I have another project for science. I have a few unanswered questions as well.

 

The object of this is to find a "Practical and easy ethical method of calculating longitude to the nearest 30 minuts!"

Does anyone know of an easy way to find longitude?:

 

•Does anyone know much about the lunar distance method?

•What are some instruments that I can build to calculate longitude?

•How can I use the instruments?

 

I am open to many ideas of calculating longitude, but please do not recomend rebuilding H4 .

well the most simple method I know of is to use a GPS, I have a little Garmin GPS here and it works great, maybe you can borrow one?

no, sry, but I need to build something to find longitude, and I cant use prebuilt instruments.

Hmmm... thats a toughy then

I think you`ll certainly need a compass for sure!

other than that, I have no idea in all honesty, other than maybe making a sextant(sp?) and using star charts.

sorry dude

Longitude depends on time so you need a good clock and you need to know what time it is at 0 longitude to compare the time to. A sundial will work on land if you use two lenses to get the divisions down to second increments. You also need a compass to set your sundial.

When you calculate exact noon where you are and compare it to GMT you will know your longitude difference.

On a ship you need a really good timepiece set at GMT and a sextant to measure your local time.

Just aman

aha! yeah, good point aman, I completely forgot about needing the timepeice!

I thought sundial, then figured star charts instead. DOH! nice one dude

YT2095 said in post #6 :

aha! yeah, good point aman, I completely forgot about needing the timepeice!

I thought sundial, then figured star charts instead. DOH! nice one dude

 

Right. Sundials don't work because the sun is not exactly overhead at noon most days of the year, and they just plain aren't going to be precise enough. Plus, you want to be able to make the measurement at your convenience.

so then my second guess at star charts would have been the right choice then?

 

I don`t feel so silly after all now

 

but aman was right though, a timepeice of SOME description IS needed.

time piece wise, i really csnt do it, because i need to make the instrument. Anyone know much about the lunar distance method, links?

Timepiece?

 

What do you need that for?

 

Use the North Star and build a sextant type instrument and you have your longitudenal measuring device. I suggest using a level (the measuring tools with the bubbles in them) and the north star as your key reference. That way you wont need to see the horizon.

 

Attach the big ole rig to a tripod with a pivoting top, level the level, and make the correct calculations, whatever those may be.

Since the Earth spins, the only way to find longitude is by your relative position under the sky. When longitude was standardized on maps it was decided that 0 degrees was at Greenwich, England. Because of this arbitrary placement, you need to know what time it is where you are and what time it is GMT (Greenwich Mean Time) and you will know how many degrees you are from zero (Greenwich). Each 4 minutes of time difference equals 1 degree of longitude.

Just aman

hmmm, well, if I use the time difference method, I could not build a clock, but I could make a sundial. I have heard that sundials need corrections for latitude, but, if they need corections for longitude, what if I could use the angle of correction on my clock to simulate a sundial in Greenwich, or would that all depend on my longitude anyway, and defeat the purpose? Anyone an expert on sundials?

Cripes... I mixed up lat and lon.

 

In gr5 I remembered longitude b/c the lines were longer but I confused the vertical lines with the vertical measurement.

 

Humbug, and I liked the north star idea too.

 

What is this for? I'm sure Leonardo or some cool ancient nerd came up with the solution yonks ago and you can find some calculations on the net. Google is no more cheating than asking a science forum.

believe me, I have searched google for long hours, it seems, however that all web sites say that a nocturnal, or astrolabe, or sextant can be used to find longitude, but they Never Say How!

try

http://rubens.anu.edu.au/student.projects97/naval/home.htm

Just aman

swansont said in post #7 :

 

Right. Sundials don't work because the sun is not exactly overhead at noon most days of the year, and they just plain aren't going to be precise enough. Plus, you want to be able to make the measurement at your convenience.

 

 

It's not exactly overhead, but its location is predictable and can be corrected for. It follows a shape called an analemma.

Well I just found out that my science teacher is giving us GMT (Greenwitch mean Time) so all we have to do is find our time in our "Zone" If Anyone Can Find A Better Device to make to find time, please tell me. Also, is there anyone that knows of good website for NOCTURNALS(The insatrument). Do NOT recomend building a clock.

 

The bottem Line:

What is a good instrument to use to tell time (at night)

I have allready done research on a nocturnal, but if you have a good template site, your ideas are well accepted.

You can use a rotating star chart.

(but using it reversed)

 

http://bj.canon.co.jp/image/papercraft/download/nature/starchart_e_a4.pdf