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Earth's magnetic field deflects most of the solar wind, the stream of charged particles flowing from the Sun, but steers some of them down towards the polar regions. When they hit the thin upper air, it glows as an aurora.

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The particles, mostly electrons and protons, are funnelled into two rings around the magnetic poles, called the auroral ovals, and strike oxygen and nitrogen in the upper atmosphere, most often around 100 km up. The atoms and molecules give off the energy they receive as light. Oxygen gives the common green glow and, higher up, a rarer red; nitrogen adds blue and purple lower down. Galileo used the name aurora borealis in 1619, after Aurora, the Roman goddess of the dawn, and Boreas, the Greek god of the north wind; its southern twin is the aurora australis. During strong solar storms the ovals widen and auroras appear far from the poles. In May 2024, in the strongest geomagnetic storm for more than 20 years, they were seen from Spain, Turkey and Cyprus, and even from the Canary Islands.

Türkçe oku
Dünya'nın manyetik alanı, Güneş'ten gelen yüklü parçacık akınının, yani güneş rüzgârının çoğunu saptırır; ama bir kısmını kutup bölgelerine yönlendirir. Bu parçacıklar atmosferin seyrek üst katmanlarına çarptığında hava ışıldar ve kutup ışıkları oluşur.

Çoğu elektron ve protondan oluşan bu parçacıklar, manyetik kutupların çevresinde halka biçimli iki kuşağa yönelir; bunlara aurora ovali denir. Parçacıklar üst atmosferdeki oksijen ve azota çoğunlukla 100 km kadar yükseklikte çarpar; atomlar ve moleküller aldıkları enerjiyi ışık olarak geri verir. En sık görülen yeşil ışık oksijenden gelir; oksijen daha yükseklerde, daha seyrek görülen kırmızıyı da üretir. Azot ise alt kısımlara mavi ve mor tonlar katar. “Aurora borealis” adını 1619'da Galileo kullandı: Aurora, Romalıların şafak tanrıçası, Boreas da eski Yunanlıların kuzey rüzgârı tanrısıdır. Güney yarımküredeki kardeşine “aurora australis” denir. Güçlü güneş fırtınalarında bu kuşaklar genişler ve kutup ışıkları kutuplardan çok uzakta da görülür. Mayıs 2024'te, 20 yılı aşkın sürenin en güçlü jeomanyetik fırtınasında kutup ışıkları İspanya'dan, Türkiye'den ve Kıbrıs'tan, hatta Kanarya Adaları'ndan görüldü.

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WonderScience

In a cave in Jujuy, northern Argentina, archaeologists found two pipes carved from puma bone, with seeds of cebil, a tree whose seeds are psychoactive, lying beside them. Chemical traces inside the pipes point to plant smoking more than 4,000 years ago, among the oldest evidence of such use in South America.

Cebil, Anadenanthera colubrina, is a South American tree whose seeds contain tryptamines, compounds that strongly alter perception; further north in the Andes it is called vilca. The pipes come from Inca Cueva 7, a small rock shelter near the Humahuaca valley at the edge of the high Andean plateau, where seeds of cebil and of mesquite lay in the same layer. Radiocarbon measurements, which gauge how much of the carbon-14 in once-living material has decayed, give ages of about 4,000 years, roughly 2100 BC. The residue shows that a tryptamine-bearing plant was smoked, but it cannot prove exactly which one. Cebil use continued in the region for thousands of years: Wichí healers in northern Argentina still used its seeds, which they call hatáj, in the 1990s.

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WonderScience

About 155,000 species of fungi have been formally described, yet the true number is estimated at 2.2 to 3.8 million. That means more than nine in ten fungal species have never been named.

That range comes from a 2017 review by two fungus specialists, David Hawksworth and Robert Lücking. They combined several lines of evidence: how fast new species are still being described, how often one familiar-looking species turns out to be several once its DNA is checked, and the ratio of fungi to plants at well-studied sites. A 2023 study put the likeliest total at about 2.5 million. Most fungi never form mushrooms. They live as microscopic yeasts or as networks of fine threads called hyphae, in soil, inside plants, in lichens and in water, and many are known only from DNA found in soil or water samples. Around 2,500 new species are named each year; at that pace, scientists at Kew Gardens in London estimate, naming them all would take 750 to 1,000 years.

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WonderScience

In the double-slit experiment, light or particles such as electrons pass through two narrow slits and leave bright and dark bands on a screen, the mark of overlapping waves. If a detector records which slit each particle went through, the bands disappear.

In the early 1800s, Thomas Young shone light through two narrow openings to argue that light is a wave. Where two waves meet crest to crest they reinforce each other, and where a crest meets a trough they cancel out; physicists call this interference. The real surprise came with matter. Claus Jönsson repeated the experiment with electrons in 1961, and in 1974 Italian physicists sent electrons through a similar set-up one at a time. Each landed as a single dot, yet thousands of dots built up the striped pattern. Similar interference has since been seen with molecules of up to 2,000 atoms and, in 2026, with clusters of more than 7,000 sodium atoms. The pattern does not vanish because a person is watching: any physical interaction that records the path, even with no one looking, disturbs the delicate quantum state that produces the interference.

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WonderScience

A lichen is a partnership rather than a single organism. A fungus builds the body and shelters a green alga or a cyanobacterium, a bacterium that makes food from sunlight, and that partner feeds the fungus sugars in return.

For a long time lichens were thought to be single organisms. In 1867 the Swiss botanist Simon Schwendener proposed that a lichen is really a fungus living with algae, and many experts of his day rejected the idea. Lichens were the first partnership for which biologists used the word “symbiosis”, meaning different organisms living closely together. In 2016 a team led by Toby Spribille found that many lichens also contain a yeast, a second kind of fungus, as a third partner. About 20,000 species are known, growing on bark, bare rock, Arctic tundra and even in deserts. People have long made use of them: litmus, the dye in school acid tests, comes from a lichen, and “reindeer moss”, a winter food of reindeer, is a lichen too.

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WonderScience

Coral reefs are built by polyps, tiny animals related to jellyfish. Microscopic algae living inside their tissues turn sunlight into food for them, and together they build some of the richest habitats on Earth.

Each polyp lays down a skeleton of limestone (calcium carbonate) beneath it, and over thousands of years these skeletons pile up into reefs; most living reefs are less than 10,000 years old. The algae inside the polyps, called zooxanthellae, supply up to 90% of the coral's nutrients. Partnerships like this, which recycle nutrients instead of losing them, help explain a puzzle Charles Darwin described in 1842: how reefs can flourish in tropical seas that are poor in nutrients. When the water stays too warm for too long, corals expel their algae and turn white, which is called bleaching. Bleached coral is not yet dead, but it starves if the heat lasts. The fourth global bleaching event, which began in 2023 and was confirmed by the US agency NOAA in April 2024, has affected reefs in at least 82 countries and territories.

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