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On 24 August 2006, at the close of the International Astronomical Union’s General Assembly in Prague, 424 astronomers raised yellow cards to decide what a planet is. When student volunteers had counted the votes, the solar system had eight planets. Pluto, a planet since its discovery in 1930, was not one of them. Image Via: @SETIInstitute on X One of the most common questions about space, how many planets are in the solar system, was settled by a show of hands. Two decades later the definition still stands in the union’s rules and in textbooks worldwide. Some scientists reject it, and a telescope in Chile is now searching for a world that could make the count nine again. What Forced The Vote The trouble began at Palomar Observatory in California. On 21 October 2003, a telescope there photographed a faint point of light moving slowly far beyond Neptune. The astronomers Mike Brown, Chad Trujillo and David Rabinowitz noticed it only in January 2005, on a second pass through the imag...

On 10 April 2019, astronomers released the first image of a black hole: a bright ring of glowing gas around a dark centre in the galaxy M87, about 55 million light years from Earth. A black hole is a region of space where gravity is so strong that nothing, not even light, can escape once it crosses a boundary called the event horizon. Image Source: @LuisADomDaly on X For most of the 20th century, black holes existed only as solutions to equations. In less than a decade they became objects that scientists can weigh, hear and photograph, and the discoveries behind them won the Nobel Prize in Physics in both 2017 and 2020. How A Black Hole Forms The idea began months after Albert Einstein published his general theory of relativity in 1915. In 1916, the German astronomer Karl Schwarzschild found a solution to Einstein’s equations describing a mass so compact that space around it closes in on itself. For decades many physicists, Einstein among them, doubted that nature would ever pro...

In 1964, two radio astronomers at Bell Telephone Laboratories in Holmdel, New Jersey, could not get rid of a faint hiss in their horn antenna, even after evicting the pigeons nesting inside it and cleaning out their droppings. The hiss turned out to be the afterglow of the Big Bang, and it is the main reason scientists can say the universe is about 13.8 billion years old. Representational Image Via: @Nereide on X Arno Penzias and Robert Wilson had stumbled on the oldest light in existence. Six decades of measurement since have turned that discovery into one of the most precise numbers in science. Now a stubborn disagreement over how fast the universe is expanding is testing the theory that produces it. An Expanding Universe The story starts with the discovery that the universe is growing. In 1927, the Belgian priest and physicist Georges Lemaître published calculations showing that galaxies should be moving away from one another, faster the farther apart they are. Two years late...

The sunlight falling on Earth left the Sun about eight minutes and 20 seconds earlier. The oldest light astronomers can detect has been travelling for about 13.8 billion years, and the matter that released it now lies about 46 billion light years away. That makes the observable universe about 93 billion light years across. Representational Image Via: @AMAZlNGNATURE on X No one knows how big the whole universe is beyond that. Astronomers have measured the part they can see with growing precision, using a chain of methods built over a century. Past its edge, the universe may go on for ever. What A Light Year Measures A light year is a distance, not a time: how far light travels in a vacuum in one year. At almost 300,000 km a second, that comes to about 9.46 trillion km. Kilometres stop being useful almost as soon as you leave the solar system. The nearest star after the Sun, Proxima Centauri, is about 4.24 light years away, close to 40 trillion km. Its light reaching Earth tonight...

At 22:54 UTC on 14 December 1972, Eugene Cernan and Harrison Schmitt lifted off from the Moon’s Taurus-Littrow valley in Apollo 17’s lunar module, ending humanity’s last visit to its surface. Twelve people have walked on the Moon, all of them American men who flew on NASA’s Apollo missions between July 1969 and December 1972. Representational Image Via: @konstructivizm on X In the five decades since, no one has gone back. That is about to change. The United States, China and India have each set dates for putting astronauts on the Moon, and the next person to stand there may be the first woman or the first person from a country other than the United States. The Twelve Moonwalkers Six Apollo crews landed on the Moon, each putting two astronauts on the surface while a third stayed in lunar orbit. Mission Moonwalkers Landing date Apollo 11 Neil Armstrong, Buzz Aldrin 20 July 1969 Apollo 12 Pete Conrad, Alan Bean 19 November 1969 Apollo 14 Alan Shepard, Edgar Mitchell 5 February 197...

In July 2024, NASA’s Perseverance rover drilled a core from an arrowhead-shaped rock called Cheyava Falls, at the edge of an ancient river valley in Mars’s Jezero Crater. No life has been found on Mars, but scientists say that sample, named Sapphire Canyon, carries a potential biosignature: features that microbes could have made long ago, which still need to be confirmed. Representational Image Via: @AMAZlNGNATURE on X Confirming it would mean examining the rock in a laboratory on Earth. NASA’s plan to bring it back has been cancelled, and the first Martian samples to reach Earth may now come from China, from somewhere else on the planet. Fifty Years Of Looking The search began in 1976, when NASA’s two Viking landers scooped Martian soil into onboard experiments designed to detect living organisms. One, the labelled release experiment, produced a burst of gas when nutrients were added, as microbes might. Repeat doses produced nothing further, unlike living soil on Earth. Most sci...

On 2 November 2000, American astronaut Bill Shepherd and Russian cosmonauts Yuri Gidzenko and Sergei Krikalev docked their Soyuz capsule at the International Space Station and moved in. The station, a laboratory orbiting about 400 km above Earth, has had people aboard ever since. NASA and its partners plan to run it until the end of 2030 and then steer it into the ocean. Image Credit: Scott Kelly, Expedition 44, NASA That unbroken run of human presence in orbit, now more than a quarter of a century long, is entering its last years. What replaces the station will decide which countries and companies keep people in space, and on whose terms. What The Station Is The International Space Station is the largest structure humans have put in orbit, weighing about 450 tonnes. It was assembled piece by piece, starting with the Russian-built Zarya module, launched on 20 November 1998. Five space agencies run it: NASA, Russia’s Roscosmos, the European Space Agency, the Japan Aerospace Exploratio...

On 18 August 1868, as the Moon covered the Sun over Guntur in southern India, the French astronomer Jules Janssen turned a spectroscope on the glowing gas at the Sun’s edge. He saw a bright yellow line that matched no known element: the first evidence of helium. On 2 August 2027, a total solar eclipse lasting up to 6 minutes and 23 seconds will cross North Africa and the Middle East, the longest over easily reached land until 2114. Representational Image Via: @AMAZlNGNATURE on X A total solar eclipse happens when the Moon passes directly between the Sun and Earth and blocks the Sun’s bright face completely. For a few minutes, day turns to dusk along a narrow strip of the planet. Eclipses have changed science for centuries, and the 2027 event is likely to draw large crowds to its path. A Cosmic Coincidence Total eclipses depend on an accident of geometry. The Sun is about 400 times wider than the Moon, and also about 400 times farther away. From Earth, the two discs look almost t...

A few days after 15 August 1977, the astronomer Jerry Ehman was reading computer printouts from Ohio State University’s Big Ear radio telescope when he found a burst of signal so strong that he circled it and wrote “Wow!” in the margin. It was never heard again. Almost half a century later, no one has found confirmed evidence of life anywhere beyond Earth. Representational Image Via: @WorldAndScience on X The search for an answer to whether we are alone in the universe has changed since then. Astronomers have stopped waiting for a message and started reading the air of distant worlds. NASA’s archive counted 6,451 confirmed planets around other stars on 15 October 2026, and each is a place where the question can be asked. The Signal That Never Returned The Wow! signal lasted 72 seconds, the full time Big Ear could watch any point in the sky as Earth turned. Ehman searched the same patch of sky for months afterwards and found nothing. So did later searches with larger telescopes i...