Twinkle, twinkle, little star -
I know exactly what you are:
An incandescent ball of gas,
Condensing to a solid mass.

Twinkle, twinkle, giant star -
I need not wonder what you are,
For seen through spectroscopic ken
You're helium and hydrogen.

-- Peter Marshall

(Quoted in Robert Ettinger's "The Prospect of Immortality." Ettinger says that Gene Lund credited it to Peter Marshall. I haven't been able to find a more direct source that confirms this.)

Edit: How do you force a line return so that a poem will read correctly? Thanks, fixed now.