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NASA Astronomy Picture of the Day:

Did this meteor come from that comet? Probably not. Although many meteors do originate from comets, there are thousands of comets that have visited the inner Solar System recently, and matching meteors to them can be tricky. And to be clear, the pictured comet is far behind the streaking meteor. Comet C/2025 R3 (PanSTARRS) was captured from Hautacam, France in April when the giant space iceberg sported impressive ion (blue) and dust tails. Sand-sized rocky debris that enters Earth’s atmosphere typically appears as meteors, while the colorful foreground streak here may indicate a complicated composition. This month three notable meteor showers will reach their peaks. Over the next few days, the Southern Taurids will be reaching their apex, while the Northern Taurids will top out about a week later. Both originate from Comet 2P/Encke. November is most famous for the Leonids Meteor Shower, though, which originates from Comet 55P/Tempel-Tuttle and will reach its crescendo in about two weeks.

Photo by Eddy Metais

Tattooing: An Ancient Mark of Human Identity | The Past That Shaped Us

Tattooing can look like a distinctly modern form of personal expression, but its history reaches thousands of years into the human past. Long before electric tattoo machines and commercial studios, people were deliberately placing permanent marks into their skin.
Tattoos have identified communities, recorded accomplishments, expressed religious beliefs, marked transitions in life, indicated status, provided protection, punished outsiders, and decorated the body simply because people found the markings meaningful or beautiful. The practice did not originate in a single civilization and then spread everywhere.

Evidence suggests that forms of tattooing arose among widely separated peoples across the world. Its extraordinary persistence reveals something deeply human: for thousands of years, people have treated the body not only as something they inhabit, but also as a surface on which identity, belonging, memory, and belief can be made visible.

Evidence Preserved in Skin

Tattooing is difficult for archaeologists to trace because human skin normally disappears long before other evidence of a civilization. Tools that might have been used for tattooing can survive, but proving their purpose is difficult. Artistic representations may show body markings without revealing whether those markings were permanent tattoos, paint, scars, or something else. Occasionally, however, the human body itself survives.

One of the most famous examples is Ötzi the Iceman, whose naturally preserved body was discovered in the Alps in 1991. He lived more than 5,000 years ago and carried numerous tattoos consisting largely of short lines and crosses.
These were not elaborate pictures resembling many modern tattoos. Their placement has encouraged researchers to consider whether some may have had therapeutic, ritual, or symbolic significance, although their exact purpose remains uncertain.

Ötzi is not evidence that tattooing began in prehistoric Europe. Rather, he demonstrates something more important: deliberate tattooing was already established thousands of years ago. Other ancient tattooed remains have since revealed that the practice in different parts of the world.

A Practice With Many Beginnings

There is no known single inventor of tattooing. That makes the practice especially interesting.People separated by enormous  distances discovered that pigment inserted beneath the surface of the skin could create permanent markings. The techniques differed, as did the meanings, but the underlying idea appeared in multiple societies.

Ancient Egyptian remains provide some of the earliest well-documented examples. Tattooed mummies show that both geometric patterns and figurative designs were used. Evidence from other parts of Africa, Eurasia, the Americas, and the Pacific further demonstrates the broad geographic reach of permanent body marking.

The reasons were rarely simple. A tattoo could communicate membership in a group, personal achievement, religious devotion, social position, or life experience. In some societies, tattoos were closely connected with adulthood or important transitions. In others, they could distinguish warriors, specialists, leaders, or particular families. The body became a kind of permanent social document.

How Early Tattoos Were Made

The basic principle of tattooing has changed surprisingly little. Pigment must be introduced into the skin deeply enough that the design remains after the outer surface continually renews itself. Ancient tattooists accomplished this without modern machinery.
Depending on the culture and period, tools could include sharpened bone, stone, metal points, needles, comb-like instruments, or other implements capable of puncturing the skin. Pigments were often derived from carbon-based substances such as soot, although other materials could be used.

