The planet Mars has inspired fascination in human observers for centuries.  Many names have been given to this glowing red jewel.  The Egyptians called it the Red One.  Babylonian observers named it the Star of Death.  The Greeks and Romans associated the "star" with war and death calling it Ares and Mars respectively.  Even in the 1950's, the planet  Mars was associated with Earth's demise with productions like H. G. Wells' War of the Worlds.  The little red planet surely was the cause of frustration and torment... and joy and wonder... for early astronomers.
     Early Greeks first thought to quantify and therefore justify Mars' nightly wanderings.  They observed that Mars "wanders" amid the background mosaic of fixed stars in a strange manner.  The planet would move across the sky, stop, back up, and then proceed as usual.  This is referred to as retrograde motion and at the time of the Greeks it was not easily explainable.
     As the human mind and civilizations grew, the desire to understand the motions of celestial bodies accelerated.  True Science had been discovered.  Ptolemy was an astronomer in the second century A.D.  He proclaimed in his book The Almegast that Mars, Jupiter, and Saturn revolve around the Earth while they simultaneously revolve around a central point that exists on their main orbit around the Earth.  Thus, the planets orbit the Earth in spiraling fashion which is the result of the two independent motions.  This notion (termed the Ptolemic theory) seemed to explain the observed retrograde motion and provided a surprisingly accurate means of predicting future locations.  For centuries all the known planets and the sun were thought to revolve around the Earth.
     For Tycho Brahae, Mars was a never-ending study in his quest to define planetary motion.  This 16th century man was a devoted observer who spent countless hours plotting on charts the positions of the known planets and the stars.  Tycho, using only his unaided eye, defined the type-cast for precision and accuracy.  Unfortunately, he never constructed a theory from his wealth of observations.  His student, Johannes Kepler, inherited the closely guarded observations and used his skills as a mathematician to formulate Three Laws of Planetary Motion.  Fortunately Kepler happened to be focusing on Mars, the planet with the most highly eccentric orbit yet discovered, for unraveling the mysteries of planetary motion.  Eventually this eccentricity revealed itself in Kepler's mind.  He was able to plot the orbit of Mars as an ellipse with the sun at one focus and predict future locations without the need of complicated theories like the one proposed by Ptolemy.  Eventually, the Ptolemic theory was laid to rest with Galileo's telescopic observation of Venus in crescent phase; but that is another story.
     Galileo indeed opened the eyes of astronomy with his use of the telescope which eventually led to telescopic observations of Mars.  Countless observers like William Hershel, Johann Schroeter, and Johann Madler began observing Mars with telescopes.  The stage is now set for the greatest controversy in the history of observing Mars.  Early telescopes were not much to be desired.  Irregularities in lens manufacture yielded images that were small and distorted at best.  Also, chromatic aberration plagued early refracting telescopes causing the Martian disk to be clouded in a wash of aggravating colors.  Finally by 1840, telescope production was improved and chromatic aberration was diminished.  It was at this time that Madler made the first map of the surface of Mars.  During the next sixty years, as telescopes continued to improve, the maps of the Martian surface enjoyed more detail.  An astronomer named Giovanni Schiaparelli made an observation with his 8.6-inch Merz refractor at the Brera Observatory in 1877 that was like the falling of small stones that starts a great avalanche.  He observed linear features on the Martian surface that he called canals.  He suggested that these canals moved precious water form the Martian poles to locations at the equator where the inhabitants of Mars could irrigate their vegetation.  Schiaparelli was already considered a highly talented observer with uncanny eyesight so if he said there were canals on Mars, no one doubted him, even if his peers could not see these canals for themselves.   His suggestion that the canals were made by intelligent inhabitants was, of course, very popular.  A few years later, a self supported and inadequately educated astronomer named Percival Lowell blew the canal hypothesis completely out of proportion.  Lowell was popular with the media, but not with other astronomers.  His observations of Mars included hundreds of canals which he said could only mean Mars is inhabited by intelligent life.
     Eventually, a scientist named Vincenzo Cerulli did a study on the manner in which the eye perceives details at various distances.  He found that a line made up of small dots looks like a solid line at a great distance, but appears to be made up of dots at closer distances.  This is the key to the Martian canal controversy.  The first telescopes revealed almost no detail on the Martian surface.  As telescopes improved, more detail was revealed, but not enough to resolve surface features as individual structures.  Hence, the Martian canals.  Eventually, around the turn of the century, large high quality telescopes were manufactured that had the resolving power to discern individual surface features on Mars.  It became clear that there were no linear canals on Mars, only natural undulating surface features one would expect to see on a terrestrial surface.
     The thought that Mars must be inhabited by intelligent life did not, however, diminish with the fall of the Martian canal reign.  Finally, the spacecraft era laid to rest the notion of Martian life with Viking, Mariner, and Pathfinder spacecraft.  It is with these spacecraft that scientists have been able to learn nearly all that is presently known about Mars' atmosphere (Sheehan, 1996).