View Single Post
Old 06-15-2019, 12:16 AM
TokyoBayer's Avatar
TokyoBayer is online now
Join Date: Oct 2003
Location: Taiwan
Posts: 10,511
Originally Posted by brossa View Post
I will argue that you can't determine hemisphere by whether the shadow is to the north or south of the bottle; instead you can determine whether you are north or south of whichever latitude line has the noon sun directly overhead for that date. There may be a more elegant way of putting that. This line of latitude varies from the Tropic of Capricorn to the Tropic of Cancer depending on the date. So, on June 21st (summer solstice) if the shadow at noon is pointing south, the most that you can say is that your latitude is somewhere between ~23.5 deg North, and 66.5 deg South (any further South on that date and the Sun wouldn't ever rise). But on December 22nd, if the noon shadow was pointing South, you would say that you were between ~23.5 deg South and 66.5 deg S (again, any farther South and the Sun wouldn't have ever set).
Actually, they are correct. They are only discussing using the direction of the shadow on the special case of an equinox.
Had you been kidnapped at equinox season, when daylight has the same duration the world over, finding your latitude would be more involved, requiring, for example, finding the ratio between a shadow’s length and the height of a water bottle at noon, and identifying the hemisphere by which side of the bottle the shadow extends from (north or south).
This also addresses your second point about determining latitude, which can be done can be found by the length of the bottle’s shadow at noon. No shadow means that there are six more weeks of winter that you are on the equator. The increasing length of the shadow as a ratio of the height of the bottle will tell you your latitude.