Similarities and Differences
The similarities and differences between the first and third quarter moon phases are that the sun lights up half the moon on both occasions, but the light is on different sides. A 1st quarter moon also only occurs when the moon is approaching full moon, and 3rd quarter when the moon is approaching the new moon.
A perspective from the Earth would show you that the moon appears to shrink and grow. This is because the light from the sun is reflecting off of the moon on different sides on each point of its orbit. From an observer looking up above Earth, higher than the moon's orbit, the moon would appear to be half lit. The moon orbits around the Earth every 28 days, and the moon reflects that because the moon is always lit in one particular hemisphere.