave length. But sunlight also consists of physical components, particles, called solar wind.
Light as essential source for life on earth, sunlight as energizer, basis for the production of oxygen. Warmer sun beams as reawakener of a sleeping forest.

Blooming

They bloom most early in the year, do not avoid to attract early insects inmidst of snow layers: snowdrops, winter aconites and crocuses.

Snowdrops (genus Galanthus) generate thermal energy due to the absorption of sunlight. This energy is essential for growth processes in cold environments.

Winter aconites (Eranthis hyemalis) have their blossoms only opened in the sunlight. Blossoms are closed over night. Opening and closing are temperature dependent growth processes. The blossoms themselves are resistant against cold. When temperatures rise to 10 – 12 degrees, first honey bee visits can be observed.

In crocuses (genus Crocus) blooming depends on the availability of moisture and warmth. Some species bloom in autumn, others in the late winter period.

All early blooming plants save nutrients as energy resources in tubers or bulbs.

Blue hour

When the sun disappears behind the horizon, an explosion of colors in red or yellowish cover the sky. In fact indicating the end of a day, in some cultures even officially a new day was dawning, when the sun disappeared, such as in Judaism, Islam or ancient Germanic peoples.

Saying „the sun is setting“ is a relict of a geocentric model of perspective. Not the sun is moving, but the observer.

When the sun is far enough underneath the horizon, the blue light spectrum dominates and creates a shiny blue sky, forming a photogenic contrast to the silhouettes of trees and landscape structures.

Moon

The only recent Trabant of our earth, presumably sirvivor of two or even several natural earth satellites in early times of our solar system.

Reflecting sunlight at night, lightening up the sky in the dark. Orientation aid for nocturnal animals, especially insects. Rhythm generator for the reproduction periods of numerous organisms.

The only extraterrestrial body that was so far ever visited by human beings. The first, which might be colonized before Mars.

All copyrights Stefan F. Wirth, Berlin March 2021