The third lecture was given by Dr Chris North from the University of Cardiff and the European Space Agency about the Herschel and Planck space observatories (telescopes that study long wavelength light from the early universe). Chris.North@astro.cf.ac.uk
Herschel and Planck are Europe’s cosmic explorers (http://herschel.cf.ac.uk/ and http://planck.cf.ac.uk/). They were launched in 2009. Herschel carries the largest, most powerful infrared telescope ever flown in space. A pioneering mission to study the origin and evolution of stars and galaxies, it helps us understand how the Universe came to be what it is today.
Planck is the first European space observatory whose main goal is the study of the Cosmic Microwave Background – the relic radiation from the Big Bang. The spacecraft will measure the fluctuations of the CMB with an accuracy set by fundamental astrophysical limits.
Dr North gave a brief history of Man’s exploration of deep space. William Herschel (1782 to 1802) conducted systematic surveys in search of deep sky and ultimately discovered over 2400 objects defined by him as nebulae. (At that time, nebula was the generic term for any visually extended or diffuse astronomical object, including galaxies beyond the Milky Way, until galaxies were confirmed as extragalactic systems by Edwin Hubble in 1924.) He was also the first person to attempt to describe the shape of the Milky Way and the position of the Sun within it, in 1785, by carefully counting the number of stars in different regions of the visible sky. He produced a diagram of the shape of the Galaxy with the Solar System close to the centre. On 11 February 1800, he was testing filters for the sun so he could observe sun spots. When using a red filter he found there was a lot of heat produced. Herschel had discovered infrared radiation in sunlight by passing it through a prism and holding a thermometer just beyond the red end of the visible spectrum. This thermometer was meant to be a control to measure the ambient air temperature in the room. He was shocked when it showed a higher temperature than the visible spectrum. Further experimentation led to Herschel’s conclusion that there must be an invisible form of light beyond the visible spectrum.
In 1888 Isaac Roberts took a long exposure photograph of the Great Andromeda Nebula (now known as the Andromeda Galaxy) revealing that the nebula had a spiral structure, which was quite unexpected at the time. Photographs such as this changed astronomy by revealing the true form of nebulae and clusters, and eventually helped to develop the theories about galaxies. He published his celestial portfolio in a large format book that is the first popular account of celestial photography of the deep sky. The Andromeda galaxy was the first galaxy to be identified as outside our own.
Edwin Hubble’s work enabled the distance to the Andromeda galaxy to be determined.
Herschel and Planck are looking at the history of our universe. They had to be sent in to space due to the fact that water vapour in our atmosphere absorbs infra red light.
The next stage will be to launch the James Webb Space Telescope (also looking at Infra-red).It is a collaborative effort between NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA) to develop a large, near- and mid-infrared optimized space telescope to be launched in the middle of this decade. JWST will see fainter and further than previous telescopes such as the Hubble Space Telescope (HST), thereby enabling new scientific discoveries and providing answers to questions as old as human imagination: How did planets, stars, and galaxies come into existence and are we alone in the Universe? The telescope will be equipped with four ultra-sensitive scientific instruments, which have multiple imaging, spectroscopic, and coronographic modes. Development of the JWST is led by the JWST project at NASA’s Goddard Space Flight Centre. During the feasibility studies (1995-96), NASA and the STScI considered a wide variety of orbits for JWST. The most promising was the second Lagrange point (L2), approximately 1.5 million km from Earth, outside the orbit of the Moon. The region about L2 is a gravitational saddle point, where spacecraft may remain at roughly constant distance from the Earth throughout the year by small station-keeping manoeuvres. JWST will be placed in a large halo orbit in a plane slightly out of the ecliptic plane. This orbit avoids Earth and Moon eclipses of the Sun. The halo orbit period is about 6 months. Nominal station keeping manoeuvres will be performed every half orbit (3 months). JWST, near the L2 point, is in a benign and essentially unchanging environment. There is no significant gravitational torques and thermal influence from the Earth and Moon are greatly reduced. The main operational influence to consider is the torque created by the Solar wind on the sunshield.
Planck and Herschel observatories are actually the coldest places in space. Infra-red telescopes have to be cooled to prevent them emitting Infra-red radiation themselves. This is done by using Liquid Helium in a system very similar to a domestic fridge cooling your food. When they finish their mission they will simply orbit the Sun.
Further references: http://en.wikipedia.org/wiki/William_Herschel http://en.wikipedia.org/wiki/Milky_Way http://en.wikipedia.org/wiki/Isaac_Roberts http://en.wikipedia.org/wiki/Andromeda_Galaxy http://www.stsci.edu/jwst/ http://www.stsci.edu/jwst/overview/design/orbit