# Local Noon?

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I'm going to keep this post as anonymous as possible so I won't give away the cache or the placer of this cache.

An individual placed a cache with the longitude coordinates as (local noon) with the intention of having the seeker figure out how to convert local noon (when the sun is highest at an exact spot) into longitude. The coordinates are: N48°11.859 and 1:10:51.492 PM pacific daylight time.

I really want to learn how to do this so I can find this cache so thought I'd start here.

Will anyone help?

To the person who placed this cache. I know you'll read this. I created this new screen name so you won't be able to figure out who I am until I find the cache.

They must have had acces to an atomic clock at the cache site to get that precise time. Now, where to go to find that info?

Haven't found an answer for you yet, but at least my computers clock is now synchronized with the atomic clock at the U.S. Naval observatory.

There are starting point coordinates. Listed below I pasted directly from the cache description:

THIS CACHE is unusual in that I will give you the latitude for it and LOCAL NOON instead of longitude. You must figure out how to convert local noon (when the sun is highest at this exact point) into longitude. Those coordinates are:

N48° 11.859? and 1:10:51.492 pm Pacific Daylight Savings Time.

try figuring out how many hours that is from UCT(GMT)...move one longitude line from greenwich observatory west for each hour. when you hit that line use the min/sec from there.

either that or determine when noon actually occurs by observing the moons of jupiter like they did before an accurate timepiece was invented to carry aboard ships in order to figure longitude.

happy hunting.

X.

try figuring out how many hours that is from UCT(GMT)...move one longitude line from greenwich observatory west for each hour. when you hit that line use the min/sec from there.

either that or determine when noon actually occurs by observing the moons of jupiter like they did before an accurate timepiece was invented to carry aboard ships in order to figure longitude.

happy hunting.

X.

If that's local apparent noon you'll need the date so you can apply the equation of time, found in a solar table or nautical almanac. Take the timezone of the solar meridian observation (local noon) hours and count the number of hours between GMT and the LAN timezone. Noon occurs at 12:00 hours in Greenwich, England (GMT), which is the prime meridian of longitude (0 degrees). Since the earth turns 360 degrees every 24 hours, it rotates 15 degrees every hour. For example, eight timezones west = 15 degrees x 8 = 120 degrees. Since the Earth rotates at 15° per hour each minute's difference in Local Noon Time translates to 1/4 degree of longitude. (15° / 60 min. = 1/4 / 1 min.) So each minute after the given time zone's Noon Time represents 1/4 or 0.25 degrees added to the eastern boundary longitude of that time zone. From the figures given, you should be able to calculate approximate longitude, measured as a certain number of decimal degrees west of the prime meridian (when you specify your longitude, it is important to specify West (W) or East (E) of the prime meridian).

If it's only the local apparent noon given for a certain date, the longitude you have calculated will not be strictly correct, and needs to be adjusted for one more effect. The earth does not revolve about the sun at a constant speed throughout the year, because the earth's orbit is not perfectly circular. This slightly affects the length of the solar day (the time from one solar transit across our meridian until the next as the earth rotates on its axis). Clocks and watches, therefore, keep the time of a imaginary or 'apparent' sun that travels across the sky at the same average speed throughout the year. The time of the true sun transit across your meridian lags or precedes the time it would have if the earth's orbit were round. The difference in time between the true sun transit and the imaginary or apparent sun transit is called the equation of time. In the Nautical Almanac or a current solar table, find the equation of time for the date of the local noon observation. If the equation of time is listed as W, then you would add the equation of time to your W measurement of longitude. If the listed equation of time is E, subtract the equation of time from your W longitude measurement.

There's also a secondary effect on the apparent motion of the sun having to do with the fact that the yearly motion of the sun is along the ecliptic and not parallel to the equator, but this is also corrected by the equation of time table.

[This message has been edited by Jebediah (edited 04 August 2001).]

