Analemma at Ancient Nemea ... #3/11

Dave Eastabrook wrote

(reply to self, it's one of those things)

Here's another thought, maybe if you could have a reference source of
light like a focused fixed spotlight to check that the pole hasn't moved
wrt the ground, or your pin-cushion board!).

Two lights, dam-buster fashion. And (if it worked accurately) you could
even store the board indoors in gales or floods.

Dave
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JRS: In article , seen in
news:uk.sci.astronomy, Pen Phill posted at
Fri, 9 Jan 2004 17:15:51 :-
From: Dr John Stockton

Running a sky-map program in steps of 24 hours is amusing.

Will sky map actually produce the actual analemma or just show the solar
position at each 24 hr interval?

I wrote "a sky map program" to be general, not "SkyMap" to be specific.

The program that I recall using, long ago, actually displayed, as a
function of time, a Mercator map of the Earth with twilight and dark
shown and with a small Sun at the subsolar point. One could have traced
an analemma.

My largest dictionary does not actually, AFAICS, define analemma.

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Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
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Dave Eastabrook wrote:

Problem is that the pole can move (even sideways) or tilt unless it has
foundations, or warp or even shrink with rain, especially if wood.
Think for an 8 foot pole with 1 foot stuck into the ground, if the
bottom shifts over 1 inch, the top moves 7 (hence upsets the shadow).
It can also sink down.

I suspect a small stick will do the trick: the gnomon on a sundial
doesn't have to be huge to tell the time.

Similar only more so to the pole, unless you can find a way of attaching
them to the pole along the ground so they don't move in relation?

Probably makemarks on a slate or indents in a tray of plasticene

I don't think high degrees of accuracy are needed - we're after the
general idea, no rocket science. I'll start a test bed tomorrow, sun
permitting

Thanks. Basically, nobody has said that the tip of the shadow won't
trace out a figure 8 over the year - which is what worried me most.

--
Martin Frey
http://www.hadastro.org.uk
N 51 02 E 0 47

Dave Eastabrook wrote:

Dave Eastabrook wrote

(reply to self, it's one of those things)

Here's another thought, maybe if you could have a reference source of
light like a focused fixed spotlight to check that the pole hasn't moved
wrt the ground, or your pin-cushion board!).

Two lights, dam-buster fashion. And (if it worked accurately) you could
even store the board indoors in gales or floods.

Dave

Good idea - some kind of reasonably repeatable register is needed. The
thing could be done indoors if it could be moved after use and then
put back exactly.

Cheeers

--
Martin Frey
http://www.hadastro.org.uk
N 51 02 E 0 47

Martin Frey wrote
Dave Eastabrook wrote:

Problem is that the pole can move (even sideways) or tilt unless it has
foundations, or warp or even shrink with rain, especially if wood.
Think for an 8 foot pole with 1 foot stuck into the ground, if the
bottom shifts over 1 inch, the top moves 7 (hence upsets the shadow).
It can also sink down.

I suspect a small stick will do the trick: the gnomon on a sundial
doesn't have to be huge to tell the time.

Relatively speaking though for a sundial the sun is moving around 180
degrees, whereas with the Analemma it would only be a few degrees (??),
and you'd want there to be enough separation between the narrowest parts
of the - squashed - figure of 8, as your canvas is smaller than the sky.

Worth maybe guessing how large you'd want it, and doing a little maths.

I loved Anthony's picture - it really makes you think.

I don't think high degrees of accuracy are needed - we're after the
general idea, no rocket science. I'll start a test bed tomorrow, sun
permitting

Good Luck! Sounds like a great project.

Dave
--
to send mail I think postmaster will still work at elmbronze dcu.

On 01/10/04 11:22 +0900, Martin Frey wrote:

I suspect a small stick will do the trick: the gnomon on a sundial
doesn't have to be huge to tell the time.

Moreover, a short gnomon keeps the scale of the analemma manageable.

Thanks. Basically, nobody has said that the tip of the shadow won't
trace out a figure 8 over the year - which is what worried me most.

It most assuredly will.

trane
--
//------------------------------------------------------------
// Trane Francks Tokyo, Japan
// Practice random kindness and senseless acts of beauty.

Martin Frey wrote:

Dave Eastabrook wrote:



Problem is that the pole can move (even sideways) or tilt unless it has
foundations, or warp or even shrink with rain, especially if wood.
Think for an 8 foot pole with 1 foot stuck into the ground, if the
bottom shifts over 1 inch, the top moves 7 (hence upsets the shadow).
It can also sink down.


Hi Martin,

I suspect a small stick will do the trick: the gnomon on a sundial
doesn't have to be huge to tell the time.

I apologize for the delay in responding .... I have been flooded with
emails in relation to my most recent analemma.

As you know, it is vital that the stick remain stable during the twelve
months and I hope the weather (rains, winds) do not do anything to move
it (however slightly).

This is a very good time to start since the sun will start to move
appreciably every three to four days when observed at the same time. Be
quick! :-)

All the best with the project.

Anthony.

Similar only more so to the pole, unless you can find a way of attaching
them to the pole along the ground so they don't move in relation?



