diurnal motion is when objects in the sky appear to move due to earth 's rotation on its axis & stars appear to move relative to the horizon during the night ->  stars apearing to move relative to the horizon during the night is an example of diurnal motion  stars apearing to move relative to the horizon during the night is an example of diurnal motion & the earth rotating on its axis causes stars / the moon to appear to move across the sky at night -> the earth rotating on its axis causes stars to appear to move relative to the horizon during the night