Vargaus, I have a guess who you are. Happy to have your interest. Jebediah, you sound like you know what you're talking about. But, I can understand true transit varying, but why would apparent local noon be dependent on date or variation. Is not the idea of apparent local noon to match longitude. Longitudinal lines never vary. You can convert longitude and local noon back and forth easily if you're not concerned with actual solar variation. The Earth rotates at about once every 24 hrs. 15 degrees always equals one hour and visa versa. The Earth always turns a full 360 degrees, and with the exception of minute variations it always does it in 24 hours. This is why sailors need a good clock so bad. There was no other good and easy way to figure out how far east or west they were. But you are right, true transit is a different issue.

The Earth rotates at about once every 24 hrs.

It's that 'about' part that is the problem. I had no way of knowing if the noontime given was actual, or apparent (sun at highest apparent point via sextant or short shadow). If the latter, you need the date and access to a table (or calculator) to compensate for precession, recession and ecliptic error for a precise plot.

[This message has been edited by Jebediah (edited 02 August 2001).]

But our clocks stay the same until we adjust them. So how do I make this cache work better? Should I simply take out the thing about the sun and simply say 8hrs and so many mins from GMT? Would it work to still use the term local noon in that case? I agonized over whether I had this thing right and I thought I did as how several people found my other cache like this. So how would you do it? AND Vargaus..What is that name? All I come up with is foriegn web sites when I do a search for it.

by .25° for each minute I get 2.5°. Adding the 2.5° to 120° gives me 122.5°

My guess to the coordinates is W122°51.492, but I want to make the math fit so learning this, to me, is more important than finding the cache.

Am I on the right track? Once I figure this out, the joy of seeking this cache will be greatly enhanced because of the schooling I had to go through to find it.

Thanks everyone for helping so far.

You can do a quick search on the web to find out how to compute local noon. For example, see http://www.ed.uiuc.edu/courses/satex/sp96/noon-project/noontime.html . This site tells you how to figure local noon from your longitude; for figuring out longitude from local noon, just work backward through the calculations.

------------------

Jon (Moun10Bike)

27H/71F/3C/2S/2X

N 47° 36.649', W 122° 3.616'

www.switchbacks.com/geocaching.html

Just to see if I follow this correctly... My local noon according to Moun10bike's link is:

12:45 and 16seconds.

Given that Marietta, GA is in the eastern timezone(Hint: GMT-5), calculation of my longitude is left as an exercise for the reader.

My God, I'm a geek! muahahaha

Yeah, I'm not quite sure why we are using AKA's for our AKA's, maybe to protect the cache, but it makes it a fun mystery. Please be sure and let know know sometime what your other screen name is! I want to see if I'm right. I didn't mean to get this all tangeled up with sun transits and such, but now I've got a lot more things to learn. I love this stuff! I especially need to check on terminology such as apparent local noon and such. What I really mean to do is determine noon by local time, by what our clocks would tell us when noon hits if they weren't locked into a time zone. The purpose of my two time caches is to make people think about how time and longitude work hand in hand, and to provide a challenging and interesting cache. I guess I get to learn more too. Here is how I described the process to someone else who wanted to know how to do my other cache:

The degrees of longitude are divided into 360 degrees. The earth takes 24 hours to turn those 360 degrees. To find what one hour equals you'd divide 360 by 24. That equals 15 degrees. 1hr = 15 Degrees. Longitude starts at the prime meridian. If noon passed over there and is now passing over us, what is the time difference between them and us? You can look at the time setup on your gps and it will tell you -7hrs. But that is adjusted for day light saving time so it is really -8hrs, or 8 hrs difference. Or you can get a general idea by takeing any longitude in our time zone and dividing it by fifteen, 120/15=8 or 122/15=8.133333. So our local noon at the cache is 8hrs 9mins 00.03816secs from the prime meridian. I would convert all that into hours in decimals (60secs in a min, 60 mins in an hour) or 8.1500106 hrs. Times that by your fifteen degrees per hour and you get you longitude or 8.1500106 x 15= 122.25015degrees. Now convert the decimals back into minutes of longitude (60 mins in a degree) and you have 122d 15.010'. Hope I did that right. I really am a math dummy and always have to check myself.