Some techniques involved puncturing the skin repeatedly and introducing pigment into the wounds. Others used instruments that could be tapped into the skin in rhythmic patterns. The process required considerable skill. A permanent design offered little opportunity for correction, and traditional tattooists in many societies became specialists whose knowledge included not only technique but also the cultural rules governing which designs could be applied, where they belonged, and who had the right to wear them. Tattooing could therefore be both a craft and a social institution.

Tattoos as Belonging
In societies without identification cards, passports, uniforms, or digital records, the human body could communicate information immediately. Permanent markings could show that someone belonged to a particular community. This did not mean that every tattoo functioned as a simple label. Designs could contain layers of meaning understood most fully by members of the culture that created them.
Among many Indigenous peoples, body marking became connected with ancestry, kinship, spiritual life, social responsibility, or achievement. In some traditions, receiving a tattoo was itself an important event requiring preparation, ceremony, endurance, or community participation.

The permanence mattered.

Clothing could be changed. Jewelry could be removed. A tattoo remained with its wearer. That made it unusually powerful as a symbol of belonging.

The Pacific and the Language of Tattoo

Some of the world's most elaborate tattooing traditions developed across the Pacific. Polynesian societies created sophisticated systems of body marking in which designs could communicate identity, genealogy, status, accomplishment, spirituality, and community relationships. Traditions differed greatly from island group to island group; there was never one universal Polynesian system.

European voyagers encountered these practices during Pacific exploration. The English word tattoo entered widespread European usage from a Polynesian word encountered in the Pacific, commonly associated with the Tahitian tatau. Europeans did not discover tattooing there—forms of permanent body marking had existed elsewhere for millennia—but Pacific traditions profoundly influenced the vocabulary and later Western understanding of the practice.
Sailors became especially important in carrying tattoo customs between ports.A practice deeply rooted in Indigenous Pacific cultures entered a new global phase as maritime travel connected distant societies.
 
Marks of Honor—and Marks of Control

Tattooing has not always been voluntary.. That is an essential part of its history. The same permanence that made tattoos powerful symbols of identity also made them useful to authorities seeking to mark people against their will.

In different periods and societies, permanent body marks could be used to identify enslaved people, criminals, prisoners, soldiers, or marginalized groups. The specific practices varied, but the underlying purpose was often control: the body could be marked so that a person's status followed them wherever they went.

One of the darkest modern examples occurred during the Holocaust, when the Auschwitz concentration camp complex used tattooed identification numbers for many registered prisoners. These markings were not decorative or chosen expressions of identity. They were instruments of a system that reduced imprisoned human beings to administrative numbers.Tattoo history therefore contains a profound contradiction. A permanent mark can represent personal identity and freedom, or it can be imposed to deny both. Context determines the difference.

Sailors, Soldiers, and Outsiders

In Europe and North America, tattooing became strongly associated during the eighteenth and nineteenth centuries with sailors.
Maritime culture was well suited to tattooing. Sailors traveled between societies with different tattoo traditions and spent long periods within close-knit communities. Tattoos could commemorate voyages, occupations, relationships, religious beliefs, or personal experiences.
Soldiers also adopted tattoos, particularly as military service moved large numbers of people across regions and countries.

By the nineteenth century, tattooing occupied an unusual position in Western societies. It could be associated with sailors, soldiers, laborers, prisoners, performers, and other groups considered outside conventional middle-class respectability.
Yet tattooing was never confined entirely to those groups. Wealthy and socially prominent people also received tattoos, sometimes inspired by travel or fascination with other cultures.
The practice could be simultaneously fashionable and disreputable. That tension would continue well into the twentieth century.

The Tattoo Machine Changes the Craft

Tattooing became increasingly mechanized during the late nineteenth century. Electric tattoo machines allowed needles to puncture the skin rapidly and repeatedly, increasing the speed with which designs could be created. Professional tattoo shops became more established, particularly in port cities and urban centers.

The craft developed recognizable styles. Design sheets allowed customers to select popular images. Anchors, hearts, ships, patriotic emblems, religious symbols, names, animals, and military designs became familiar parts of Western tattoo culture.
Tattooing was becoming commercialized. At the same time, it retained associations with particular communities. A tattoo might reveal military service, membership, personal loyalty, rebellion, mourning, or simply a preference for decoration.

