Sundial layout and design
 

I know that there is a member here that makes really nice sundials. I think that I remember it coming up that one had maybe been gifted as part of the Christmas exchange or something.

Anyway, in the discussion about the DIY sundial, it was mentioned that the sundial was setup for the recipient's lattitude. I wasn't aware that the lattitude was important. It turns out that a lot more than that can go into the layout and design of a sundial.

My grandson (6yo) has been doing some educational stuff about shadows out of a book with my wife today while I've been working. When I heard that I decided to make a sundial, but I wanted to see if I could get a better understanding of how the lines and everything get laid out correctly.

I learned a bunch of stuff, ie, the gnomon should be leaning at an angle that corresponds to your lattitude. I even know the reason for this (corresponds to the axis of the earth). And the gnomon should point north (geographic, not magnetic). And the lines are not laid out equally (because technically the dial plate should be perpendicular to the gnomon, and since they aren't they vary like they would if you cut through the sections of an orange or grapefruit).

Then you've got the problem with DST, and the fact that the "apparent time" varies per location (longitude), but the time that we all use is based on a time zone (and the time zone's time is based on the center of the timezone) so as you get farther from the center of the timezone the apparent time varies from the time we use more and more. Apparently, back in the day, apparent time was used by railways (and others, presumably), and that was very cumbersome. Then you've got that the timezones aren't equal and don't follow the lines of longitude, and sheiße gets way out of whack.

Anyway, I learned a bunch that I thought was interesting.

This video has some nice visualizations to show the reason for the orientation of things.
<iframe width="560" height="315" src="https://www.youtube.com/embed/B8XXz-_-GAg" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

This guys stuff while a little dry, is, to me, more informative and easier to watch.
<iframe width="560" height="315" src="https://www.youtube.com/embed/7DDHoybER4U" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

this one expands on the first a bit, the info about longitude, apparent time, railways, etc...
<iframe width="560" height="315" src="https://www.youtube.com/embed/CmQBlGEYDRU" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

This one is about a different type of sundial and is pretty cool. This one shows how to adjust for the varying length of days, your longitude, and DST to get the "real" time from the apparent (solar) time.
<iframe width="560" height="315" src="https://www.youtube.com/embed/ImQDbCF9Cm0" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

Same guy has a few more videos, polar sundial, equatorial sundial

Tangentially related...

We built a street sign for the Lab, and illuminated it with several LEDs. The LEDs were being controlled via an Arduino microprocessor.
We didn't want to leave the lights on all of the time, so we decided to turn them on at dusk. Option one was to just turn them on every night at 6pm. Option two was to use a light sensor. But, we're super nerds, so we used option three. We wrote code to solve the solar equation of time and calculate on the fly, each day, the local sunset time for the sign, and turn the lights on then. We approximated a few lines for brevity and to fit in the Arduino memory, but it's within 5 minutes on any given day.

Nice. So you cover the changing daylight throughout the year as well as DST. Cool.