24 01-2009 Great Astronomers: Herschel (Article 171)

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Simon Kenny
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24 01-2009 Great Astronomers: Herschel (Article 171)

Post by Simon Kenny » Wed Feb 04, 2009 10:23 am

Herschel: the astronomer and the telescope. (Article 171)

Frederick Herschel was born in Germany in 1738, but spent most of his long life in England. Starting as a musician, he later adopted astronomy, his life long passion. His list of achievements includes the discovery of the planet Uranus in 1781. Herschel named the new planet after King George III, who appointed him ‘King’s Astronomer’ the following year. Herschel was a pioneer telescope builder and these were instrumental to his discoveries. His forty-foot reflector telescope was the biggest of its time. Through it he discovered new moons around Saturn and Uranus. By studying binary stars, he found they actually circle each other, proving Newton’s laws of gravity apply outside the Solar System. From his studies of the proper motion of stars he concluded the Solar System was moving through space. He also discovered, accidentally, that heat was part of the electromagnetic spectrum when he split sunlight with a prism into its component colours, leaving a thermometer beside the red end of the spectrum. He noticed the temperature rose dramatically. This led to the discovery of infra-red radiation.

Herschel’s name will be in the news again this year when a telescope bearing his name will be launched into space. At present, a launch date of 10 April 2008 is under active consideration. Created by the European Space Agency, Herschel’s 3.5 metre mirror makes it the largest ever space telescope. It is designed to study objects that existed in the early universe and understand the dynamics that led to the evolution of the cosmos since its creation 13.5 billion years ago. The observatory will study these ancient objects from their infra-red signatures. Great care must be taken to ensure the signals are not swamped by the massive infra-red output from the Sun. The telescope’s instruments are cooled continuously to near absolute zero to enable detection of these weak signals from deep space. Secondly, elaborate heat shields protect the liquid helium that keeps the sensors at operating temperature. Thirdly, the telescope will not orbit the Earth, as its infra-red radiation and orbital temperature variations would upset its sensitive detectors. Instead, it will orbit the Sun at a stable point 1.5 million kilometres from Earth, where its orbital motion around the Sun will keep pace with the Earth’s orbit. The position in space is known as the Second Lagrange Point (L2) of the Earth-Sun system.

Once again, the Herschel name is linked to technical innovation and discovery in the science of astronomy.

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