# Creating a rectangular star map

I'm trying to find/create a star map between the declinations of -45 to +60, and need it to be a rectangle. Is there any software/website that would let me create this? Is there a name for this kind of map/projection?

(I've attached a diagram to try and make myself clearer)

Thanks for any help :)

• Isn't this just a Plate Carrée, or simple cylindrical, projection: turn the declination into the y-coodinate, the right ascension the x-coordinate? – Anders Sandberg Jan 25 '18 at 14:33
• As @AndersSandberg notes, this is a cylindrical projection. astronomy.stackexchange.com/questions/13488 may be helpful – user21 Jan 25 '18 at 15:35

Equirectangular or equidistant cylindrical projection is the simplest way to meet these requirements. Plate Carrée is the case where distortion is minimal at the equator. Dominic Ford's Map of the Constellations uses it, as do the Deep Star Maps by Ernie Wright of the NASA Scientific Visualization Studio. In free software, Stellarium calls it "Cylinder," and Cartes du Ciel calls it "Cartesian." If you plot your own, you could scale the horizontal dimension by $\cos 30^\circ \approx 0.866$ to minimize distortion at $\pm30^\circ$ declination.

Since you are not plotting the polar regions, other cylindrical projections are possible. The Mercator projection is available in both Stellarium and Cartes du Ciel. Stellarium also offers the Miller cylindrical projection.

• Sorry I never responded sooner, but Cartes du Ciel did this perfectly :) Thank you! – Airgiraffe Jun 15 '18 at 9:01

You'd be converting some images from spherical coordinate system to cartesian coordinate systems.

You can find a texture mapping environment which can do the maths for you. I'd use Unity3D. You are converting spherical coordinate graphs to XY graphs. I think polar is XY and spherical does distance from origin so XYZ, X is the lattitude, Y the longitude. perhaps check this.

The equations are 1 line of code. I learnt it myself having had 2/10 at my school maths exams. it's a copy/paste kind of equation written in every programming language. It's vaguely rated to orthographic projection.

You can say you are doing the inverse of spherical texture mapping.

You can search for resources to convert the map of the earth to and from a sphere and a square.

You can check cubemap.skybox projection.

spherical texture mapping

You will probably find many many programs that can do it, mathsworks, unity3d, blender, mathcad, texture mapping apps for games designers and cartographers, and they'll have different memory management, image conversion from bitmap/rgb32 and so forth and you'd find which is ok for your images.