NavList:

Frank,

         I did some mulling on the Starfinder. In its current form almost all of the sky is covered on both sides of the backing plate. You couldn’t have that with the stereographic projection. However as a result of a recent set of discussions on Navlist conformal maps I went back and reread the sections in “Flattening the Earth” by Snyder on that topic. I was introduced to the so-called Lagrange projection (actually it’s one on Lambert’s projections) that represents the whole of the Earth’s surface in circle and is conformal. Normally it’s centred on the equator and prime median but a polar version might be worth investigating.

Other free format thoughts are:

Maybe it’s not necessary to have the whole sky represented on both sides of the backing plate. The Starfinder is a rather poor representation of the sky and may be better thought of as a slide rule. The astrolabe is a slide rule, uses stereographic projection and surely must be able to perform the calculations that the Starfinder does. Should the Starfinder really look anything like a planisphere.

It may not be possible to build something that doubles as an altitude-azimuth calculator and planisphere without making the backing plate too busy to be able to be read easily.

One important consideration is that if a new projection were to be used it should not reduce the accuracy with which the altitude and azimuth can be read.

I happy to act as a sounding board on this.

Regards,

Robin