answer:
the 1800s (the canal craze)
1809
honore flaugergues, a french amateur astronomer, notices "yellow clouds" on the surface of mars, which were later found to be dust clouds.
1813
flaugergues notices that the polar ice cap melts significantly in the martian spring. he concludes that this implies that mars is hotter than earth.
1840
wilhelm beer (1797 - 1850) and johann von maedler (1794 - 1874) observe mars over periods of 759, 1604, and 2234 days, and determine that the rotational period of mars is 24 hours, 37 minutes, 22.6 seconds, which is surprisingly close to the currently accepted value of 24 hours, 37 minutes, 22.7 seconds.
1854
william whewell concludes that mars has green seas and red land, and wonders if there is extraterrestrial life.
1858
angelo secci (1818 - 1878), a jesuit monk, draws mars and calls syrtis major the "atlantic canal".
1862
frederik kaiser calculated the rotational period of mars to be 24 hours, 37 minutes, 22.62 seconds (today's accepted value - 24h, 37m, 22.663 +/-0.002s.
1867
richard anthony proctor publishes a map of mars with continents and oceans. his choice of zero meridian is still the currently accepted convention.
1867
pierre jules janssen (1824 - 1907), sir william huggins (1824 - 1910) make the first (unsuccessful) attempt to detect water vapor and oxygen spectroscopically.
1877
giovanni schiaparelli (1835 - 1910) develops a nomenclature for mapping the features of mars. the names are drawn from mythology, history, and various terms for hell. 1877
schiaparelli uses the term "canali" to describe the streaks on the surface of mars. this is wrongly thought to mean "canals," and is thought to imply that mars has intelligent life that has built a system of canals.
1877
asaph hall discovers the moons of mars. he names them phobos (fear) and deimos (fright), after the horses of the greek war god, ares (counterpart to the roman war god, mars).
1879
schiaparelli observes double "canali", to him an example of "germination".
1894
percival lowell (1855 - 1916) begins observation of mars at his observatory in flagstaff, arizona. that same year, edward emerson barnard (1857 - 1923) reports that he has found no evidence of canals on mars.
1895
percival lowell publishes mars.
