Then, in the 1930s, Bell Laboratories in the US detected radio waves coming from the Milky Way galaxy, and researchers became aware that there are many signals in the universe that are invisible to the naked eye. Some of these electromagnetic waves can pass through dust clouds that block visible light, and can thereby reveal many unknown celestial worlds.
一九三○年代，美國貝爾實驗室偵測到銀河系發出的無線電波，得知宇宙中有許多肉眼不見的能量訊號，這些電磁波可以穿透擋住可見光的塵埃雲，揭開更多未知的天文世界。