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Re: Index Error - Real vs. Artificial Horizon
From: Bill B
Date: 2013 Feb 28, 22:59 -0500
From: Bill B
Date: 2013 Feb 28, 22:59 -0500
On 2/28/2013 7:49 PM, Örjan Sandström wrote: > >In other words, since the index mirror is a few inches above the > horizon mirror, >wouldn't there be a parralax error here as well, since > we are looking at the >reflected image in the artificial horizon, not > miles away at an actual horizon? Paul Another way to look at this is follows: When you are using an artificial horizon (AH) you are not looking at the mirror, you are look at images of a body a long way away. Try this experiment. Stand fairly close to a mirror and focus on its frame. When the frame is in focus, background objects at a distance will be out of focus and vice versa. Unless you arer using the 0 mag sight tube supplied, I doubt you could focus on the AH frame (with the scope). Even if the apparent distance between the mirrors increases by a few inches, that is just noise when viewing a most celestial objects. That is not to say there is no parallax between you and the celestial object depending where you are located on the earths surface, but that has nothing to do with sextant mirrors. (Angles are measured from the center of the earth to the center of the body, not from someplace on the surface of the earth to the center of the body,) There is also a slight bit of parallax between the earth and sun. Even between the stars and earth (google "parsec"). When you get around to trying a reduction with the moon you will notice an "hp" correction. This is for horizontal parallax. But these are topics for another day. Bill B