diff --git a/changelog/7352.doc.rst b/changelog/7352.doc.rst new file mode 100644 index 00000000000..7006c8695e6 --- /dev/null +++ b/changelog/7352.doc.rst @@ -0,0 +1 @@ +Added explanation text to :ref:`sphx_glr_generated_gallery_plotting_plotting_blank_map.py` about the offset between "(0, 0)" in helioprojective coordinates and the heliographic equator. diff --git a/examples/plotting/plotting_blank_map.py b/examples/plotting/plotting_blank_map.py index 2e16b705b90..93f2fe42bad 100644 --- a/examples/plotting/plotting_blank_map.py +++ b/examples/plotting/plotting_blank_map.py @@ -54,11 +54,17 @@ yc = [0, 100, 400] * u.arcsec ################################################################################ -# Place and mark coordinates on the plot. +# Plot the blank map with the specified coordinates. Note that the marker for +# (0, 0) in helioprojective coordinates is at the center of the solar disk, yet +# the heliographic equator (zero degrees latitude) does not go through the disk +# center and instead curves below it. The reason for that is the observer, +# specified as Earth in this example, is almost always at non-zero heliographic +# latitude, and disk center as seen by such an observer will have that same +# heliographic latitude. The :func:`~sunpy.coordinates.sun.B0` function returns +# Earth's heliographic latitude at a specified time. coords = SkyCoord(xc, yc, frame=blank_map.coordinate_frame) -p = ax.plot_coord(coords, 'o') -# Set title. +ax.plot_coord(coords, 'o') ax.set_title('Plotting fixed points on a blank map') plt.show()