Geocentric Earth view on the sky

[sep-don-barrett]

One projector found on old Spitz planetarium instruments was "Geocentric Earth." It projected the outlines of the continents of the Earth onto the sky aligned with the star projector, allowing one to visualize the relationship of the Earth and the Sky.

In particular it was incredibly useful for teaching navigation, one of the key motivators of small planetaria in the post-WWII period when many small schools gained planetaria. The projectors were also equipped with a spherical triangle projector that allowed one to draw on the sky the spherical triangles involved in solving navigation problems.

It would be wonderful to add to the coordinate/ecliptic/equator grids a continent overlay from the point of view of the observer's location (i.e., their location at the zenith). A star at the zenith of an observer would naturally lie on the position of the Earth map projected onto the sky. A star at some positive zenith distance would be somewhere on the circle of that same zenith distance around the map position of the observer.

(having the script language capable of drawing great circle segments on the sky and non-great-circle arcs and circles on the sky would finish the capability of illustrating spherical trig as a whole)

[gzotti]

Interesting idea, thanks. It could be done with a HiPS texture for Earth (or at least a sphere module similar to the Milky Way with a decent 8k earth texture) seen from the inside, rotated to match longitude and latitude. It would then answer the question "where on earth is this star in the zenith". May be a nice "first plugin", not sure about being a core feature.
Regarding the spherical trig lines, you can find a few of those in the ArchaeoLines plugin. Tooling for navigational education would however require more knowledge of the developers about navigational education requirements. It would probably go into the NavStars plugin.

[10110111]

There indeed exists a HiPS for this, and it's easily accessible if one can rebuild Stellarium from source. If you add one more item to the type combobox like in the patch below, you'll get "Blue Marble Next Generation w/ Topography and Bathymetry" (among others) under "Other".

diff --git a/src/gui/ViewDialog.cpp b/src/gui/ViewDialog.cpp
index 4a91e6998c..ef990178bd 100644
--- a/src/gui/ViewDialog.cpp
+++ b/src/gui/ViewDialog.cpp
@@ -768,6 +768,7 @@ void ViewDialog::populateHipsGroups()
     typeComboBox->clear();
     typeComboBox->addItem(q_("Deep Sky"), "dss");
     typeComboBox->addItem(q_("Solar System"), "sol");
+    typeComboBox->addItem(q_("Other"), "other");
     index = typeComboBox->findData(selectedType, Qt::UserRole, Qt::MatchCaseSensitive);
     typeComboBox->setCurrentIndex(index);
 }

Not sure though how well it's oriented. Looks like the latitude of the equatorial grid is more or less correctly showing my reference city, but longitude is off.

[Atque]

Hmm, why is this set of HiPS hidden from the standard distribution?

The longitude offset is likely due to J2000.0 coordinates given.

Ah, yes. And to precisely meet OP's request, we need a stationary Earth projected. This one follows the sky movement.

[gzotti]

Probably the "other" HiPS didn't appear too useful for us. I did not check details, but when the "Solar System" HiPS are observed as high-res textures mapped on the planets, this earth-HiPS would have to be observed from other planets, not from its inside. Not sure who defines these sol/dss/other types, though. In any case, using is as OP proposes needs special handling. HiPS or simpler textured sphere, It could probably fit in thematically as extension to the NavStars plugin.