Thoughts On An Offset Cache Idea

[+DubbleD70]

In a given year, would the shadow of a flagpole differ too much at a given time to use it as an offset point?

 

Hypothetically like this:

 

coords take you to the base of a flagpole and the cache must be done at precisely 2:15pm... You then have to walk to the tip of the flagpole's shadow and find the cache within x number of feet from there...

 

Or would it have more appeal (being that it can only be done on one day a year or only at a certain time of year)and cancel out the problem of shadow differences by time of year, like this:

 

coords take you to the base of a flagpole and the cache must be done at precisely 2:15pm on December 31st... You then have to walk to the tip of the flagpole's shadow and find the cache within x number of feet from there...

[+StarBrand]

In a given year, would the shadow of a flagpole differ too much at a given time to use it as an offset point?....

Depends on location (North/South of Equator) and height of pole. Differences could be big if you are far north and pole is really tall.

[+Jhwk]

Too much varience throughout the year. Can see the typical movement (figure 8) at numerous Stonehenge replicas - like this one.

 

Look under the FAQ for "analemma"

Edited January 27, 2006 by Jhwk

[+BigWhiteTruck]

In a given year, would the shadow of a flagpole differ too much at a given time to use it as an offset point?

 

Hypothetically like this:

 

coords take you to the base of a flagpole and the cache must be done at precisely 2:15pm... You then have to walk to the tip of the flagpole's shadow and find the cache within x number of feet from there...

 

Or would it have more appeal (being that it can only be done on one day a year or only at a certain time of year)and cancel out the problem of shadow differences by time of year, like this:

 

coords take you to the base of a flagpole and the cache must be done at precisely 2:15pm on December 31st... You then have to walk to the tip of the flagpole's shadow and find the cache within x number of feet from there...

Surprisingly enough, the angle of the shadow at a certain time of day will vary by 47 degrees across a year's time. No matter where on the globe you are. the exception of course above the arctic or below the antarctic circle, where there are parts of the year with no sun at all.

[+DubbleD70]

Well crap!!!

 

Would it be stupid to make the cache only available at a certain time of year? Like some kind of anniversary or birthday cache?

[+VegasCacheHounds]

Well crap!!!

 

Would it be stupid to make the cache only available at a certain time of year? Like some kind of anniversary or birthday cache?

I don't know if that would get approved.

 

The other problem that comes to mind is DayLight Savings. That'd throw everything off for half the year.

[+tozainamboku]

It might make a interesting puzzle. Given a particular date and time of day, the finder could determine the azimuth and elevation of the sun. Provide the height of the flagpole and make the finder calculate the position of the shadow on that date.

 

Here's a site that makes it easy

[+VegasCacheHounds]

It would take some work, but you could do the cache as you planned, but instead of a set time, you'd need a table that showed the correct time of day versus the time of year.

[+nfa]

if you could place the cache along the equator, wouldn't it work as the OP suggested

 

jamie

[+StarBrand]

if you could place the cache along the equator, wouldn't it work as the OP suggested

 

jamie

It would if the Earth wasn't tilted a bit off the plane of rotation around the sun. That is why most globes are mounted tilted and not straight up and down.

[+nfa]

if you could place the cache along the equator, wouldn't it work as the OP suggested

 

jamie

It would if the Earth wasn't tilted a bit off the plane of rotation around the sun. That is why most globes are mounted tilted and not straight up and down.

doh!!!

 

{{{slaps forehead}}}

[+BigWhiteTruck]

if you could place the cache along the equator, wouldn't it work as the OP suggested

 

jamie

Unfortunately, no. The sun's position in the sky varies throughut the year no matter where you are. The tropic of cancer and capricorn, at 23.5 degrees north and south respectively, outline the band of earth that get's the sun directly overhead. The sun is directly over the tropic of cancer on the longest day of the year in the northern hemisphere, June 21st. On Dec 21st, the sun is directly overhead at the tropic on capricorn, 47 degrees south of it's position 6 months prior.

 

For you and I, at 43 and 42 degrees north latitude, we observe the sun at around 70 degrees elevation from the southern horizon at noon on June 21st. This is 20 degrees off of overhead, because we are about 20 degrees north of the tropic of cancer. On the first day of winter, we would observe the noon sun to be 47 degrees lower in the sky, because it has migrated 47 degrees south to the tropic of capricorn. During the equinoxes, the sun travels the sky in the middle of this band, and some 40-someting degrees to the south, it is directly overhead on the equator.

 

As you see, even at the equator the sun changes position in the sky. In the months that we northerners know as summer, the noon sun at the equator appears slightly to the north, and slightly to the south in december.

[+BigWhiteTruck]

if you could place the cache along the equator, wouldn't it work as the OP suggested

 

jamie

It would if the Earth wasn't tilted a bit off the plane of rotation around the sun. That is why most globes are mounted tilted and not straight up and down.

nicely put

[+tozainamboku]

if you could place the cache along the equator, wouldn't it work as the OP suggested

 

jamie

It would if the Earth wasn't tilted a bit off the plane of rotation around the sun. That is why most globes are mounted tilted and not straight up and down.

nicely put

But then we wouldn't have seasons..... Wait, I live in Southern California. We don't have seasons. The weather is always perfect here. Hey, I'm going geocaching

[+the hermit crabs]

There's a cache based on this idea in Massachusetts (Raiders of the Lost Geocache). On a linked page, they include a solar calculator so that you can enter the exact date and time that you plan to to do the cache, and it tells you the length of the staff you need to bring with you to measure the shadow of.

[+Wacka]

What happens if it is foggy or cloudy?

[+DubbleD70]

Well crap!!!

 

Would it be stupid to make the cache only available at a certain time of year? Like some kind of anniversary or birthday cache?

I don't know if that would get approved.

 

The other problem that comes to mind is DayLight Savings. That'd throw everything off for half the year.

Not really... AZ doesn't do daylight savings...

[AZcachemeister]

It's been done:

Saguaro Sundial Sunrise

Saguaro Sundial Sunset

[+tozainamboku]

It doesn't suprise me that this has been done in Arizona. Isn't the shadow of Weaver's Needle at a certain date and time supposed to point to the Lost Dutchman Mine in the Superstition Mountains?

Edited January 28, 2006 by tozainamboku

[+Mule Ears]

It's been done:

Saguaro Sundial Sunrise

Saguaro Sundial Sunset

We solved these puzzles mathematically (rather than by observation or brute-force search). There are excellent resources online for calculating shadow positions in a given location at a particular day/time. They're apparently used by architects to work out sun angles through windows, over walls, etc. Google "sun angle calculator." If you get stuck, let me know and I'll dig up the link.

[+BigWhiteTruck]

There's a cache based on this idea in Massachusetts (Raiders of the Lost Geocache). On a linked page, they include a solar calculator so that you can enter the exact date and time that you plan to to do the cache, and it tells you the length of the staff you need to bring with you to measure the shadow of.

Yes, but how can you be sure you have the markings from both sides of the medallion?

 

[+5¢]

I think most cachers are semi smart and if it wasn't a micro could figure out where the cache was hidden. I did most of my offset caches in the beginning before I knew how to do them by going a 100 feet from the point and searching the radius.