But what happens on a cloudy day?

Irrelevant if you can take enough regular measurements when there is no cloud cover. Knowing the geometry of the earth and the axis of rotation, time and coordinates can be calculated.

 

A camera could take a photo of the crosshair shadow produced by this sundial.

View attachment 274526

Nice! Who makes this sundial? If I am reading it correctly, it looks like 1415 or 2:15PM?

 

But what happens on a cloudy day?

When I was young (1980's) my parents had me use the sun to tell time along with the farm I worked on. I was told, plow this field but be back before the sun hits the horizon or be home for dinner when the sun is two handbreadths from the horizon. But for some reason I was not allowed to use the excuse of it got cloudy for being late for dinner. Before the era of GPS I looked at the sun's position in the sky to navigate through a city I was never in to determine North/South etc. To this day I can usually get the time correct to within an hour or so when outside working by just looking at the position of the sun. Brings back memories.

 

I often use the position of the sun to figure out the time and get my bearings.
When our kids were young I would show them how to make a sun dial in the sand whenever we went camping.
When driving in unknown territory I prefer to use visual cues rather than rely on GPS.

 

Saw this on the 'Tube. It's a teacher's project for his EE class in Thailand. I thought it was pretty cool. No IC's! I like how he did the mains counter/divider.

Video is 2 years old...Sorry if this has been posted/discussed before.

Glad you enjoyed my video!

 

Nice! Who makes this sundial? If I am reading it correctly, it looks like 1415 or 2:15PM?

https://en.m.wikipedia.org/wiki/Bifilar_sundial

This one has been on my build list for a while. It's the coolest representation I've seen.

 

Here's the schematic of a motor-driven, all-transistor quartz clock.



Nandu.

 

https://www.meridianum.it/ manufactures the sundials in the Wikipedia photo.

 

Edit: why are you only concerned with cloudy days?

"Horas non numero nisi serenas"

 

The world's oldest clock - still installed in its original place and still working is thought to be at Cotehele House, Cornwall, UK. See here. Installed about 1493 so just over 500 years old.
Would an electronic clock made of discrete transistors be more or less reliable than IC's?
My bet is that IC's are more reliable. You certainly don't want any electrolytic capacitors.
Corrosion, damp, thermal effects (expansion and contraction) over the years will be the biggest problems. What about spare parts 100 years from now? At least with the old mechanical clocks all you need to do is machine up a new metal part. Electronic clocks could be more of a problem!

 

I often use the position of the sun to figure out the time and get my bearings.
When our kids were young I would show them how to make a sun dial in the sand whenever we went camping.
When driving in unknown territory I prefer to use visual cues rather than rely on GPS.

I used to do that, growing up and working in California. Then one day I came out of a restaurant at noon in Singapore and couldn't find my way over to where I got out of the taxi.

 

When I was young (1980's) my parents had me use the sun to tell time along with the farm I worked on. I was told, plow this field but be back before the sun hits the horizon or be home for dinner when the sun is two handbreadths from the horizon. But for some reason I was not allowed to use the excuse of it got cloudy for being late for dinner. Before the era of GPS I looked at the sun's position in the sky to navigate through a city I was never in to determine North/South etc. To this day I can usually get the time correct to within an hour or so when outside working by just looking at the position of the sun. Brings back memories.

At night, when the moon is visible, you can also get a pretty good estimate of the time from looking at the terminator on the moon and imagining that you are standing "on top" of the moon, from your perspective.

 

At night, when the moon is visible, you can also get a pretty good estimate of the time from looking at the terminator on the moon and imagining that you are standing "on top" of the moon, from your perspective.

Never thought of doing that. I will have to try that and see how accurately I can guess the time at night.