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In 1609 and 1610 Galileo built improved telescopes and saw mountains on the Moon, Venus going through phases like our Moon, and four moons circling Jupiter. These discoveries undermined the old view that the Earth sits still at the centre of the universe.

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Galileo first saw Jupiter's moons on 7 January 1610 and announced them that March in a short book, Sidereus Nuncius (The Starry Messenger). He named them the Medicean stars after his future patron, Cosimo II de' Medici; today they are called Io, Europa, Ganymede and Callisto. The phases of Venus were an even stronger argument. In the model of the ancient astronomer Ptolemy, Venus always stays between the Earth and the Sun, so it could never appear fully lit. Galileo watched it pass through a complete set of phases, which only makes sense if Venus orbits the Sun. The debate did not end there: in 1633 the Roman Inquisition found him 'vehemently suspect of heresy' for defending a Sun-centred universe, and he spent the rest of his life under house arrest.

Türkçe oku
Galileo 1609 ve 1610'da geliştirdiği teleskoplarla Ay'daki dağları, Venüs'ün tıpkı Ay gibi evreler geçirdiğini ve Jüpiter'in çevresinde dönen dört uyduyu gördü. Bu gözlemler, Dünya'nın evrenin merkezinde kıpırdamadan durduğu yolundaki eski görüşü sarstı.

Galileo, Jüpiter'in uydularını ilk kez 7 Ocak 1610'da gördü ve aynı yılın mart ayında Sidereus Nuncius (Yıldız Habercisi) adlı kısa kitabında duyurdu. Onlara, sonradan hamisi olacak II. Cosimo de' Medici'nin onuruna “Medici yıldızları” adını verdi; bugün Io, Europa, Ganymede ve Callisto olarak bilinirler. Venüs'ün evreleri ise daha da güçlü bir kanıttı. Antik gökbilimci Batlamyus'un modelinde Venüs hep Dünya ile Güneş'in arasında kalır, bu yüzden hiçbir zaman tümüyle aydınlık görünemezdi. Galileo ise gezegenin bütün evrelerden geçtiğini gördü; bu ancak Venüs Güneş'in çevresinde dönüyorsa mümkündü. Tartışma bununla bitmedi: 1633'te Roma Engizisyonu, Güneş merkezli evreni savunduğu için Galileo'yu “sapkınlıktan şiddetle şüpheli” buldu. Galileo ömrünün geri kalanını ev hapsinde geçirdi.

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Background reading: Galileo Galilei
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WonderHistory

When Neil Armstrong radioed “Houston, Tranquility Base here. The Eagle has landed” on 20 July 1969, his words reached Earth about 1.3 seconds later. Radio waves travel at the speed of light, and the Moon is about 384,000 km (239,000 miles) away.

Eagle was the lunar module that carried Armstrong and Buzz Aldrin down to the surface. Light, and so radio, travels at almost 300,000 km per second. At the Moon's average distance of about 384,400 km, a signal takes roughly 1.28 seconds each way, so every exchange with Mission Control in Houston had a built-in pause of about 2.6 seconds before an answer could arrive. Large dish antennas at Goldstone in California and at Honeysuckle Creek and Parkes in Australia picked up the signals; the clearest pictures of the first steps came through Australia and were watched live by an estimated 600 million people. Before leaving, the crew set up a panel of reflectors on the surface. Scientists still fire lasers at it and time the light's return, which is how we know the Moon is drifting away from Earth by about 3.8 cm a year.

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WonderTechnology

The Apollo Guidance Computer that steered astronauts to the Moon had about 4 kilobytes of rewritable memory and 72 kilobytes of permanent memory. Its programs were woven by hand into “rope memory”: a wire threaded through a tiny magnetic ring stored a 1, and a wire passing it by stored a 0.

Designed at the MIT Instrumentation Laboratory and built by Raytheon, the computer was one of the first to use silicon chips (integrated circuits) and fitted into about 28 litres. Its memory was counted in “words” of 16 bits, or binary digits: 2,048 rewritable and 36,864 permanent. During Apollo 11's descent on 20 July 1969 it flashed 1202 and 1201 alarms: a radar left on in case the landing had to be abandoned was stealing processing time and overloading it. Its operating system, designed by J. Halcombe Laning, dropped less urgent jobs and restarted in a moment while the landing programs kept running, so Mission Control told the crew to carry on. The flight software was written by a team led by Margaret Hamilton, who received the Presidential Medal of Freedom in 2016. Its power was similar to that of the first home computers of the late 1970s.

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WonderTechnology

The Antikythera mechanism, an ancient Greek geared device probably made in the 2nd century BC, had a spiral dial covering 223 lunar months for predicting eclipses. Symbols on the dial marked the months when an eclipse of the Sun or Moon was expected, and inscriptions gave details such as the hour.

Sponge divers found the mechanism in 1901, a corroded lump among treasures from a Roman-era ship that sank off the Greek island of Antikythera around 70 to 60 BC. Its hand-turned bronze gears modelled the movements of the Sun and Moon, and it is called the oldest known analogue computer, a machine that calculates with moving parts rather than digits. The eclipse dial follows the Saros cycle: after 223 lunar months (new moon to new moon), about 18 years and 11 days, the Sun, Earth and Moon return to almost the same positions, so eclipses repeat in a similar pattern. Symbols in 51 of the dial's cells mark 38 lunar and 27 solar eclipses. Much of this was read only in the 2000s, when researchers including Mike Edmunds and Tony Freeth used X-ray scans to see inside the fragments. The front, which probably showed the planets, is largely lost.

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WonderTechnology

On 4 October 1957 the Soviet Union launched Sputnik 1, the first artificial satellite: a polished metal ball 58 cm wide that sent out radio beeps anyone with a receiver could pick up. Its success shocked the United States and started the Space Race.

Sputnik weighed 83.6 kg and circled Earth every 96 minutes. It was launched from Tyuratam in Soviet Kazakhstan, now the Baikonur Cosmodrome, on an R-7 rocket built under the chief designer Sergei Korolev. Radio amateurs around the world tracked its simple signal, and scientists used the way its orbit changed to measure the density of the upper atmosphere. The batteries ran out after 22 days, and on 4 January 1958, after about 1,440 orbits, the satellite burned up as it fell back into the atmosphere. In the United States the launch caused alarm that the Soviets were ahead in technology. America launched its first satellite, Explorer 1, on 31 January 1958 and created NASA later that year. In Russian, 'sputnik' means travelling companion as well as satellite.

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WonderTechnology

The astrolabe is a handheld brass instrument that models the turning sky on a flat disc. With it, a user could tell the time, find stars and work out the hours of prayer.

An astrolabe relies on stereographic projection, a way of drawing the dome of the sky on a flat surface worked out by Greek astronomers; Hipparchus may have used it, and Theon of Alexandria wrote a treatise on the instrument in the 4th century AD. A pierced, rotating plate called the rete carries pointers for bright stars. Turning it over a plate engraved for the user's latitude shows the sky as it is at any hour, day or night. Scholars in the Islamic world took up the instrument from the 8th century, when al-Fazari is said to have built the first one there, and added scales for prayer times and, on some models, the direction of Mecca. The design reached Europe through Muslim Spain, and in about 1391 the English poet Geoffrey Chaucer wrote a treatise on the astrolabe for his son.

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