Make a Viking Sun Compass

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Introduction: Make a Viking Sun Compass

Imagine the situation - you're due to go on a raid tomorrow, but Bjorn Hammersson won your lodestone in a game of hnefetafl last night. No magnetic lodestone, nothing to indicate North when you're out of sight of land. How are you going to find your way at sea?

Fortunately, with a nail, a lump of wood and a few spare hours, you can construct a sun compass.

(To do this Instructable properly, it is not absolutely vital to be wearing a Viking helmet, but it helps. It's a long time since mine last came out of the shed...)

Step 1: Make Your Sun Compass.


Bang the nail through the piece of wood. No, don't use a rock, you're supposed to be civilised. Use a hammer.

Done.

Yes, really, you're done. All you need to do now is calibrate it.

Step 2: Calibrate Your Sun Compass.


All you need is patience and a pencil.

Put your sun compass somewhere that is both sunny and won't be disturbed, or where you can make sure that you place the sun compass in exactly the same orientation each time. I stood mine on an up-turned planter, to stop folk stepping on the nail.

Spend the day near your sun compass, doing useful things to prepare for your raid (mending sails, sharpening swords, doing careful stretching exercises so you don't pull a muscle during an important ravish, you know the kind of thing).

Every so often (try for every 20 or 30 minutes, but at least every hour), mark the tip of the nail's shadow with your pencil.

At the end of the day, join the marks in a smooth curve, known as the gnomon curve.

Find the point where the gnomon curve passes closest to the nail. Draw a straight line from that point to the base of the nail. That will be your North-South line (as a Viking, living in the Northern hemisphere, North is pointing away from the nail. If you are making your sun compass in the Southern hemisphere, North is pointing towards the nail, and you must be the most utterly-lost Viking in history).

Step 3: Using the Sun Compass.


There you are, out at sea, no land in sight - where's North?

Hold your sun compass upright and look for the shadow of the nail. Turn (not tilt!) the compass until the tip of the shadow just touches the gnomon curve. The line you originally drew from nail to gnomon curve will now be pointing North - happy sailing!

Step 4: A Warning ...

Obviously, the height of the Sun changes throughout the year, so your sun compass will only be accurate for a few days.

It won't make much difference at first - you'll still get back to a recognisable stretch of coast and be able to find your way home by eye, but eventually it will be way out.

The solution is to create a larger sun compass, with a lot of gnomon curves on it - at least one per month, preferably one per week, and certainly one on each solstice and the equinoxes. Mark the gnomon curves clearly with the date they were drawn, and then, in future years, you can use the same sun compass year after year.

Copy the pattern carefully, carving into the prow of your dragonship, and you'll never get lost again, no matter what Bjorn's luck with at the table...

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41 Comments

Great Instructable and very fun to read.

On a large flat Viking ship the shadow of the tip of the mast could be drawn on the deck and a gnomic curve drawn. With the north point marked, the other compass points could also be inscribed on the deck. Then the Viking captain would just leave Stavanger and head south-south-west.

Just saying.

Reminds of a Finnish joke. X)
Jokkela and Pattimeiki were out in a row boat, fishing, one day.
They found a really good spot and caught a lot of fish.
Then, when evening fell, and they had to go home, Jokkela said "How will we find this place again?"
Pattimeiki said "No problem, we just mark where we've been." and he carved a big X in the bottom of the boat.
"But," said Jokkela, "what if we don't use the same boat next time?"

HA! good joke.

interesting, but you're only half right. yes, it was a navigational instrument to determine a course, but it wasn't used to determine what way was north. the gnomic lines terminate prematurely and would make it impossible to determine north in the late afty. another problem is the marks were a few degrees off, which would have put them many miles off course. researchers believe it's actually a sun shadow board, used to find local noon and calculate latitude. it had two gnomons, one taller than the other. the short gnomon was used to determine noon and the taller one used to find the current latitude. this would give a deviation of no more than 6 nautical miles (11km) and between greenland and norway, that deviation's not a big issue.

http://phys.org/news/2013-04-errors-viking-sun-compass-hint.html

i really enjoy your historical accuracy regaurding norse viking culture its good to see other people recognizing it as it is

Er... thank you?

sorry its a thing i have how people have strayed from their natural purpose and a viking thing a little too

Protip: if you can fix a gem of iolite (cordierite) to the top of the nail head it can show where the sun is in even the cloudy days.

Thanks for the instructable, when I find the iolite I have been hoarding away this will be invaluable!