>Dear all, > If I step out into my yard and look up the surface of my roof, does >the altitude in the sky change as I move my eyes from right to center >to left along the roof line into the sky? I think I know the answer to >this, but would like verification.
Unless you live in a circular house with the yard in the centre, yes! For a regular straight roof, as you look further to either side, left or right, the height of the roof remains the same, but it's distance from you increases. Thus the angle it subtends at your eye gets less (i.e. the effects of perspective). This angle is the altitude of the sky visible along the ridge, so yes, the altitude does change. The above all holds if you think of your observation point as being a flat plane, rather than a curved earth. If we include the curvature of the earth, the answer is even more obvious... If your roof were long enough to disappear over the horizon then its altitude would be zero there! Sadly I think none of us will ever own a house large enough to try this as a practical experiment :-) Best Wishes, David Robert Higgon 51°27' N 0°15' W
