Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: steved1980 on 30/03/2012 03:59:12
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Can you tell the latitude and longitude from a painting of a ship on the ocean? What info would you need to be in the painting?
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I am afraid there are few clues as to latitude and longitude in a painting to determine the latitude we must know the elevation of the Sun at noon and to determine the longitude we must know how the time on a clock onboard that was synchronised to UTC at 0° longitude now indicates.
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So if there were 2 paintings of the same ship in the same location. And we knew one was at noon and the other at 1pm. Would this be enough?
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does the picture include the moon and an identifiable star ? ...
https://en.wikipedia.org/wiki/Method_of_lunar_distances
(the picture would have to have photographic accuracy)
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Basically someone in 1881 knows coordinates and wants to convey this in a painting.
So he's measuring the distances and painting them accordingly. So if he painted the moon and a star and we knew the time of night... would that work?
Or does it really have to be a photograph?
PS: I'm not that smart
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Could be a painting - probably better in fact; paintings can drop hints. Others can confirm this but I think this would work:
Name: "The Young Midshipmen take readings at Noon"
Scene: The deck of a known ship with the group of midshipmen (basically young officers yet to reach lieutenant)
Details:
At least one character should be taking readings on the angle of the sun above the horizon with a theodolyte - which must be readable to the viewer (you could find some way to show the shadows that would give a definite angle to the sun - but difficult)
An clock is visible inside cabin / a fob watch showing gmt.
A compass showing that the sun is exactly in the south - or that shadows of masts are exactly north (re-iterating the title noon)
The height of the sun at noon local and the difference between GMT and local noon - will give you a position, with work and corrections all of which were well known in 1881, and are still practised by juniors now. You need to give a few more clues to do with hemisphere - but that should be easy.
Theoretically you can get down to about a fifth of an arc minute on suns angle (that's 0.2nautical miles) - but in reality you are talking a couple of miles accuracy
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If a partial eclipse of the Sun was depicted and the date was known that would give good clues as to the location of the vessel
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The solar observation idea would only work if the date of the year were known. The latitude/solar angle relationship depends critically on time of year. And the longitude/GMT relationship has a variability of about +/- 8 minutes of time (=32 minutes of arc = approx 50 km in tropical regions) because of the ellipticity of the Earth's orbit, and the variable length of the solar day. This correction always has to be made to sundial time. Once again the exact date would be needed.
A very accurate latitude indication could be given by the position of the pole star (elevation above horizon = North latitude, always, with no correction necessary unless the elevation is less than about 10°). Moonrise of an exact half moon into the night sky would fix the local time at midnight, give or take the sundial correction. The difference between the geometric moonrise and the optical moonrise would mean that the moon fully visible but touching a nautical horizon would correspond fairly closely to geometric moonrise. However you look at it the longitude is more problematic than the latitude.
Perhaps the best way for your artist to indicate the position would be to include a marked chart in the picture, casually tabled in the wheelhouse. [;D]
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If a partial eclipse of the Sun was depicted and the date was known that would give good clues as to the location of the vessel
Would it though? The path of the umbra and penumbra are quite long - and they travel at a fair speed; about 1800km/h. the umbra is about 100-200km wide and the penumbra can be thousands wide.
With other clues though it would make a fine method of positioning - and gives a good narrative reason for a painting/photograph being used to mark the occasion. "Captains Log: On the same day as we crossed from East to West, 180 degrees from our home in Greenwich we witnessed at 1100 hours the solar eclipse as predicted by Lieutenant Syhprum..." etc
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The solar observation idea would only work if the date of the year were known. The latitude/solar angle relationship depends critically on time of year. And the longitude/GMT relationship has a variability of about +/- 8 minutes of time (=32 minutes of arc = approx 50 km in tropical regions) because of the ellipticity of the Earth's orbit, and the variable length of the solar day. This correction always has to be made to sundial time. Once again the exact date would be needed.
A very accurate latitude indication could be given by the position of the pole star (elevation above horizon = North latitude, always, with no correction necessary unless the elevation is less than about 10°). Moonrise of an exact half moon into the night sky would fix the local time at midnight, give or take the sundial correction. The difference between the geometric moonrise and the optical moonrise would mean that the moon fully visible but touching a nautical horizon would correspond fairly closely to geometric moonrise. However you look at it the longitude is more problematic than the latitude.
Perhaps the best way for your artist to indicate the position would be to include a marked chart in the picture, casually tabled in the wheelhouse. [;D]
Damocles is of course correct - you need the exact date as well
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If the year was known the exact date would be no problem solar eclipses are not that frequent.
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Great! Thanks everybody. I think I can work with the info you gave me.