A Sundial for the beach or the backyard. Specifically designed to be accurate to a few seconds for a couple of days only. Takes into account local time and Daylight Savings. 6am to 6pm. Perfect for the Beach because its accuracy is only good for a couple of days but for the same reason its also super easy to setup.
See instructions for how to line it up. Because of the precalculation you don't need to determine True North to place it correctly. You just need a level surface.
Initially printed as two pieces it takes very little material to print.
Once pressed into the sand, the dial is removed and the gnomon is all you need to cast a shadow and see the time.
The gnomon can also be replaced by a stick or string to scale the sundial up to very large sizes.
Google tells you your Latitude and Longitude and you need a level surface, the sun, and a clock to set it up. See the Instructions page.
A string can extend the dial face to be very large and a broom handle and string can make a longer Gnomon. So a small 3D print will scale up at the beach to any size.
Works in both Hemispheres and all Timezones.
Note the Rroman numbers do not need to be printed. The dial always goes from 6am to 6pm with hours and half hours marked.
Determine the Latitude and Longitude of your "Beach" location using Google. Just type " Latitude 'yourcity' " into Google and note the numbers.
E.g. San Francisco is 37.7833 N, 122.4167 W.
Latitude is easy. Just enter the value(first number) and select the Hemisphere.
Longitude is more difficult. West needs to be entered as a negative number.
So for SF above. 122.4167 W becomes -122.4167
To correct for local time and make the Sundial accurate, you need to know the meridian your local time is calculated from. Check it on the map in the files list. For SF (and all of CA) you can see its TZ is -8. Every TZ is 15 degrees apart. so -8 x 15 = -120. This is your Local Meridian. The image shows how inaccurate Solar time vs TZ time is with Red late and Blue early.. The thin white line in the middle is what we're looking for. In many parts of the world geopolitics sets this value so it has to be entered manually.
Setting DST for daylight savings time will rotate the dial by an hour(15 degrees).
Knowing the date allows the calculation of the equation of time which corrects up to +/-15 minutes for the earths wobble and the elliptical nature of our orbit around the Sun.
This means - if you can get that data in - that your Sundial will be minute accurate if you line it up properly. Potentially accurate to about 4 seconds.
Setting the Dial up:
Normally you need to do two things to line up a Sundial like this one.
Ensure the surface is level (by using a level) and finding True North (which is not the same as Magnetic north regrettably).
However because all calculations have been done. Simply level the sand and place the sundial down with the gnomon in place and adjust it by rotating the dial and gnomon until the time by the Sun's shadow matches your watch, clock, or cellphone time.
The gnomon needs to be vertical and aligned in its slot and resting on the sand. The sand needs to be level.
Sources of error
If not level the time will be out by the largest margin.
If the latitude is not quite right - errors will be small.
If the Longitude is not right. You lose 4 mins for every degree you are out. So still pretty good. But this and level are the most important.
And of course the gnomon has to be vertical and not leaning over.
Scaling it up
Initially you can print this at any scale. It will still work.
The guide hole is there so you can put a peg in the sand, with a string tied to it, and manually sight along the hour lines and draw much longer lines in the sand.
If you do, you'll also need a bigger gnomon to cast a longer shadow. You can use this same hole to push a stick into the sand at the same angle as the gnomon.
Or you can use the peg and string to make a gnomon. Use a tentpole or stick to tie up the top end of the string. Make sure the gnomon is at the same angle as the printed one. The angle is 90 - your latitude.
Please note that if you publish your thing and you've entered the lat,long of your home address, people will know exactly where you live.
On the other hand - if you use your nearest beach or town - they won't :)
It wil be just as accurate.
Be safe online. Cheers...