The body continued to communicate. Only the technology had changed.

From Stigma to Mainstream Culture

During much of the twentieth century, tattoos in many Western societies carried strong social stigma. They could be associated with criminality, gangs, military life, rebellious youth, or social marginality.That perception changed dramatically during the late twentieth and early twenty-first centuries.
Tattooing became increasingly mainstream. Professional studios expanded, hygiene and equipment improved, artistic styles diversified, and tattooists gained recognition as skilled visual artists. The range of people receiving tattoos broadened enormously.

Modern tattoos may commemorate family members, mark recovery from illness or hardship, express cultural heritage, memorialize the dead, celebrate relationships, represent religious beliefs, display artwork, or have no meaning beyond aesthetic preference.
Some people cover much of their bodies. Others choose a single small mark known only to themselves.
The technology is modern. The impulse is ancient.

Lasting Impact

Tattooing has endured because it provides something few other forms of expression can offer: permanence carried on the body itself.
Across history, tattoos have connected individuals with communities, ancestors, occupations, beliefs, memories, and personal experiences. Their meanings have changed dramatically between cultures and eras, but the underlying ability to make identity physically visible has remained powerful.

Modern tattooing also illustrates the importance of understanding cultural context. Designs that function as decoration in one setting may possess deep ceremonial, religious, familial, or historical significance in another. As tattoo traditions have circulated globally, questions of cultural ownership, borrowing, and respect have become increasingly important.

At the same time, contemporary tattooing has become a major form of personal artistic expression. What was once associated in some societies with outsiders has become ordinary enough to appear in offices, classrooms, professional sports, entertainment, and everyday family life.

Historical Significance

The long history of tattooing challenges the idea that permanently decorating the body is a modern fashion. Humans were tattooing themselves thousands of years before written history recorded most of their lives.

The practice appeared in widely separated societies because the human body offered something universally available: a surface on which meaning could be made permanent. Sometimes that meaning was chosen. Sometimes it was imposed. Tattoos could celebrate belonging or enforce exclusion. They could express faith, status, achievement, grief, beauty, defiance, memory, or control. Their meanings changed, but tattooing endured.

Modern equipment may create designs with a precision and speed ancient tattooists could never have imagined, yet the essential act remains recognizable. Pigment enters the skin, a mark remains, and the body carries a message forward through time.
The history of tattooing is therefore not simply the history of decoration. It is part of the much larger human history of asking who we are—and choosing, or sometimes being forced, to make the answer visible.

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Orange-lined triggerfish (Balistapus undulatus), Red Sea, Egypt. This demersal triggerfish has a maximum body size of about 30 centimetres (12 in) and is found across the Indo-western Pacific East Africa, Red Sea and Japan, typically in coral reefs ecosystems, coral lagoons, and external reef slopes within this area. Within coral reefs, the orange-lined triggerfish are more versatile than other triggerfish species and can be found at depths up to 50 metres (160 ft), although studies have found that they prefer depths of 2 to 8 metres (6 ft 7 in to 26 ft 3 in). It's an omnivorous feeder that can, because of its strong and heavy teeth, tackle a variety of benthic prey like cnidarians, molluscs, ctenophores, crustaceans, other fish, algae, and echinoderms. This species in particular, given its broad diet and distribution, is a crucial component in coral reef ecosystems through top-down control and especially through consumption of sea-urchin.

Diego Delso, CC BY-SA 4.0, via Wikimedia Commons. View source.

NOAA on Unsplash

NASA Astronomy Picture of the Day:

What’s causing this unusually long cloud on Mars? Known as the Arsia Mons Elongated Cloud (AMEC) and first recorded by NASA’s Viking Orbiter 2 in 1977, the strange cloud has been imaged in greater detail more recently by ESA’s robotic Mars Express spacecraft. The featured image is from 2018. The cloud forms only during spring and summer seasons and then only during morning hours. Made of water-ice, the most familiar process that causes cloud crystals to form around bits of dust would fail due to the thinness and lack of dust high in the Martian atmosphere. Leading speculation holds that dust is not involved. After the cloud forms near the volcano Arsia Mons, wind blows the cloud downstream — creating a tail that can extend over 1500 kilometers. Efforts to better understand AMECs will continue, an understanding that may bolster a more complete view of cloud formation on Earth.

