When Albert Einstein confirmed the atomic theory of matter, he surprised experts by declaring that starlight would be deflected by gravity. People did not readily accept the idea. Arthur Eddington organized a worldwide experiment to prove Einstein right. Newton’s theory that light would be a straight flow was proved wrong. In the mid-1920s astronomer Edwin Hubble proved that the Universe had many more galaxies other than our own. He astounded the experts by stating that the galaxies were receding at velocities proportional to their distance. The Hubble Constant became the standard for estimating the rate of expansion of the Universe. Something totally unknown became partly known.
New theories emerged. Strange names surfaced: white dwarfs, black holes and neutron stars. The World Wars, though diverted funds and priorities from the academic field, gave new tools to astronomers: radio, rockets and radar to name a few. Radio astronomy was born. Each type of wavelength opened a new window on the Universe.
Discoveries and innovative instruments used in astronomy were quite slow until the Space Age. For example, Galileo discovered Jupiter’s four Moons in 1609, but it was only in 1655 that Huygens, with a more powerful telescope, discovered the rings of Saturn. It took 65 years after the discovery of Uranus (1781) to find Neptune (1846), a body with half its brightness. And Pluto was found only in 1930. In contrast, the first extra solar planet was discovered in 1995. Since then hundreds of planets, some of the same size as Neptune, have been found within 100 light years from the Earth.
In the Space Age, astronomers peered far into the unknown. Small telescopes were synthesized to form a big one. Whispers from outer space were heard. The technique of aperture synthesis was extended to optical telescopes as well. In fact, some of the images produced by ground-based telephones were better than the Hubble Telescope, the most expensive eye in the sky.
Strange phenomena like quasars (quasi-stellar radio sources) and pulsars (pulsating stars which are described as the most accurate clocks in the sky) were discovered. Their behaviour was even stranger. Quasars were found receding from us at a fantastic speed even as they are the brightest objects in outer space. Their age has been put around 13 billion light years away form the Earth. Yet another finding confirmed the Big Bang theory of the birth of the Universe. Cosmic microwave background radiation was found beyond the most distant quasars. In the mid-1960s, the remaining faint glow of the Big Bang was almost universally accepted, though still some favoured the steady state theory.
Extreme accuracy in telescope mirrors became the ideal. For instance, a mirror defect only 1/25th the width of a human hair prevented the Hubble telescope from focusing all light to a single point. Increasing the sensitivity of the instruments called for ultra cold temperature inside the telescopes for some of the payload. The coldest temperature ever reached in a space telescope is just 0.1 K.
In the beginning of the 20th century, telescopes had better resolving power and bigger apertures, though they were restricted to the visible spectrum. The development of radar and rockets during World War II opened the radio and ultraviolet regions to astronomers. By the mid-1950s, near infrared was also open. Today, astronomers have access to almost all regions of the electromagnetic spectrum. Improved angular resolutions revealed new classes of cosmic objects: quasars, X-ray and infrared stars as well as the cosmic microwave background.
Time resolution also improved, leading to the discovery of transient and variable phenomena. Supernova remnants (1939), rapid flare stars (1949), millisecond pulsars (1968), gamma-ray bursters (1973), black holes accretion disks (1996) and rapid X-ray repeater (1996) were identified.
Spectral resolution too increased, almost to the limits set by thermal motion and intrinsic line/ widths. As a result, magnetic stars (1946), masers (1965), X-ray galaxies (1996) and exoplanets (1995) were discovered.
Telescope of recent times have benefited from the advances made in electronics and materials research. For instance, the Hubble Space Telescope has only 1/15th of light collecting area of ground-based telescopes and yet it is much sharper to image fainter objects. The Herschel Infrared Telescope has a primary mirror with a diameter of 3.5 m, the largest space telescope ever built. This would also have an ultra-thin surface, few thousandths of a millimeter.
The forthcoming space telescopes (named after Kepler, Herschel, James Webb and Megellan) would be able to observe 1000 times as dim as what Hubble can observe. The first Earth-like planet may well make the headlines in 2010. After all, the Sun is just one of 200 to 400 billion stars within the Milky Way Galaxy, which itself is just one among thousands of billions of galaxies in the known Universe not to speak of the unknown.
The James Webb Telescope, expected by 2013, will be three times bigger than Hubble with a hexagonal mirror 6.5 m in diameter. It can ‘see’ more than a hundred objects simultaneously. Its guidance sensor would be another piece of unprecedented precision: its pointing error would be corrected in terms of a milli arcsecond level. An innovative device on the James Webb telescope would be four grids of 62,000 micro shutters, each with a width of 3 to 6 human hairs (100 X 200 micrometres) to block unwanted light from objects close to the camera in space and let only the light from faraway sources.
It is like what our eyes do, when we squint to have a clearer view of objects. The telescope’s near-infrared spectrograph will break up the light from galaxies into a rainbow of different colours and enable scientists to peer back to the fist stars after the Big Bang and determine the kinds of stars and gases that eventually made up the galaxies and measure their distances and motions.
The deployment of telescopes nowadays is aided by simulations done by supercomputers. For instance, the Centre for Astrophysical and Thermonuclear Flashes at the University of Chicago performs (with 6000 processors) one of the most advanced simulations of exploring white dwarf stars.