One hundred and sixty-four years ago, or one Neptunian year, Neptune was first observed by telescope. Significantly, it was the first planet to be discovered deliberately; the existence and location of the gas giant was calculated mathematically. Subsequently, it was located by telescope, on 24 September 1846, and found to be within one degree of the mathematically predicted location. Astronomers hypothesized Neptune’s existence due to perturbations in the orbit of its planetary neighbor, Uranus, around the sun, which could only be explained by the presence of another object in nearby orbit. A triumph for the scientific method, and besides, it’s beautiful too.

[div class=attrib]Image courtesy of NASA.[end-div]