Take the moon, for example. The Moon is far more than just a beautiful object in the sky. Without it, humans could not live on Earth. Our Moon has made a huge impact (no pun intended) on the geography, climatology, and biosphere of the Earth. Here are just a few examples.
- Stabilization of the Earth's tilt - The Moon exerts just the right amount of force on the Earth to stabilize the tilt of the Earth and keep it at just the right angle (23.5 degrees). Without the Moon, the Earth's tilt would become unstable. An unstable tilt would, in turn, cause wild seasonal variances - unbearable heat in the summer and frigid cold in the winter. (For more, read the sidebar here.) It probably goes without saying that a wobbly planet isn't exactly conducive to sustaining complex life.
- Rotation rate - Early in its history, the Earth rotated much fast than it does today. The Moon acts like a set of brakes that has slowed the Earth's rotation down to just the right rate. If the Earth rotated any faster, the wind force would be too strong. Likewise, if the rotation rate was any slower, life would not be possible. Also, if the Moon were smaller, it wouldn't exert enough gravitational force on the Earth to be able to slow it down to the proper speed. See how all of these things are so interconnected?
- Atmosphere - Most scientists believe the Moon was formed early in Earth's history. A Mars-sized planet/object hit the Earth. The molten mantle thrown into orbit after the catastrophic lunar-forming impact quickly coalesced into our Moon. Here is a short animation that illustrates this. The result of this event wasn't just a beautiful Moon, however. Within a few thousand years after the Moon collider, Earth cooled to an object with a molten surface and a steam atmosphere. This event helped to clear the atmosphere so we didn’t end up like Venus - suffocated by harmful greenhouse gasses. This helped to pave the way for later life that would need a planet to live on that had just the right temperature and atmospheric conditions.
- Tides - The waxing and waning of the moon, along with the tides, influences life processes. The oceans' tidal flow helps transport heat from the equator to the poles, thereby acting as a thermostat (temperature regulator) for the planet. Besides, for some surfers, life without tides would be unbearable. =)
- Body clocks - Animals, including humans, rely on the light of the moon at night to regulate their body clocks.
- What does the Psalmist compare the Moon to? [he compares the Moon with the longevity of David’s inheritance; there will always be a descendant of David’s on the royal throne (namely, Jesus Christ); the best analogy for something that will last forever is the longevity of the Sun and Moon]
- Why do you think it matters that the Moon is called a “faithful witness”? [A “faithful witness” means that the Moon is a “truthful” witness. It is not a deceptive witness. It gives us true and discernable information.]