Atoms of the same element always have the same number of protons. But, Atoms of the same element can have a different number of neutrons.<em> We call these isotopes.</em> These 3 examples of uranium have the same amount of protons within them but a different number of neutrons, hence the change in atomic mass.
Earth’s tilt from its axis. For explanation: The angle in which Earth is at is 23.5°. This causes its tilt which affects how the Sun’s light hits Earth