The intellectual climate changed, albeit slowly. For example, a Jesuit astronomer, Johannn Schreck took a telescope to China in 1621, but he stuck to pre-Copernican astronomy. Galileo’s telescope marked a breakthrough capacity of instruments, which continues even today.
Until World War II , telescopes were restricted to the visible spectrum , today ,observers have access to almost all regions of the electromagnetic spectrum. The angular resolution has improved at different wavelengths, yielding big surprises. New classes of objects such as quasars, infrared stars and other radio sources have been discovered.
Progress in time resolution led to the discovery of transient and variable phenomena. They included not only slowly expanding supernova remnants (when a massive star runs out of fuel and collapse), but also millisecond pulsars and brief gamma ray bursts . Equally significant has been the progress in spectral resolution, which enables an observer to deduce features of an object from a study of the spectral lines emitted by it.
The recent rapid progress in observational tools stands in sharp contrast with the slow advances made over the last four centuries in terms of astronomical instruments . Yet the early pioneers made significant contributions , limited of courses by the level of technology prevalent at that time. Moreover, news of the progress sped rather slowly; there was no world wide web or Internet to splash the discoveries in no time!
Almost three decades after Galileo, Robert Hook (1635-1703) in England built a reflecting telescope in 1664. He was familiar with telescopes in Italy where he studied for a while. Four year later, Newton came out with his own version. He was able to show that the universal law of gravitation held good not only for circular orbits but also for elliptical orbits. A French man, Cassegrain invented a better reflecting telescope with a concave parabolic primary mirror and a convex secondary mirror.
Across the English Channel, Claude Perrault in France built the Paris Observatory in 1667, which is the oldest functioning observatory in the world.
The next round of significant discoveries, based on instruments, was achieved only in the 19th century. The most notable of them was the study of the solar spectrum by Joseph Fraunhofer (1787-1826), who created the first spectroscope.
Fraunhofer was the first to discover the dark lines in the sun’s spectrum in 1814. The lines have since been named after him. Over 500 such lines that crossed the spectrum were identified by him. All these lines are called absorption lines, as they are caused by the absorption of light by the relatively cooler regions of the solar atmosphere above the visible surface.
The nine most prominent starting from the red end A , B , C , D , E , F , G , H and K. He found that the spectrum of sunlight and spectra of reflected light from the Moon and Venus were similar.
He magnified the sun’s spectrum with a small telescope and tallied 574 dark lines. However, he could not explain why a solar line was dark and why the yellow lines by a candle flame was bright. However, celestial spectroscopy took a giant leap with this small step; it went in a slumber for the next four decades.
Another significant discovery was the wave nature of light. James Maxwell (1831-1879) pointed out that light was but one from of the electromagnetic spectrum. It is one of the greatest leaps of human intelligence. His theory underlines all of the exploration of cosmic phenomena in all areas of the electromagnetic spectrum.
In 1870, three years before Maxwell published his papers, an English scientist. John William Strut (1842-1919), (later known as Lord Raleigh), discovered the phenomenon of scattering of sunlight in the atmosphere. His explanation is now known as Raleigh scattering. Basically he answers the famous question often asked by children: why the sky is blue? His description of the scattering phenomenon has triggered many discoveries on the nature of light and our atmosphere.