I need to produce the star map with constellations etc in the Mollweide projection (elliptical projection giving 360 view angle, used in plotting night sky). I found a recipe at https://kimnewzealand.github.io/2019/02/21/celestial-maps/ with the use of sf package and converting the default EPSG:4326 data of the sky objects into Mollweide projection.
At some stage the data is converted to the Mollweide projection using the command:
constellation_lines_sf_trans<- st_transform(constellation_lines_sf_trans, crs = "+proj=moll")
The resulting image, reproduced along the lines as described in the link, looks like:
It is fine, however, the coordinate system is equatorial, that is basically with the same rotation axis as all coordinate systems on the Earth, like WGS84 (North Pole upwards). For example, the Milky Way is shown on this plot, going at some angle 60 degrees. We need the so called galactic coordinates: this is the coordinate plane coinciding with the plane of our Galaxy. So, Milky way here would be just a horizontal line of the ellipse axis. For example, the solution found elsewhere, seems to use the same technique, but the code is not given there:
Here Milky Way is a horizontal line, and the North Pole is in the upper left corner (denoted as np; for example, here one can see the distorted recognizable constellations of Ursa Major/Minor around the North Pole). I would take this image, but there is a blind spot (showing the blind zone of an observatory which cannot reach this region in the sky), so I would like to reproduce this image: constellations + Mollweide projection + "galactic" orientation of the reference frame.
We are able to convert between variety of coordinate systems in R packages. It seems that most GIS tools use various flavors of Earth-related coordinate systems and projections, based to the rotation of the Earth (North Pole up), for majority of applications, needed for GIS. The question is whether it is possible to load and convert to a predefined galactic coordinate system (or, for example, to the ecliptic system), or to perform this conversion on the fly in the scripts with manual conversion of star data