Castor is a star?
"Castor" is the name that people have given to one of the first magnitude
stars visible from the northern Hemisphere, in the constellation of Gemini.
Present estimates of the dimensions of the Milky Way galaxy place its diameter at roughly 100,000 light years. The star "Castor" in the constellation of Gemini is about 50 light years distant from our solar system, or roughly 0.05 percent of the distance across the galaxy. Castor is closer to us than your average next-door neighbor.