Photo by ESA, DLR, FU Berlin; Processing & License: J. Cowart

The Ocean’s Hidden Landscape || Kudos365 - Exploring Our World Series.

Overview

Beneath the water lies a changing world of mountains, canyons, plains, and trenches that helps explain how Earth works. Stand on a beach and the ocean appears to begin where the land ends. The surface stretches toward the horizon, concealing almost everything beneath it. Yet the shoreline is only where the ground disappears from view. Continue outward underwater and you may cross a submerged continental platform, descend a steep slope, pass through a canyon, and reach a plain several miles below the waves.

Farther away, mountains rise from the darkness. Some form long volcanic ridges; others stand alone. In certain regions, the seabed bends into trenches deeper than Mount Everest is high. These features are connected by processes that build rock, move it across the planet, break it apart, and bury it. The useful question is therefore more than what the ocean floor looks like. It is why that landscape has its particular shapes—and how we can know when so much of it remains hidden beneath deep water.

Learning to see beneath the surface

Early depth measurements used weighted lines lowered from ships. Each sounding supplied a depth at one location, leaving the ground between measurements largely uncertain. Sound-based instruments eventually allowed ships to measure depths more efficiently, revealing underwater relief on a much larger scale.

Those discoveries helped change geology. During the twentieth century, evidence from submarine ridges, earthquakes, magnetic patterns in seabed rocks, and the ages of those rocks contributed to the development of plate tectonics. The ocean floor became evidence that Earth’s outer shell moves. What had been difficult terrain to measure also became a record of how the planet continually reshapes itself.

Key Terms at a Glance

Continental shelf: The continent’s shallow underwater edge.

Submarine canyon: A valley carrying material toward deeper water.

Abyssal plain: A broad, relatively flat stretch of deep seabed.

Mid-ocean ridge: A mountain system where new oceanic crust forms.

Seamount: A mountain rising from the seabed.

Ocean trench: A deep depression where a plate bends downward.

Hydrothermal vent: An opening where heated water returns to the ocean.

Bathymetry: Measuring and mapping underwater depths.

The continent continues underwater

Our imagined journey begins on the continental shelf, the relatively shallow, gently sloping submerged edge of a continent. Its width varies enormously. In some places, deep water lies close to shore; elsewhere, the shelf extends far out to sea.
This explains why distance from a beach is a poor way to judge depth. A vessel can travel a considerable distance over a broad shelf while remaining above comparatively shallow ground. Along a narrow margin, it may encounter deep water much sooner.

Beyond the shelf, the continental slope descends toward the deep ocean. Where sediment accumulates at its base, it can build a gentler region called the continental rise. This arrangement is common along some margins, but it is not a universal staircase. At active plate boundaries, trenches and other structures can replace that simple sequence. Coastlines mark the water’s edge; they do not consistently mark the edge of a continent’s underlying crust.

Canyons carry material into deep water

A canyon can interrupt the descent. Submarine canyons cut into continental margins, sometimes beginning near shore and sometimes far offshore. Their branching channels can resemble valleys on land, but resemblance alone does not establish how they formed.
Underwater landslides and sediment-carrying flows help excavate and enlarge them. When enough sediment becomes mixed with water, the mixture can become denser than surrounding seawater and move downslope under gravity. Such movements, called turbidity currents, can transport sand and mud into deep water. Some also mobilize substantial material from the seabed itself.

The comparison with a river is useful only up to a point. A submarine canyon does not require an ordinary river flowing through air, and many were not simply dry valleys drowned by rising seas. Their histories can combine erosion, slope failure, changing sea levels, and connections to rivers. They are routes through which coastal material reaches the deep ocean.

