Astronomy wizard required for calculation

Hi. I've got a flat lawn (horizontal) and at the end of the lawn a
perpendicular wall. In front of the lawn and wall is my house and during
winter the sun fails to shine on the wall and lawn.

Assume the house ridge runs east and west.

The wall is not quite east and west, but I want to discover at what day
and month the sun shines at the intersection of lawn and the wall at the
mid point of the wall.

Right now the sun shines onto the lawn at noon. Of course as the sun
gets lower afer summer solstice the shadow line starts to move down the
lawn and up the wall.

If I measure the distance from the wall/lawn interection and the
shadow-line at noontime sometime this week - and post it here - can it
be determined at what day and month the shadow line rests at the
wall/lawn intersection - at noontime? Of course there will be two
times, one in spring, and one in fall.

I cannot do the calculation. Easy peasy for and astronomer. Right? :c)

Thanks.

On 27/03/2011 15:01, Richard wrote:
Hi. I've got a flat lawn (horizontal) and at the end of the lawn a
perpendicular wall. In front of the lawn and wall is my house and during
winter the sun fails to shine on the wall and lawn.

Assume the house ridge runs east and west.

The wall is not quite east and west, but I want to discover at what day
and month the sun shines at the intersection of lawn and the wall at the
mid point of the wall.

Right now the sun shines onto the lawn at noon. Of course as the sun
gets lower afer summer solstice the shadow line starts to move down the
lawn and up the wall.

If I measure the distance from the wall/lawn interection and the
shadow-line at noontime sometime this week - and post it here - can it
be determined at what day and month the shadow line rests at the
wall/lawn intersection - at noontime? Of course there will be two times,
one in spring, and one in fall.

I cannot do the calculation. Easy peasy for and astronomer. Right? :c)

Thanks.

I think I only need to get hold of a table that shows sun height above
zenith for my location for every day of the year.

On or about 2011-03-28,
Richard illuminated us with:
On 27/03/2011 15:01, Richard wrote:
Hi. I've got a flat lawn (horizontal) and at the end of the lawn a
perpendicular wall. In front of the lawn and wall is my house and during
winter the sun fails to shine on the wall and lawn.

Assume the house ridge runs east and west.

The wall is not quite east and west, but I want to discover at what day
and month the sun shines at the intersection of lawn and the wall at the
mid point of the wall.

Right now the sun shines onto the lawn at noon. Of course as the sun
gets lower afer summer solstice the shadow line starts to move down the
lawn and up the wall.

If I measure the distance from the wall/lawn interection and the
shadow-line at noontime sometime this week - and post it here - can it
be determined at what day and month the shadow line rests at the
wall/lawn intersection - at noontime? Of course there will be two times,
one in spring, and one in fall.

I cannot do the calculation. Easy peasy for and astronomer. Right? :c)

Thanks.

I think I only need to get hold of a table that shows sun height above
zenith for my location for every day of the year.

http://www.heavens-above.com does exactly that. Among many other
things. Set up an account (so you put in your location) then go to
the Solar data page. I'm not sure whether there is a table available
with all the days on one page, but fundamentally you can get at what
you're after.

--
Mark
Real email address | Blinky lights are the essence of technology.
is mark at | Everything else is fluff.
ayliffe dot org |

On 28/03/2011 10:16, Mark Ayliffe wrote:
On or about 2011-03-28,
illuminated us with:
On 27/03/2011 15:01, Richard wrote:
Hi. I've got a flat lawn (horizontal) and at the end of the lawn a
perpendicular wall. In front of the lawn and wall is my house and during
winter the sun fails to shine on the wall and lawn.

Assume the house ridge runs east and west.

The wall is not quite east and west, but I want to discover at what day
and month the sun shines at the intersection of lawn and the wall at the
mid point of the wall.

Right now the sun shines onto the lawn at noon. Of course as the sun
gets lower afer summer solstice the shadow line starts to move down the
lawn and up the wall.

If I measure the distance from the wall/lawn interection and the
shadow-line at noontime sometime this week - and post it here - can it
be determined at what day and month the shadow line rests at the
wall/lawn intersection - at noontime? Of course there will be two times,
one in spring, and one in fall.

I cannot do the calculation. Easy peasy for and astronomer. Right? :c)

Thanks.

I think I only need to get hold of a table that shows sun height above
zenith for my location for every day of the year.

http://www.heavens-above.com does exactly that. Among many other
things. Set up an account (so you put in your location) then go to
the Solar data page. I'm not sure whether there is a table available
with all the days on one page, but fundamentally you can get at what
you're after.

Thanks.

I'm not sure of my terminology though.

I should have said ALTITUDE above HORIZON. I think.

