- #1
one_raven
- 203
- 0
I bought a cool new watch with a Planisphere face.
http://shop.store.yahoo.com/imagedesign/planwat1.html
All along the outer ring of the watch face it has the 12 months broken down in five day increments.
There is a dial on the face with a solid shape (something like a crescent moon, but larger).
Around the outside diameter of the crescent it has the times from 6PM to 6AM.
On the crystal there is a sky map showing the major constellations.
When you align the time on the dial with the date around the ring of the face, the crescent represents the earth, and everything that is not covered by it is what is visible in the night sky.
Turn the watch to face north (the directions are on the outer dial) and you have a map of the current visible sky with the horizon at the bottom.
It really is a pretty cool watch.
Anyway, onto the questions...
The planisphere built into this watch is designed for the Northern Hemisphere (between 35 - 50 deg. lat.).
How much is the accuracy affected with each degree of lattitude?
Let's say I designed a planisphere that was 100% accurate on the equator.
If I travel to 60 deg lattitude, how far off would it be?
Is the correction that would have to be made linear? In other words, would I have to make the same level of correction going from 20 deg to 40 deg as I would going from 40 deg to 60 deg, or would the correction be less as I head further towards the pole?
It seems that I could tell the exact date and time by the position of the stars in the sky. It doesn't seem too difficult of a task to create a star calendar/clock if it were stationary, say bolted to the ground in my back yard. Let's say, though, that I were traveling by boat and did not know the what lattitude I was at, could I determine the date and time by star positions?
Or is it that I could find my position if I knew the date and time, or I could find the date and time if I knew my position? Do I need one to determine the other?
Basically this has been a too long post to ask, "How do these darned thingies work?"
Thanks
http://shop.store.yahoo.com/imagedesign/planwat1.html
All along the outer ring of the watch face it has the 12 months broken down in five day increments.
There is a dial on the face with a solid shape (something like a crescent moon, but larger).
Around the outside diameter of the crescent it has the times from 6PM to 6AM.
On the crystal there is a sky map showing the major constellations.
When you align the time on the dial with the date around the ring of the face, the crescent represents the earth, and everything that is not covered by it is what is visible in the night sky.
Turn the watch to face north (the directions are on the outer dial) and you have a map of the current visible sky with the horizon at the bottom.
It really is a pretty cool watch.
Anyway, onto the questions...
The planisphere built into this watch is designed for the Northern Hemisphere (between 35 - 50 deg. lat.).
How much is the accuracy affected with each degree of lattitude?
Let's say I designed a planisphere that was 100% accurate on the equator.
If I travel to 60 deg lattitude, how far off would it be?
Is the correction that would have to be made linear? In other words, would I have to make the same level of correction going from 20 deg to 40 deg as I would going from 40 deg to 60 deg, or would the correction be less as I head further towards the pole?
It seems that I could tell the exact date and time by the position of the stars in the sky. It doesn't seem too difficult of a task to create a star calendar/clock if it were stationary, say bolted to the ground in my back yard. Let's say, though, that I were traveling by boat and did not know the what lattitude I was at, could I determine the date and time by star positions?
Or is it that I could find my position if I knew the date and time, or I could find the date and time if I knew my position? Do I need one to determine the other?
Basically this has been a too long post to ask, "How do these darned thingies work?"
Thanks
Last edited by a moderator: