• Feb 11, 2008, 01:16 AM
Uma Maheswari
Hi..
Can anyone able to give me answer for this question..
How to show the shadow of an object for(e.g.Buildings) when the position of sun and geographical position of building is known?
Also say me in which direction the shadow will fall and what will be the length of the shadow?
Is their any formula to calculate the length,angle,direction of the shadow fall according to sun position or time?
• Feb 11, 2008, 06:00 AM
Capuchin
It's fairly simple, just draw rays of light from the sun to the verticies of the building and project them onto the ground.

You should be able to see that the rays of light form triangle which you can easily use to find what you are looking for if you know, say, the height of the building and the elevation of the sun. It's all simple trigonometry.

If you still are confused, you'll need to give a little more information on what you're looking for.
• Feb 12, 2008, 04:29 PM
Stratmando
If you held up a 10' pole and it cast a 20' shadow, then if you measure the shadow of a building(both on flat ground, A Slope would complicate right now),
Then if you measure a building's shadow and it is a 100' shadow, the building is 50' Tall.
A shadow will move from West to east, as the sun does the opposite.
If I was trying to find height of building, and no shadow, I think I would walk any direction from building with a clinometer or anything that will show 45 Degrees and walk with the bottom level until the angle of the 45 points at the top of the building. The distance from the building will be equal to the Height.
Like Capuchun says, other info you provide can help.
Also the sun angle changes as you go from equinox(Equal day/equal night) to solstice, to equinox, to solstice and back to equinox completing 1 year.
Almost forgot, the sun moves at 15 Degrees per hour.
• Mar 24, 2008, 09:03 AM
Credendovidis
Quote:

Originally Posted by Stratmando
... Almost forgot, the sun moves at 15 Degrees per hour.

That even was so in the early stages of the solar system, when a day was much shorter than it is today... And as it will be in the future when a day will be much longer than it is today. All it takes is being flexible with what a second is...
:D :D :D
• Mar 24, 2008, 09:14 AM
Capuchin
Quote:

Originally Posted by Credendovidis
That even was so in the early stages of the solar system, when a day was much shorter than it is today ... And as it will be in the future when a day will be much longer than it is today. All it takes is being flexible with what a second is ...
:D :D :D

How can you be flexible with a second? A second is the amount of time it takes light to travel 299792458 meters in a vacuum.
• Mar 24, 2008, 09:35 AM
Credendovidis
Quote:

Originally Posted by Capuchin
How can you be flexible with a second? A second is the amount of time it takes light to travel 299792458 meters in a vacuum.

I clearly referred to Stratmando's "the sun moves at 15 Degrees per hour".
That value you provided is based on the specification of a second we use today.
However we also call one rev. of earth (i.e. 360 degrees) 24 hours.
4 Billion years ago "24 hours" on earth took less than 18 of our current hours.
In about 1 Billion years - based on the "breaking" influence caused by the expanding orbit of our moon - "24 hours" on earth will take around 26 of our current hours.
A second / minute / hour is indeed flexible. On long term that is.
:D
• Mar 24, 2008, 09:43 AM
Capuchin
Quote:

Originally Posted by Credendovidis
I clearly referred to Stratmando's "the sun moves at 15 Degrees per hour".
That value you provided is based on the specification of a second we use today.
However we also call one rev. of earth (i.e. 360 degrees) 24 hours.
4 Billion years ago "24 hours" on earth took less than 18 of our current hours.
In about 1 Billion years - based on the "breaking" influence caused by the expanding orbit of our moon - "24 hours" on earth will take around 26 of our current hours.
A second / minute / hour is indeed flexible. On long term that is.
:D

I understand what you are saying, but a second is not defined by how fast the Earth spins, so I don't see how it's relevant.
• Mar 24, 2008, 10:09 AM
Credendovidis
Quote:

Originally Posted by Capuchin
I understand what you are saying, but a second is not defined by how fast the Earth spins, so I don't see how it's relevant.

So you suggest that in the far future a day/night will take anything else than 24 hours?
Get real!! Over time humanity - if not becoming extinct - will change the value of hours and seconds to suit their purpose. Already now we are fiddling with the "year" to suit our need...
:rolleyes:
• Mar 24, 2008, 10:18 AM
Capuchin
Quote:

Originally Posted by Credendovidis
So you suggest that in the far future a day/night will take anything else than 24 hours?
Get real !!! Over time humanity - if not becoming extinct - will change the value of hours and seconds to suit their purpose. Already now we are fiddling with the "year" to suit our need ...
:rolleyes:

I think it's more likely that the definition of second will stay the same, and we will just have leap seconds or leap minutes, if we don't revamp the whole time thing, 24 hours is a silly number to have anyway. But I doubt they will change how a second is defined, as that will change our definition of the speed of light.
• Mar 24, 2008, 10:38 AM
Credendovidis
Quote:

Originally Posted by Capuchin
But I doubt they will change how a second is defined, as that will change our definition of the speed of light.

You may be good in science, but I fear you are poor in forecasting human behaviour!
Please note that essentially we both agree on the standard of lightspeed, but we differ on validating human nature...
;)
• Mar 24, 2008, 11:44 AM
Stratmando
In addition to agreeing with Capichun, I could see where a different system could be developed, We have had Standard measurments, then Metric in the last few years.
In 50 Thousand Years they could say that the "second" was old 30th century stuff.
I don't think humans will last 50 thousand years, Any bets?
• Mar 24, 2008, 08:08 PM
Credendovidis
Quote:

Originally Posted by Stratmando
... I don't think humans will last 50 thousand years, Any bets?

If we go on like we are doing now you have a winning bet...
:rolleyes:
• Mar 25, 2008, 05:42 AM
Capuchin
Quote:

Originally Posted by Stratmando
I don't think humans will last 50 thousand years, Any bets?

Sure I'll take that bet. Oh look I won, humans have lasted 200 thousand years.

However what I'm sure you meant to say, that we last 50 thousand more years... hmm... maybe we are too advanced to survive?
• Mar 25, 2008, 06:22 AM
Stratmando
I did mean 50K more, More likeky less than a thousand, The chemicals, and drugs we produce Are so bad for people, and animals. Earth will be fine?

•  All times are GMT -7. The time now is 06:46 PM.