On 28/03/2011 12:22, Richard wrote:
On 28/03/2011 10:16, Mark Ayliffe wrote:
On or about 2011-03-28,
illuminated us with:
On 27/03/2011 15:01, Richard wrote:
Hi. I've got a flat lawn (horizontal) and at the end of the lawn a
perpendicular wall. In front of the lawn and wall is my house and
during
winter the sun fails to shine on the wall and lawn.

Assume the house ridge runs east and west.

The wall is not quite east and west, but I want to discover at what day
and month the sun shines at the intersection of lawn and the wall at
the
mid point of the wall.

Right now the sun shines onto the lawn at noon. Of course as the sun
gets lower afer summer solstice the shadow line starts to move down the
lawn and up the wall.

If I measure the distance from the wall/lawn interection and the
shadow-line at noontime sometime this week - and post it here - can it
be determined at what day and month the shadow line rests at the
wall/lawn intersection - at noontime? Of course there will be two
times,
one in spring, and one in fall.

I cannot do the calculation. Easy peasy for and astronomer. Right? :c)

Thanks.

I think I only need to get hold of a table that shows sun height above
zenith for my location for every day of the year.

http://www.heavens-above.com does exactly that. Among many other
things. Set up an account (so you put in your location) then go to
the Solar data page. I'm not sure whether there is a table available
with all the days on one page, but fundamentally you can get at what
you're after.

Thanks.

I'm not sure of my terminology though.

I should have said ALTITUDE above HORIZON. I think.

Useful rough data are (for eg. latitude 51.5):

Midwinter solstice : 90 - 23.5 - latitude (15)
Equinox : 90 - latitude (38.5) about now
Midsummer solstice : 90 + 23.5 - latitude (62)

And to the accuracy you will need for gardening if you fit a sine wave
to that with period 12 months it will be close enough.

Regards,
Martin Brown

On Mar 27, 4:01*pm, Richard wrote:
Hi. *I've got a flat lawn (horizontal) and at the end of the lawn a
perpendicular wall. In front of the lawn and wall is my house and during
winter the sun fails to shine on the wall and lawn.

Assume the house ridge runs east and west.

The wall is not quite east and west, but I want to discover at what day
and month the sun shines at the intersection of lawn and the wall at the
mid point of the wall.

Right now the sun shines onto the lawn at noon. Of course as the sun
gets lower afer summer solstice the shadow line starts to move down the
lawn and up the wall.

If I measure the distance from the wall/lawn interection and the
shadow-line at noontime sometime this week - and post it here - can it
be determined at what day and month the shadow line rests at the
wall/lawn intersection - at noontime? *Of course there will be two
times, one in spring, and one in fall.

I cannot do the calculation. Easy peasy for and astronomer. Right? :c)

Thanks.

There are two noons to consider - natural noon and clock noon.

The difference between these two noons is that one varies when you use
a shadow to gauge the return of noon each cycle while the 24 hour
clock noon is basically an average of these uneven natural noon
cycles. A great astronomer called Christian Huygens outlines how to
determine natural noon using a shadow and then convert it into 24 hour
noon -

"... hang two plummets, each by a small thread or wire, directly over
the said Meridian, at the distance of some 2. feet or more one from
the other, as the smallness of the thread will admit. When the middle
of the Sun (the Eye being placed so, as to bring both the threds into
one line) appears to be in the same line exactly.....you are then
immediately to set the Watch, not precisely to the hour of 12. but by
so much less, as is the Aequation of the day by the Table." Huygens

http://www.xs4all.nl/~adcs/Huygens/06/kort-E.html

If you do the exercise yourself,and feel free to use a watch, you will
discover a number of things and one thing in particular.the variations
in the length of the shadow from day to day and season to season have
no bearing on the length of time the shadows align to determine
natural noon insofar as the movement of the shadow behaves like the
hands of a watch that does not run smoothly,at least from one noon
cycle to the next.The great astronomers,and this goes back to
antiquity,managed to determine an average cycle which was then turned
into a 24 hour day and eventually the calendar system made up of the
steady progression of these days which in turn was then used to
substitute for steady rotation.

So,the point is that there is no calculation involved,there will be
plenty of ingenuity if you take up the challenge and you will get a
cracking good education and enjoyment of astronomy and genuinely
admire our ancestors who worked with the movement of shadows for all
sorts of purposes.

Many imagine what you are doing is trivia but it is not,it is how
people come to understand the geometric language of astronomy by
working through the details themselves and a lot of it has to do with
interpretation and not calculation.

In uk.sci.astronomy message , Sun, 27
Mar 2011 15:01:01, Richard posted:

Hi. I've got a flat lawn (horizontal) and at the end of the lawn a
perpendicular wall. In front of the lawn and wall is my house and
during winter the sun fails to shine on the wall and lawn.

...

Measure, or determine from the plans, the angular height (altitude) of
your roof-ridge as seen from the foot of the wall. It may help to throw
a length of string over the house, fix it at the foot of the wall, and
pull it tight from the front.