Sediment smooths parts of the deep seabed

At the bottom of the slope, broad, relatively level stretches may extend across the deep basin. These are abyssal plains, commonly found several kilometers below the surface. Their smooth appearance can conceal a much rougher rocky foundation.
Imagine filling the low places in a crumpled surface with fine powder. The top becomes smoother even though the original relief remains underneath. Sediment can have a similar leveling effect on seabed rock, although its transport and accumulation involve several processes rather than one even sprinkling. Material arrives through sediment flows and by particles settling through the water.

Not every deep region is flat or thickly covered. Hills, exposed rock, and other relief interrupt the seabed. Even the proportion classified as abyssal plain depends on how strictly researchers define flatness. The important idea is that the surface we map can reflect both the rock originally formed there and the material deposited over it.

Underwater ridges mark where new crust forms

Eventually our journey reaches rising terrain. The connected mid-ocean ridge system runs roughly 65,000 kilometers, or 40,000 miles, through the ocean basins. Much of it is submerged, making Earth’s longest mountain system largely invisible from the surface.
Along these spreading centers, tectonic plates move apart and molten rock rises, cools, and adds new oceanic crust. A plate includes the crust and a rigid portion of the upper mantle beneath it. The moving pieces are therefore thicker than the thin surface layer we might imagine from a cracked eggshell.

The ridge is elevated partly because the underlying material is hot. As oceanic lithosphere moves away, it cools, becomes denser, and generally subsides. This helps explain why broad ocean basins tend to deepen away from spreading ridges. The mantle beneath the plates is mostly solid rock capable of slow deformation; the plates do not sail across a worldwide ocean of liquid magma.

Volcanoes build mountains that may never become islands

Away from the main ridges, individual mountains rise above the surrounding seabed. Many of these seamounts are volcanoes built by repeated eruptions. A mountain can be substantial while its summit remains far below the ocean surface.
An island is therefore an incomplete view of a much larger structure. Where volcanic construction reaches above sea level, the exposed land represents only the upper part. Elsewhere, the entire mountain remains submerged.

Some underwater mountains have broad, flattened tops and are called guyots. Many preserve a history in which an island’s summit was worn down near sea level before subsidence carried it into deeper water. Their shape records a sequence of construction, erosion, and sinking. A flat top is evidence to investigate, rather than proof that every such feature followed an identical history. Understanding a seamount requires measurements of its form together with geological evidence about its age and composition.

Trenches mark places where plates descend

The deepest seabed occurs in long, narrow trenches associated with subduction, where one tectonic plate bends beneath another and descends into the mantle. Challenger Deep in the Mariana Trench lies about 11 kilometers, or nearly seven miles, below sea level. Exact depth estimates vary with measurement and analysis. A trench is not a bottomless crack opening through Earth. It is a depression in the surface associated with a plate bending downward. The descending plate remains solid to considerable depths.

At some subduction boundaries, plates can lock together while their continued motion builds strain. Sudden slipping releases earthquakes, including the largest kinds known. If an event displaces a large volume of seawater, it can generate a tsunami. Underwater landslides can also produce tsunamis. The danger depends on the movement and displacement involved; a deep trench by itself does not continuously produce destructive waves.

Hot water changes rock beneath the seabed

The landscape also contains places where water circulates through fractured rock, heats up, reacts chemically, and returns to the ocean. These hydrothermal systems connect seawater with heat inside Earth, often in volcanically active regions. Some vents build mineral chimneys. Hot fluid carrying dissolved material meets cold seawater, and minerals precipitate, producing deposits around the opening. The dark plume of a black smoker contains tiny mineral particles; its smoke-like appearance does not mean that an underwater fire is burning.

A map can reveal a volcanic ridge without showing whether a particular fracture is venting today. Researchers need other evidence, including water measurements, temperature readings, samples, and observations near the bottom. This is a useful distinction throughout ocean exploration: the shape of the ground tells part of the story, while its chemistry and present activity require additional investigation.

