Dan—
.
Here are the maximum errors, in degrees, of the three solar
direction-finding methods I’ve been discussing, for Romania.
.
I used lat 45 as a typical latitude there. Of course a person is most
likely to need a direction-finding method in a district that they don’t
live in.
.
For the
I said, " a reasonable estimate can be gotten by substituting dec for tan
dec."
I meant "...dec in radians".
Michael Ossipoff
On Thu, Oct 25, 2018 at 12:44 PM Michael Ossipoff
wrote:
>
> One more thing about AW:
>
> When dec Sun is positive, especially when it's positive and large, it
>
One more thing about AW:
When dec Sun is positive, especially when it's positive and large, it would
be desirable to at least have a good estimate of when the Sun will be due
east or due west, to avoid an ambiguity that W and AW could otherwise be
subject to.
That's because, (in afternoon) when
Steve—
.
I was surprised to find that, at lat 55, the ordinary watch-method (W), at
the summer-solstice, used at the edge of a standard-size timezone, and when
disregarding longitude and EoT, is still a little more accurate than ST.
(…but that isn’t entirely fair, considering that someone who
Ok, I see what you mean--I misunderstood because it's a kind of dial that
hadn't occurred to me. It sounded good, but then I realized that latitude
is built into such a dial, so it's only usable at a certain latitude. I've
sometimes used a compass or solar direction-finding when hiking in my own
Michael,
On 2018-10-24 8:25 p.m., Michael Ossipoff wrote:
A Shephard’s Dial wouldn’t help as a sun-compass. It just gives time
if you know the date, or date if you know the time.
By writing "a Shepard's Dial marked out as a solar compass" I meant that
one for which the lines drawn on the
When I used the standardly assumed solar altitude at Sunset (-5/6 degree
for the center of the solar disk), I get 45.59 degrees for the summer
maximum error. …which is almost the same as what you said.
.
A Shephard’s Dial wouldn’t help as a sun-compass. It just gives time if you
know the date,
I’d said:
.
The Shadow-Tip method [has] accuracy is greater at lower latitudes.
.
You replied:
.
That's putting it mildly, I think. The method would be OK everywhere around
midday or near an equinox but I suspect it's really, really bad if used
early or late on a midsummer day at higher
Hello, Michael,
On 2018-10-24 8:42 a.m., Michael Ossipoff wrote:
The Shadow-Tip method [has] accuracy is greater at lower latitudes.
That's putting it mildly, I think. The method would be OK everywhere
around midday or near an equinox but I suspect it's really, really bad
if used early or
I meant: Multiply h * sec Alt Sun by cos dec
In my example, sec Alt Sun was 1.25, and cos dec is somewhere between 1 and
1 - 1/12 (as it always is).
Michael Ossipoff
On Wed, Oct 24, 2018 at 10:55 AM Michael Ossipoff
wrote:
>
> I mis-stated what the secant is. I said:
>
> 'The secant of the
I mis-stated what the secant is. I said:
'The secant of the Sun's altitude is the *direct* distance from the tip of
the object to the tip of its shadow, divided by the height of the object.
Of course you probably don't have time to measure with measuring-tape, and
you just estimate that ratio."
Dan--
It's as you said. The Watch Method works best (and is only really any
good) when the Sun is low. So, it's really only any good in winter, or very
late or early in the day.
...and a lot of people do most of their hiking in the summer.
Its accuracy increases with latitude.
But, as Favio
Dan, Using a watch seems too imprecise to give more than a general idea of
the direction of North. However, the basic concept has been developed to
provide precision solar compass instruments. In most cases these come with
tables to correct latitude, date and local solar time. If you don't know
dear Dan
the wristwatch as compass has 3 problems:
a) it shows the time of a different longitude, the one of the time-zone
(GMT or DST).
You should correct it for the local time but it is possible only if you
know your longitude.
b) you should correct the time also for eot, it means you
Hi Dan,
Sorry for the delay in replying.
>From a PRACTICAL point-of-view, as we all know, analogue watches replaced
>sundials, digital watches replaced analogue watches, and smart phones have
>replaced watches. Digital compasses replaced analogue compasses, and now smart
>phones have
Hi Walter,
I too thought some small pictures were nice, but, as I have a few
websites I can post items to, I'll do that in the future, so that
those that want to see the pics can, those that don't, wont. I'm
hoping the adobe Acrobat pdf format I've chosen will work for
everyone, since
I think I have to disagree here, Edley: A small mirror does indeed mimic a
pinhole aperture, and the resulting image would also move quickly along
the tangent surface. However, neither a plane mirror nor a pinhole
actually focusses the Sun's image! A pinhole lens works by limiting the
rays passed
Interesting question. I too would be interested in an answer (other than the
spot shadow sharpener which has been discussed at length in the past).
-Bill Gottesman
In a message dated 12/22/2001 8:46:59 PM Eastern Standard Time,
[EMAIL PROTECTED] writes:
Accurate Diaists ,
Maybe this is
Hello Shadow Watchers(?),
This dial that came to the list as spam, but also
seems to give resolution of a time down to 1 minute.
I do not know how accurate it is but gennerally
Pilkington Gibbs dials seem pretty professional.
Patrick powers is correct in noting that the 0.5 degree width of the sun
(corresponding to 2 minutes of time) creates a shadow penumbra that is
virtually impossible to read to the second. But, a sharp edge can be
achieved by a focusing dial, which creates an crisply defined image of the
sun,
I consider a
second ideal as one can feel it, I mean it is a timespan well related to the
human body, one second you live, the next you may be dead;
Walter,
This is very strange statement. True that you live one second and are dead
the next, but by the time that happens it's a bit late to
Dear Walter,
Greetings.
There is another factor which limits sundial accuracy to about +/-22
seconds. This is the variation in the value of Equation of Time from
year to year within a leap cycle. See
www.sunlitdesign.com/infosearch/sundialaccuracy.htm
David
www.sunlitdesign.com
At 08:25 AM 12/21/01 +1100, David Pratten wrote:
Dear Walter,
Greetings.
There is another factor which limits sundial accuracy to about +/-22
seconds. This is the variation in the value of Equation of Time from
year to year within a leap cycle. See
John Pickard wrote:
Fernando,
Good to hear that you decided to ignore Ruby! Oxygen thief!
Thank you.
I have a rather old (i.e. 5 years!) Garmin GPS45 which I have used
all over Australia, Argentina, Chile and Antarctica. Out of curiosity
I have checked the clock against the time beerps
Fernando,
Good to hear that you decided to ignore Ruby! Oxygen thief!
I have a rather old (i.e. 5 years!) Garmin GPS45 which I have used
all over Australia, Argentina, Chile and Antarctica. Out of curiosity
I have checked the clock against the time beerps on our national
radio. Spot on to
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