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Step 8Making it Work
After all this, it does tell the time, and it does point north, but there's one thing missing.
You need to know your latitude (Perth, Australia is 32 degrees south).
Look at your dome as if it were a globe. You have an equator, and the solstice marks can substitute as poles. Place your mark in line with the top and a solstice mark, at the same position as your latitude.
Now position the dial such that the bubble is exactly under this mark.
At the December solstice, the sun is the furthest south so it should cast a shadow further north in your dial. That means that December is the north-most month in your dial.
If you're in the northern hemisphere, the bubble should be closer to the mark for the December solstice. Opposite in the southern hemisphere.
In step4, I said to place January a third of a month clockwise around the circle. If you did that, count your months clockwise around the circle. Follow that line (toward the centre) to the inner circle, then horizontally to the line in the middle of the dial.
(mine has heaps of horizontal lines to help with this, but i can't see the shadow the equatorial casts).
That gives you a height on the line which relates to how far the sun is away from the equator. (December and June are pretty much at the very ends of this line)
That spot on the line is what you need to align your equatorial shadow over. You do this by rotating the dial (and usually your body) while keeping the bubble under the spot at your latitude.
When the equatorial shadow is over that spot, the December solstice mark is pointing true north.
Then it's a matter of reading the marks in the shadow from one end to the centre line. The very edges are six o'clock morning and night. This picture shows the dial at 11:20 in Perth AU, December 22.
The mark for seven o'clock is not visible in this view because of the shape of the dome. However, you can see the bright spot surrounding the noon mark (the dome is actually quite distorted, you can see that in the lines on the base plate). The equatorial line doesn't need to be this thick unless you want the shadow to be photogenic.
There are a few offsets you need to account for, first is the equation of time which makes local solar time fast or slow, the next is daylight saving, the next is only if you're in a very large time zone (like China) and the sun isn't overhead at "noon".
Problems:
The bubble sticks to the plastic a little bit making it hard lo line up properly (detergent might help).
The permanent marker runs and turns the water purple.
Taking it further:
A watch that only works from six to six isn't much help, but if you place the latitude mark and the noon mark further to the east, it works longer when the sun is in the west.
Taking it too far:
Because it's december and everyone seems to be feeling extremely festive, you could try putting 'snow' in your wearable snow dome. This will, of course, make it almost impossible to read.
You need to know your latitude (Perth, Australia is 32 degrees south).
Look at your dome as if it were a globe. You have an equator, and the solstice marks can substitute as poles. Place your mark in line with the top and a solstice mark, at the same position as your latitude.
Now position the dial such that the bubble is exactly under this mark.
At the December solstice, the sun is the furthest south so it should cast a shadow further north in your dial. That means that December is the north-most month in your dial.
If you're in the northern hemisphere, the bubble should be closer to the mark for the December solstice. Opposite in the southern hemisphere.
In step4, I said to place January a third of a month clockwise around the circle. If you did that, count your months clockwise around the circle. Follow that line (toward the centre) to the inner circle, then horizontally to the line in the middle of the dial.
(mine has heaps of horizontal lines to help with this, but i can't see the shadow the equatorial casts).
That gives you a height on the line which relates to how far the sun is away from the equator. (December and June are pretty much at the very ends of this line)
That spot on the line is what you need to align your equatorial shadow over. You do this by rotating the dial (and usually your body) while keeping the bubble under the spot at your latitude.
When the equatorial shadow is over that spot, the December solstice mark is pointing true north.
Then it's a matter of reading the marks in the shadow from one end to the centre line. The very edges are six o'clock morning and night. This picture shows the dial at 11:20 in Perth AU, December 22.
The mark for seven o'clock is not visible in this view because of the shape of the dome. However, you can see the bright spot surrounding the noon mark (the dome is actually quite distorted, you can see that in the lines on the base plate). The equatorial line doesn't need to be this thick unless you want the shadow to be photogenic.
There are a few offsets you need to account for, first is the equation of time which makes local solar time fast or slow, the next is daylight saving, the next is only if you're in a very large time zone (like China) and the sun isn't overhead at "noon".
Problems:
The bubble sticks to the plastic a little bit making it hard lo line up properly (detergent might help).
The permanent marker runs and turns the water purple.
Taking it further:
A watch that only works from six to six isn't much help, but if you place the latitude mark and the noon mark further to the east, it works longer when the sun is in the west.
Taking it too far:
Because it's december and everyone seems to be feeling extremely festive, you could try putting 'snow' in your wearable snow dome. This will, of course, make it almost impossible to read.
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