Them go to http://www.heavens-above.com/, set your approximate
location, select "_Sun_ ... data for today", and step through the year
looking at "Maximum altitude:".

After the first step you should see something like
&Date=40631.8745833333 in the address bar; do the obvious to step, say,
a fortnight at a time.

Note that the date will vary slightly, since the year is not a multiple
of a day long.

--
(c) John Stockton, nr London, UK. Turnpike v6.05 MIME.
Web http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms and links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

On Mar 28, 11:18*pm, Dr J R Stockton
wrote:

Note that the date will vary slightly, since the year is not a multiple
of a day long.


Astronomy is no more a hobby than the practice of medicine is and
while you certainly give yourselves the title of 'doctor',I have yet
to encounter one genuine astronomer in all my years on the Usenet.

Let me give you an education son and drop that Dr title until you get
the facts straight.As determined by steady daily rotation,the orbital
circuit of the Earth is never more than a full 365 rotations or day/
night cycles and the refined value is 365 days 5 hours 9 minutes or
almost 365 1/ rotations.The amount of rotations from Mar 1st 2008
until Feb 29th 2012 are 1461 rotations and the corresponding number of
1461 day/night cycles representing a proportion of 1461 rotations to 4
orbital circuits and 365 1/4 rotations to one orbital circuit.

Empiricists try to assess daily rotation by looking at the average 24
hours day within the calendar system or grouping of 3 years of 365
rotations and 1 year of 366 rotation and are therefore either
incompetent or frauds,take your pick.

The title of doctorate is even more meaningful in astronomy as it is
in medicine as it relies on interpreting cause and effect on motions
and structures that already exist and from which life springs,today
that title is totally debased by people who are fond of making readers
believe that mathematical notation dictates astronomy when the
language of astronomy is pure geometry -

"The laws of Nature are written in the language of mathematics ... the
symbols are triangles, circles and other geometrical figures, without
whose help it is impossible to comprehend a single word." Galileo









--
*(c) John Stockton, nr London, UK. *Turnpike v6.05 *MIME.
* Web *http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms and links;
* Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
*No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

On 28/03/2011 13:07, Martin Brown wrote:
On 28/03/2011 12:22, Richard wrote:
On 28/03/2011 10:16, Mark Ayliffe wrote:
On or about 2011-03-28,
illuminated us with:
On 27/03/2011 15:01, Richard wrote:
Hi. I've got a flat lawn (horizontal) and at the end of the lawn a
perpendicular wall. In front of the lawn and wall is my house and
during
winter the sun fails to shine on the wall and lawn.

Assume the house ridge runs east and west.

The wall is not quite east and west, but I want to discover at what
day
and month the sun shines at the intersection of lawn and the wall at
the
mid point of the wall.

Right now the sun shines onto the lawn at noon. Of course as the sun
gets lower afer summer solstice the shadow line starts to move down
the
lawn and up the wall.

If I measure the distance from the wall/lawn interection and the
shadow-line at noontime sometime this week - and post it here - can it
be determined at what day and month the shadow line rests at the
wall/lawn intersection - at noontime? Of course there will be two
times,
one in spring, and one in fall.

I cannot do the calculation. Easy peasy for and astronomer. Right? :c)

Thanks.

I think I only need to get hold of a table that shows sun height above
zenith for my location for every day of the year.

http://www.heavens-above.com does exactly that. Among many other
things. Set up an account (so you put in your location) then go to
the Solar data page. I'm not sure whether there is a table available
with all the days on one page, but fundamentally you can get at what
you're after.

Thanks.

I'm not sure of my terminology though.

I should have said ALTITUDE above HORIZON. I think.

Useful rough data are (for eg. latitude 51.5):

Midwinter solstice : 90 - 23.5 - latitude (15)
Equinox : 90 - latitude (38.5) about now
Midsummer solstice : 90 + 23.5 - latitude (62)

And to the accuracy you will need for gardening if you fit a sine wave
to that with period 12 months it will be close enough.

Regards,
Martin Brown

I can do it using triangulation as follows:

The roof ridge is central. Therefore I can measure width of house and
divide by 2 to get postion of ridge wrt wall of the house facing back
garden. I have to add this figure to the distance from wall house to
shadow-line in back garden.

I look up noon ALTITUDE of sun at www.heavens-above.com on a certain day.

Then I find distance from ridge to ground level by:

O = A1 x tan a1 -: where O is opposite side (and vertical distance to
ridge), a1 is sun angle, A1 distance from shadow-line to point under
house ridge.

The tangent of the angle of ALTITUDE required so that shadow-line hits
end of garden at the junction if the back wall is derived from:

tan a2 = 0/ A2 -: where O is oppposite side, A2 is distance from
shadow-line at lawn/wall junction to point under house ridge.

Look up tan in tan table to get angle when sun shines at backyard
law/wall junction.

If my math is correct.