The song states that the sun is so hot that everything in it is a gas; however, this is incorrect. The sun is SO hot that all gases are ionized and turned into plasma, which is gas with the ability to conduct electricity. However, plasma is considered a completely separate state of matter, so the sun is not, in fact, gas.
This mellow studio recording of Why Does The Sun Shine? isn't responsible for the song's huge popularity; the rocking live version featured on Severe Tire Damage is. TMBG hardly ever performs the slow-paced version of the song.
This is a remake of the song by Hy Zaret And Lou Singer, performed by folk singer Tom Glazer on the album Space Songs (Motivation Records, 1959). MP3s of the song and others from that album and 5 others can be found Here.
TMBG have been performing their version since at least 1985, with a performance from this year appearing on the television show Nick Rocks.