Topo-Geo Persp/Ortho
First, some definitions:
- Geocentric: this is the view from the center of the Earth. Almanacs and ephemerides always publish geocentric values, which acts as a common base, and so that no one is given special status. This is useful for comparing values to official almanacs.
- Topocentric: it is always possible to take geocentric values and correct them for any topographic location on the planet. You will almost always use a topocentric view because you will want to match the view from your observatory.
- Projection: the Mercator projection is well known for making Greenland look huge (but is useful for navigation); equal-area projections are great for making comparisons between different areas, but would make poor a navigation tool. Cartographers must choose the best projection for their map.
- Perspective: this is the projection normally used in Lunar Calculator because it will match the view from your observatory.
- Orthographic: this is the projection is found in most lunar atlases because it has a minimum of distortion. You will want to use an orthographic projection when comparing Lunar Calculator to atlases.
Lunar Calculator creates a view of the Moon that is either "topocentric and perspective" or "geocentric and orthographic". The reason I've paired them is simple. Since it is impossible for anyone to see the Moon from the center of the Earth, there is no point having a perspective view, so it might as well be orthographic. Likewise, since no one on earth can use a telescope to see the Moon in an orthographic way, there is no point creating one from a particular topographic (topocentric) location.
To shift from perspective to orthographic, use the View menu, and click on Orthographic:
