by Prasad Ganti
From the human eye to AI
It all started with humans observing points of light in the sky with their naked eyes. The quest to understand our planet earth, our solar system, our galaxy, and ultimately the whole universe. Astronomy grew from such humble beginnings. Aided by imagination, technology inventions, growth in science, we have come a long way. And astronomy today is no longer just looking at the sky with the naked eye. Although that task still forms the basis of human curiosity.
Some material for this article has been taken from the book “The Big Bang” by Simon Singh. This book had a great impact on me by laying down the astronomy timeline very clearly. The AI (Artificial Intelligence) part is an addition of my 2 cents. Observation of the skies with naked eye reached its peak with the Danish astronomer Tyco Brahe’s gathering a lot of experimental data which Johannes Kepler used to firmly establish the sun centric model of our solar system with the planets going around. Planets up to Saturn were known and distinguished from stars which stayed relatively fixed in the skies. Comets were known as well.
Hans Lippershey, a Flemish spectacle maker invented the telescope in 1608, which Galileo Galilei made use of. Galileo first observed that Jupiter had four moons and also discovered the rings of Saturn. The telescope extended man’s vision to distant skies. Telescopes became more and more powerful as time went by. Also enabling seeing near objects in much greater detail.
After Galileo, William Herschel was a great user of the telescope. He discovered Uranus, who was the father of Saturn and grand father of Jupiter in Greek mythology. Other than the planets and the stars, there were hazy objects called nebulae. Charles Messier compiled a catalog of 103 nebulae in 1781. These are distant objects, like M31 (31st object in Messier catalog) which is Andromeda, now known as a separate galaxy.
The next milestone came when John Herschel, son of William, started photographing stars. This let the pictures to be analyzed by different teams at future points in time. John Goodricke discovered the Cepheid stars which have variable brightness. Because they go through contraction and expansion cycles. Henrietta Leavitt found a relationship between the period of fluctuation and the apparent brightness by collecting data from a group of Cepheids in the Magellanic cloud. A team of astronomers found the distance to one Cepheid. Henrietta’s graph was used to calculate distances to other Cepheids. Thus Cepheids are known as standard candles.
Edwin Hubble has been the first astronomer to find Cepheids outside the Milky Way and thereby measure the distance to our neighboring Galaxy, namely the Andromeda Galaxy. Finding Cepheids in distant galaxies was not possible. Astronomers made an assumption that the brightest star in all the galaxies have the same absolute brightness. By comparing the apparent brightness, a Galaxy’s distance could be measured.
After Isaac Newton used a prism to split the sunlight into rainbow colors, Joseph Von Fraunhofer, Robert Bunsen and Gustav Kirchhoff built a spectroscope for measuring wavelengths of lights emitted by an object. Each element has its own characteristic emission and absorption line. A great achievement of this technique has been the discovery of an absorption line in sunlight which did not match any element on the earth. It was called Helium. This technique is used to find the contents of a remote object and its atmosphere.
William Herschel accidentally discovered infrared rays. He placed a thermometer in different colors produced by a prism. He tried to measure the temperature of something invisible beyond the red light. He found that portion to be the hottest. Heat radiation is now what is known as infrared rays. In the last half century or so, astronomy galloped to detect other parts of the electromagnetic spectrum, ie. radio waves, infrared waves, ultraviolet waves, x-rays, gamma rays etc. Different telescopes detect different parts of the electromagnetic spectrum. Astronomical objects in the Universe emit more than light. In fact, the complete story of an object can be constructed by detecting emissions at various frequencies.
Radio telescopes began with the accidental discovery of a Bell Labs engineer named Karl Jansky. A radio telescope is set of radio antennas connected to a radio receiver receiving. It does not resemble an optical telescope in any way. Bell Labs also contributed to Astronomy with another accidental discovery of what now is known as cosmic background radiation at microwave frequencies.
Most recent trend has been the discovery of exoplanets. Planets which are outside of our solar system and which can harbor life. Obviously the stars cannot harbor any life. The exoplanetshave to be discovered indirectly, by the dimming of the light from its parent star, or by the wobble it causes to its parent star. It means measuring very subtle variations in light and movement and interpreting the data. This is where AI comes into picture. Recent trends in machine learning involves taking vast amount of data and finding hidden patterns. Quicker than what a human being could have done. In fact with Google’s help, some exoplanets were found using the gathered data. This bodes well for astronomy.
Telescopes have moved to space to avoid the terrestrial disturbances. While bigger and bigger ones get built on the ground. Reams of data is being collected and analyzed by the computers. Big data and AI are coming to the aid. Newer discoveries are being made. We certainly have come a long way from the days of gazing at the night skies or peeping into an optical telescope.