We’ve all lived thousands of days already here on Earth. For most of us, a day on Earth involves waking up, performing whatever tasks we have lined up, eating a few meals, reading our favorite astronomy blogs, and then going to bed. What would this look like if we lived on the Moon?
What is a Day?
In order to understand what a day looks like on the Moon, we need to first identify what a day actually is. As our planet moves in orbit around the Sun, it is spinning at the same time. Think along the lines of a top dancing on a surface or a basketball whirling on someone’s finger. This phenomenon is known as rotation.
A day on Earth reflects how long it takes our planet to rotate in a 360° circle one time. If you thought that a top or a basketball spins quickly, you’d be surprised to know that our Earth spins just over 1000 miles per hour (460 meters per second)!
Every planet and moon in our Solar System rotate similarly, but not all at the same speed.
Why Do Planets and Moons Rotate at All?
To answer this question, we have to head back in time to when the Solar System was formed. Scientists theorize that as clumps of matter came together to form these objects, the impacts as these objects collided started them spinning.
In the vacuum of space, there’s no resistance to ever slow them down. In theory, the planets and moons of the Solar System will continue to spin until the end of time.
Just about every object in the Solar System rotates in the same direction. The known exceptions, Venus and Uranus, were likely caused by massive planetary impacts that completely changed their rotation.
Earth’s Rotation – Day and Night
As you are very likely aware, the Earth’s rotation leaves us facing the Sun at times and facing away from the Sun at others. Our time basking in the Sun’s glow is our day, and as we rotate out of view of the Sun, day fades to night. Sunrise to sunrise on Earth takes almost exactly the 24 hours that constitute one full day. This is so familiar to us, but it’s not quite so simple on some other worlds.
The Moon’s Rotation (A Day on the Moon)
Assume you go out on a clear night to take a few photographs of the Moon. Should you come back the next night to snap a few more photos, you’ll see the exact same side of the Moon. Phases of the Moon aside, any time you look up at the Moon, you see the same side!
Because we always see the familiar “Man in the Moon”, it seems like the Moon doesn’t rotate at all.
It may come as a surprise to you that the Moon is, in fact, rotating. Interestingly, the Moon takes right around 28 Earth days to complete a full rotation. What’s even more interesting is that it takes the Moon precisely the same amount of time to make one revolution around the Earth.
It’s true; the Moon rotates exactly one time for every revolution it makes around the Earth. The term given such an event is “tidal locking”. This means that the Earth’s gravity pulls so strongly on the Moon that the Moon is stuck looking at us from the same side.
In fact, no one on Earth had any idea what the other side of the moon looked like until 1957, when a Soviet spacecraft took pictures of it.
What Are Days and Nights Like on the Moon?
To anyone hiding out on the Moon, one Lunar day is the same as a Lunar year. A stationary being would either always or never see the Earth, depending on which side of the Moon they are located.
Daylight at any spot on the Moon lasts almost exactly 14 Earth days long from sunrise to sunset. Since the Moon has virtually no atmosphere, the Moon is left without protection from the Sun’s rays during that time. During the Moon’s day, temperatures on the surface are known to 260 °F (127 °C).
In contrast, during the Moon’s 14 Earth days of consecutive night, temperatures really plummet. The surface of the Moon reaches temperatures as low as -280 °F (-173 °C). That’s a massive shift from day to night.
Phases of the Moon
Although we always see the same face of the moon, we don’t always see it in the same light. Sometimes the Moon appears to be full, while other times, the Moon looks only half there. There are even times during an Earth month where we can’t see the Moon even on a clear night.
The answer to this puzzle comes back to how the Sun affects the Moon as it rotates and revolves. As the Moon moves through space around our Earth, its position relative to the Sun gradually changes over its 28-day journey.
Since the Sun, Moon, and Earth don’t usually sit on the same plane in space, whenever the Moon is behind the Earth in relation to the Sun, we see the entire face of the Moon smiling down on us.
When the Moon finds its way between the Earth and the Sun, the side of the Moon we can’t see is illuminated, leaving the Moon appearing dark to us.
As the Moon moves slowly between those two positions over 14 Earth days, we experience the Moon appearing in various shapes. In actuality, the Sun casts its light on a part of the Moon we can see and a part that we can’t.
Is the Moon the Only Tidally Locked Object?
In addition to our Moon, the major moons of Jupiter and Saturn are also tidally locked with their planets. Dwarf planet Pluto and its moon Charon have a bizarre relationship where their respective gravities have them perpetually tidally locked with each other.
As you snap some great shots of the Moon, remember that the face that we see on a clear night is the same never-changing face that our ancient ancestors gazed at. It will be the same one that our distant descendants will someday see. Many things in our lives come and go, but the same face of the Moon will be looking down on us forever.