(Remember, these coordinates are for my other cache.)

[This message has been edited by Grendel (edited 02 August 2001).]

By the way Vargaus, those coordinates you came up with aren't right. Just use the above method and it should work. Vargaus? Vargaus, what is taht a philosopher.

I've been stewing over this for awhile now. It's simple enough to divide 15 into 122 to get 8.1333, but how did you get the 9 minutes 00.03816 seconds? I've been reading over the site that Moun10Bike suggested. I'm learning some great stuff, but I don't have it yet. Rats, because I was hoping to head out and seek out this cache today.

That 9mins and 00.03816 secs is the time coordinates for my othe cache. I was just using that as an example. You have to deal with 1:10:51.492pm for the cache you're looking for. Count the time zones from the prime meridian. That will tell you that you are 8 hours away. so you have to deal with 8hrs 10 mins 51.492 seconds. Divide your seconds by 60 to get them into decimals in minutes, the add the 10 minutes on. it would be 10.852 mins. Then divide that by 60 to get the mins into decimal hours and add the 8 hrs on. Then times that by how many degrees are in an hours passage (15). Reduce out the degrees so you can convert the fractional part back into longitudinal minutes (times by 60). And you have it.

Remember on the above message... I'm going by how our clocks work not how our celestial bodies work, so I'm not adjusting for deviation as you would need to for that. (as Jebediah pointed out). To avoid going through the date adjustments and such I'm using the passage of local time, not solar transit.

nt to be able to know how to do this well enough to take any longitude coordinates and convert it to time like 1:10:51.492 and back again. I'm certainly not there yet.

Am I getting closer?

Yes, gosh I'm sorry I did miss a digit there. And so did you on the top of you post. 42.873 is right not 43.873. The longitude is: W 122 42.873.

To do it the other way around just reverst the process. And it is easier I think.

Covert longitudinal minutes to degrees

42.873 / 60 = .71455 or 122.71455

Divide by 15 = 8.18097

-8 = .18097

Times by 60 to get minutes = 10.8582

- 10 = .8582

times .8582 by 60 for secs = 51.492

8hrs 10mins 51.492secs

change the 8hrs to pacfic daylight savings time = 1:10:51.492pm

[This message has been edited by Grendel (edited 03 August 2001).]

EXCELLENT! I'm up at the crack of dawn tomorrow and will be geocaching all day. I'll enter the cache log and the site log who I really am. This is going to be a wonderful cache hunting day. Thanks Ara..., I mean Grendel.

To Vargaus and beyond

quote:
Originally posted by Grendel:

Y

change the 8hrs to pacfic daylight savings time = 1:10:51.492pm

Cept Pacific "Daylight" Time is only 7 hours off Grenwich Mean, so you're off by a time zone.

-- Mitch

No, we are 8 hours (time zones)away and I am saying to adjust to Pacific DAYLIGHT time (7 hours difference). That -7 offset instead of -8 hr offset change the local time from 12:00 to 13:00(or 1pm). Remember the closer to GMT you are in the West longitudinal coordinates the latter in the day it is, and the further to the west you are the earlier you are in the day.

Just an add on to that. With daylight savings time (a dumb idea) we change our clocks but not our position on the globe or our distance from Grenwich. So in terms of longitudinal time we are still 8hrs away. 8 units of 15 degrees. I think that is the proper terminology. I'm am looking for a good glossary on this stuff. If anyone knows where I can find one please let me know. I think I now understand why Jebediah was using the term "APPARENT" local noon. I can see proper terminology is important here to understanding the topic.

All that schooling paid off. I found the cache and what a beautiful area it's in.

For those interested in this topic here is a world map of timezones and how they relate to longitude.

http://www.time.gov/images/TimeZoneMap2000.gif

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