Percival Lovell using the Clark Telescope
Over history, changing technology has brought Mars ever closer to us, before it finally took us to it. However, what technology couldn’t definitively supply, human imagination has always been ready to provide.
So long as they were Earth-bound, astronomers were limited not only by the capabilities of their instruments but also by the atmosphere through which they peered. The motion of the air makes the detail of planetary surfaces flicker and deceive the eye. Tantalisingly clear glimpses appear when the air stills, which, pre-photography, had to be committed to memory and reproduced in sketches.
Robert Hooke, working with a small-lensed refracting telescope in 1666, described the difficulties of observing Mars: “I could find nothing of satisfaction, though I often imagin’d, I saw Spots, yet the inflective veins of the Air … did make it confus’d and glaring, that I could not conclude upon any thing.” Yet, at the same period, Christiaan Huygens and Gian Domenico Cassini (celebrated in the Cassini-Huygens Mission) noted the presence of distinct features, including white areas toward the poles and patches identified as bogs.
William Herschel, a pioneer of large reflecting telescopes, quickly came to the conclusion that the white areas were ice caps. In 1784 he further reported to the Royal Society that Mars “is not without considerable atmosphere”, with evidence of clouds, and that “its inhabitants probably enjoy a situation in many respects similar to our own.” The instinct to describe what were, necessarily, incredibly indistinct features with words with terrestrial connotations undoubtedly reinforced the sense that Mars was Earth’s mirror.
By the 19th century, the magnification and light-gathering power of reflecting telescopes had increased dramatically, allowing a much greater degree of detail on the surface of Mars to be defined. Of course, more visible features gave eyes and imaginations more to play with.
Read the rest of this interesting article by Rebekah Higgitt here Mapping Mars: a long and highly imaginative history