Thanks Gordon, that's just the number I was looking for. The minimum projection distance at of the telescope sundial is 8 meters and the maximum is distance is 8 meters.
According to the ratio of 1/107 (or multiplication factor of .0093), then the penumbra width varies from .07meters (= 7cm or 2.5in.) to .21meters (=21cm or 8in.) Is this correct? It seems about right. Thanks John John L. Carmichael Jr. Sundial Sculptures 925 E. Foothills Dr. Tucson Arizona 85718 USA Tel: 520-696-1709 Email: [EMAIL PROTECTED] Website: <http://www.sundialsculptures.com> ----- Original Message ----- From: "Gordon Uber" <[EMAIL PROTECTED]> To: <[email protected]>; <[EMAIL PROTECTED]> Sent: Saturday, June 15, 2002 12:05 PM Subject: Re: Penumbra Ratio > John, > > The width of the penumbra on a surface is the distance from the style to > the surface times the angular diameter of the sun in radians (about 1/107) > divided by the cosine of the angle between the normal (perpendicular) to > the surface and the sun's ray. So basically you are correct, although 1/107 > would be a better value. The value varies by about +/- 2% during the year > due to the elliptical orbit of the earth. > > For the year 1999 the following web page gives a mean solar diameter of > 1923 arc seconds, corresponding to 1/107.3 radians = 0.009323 radians. > The maximum is 1955 arc seconds, and the minimum is 1891 arc seconds. > Angular diameters from > http://www.astrosurf.com/taf/dim-ogg-neg/don-sole-eng.htm > > Gordon > > > At 06:18 AM 6/15/02 -0700, you wrote: > >Hello All > >Does anybody remember the exact ratio or multiplication factor that will > >determine the width of the a shadow's edge penumbra if you know the > >distance from the style to the penumbra's image? Isn't the penumbra's with > >about 1/100th the projection distance? And couldn't this ratio be viewed in > >graphic or tabular form? > > > >I ask because I'd like to be able to calculate the theoretical penumbra > >width at different points along the Kitt Peak Sundial perimeter timelines. > > > >John > > > >John L. Carmichael Jr. > >Sundial Sculptures > >925 E. Foothills Dr. > >Tucson Arizona 85718 > >USA > > > >Tel: 520-696-1709 > >Email: [EMAIL PROTECTED] > >Website: <http://www.sundialsculptures.com> > > > >- > > Gordon Uber [EMAIL PROTECTED] San Diego, California USA > Webmaster: Clocks and Time: http://www.ubr.com/clocks > > -