Probably makemarks on a slate or indents in a tray of plasticene

I don't think high degrees of accuracy are needed - we're after the
general idea, no rocket science. I'll start a test bed tomorrow, sun
permitting

Thanks. Basically, nobody has said that the tip of the shadow won't
trace out a figure 8 over the year - which is what worried me most.

Dave Eastabrook wrote:

Martin Frey wrote


Dave Eastabrook wrote:



Problem is that the pole can move (even sideways) or tilt unless it has
foundations, or warp or even shrink with rain, especially if wood.
Think for an 8 foot pole with 1 foot stuck into the ground, if the
bottom shifts over 1 inch, the top moves 7 (hence upsets the shadow).
It can also sink down.


I suspect a small stick will do the trick: the gnomon on a sundial
doesn't have to be huge to tell the time.


Dave,

Relatively speaking though for a sundial the sun is moving around 180
degrees, whereas with the Analemma it would only be a few degrees (??),
and you'd want there to be enough separation between the narrowest parts
of the - squashed - figure of 8, as your canvas is smaller than the sky.

To make things more complicated, for some analemmas the range of motion
of the sun described therein is much greater in altitude whereas for
others it is much greater in azimuth. For my perfectly vertical analemma
on the southern meridian (see
http://www.perseus.gr/Astro-Solar-Analemma-102816.htm), I had the Canon
A-1 in portrait mode since the analemma's range was 47-deg in altitude
and only 10-deg in azimuth. In contrast, for my Sunrise Analemma (see
http://www.perseus.gr/Astro-Solar-Analemma-060000.htm), the range in
altitude was "only" 30-deg whereas the range in azimuth was 40-deg.

For my imaging project, I needed the range in both azimuth and altitude
so as to identify which lens I would need in order to match the FOV of
the lens with the complete range of motion of the sun. Similarly, I also
had to compute the mean azimuth and altitude in order to be able to
point the camera properly.

Worth maybe guessing how large you'd want it, and doing a little maths.

If I can help with any ephemeris generation, please let me know. I use
Chris Marriott's SkyMap Pro (Pro in every sense of the word!).

I loved Anthony's picture - it really makes you think.

I have another analemma confirmed to be successful which is one hour
earlier than the one at Ancient Nemea. I will have a link ready for
distribution next week.

I don't think high degrees of accuracy are needed - we're after the
general idea, no rocket science. I'll start a test bed tomorrow, sun
permitting



Good Luck! Sounds like a great project.

It is certainly a great project. Around the two solstice points, there
is very little action even a week apart whereas immediately above and
below the cross-over point we have lots of action even after a few days.
Something that may not be obvious is that I did not use a constant
interval between imaging days (on purpose) due to the variable rate of
movement of the sun (Kepler's Second Law). My shortest duration between
exposures was five days; my greatest was 12 days (for the analemma at
Ancient Nemea) and 24 days for the other two from 2002. The latter
difference and shift from 24 to 12 days was so as to round out the
solstices a little more nicely.

Anthony.

Dave

John,

I did all of my analysis using Chris Mariott's excellent SkyMap
Pro .... the software allows you to plot the motion of the sun during a
year (for example) which will lead to the analemma. You have a choice
between coordinate systems and, of course, we must specify Az/Alt.

Anthony.

Dr John Stockton wrote:

JRS: In article , seen in
news:uk.sci.astronomy, Pen Phill posted at
Fri, 9 Jan 2004 17:15:51 :-


From: Dr John Stockton





Running a sky-map program in steps of 24 hours is amusing.





Will sky map actually produce the actual analemma or just show the solar
position at each 24 hr interval?



I wrote "a sky map program" to be general, not "SkyMap" to be specific.

The program that I recall using, long ago, actually displayed, as a
function of time, a Mercator map of the Earth with twilight and dark
shown and with a small Sun at the subsolar point. One could have traced
an analemma.

My largest dictionary does not actually, AFAICS, define analemma.

"Dr John Stockton" wrote snip


My largest dictionary does not actually, AFAICS, define analemma.

better google it then
http://www.google.com/search?sourcei...F-8&q=analemma



and click on the underlined word in the blue bar

http://dictionary.reference.com/search?q=analemma&r=67

near bottom of page

Merriam-Webster - Search for definitions


http://www.m-w.com/cgi-bin/dictionar...ry&va=analemma


Function: noun
Etymology: Latin, sundial on a pedestal, from Greek analEmma, lofty structure, sundial, from analambanein to take up, restore, from
ana- + lambanein to take -- more at LATCH http://www.m-w.com/cgi-bin/dictionar...onary&va=latch
Date: 1832


: a plot or graph of the position of the sun in the sky at a certain time of day (as noon) at one locale measured at regular
intervals throughout the year that has the shape of a figure 8; also : a scale (as on a globe or sundial) based on such a plot that
shows the sun's position for each day of the year or that allows local mean time to be determined
- an·a·lem·mat·ic /"a-n&-le-'ma-tik, -l&-/ adjectiv

or

http://www.analemma.com/Graphics/spl...plashPart2.GIF


which suggests try an image search
http://images.google.com/images?num=...ma&sa=N&tab=wi


a new word for me too
newbie am I !

enjoy

Hugh W
--

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