外太空

• 夕(evening; crescent moon (pictographic))RADICAL
• 卜(divination; fortune-telling)PHONETIC

Evening outside divining fortunes under the moon — that's an external affair.

• 大(large person; person with arms spread)RADICAL
• 丶(dot; emphasis mark)ASSOCIATIVE

A person with outstretched arms grows larger with a dot below to emphasize supreme greatness.

• 穴(row; gap)RADICAL
• 工(craftsman; work)PHONETIC

An empty cave with nothing inside is just hollow space.