Modern astronomers

RIDDLE OF THE APPLE

The story that the English astronomer Sir Isaac Newton (1642-1727) worked out his law of gravity after watching the fall of an apple is probably true. But nobody can ever know for sure. What makes some scholars doubt the story is that most of Newton's early biographers made no mention of it - an extraordinary omission considering the importance of the discovery the apple is said to have inspired.

There are only two sources for the tale and neither was an eyewitness. One is a clergyman, the Reverend William Stukely, who reported in his biography of Newton-written in the 18th century but not published until the 20th century that the scientist told him of the incident one afternoon when they were having tea together in the apple orchard at Newton's home.

The other is Newton's niece, Catherine Barton Conduitt, who looked after Newton during his latter years. Mrs Conduitt was the source of the first published account of the incident. Her report appeared in Elements of Newtonian Philosophy by the French author and philosopher Voltaire. The book was published in 1738, eleven years after Newton's death and more than 70 years after the apple was said to have fallen.

PIPPED AT THEPUBLISHER

The German astronomer Friedrich Bessel (1784- 1846) is officially credited with being the first person to measure the distance from Earth to a star. In fact, he was merely the first person to announce his results, An English astronomer, Thomas Henderson (1799 - 1844), had taken all the measurements necessary to work out a star distance about six years earlier-but had not got around to turning his obser- vations into a distance.

Both men made their calculations by trigonometry, taking two bearings on their chosen stars at intervals of six months. In this way, they got two angles - one from each side of the Earth's orbit - and since they knew the size of the orbit, they were able to work out the distance to the star. Bessel announced his findings in 1838.

He reported that the distance to a star called Cygni. In the Northern Hemisphere constellation Cygnus, was 10.3 light years (near to the presently accepted figure of 11.08 light years). The following year Henderson finally came up with his long-delayed figure of 3 light years for the distance to Alpha Centauri. in the Southern Hemisphere constellation Centaurus.

Henderson had made his observations in 1832 - 3. While he was director of the Cape Observatory in South Africa. Alpha Centauri, now known to be 4.35 light years from the Earth, is the closest star visible to the naked eye, apart from the Sun.

KARL'S SPARKS

Radio astronomy began in 1932 when the American engineer Karl Jansky (1905 - 50) intercepted radio waves from the Milky Way-by accident. Jansky was using an improvised aerial built partly from a dismantled Ford car. He made his discovery while investigating static on long-distance radio communications for the Bell Telephone Company.

Jansky never followed up his breakthrough, however, because when he published his findings they aroused little interest. After 1937, Jansky's discovery was investigated by the US radio amateur Grote Reber, whose work inspired the growth of radio astronomy after the Second World War.

TOMB WITH A VIEW

The telescope at California's Lick Observatory also serves as a tomb. The 900mm (36in) refracting telescope is mounted on a pillar that contains the remains of James Lick (1796-1876), a wealthy philanthropist and landowner who financed the observatory's construction and after whom it is named.

ACCIDENTAL OVERLOAD

The Van Allen belts (radiation-charged zones that girdle the Earth) were discovered by accident. In 1958, the USA launched its first satellite, Explorer 1. It was designed to measure the intensity of cosmic radiation from space. But as the satellite soared out beyond the atmosphere, the radiation count suddenly dropped to zero. Or seemed to. Scientists on the ground were baffled until the US astrophysicist James Van Allen (1914- ) realised that the satellite's meters had simply been overloaded, and so had broken down. The radiation belts now named after him lie between 650 and 65,000km (400-40,000 miles) above the Earth.

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