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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. |
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Astronomy wizard required for calculation
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. |
#3
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Astronomy wizard required for calculation
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 | |
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Astronomy wizard required for calculation
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. |
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Astronomy wizard required for calculation
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 |
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Astronomy wizard required for calculation
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. |
#7
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Astronomy wizard required for 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. |
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Astronomy wizard required for calculation
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. |
#9
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Astronomy wizard required for calculation
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. |
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