Sound reveals the ground that light cannot

How can researchers construct this landscape without draining the sea? A sonar instrument sends sound into the water and records returning echoes. With knowledge of sound speed, the travel time helps determine distance. Modern multibeam systems send beams across a swath beneath a vessel, collecting many depth measurements as it moves.
Sound speed varies with conditions, so accurate surveys require corrections rather than a single universal conversion. Ship position and motion also matter. The resulting study of underwater depths and relief is called bathymetry.

Satellites provide a different kind of evidence. Radar measurements of sea-surface height help reveal subtle gravitational effects associated with large underwater features. A seamount’s mass can slightly alter the sea surface above it. Researchers use these patterns to infer broad seabed structure; the radar does not pass through kilometers of water to photograph the bottom. Satellite estimates and direct soundings complement each other, but they provide different levels of detail.

A complete-looking map can still contain gaps

In its 2026 global grid release, GEBCO reported that 28.7 percent of the ocean floor had been mapped to modern standards. That figure does not mean the rest is an entirely blank space. Broad estimates already show much of the planet’s major underwater relief, while detailed direct measurements remain incomplete.
Think of knowing that a mountain range occupies a region without having a reliable map of its smaller valleys and slopes. That comparison captures the difference in detail, although marine mapping also involves distinct instruments and depth-dependent standards.

Nor does mapped mean photographed, sampled, or fully understood. A good depth survey can identify a feature worth investigating without establishing its composition or history. Robots and other instruments then provide closer observations. The scale of the ocean, survey time, operating costs, and difficult conditions all make closing the gaps a substantial undertaking.

How the landscape connects to our lives

Together, these features describe a working system. Ridges add crust, plate movement carries it away, and subduction returns oceanic material to Earth’s interior. Meanwhile, erosion and sediment transport reshape the surface, while volcanic activity and circulating hot water alter rock. The terrain records overlapping histories rather than a single construction event. Its shape matters to people far from research ships. Seabed surveys help engineers plan routes for communication cables and assess where steep slopes or powerful sediment movements could threaten them. Depth information also supports navigation and offshore construction.

Seafloor relief influences the movement of water above it. Ridges and passages can steer deep flows, while rough terrain contributes to mixing. Since ocean circulation transports heat, the underwater landscape is one part of the physical system relevant to climate. Understanding it requires combining maps with measurements of moving water, rather than assuming that terrain alone determines the currents.

What remains to be discovered

The broad explanation of spreading ridges, moving plates, and subduction is well established. Many local histories remain uncertain. A newly mapped mountain may require rock samples to determine when it formed. A canyon’s shape may leave open which episodes of erosion or collapse mattered most. An apparently quiet volcanic area may need repeated observations to reveal change.

Researchers also face a practical problem: a map is a record made at a particular time. Eruptions, earthquakes, landslides, and mobile sediment can alter the seabed. Improving coverage and detecting change are related but different tasks. Better instruments and autonomous vehicles extend what researchers can measure, while interpretation still depends on combining several kinds of evidence.

The Bigger Picture

The ocean’s smooth surface hides a landscape as varied as the land we recognize—and one that helped reveal why continents move. Its mountains, plains, and trenches are consequences of heat, moving rock, gravity, water, and time.

The next time the sea seems to stretch into an undifferentiated blue distance, imagine the ground continuing beneath it: first the submerged continental margin, then the deep basin and the structures beyond. We already understand the main processes that shape this world. Mapping and exploring it in detail is still unfinished work.

This article is for general educational purposes. Scientific understanding may change as new research becomes available.

Exploring Our World | Kudos365 © 2026. All Rights Reserved. | M1.0.4 | HSR2.4.

Saint-Charles Cemetery is the largest cemetery in Quebec City. Today is All Souls' Day.

Wilfredor, CC0, via Wikimedia Commons. View source.

Will Durant explains,  "The essential causes of Rome's decline lay in her people, her morals, her class struggle, her failing trade, her bureaucratic despotism, her stifling taxes, her consuming wars"

(Source: Will Durant, Caesar and Christ, p. 665).

Abraham Lincoln (February 12, 1809 - April 15, 1865)