We know that the Universe is expanding by measuring various properties of the stars: Luminosity, the spectrum of light, and the color. Each of these properties gives us wonderful knowledge of their elemental composition, distance from the Earth, their temperature, and many other things. This is a song about that.
...the universe is expanding...
Luminosity is a factor of distance
How bright is that star?
It seems so very far away
The spectrum of light is a factor of the temperature
How much is that heat?
Infrared is out of what we can see
Colors are a factor of the elements
Ain't got no blues
That provides us with important clues
The stars have a red shift
Cosmic radiation is always with us