4 ms·

Wait, how does that work? The shadow is always going to be opposite of the sun, so it does not provide any extra info which the sun doesn't already give you.

by hooby 4y ago

Wait, how does that work? The shadow is always going to be opposite of the sun, so it does not provide any extra info which the sun doesn't already give you. In order to estimate the current time ("it's about 5 o'clock") using the position of the sun/a shadow - you need to know the cardinal directions. So, only if you already know where north is, you can tell the time from the shadow. In order to estimate the cardinal directions from the position of the sun/a shadow - you need to know what time it is. So only if you know the time, you can tell where north is from the sun/shadow. And to know the time you need a watch or something similar? But if you can deduce both time AND cardinal directions just using the sun/shadow and no other information... yeah, I have to agree, that seems like witchcraft!

justsomehnguy 4y ago
> In order to estimate the current time ("it's about 5 o'clock") using the position of the sun/a shadow - you need to know the cardinal directions On this planet the sun is always moving from East to West. And assuming you suddenly didn't wake up on the other side of the planet you know if you are in Northern or Southern hemisphere. So if you are in Northern one, then shadows always point in the North direction, the difference between marks on the ground show you the sun direction (E-W). More so, in the morning shadows point to NW, in the evening to NE, so you can have a vague estimate even without waiting. > And to know the time you need a watch or something similar? You don't need the time per se, you need to know what sufficient time passed, it's just hard to make a precise line with a sticks. But if you have something long and thin then you can make a line in a couple of minutes. Just take a sheet of paper, anything sticky (even a pencil, just make it stay vertical), mark the shadow, browse Reddi^W HN for a couple of minutes, mark the new shadow, make a line. We just don't notice it, but Sun is hurling through the skies with astonishing speed. PS I can guess the current time with ~1-1.5h accuracy just looking through the window to see how the buildings are lit by the sun. Works only from my windows, of course.
rocqua 4y ago
The shadow measures not just the horizontal angle change of the sun, but also the vertical angle change of the sun. A very common way to measure time is to reference the horizontal angle change w.r.t. noon. In that case you need two moments where you measure the horizontal angle. Where, for the first moment, you need to measure two vertical angles (probably more) and deduce that the sun has reached its highest point. In this witchcraft, you still measure two vertical angles and two horizontal angles. You just split up when you take the vertical angles.

by hooby 4y ago

justsomehnguy 4y ago

> In order to estimate the current time ("it's about 5 o'clock") using the position of the sun/a shadow - you need to know the cardinal directions On this planet the sun is always moving from East to West. And assuming you suddenly didn't wake up on the other side of the planet you know if you are in Northern or Southern hemisphere. So if you are in Northern one, then shadows always point in the North direction, the difference between marks on the ground show you the sun direction (E-W). More so, in the morning shadows point to NW, in the evening to NE, so you can have a vague estimate even without waiting. > And to know the time you need a watch or something similar? You don't need the time per se, you need to know what sufficient time passed, it's just hard to make a precise line with a sticks. But if you have something long and thin then you can make a line in a couple of minutes. Just take a sheet of paper, anything sticky (even a pencil, just make it stay vertical), mark the shadow, browse Reddi^W HN for a couple of minutes, mark the new shadow, make a line. We just don't notice it, but Sun is hurling through the skies with astonishing speed. PS I can guess the current time with ~1-1.5h accuracy just looking through the window to see how the buildings are lit by the sun. Works only from my windows, of course.

rocqua 4y ago

The shadow measures not just the horizontal angle change of the sun, but also the vertical angle change of the sun. A very common way to measure time is to reference the horizontal angle change w.r.t. noon. In that case you need two moments where you measure the horizontal angle. Where, for the first moment, you need to measure two vertical angles (probably more) and deduce that the sun has reached its highest point. In this witchcraft, you still measure two vertical angles and two horizontal angles. You just split up when you take the vertical angles.