The Moon has many effects on planet Earth, but three major ones stand out. Today, the Moon:
- Creates tides in Earth's oceans
- Determines the length of Earth's days
- Illuminates Earth's nights
The Moon creates tides
The moon has its own gravitational force that acts upon Earth as it orbits. As Earth spins on its own axis, gravity and centrifugal force keeps ocean waters at equal levels. However, the moon's gravitational force is strong enough to disrupt this balance, causing water to accelerate towards the moon and "bulge."
This bulge moves as the moon orbits and Earth rotates, causing "high tide" in places experiencing the bulge. Without the moon, our oceans would still bulge (due to the gravitational pull of the sun), but bulges would be much smaller compared to those created by the moon.
The Moon lengthens days
We know that due to tidal friction caused by the moon, Earth’s rotation slows down (very slightly) over time. As it slows, our days get longer (because Earth is spinning more slowly, we experience longer periods of light from the sun).
When we extrapolate this backwards, we see that our 24-hour day today is a product of a slowing rotation over time (it used to spin much faster!). Without the Moon to slow the rotation, the day would be only 6 - 8 hours long!
The Moon illuminates nights
The Sun's brightness causes our daylight, and at only 1/400,000th of the Sun's brightness, the Moon's brightness doesn't really compare. However, the next brightest object in the sky, Venus, is only 1/14,000th as bright as the full Moon!
This suggests that without it, our experience at nighttime would be a very different one (much, much darker) and our night vision would never have evolved to what it is today.
One final effect the Moon has on Earth: the Moon has long been a source of inspiration for poetry, literature, and other works of art. You can read one of my favorite poems that references the moon here.