How do you know that the electromagnetic waves can travel through the vacuum?

Answer 1

-- I can see the sun, and even with my eyes closed, feel its warmth upon my brow.

-- I can see the moon, the stars, planets, and sundry other wonders of the cosmos,

by their beams of light across the trackless void.

-- When our intrepid and fearless astronauts stood upon the surface of our moon,

their radio transmissions were heard clear and crisp by their loved ones, safe on

terra firma.