Editing Sundial (section)

===Reflection sundials===
[[Isaac Newton]] developed a convenient and inexpensive sundial, in which a small mirror is placed on the sill of a south-facing window.<ref>{{harvp|Waugh|1973|pp=116–121}}</ref> The mirror acts like a nodus, casting a single spot of light on the ceiling. Depending on the geographical [[latitude]] and time of year, the light-spot follows a conic section, such as the hyperbolae of the pelikonon. If the mirror is parallel to the Earth's equator, and the ceiling is horizontal, then the resulting angles are those of a conventional horizontal sundial. Using the ceiling as a sundial surface exploits unused space, and the dial may be large enough to be very accurate.