How to set up a sundial ?

Question

Hi I have a sundial In my backyard and would love to set it up but everytime I look to set it up I get videos and they tell me to position it to my current time but if I did that it would be Incorrect As one we are on daylight saving time and two we are one hour ahead of our correct time which is stupid but w/e it's just this stupid country .. So if I did that my sundial would be almost 2 hours ahead of the correct time!? I want my true time!? So how do I set my sundial up do that I know the true current local time!?

Answer 1

Solar time and clock time are going to be different. As you correctly surmised, if you set up your sundial to your current clock time, it would be one hour off from solar time because of the time offset. I'm not sure how you got two hours.



Is it a vertical or horizontal sundial? Probably horizontal... I did a google search and came up with lots of websites that answer the question in detail. But very simply, you probably need to align the sundial such that 12 is pointing North, 6 is pointing South... Hard to do during the day.



You can get a rough alignment by going outside during the day around mid-day. Assuming you do this while you are observing Daylight Savings...Say, your wristwatch says it is 1pm. Shift the sundial so that it shows that it is noon.



If you do this when DST is not in effect, then if your wristwatch says it is 1pm, have the sundial shadow also show it is 1pm.



Later on, when you shift to DST, it will be one hour off, but as you mentioned that is a human construct and does not reflect the solar time. (ie, the sundial does not get changed for DST like we change our wristwatches or other clocks.)



Other things/nuances that you'll run into: equation of time... but with a garden sundial, it's not like you will have accuracy to the minute anyways so I wouldn't worry about it...



Some of the websites (eHow) don't take into account DST.

Answer 2

The key to getting it right is to point the gnomon directly at true polar North. The gnomon is the part in the center that casts the actual shadow. Even the North Star is off by ~1/2 degree, but will suffice for most applications. Remember that even with a properly pointed and aligned gnomon, the equation of time will throw the readings off when compared to mean solar time, with the greatest inaccuracies at early December and mid to late January.

Answer 3

There is also the fact that, unless you happen to live on a line of longitude, your watch is wrong - in the sense that it does not show local time with noon (when the sun is at the zenith) at 12:00, it shows the legal time for your timezone. If you live in Alaska, that could be a couple of hours different. Apart from the DST issue.

Answer 4

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I hope this is the right answer, but I heard that you wait until it is Midday, go into the garden, and place it so that it shows 12pm.