The WeirdMaster doesn't know why the artist who donated this image named it "planet 21".
Telescopes are often used to view planets in the night sky more closely.
People purchase refracting, and sometimes Newtonian telescopes,
that have parabolic mirrors in them along with with the usual optical lenses
that you would expect to find in quality optical instruments.
Quality telescopes are a joy to own and use for viewing celestial objects in the night sky.
