OLN.D | The Moon

On most clear nights, the easiest thing to see when you look up is the moon.

Like Earth, the moon has a rocky crust, mantle, and core. Unlike Earth, the mantle and core of the moon are both cold, and the moon’s atmosphere is very thin and can’t support human life. While the Earth’s atmosphere is made up of mostly nitrogen, some oxygen, and a few other elements, the moon’s thin atmosphere consists of some pretty surprising elements, like potassium and sodium. Neither earth, nor Mars or even Venus has those elements is their atmospheres.

Many scientists think that the moon was formed out of the debris left over from a collision between Earth and an astronomical body the size of Mars approximately 4.5 billion years ago.

It’s common knowledge that Neil Armstrong was the first person to walk on the moon in 1969; fewer people realize that since Armstrong took his giant step, eleven more people followed.  Of those dozen walkers, none of them ever did it more than once.

The most recent moonwalk was in 1972, by Jack Schmitt and Gene Cernan. Before he left the Moon, Cernan scratched the initials of his daughter Tracy into a rock on its surface. Since the Moon does not experience weather conditions like wind or rain to erode anything away, her initials will probably stay there for quite a while.

Even though there haven’t been any human visitors since then, that doesn’t mean there’s nothing happening on the moon.  In 2019, China successfully landed the first rover on the dark side of the moon.

By the way, the dark side of the moon gets just as much sunlight as the side that faces Earth.  We call it the dark side because we never see it from here on Earth, because of the way the moon rotates.

The moon is our closest neighbor, but it’s still pretty far away from us. If you think a flight from Argentina to China takes a long time, try flying to the moon. When you’re flying across our globe in a commercial airliner, you’re usually travelling at around five-hundred miles an hour, (that’s about 800 kilometres an hour). When you travel to the moon in a spaceship, you’ll be going 17,000 miles an hour, or 27,350 kilometres an hour – and it will still take you three days just to get there!

Another interesting thing you’ll notice is that when you’re closing in on the moon, if you call home to see if someone’s fed your pets, you’ll notice that it takes just a little longer for you to hear the answer come back. That’s called a Communication Delay, and it happens because radio waves travel at the same speed as light, which while incredibly fast, does still have a speed limit. In fact, it IS the speed limit since nothing goes faster than light, so radio waves can only get to the moon as fast as light does.

So just how fast is light?

Light travels at 186,282  miles per second – it’s the fastest thing there is – but it still takes 8.3 seconds for the light from the sun to reach Earth. I’ll save you the math – the sun is right around 150 million kilometres away – that’s 94 million miles.  So if it takes 8.3 seconds for light (or sound) to get from the sun to the Earth, that’s how long the Communications Delay would be if you called home from the Sun. Calling home from the moon takes about 1.4 seconds – it’s not a long delay, but it isn’t  instantaneous, either.

But we’re not ending our journey here; next we’re going to use the moon’s gravity to give us a bit of a boost in speed by doing a kind of slingshot, also known as a “gravity-assist maneuver.”

A gravity assist maneuver works like a discus throw in the Olympics. The discus thrower twirls around a couple of times before letting go his discus so that it will fly farther, instead of just throwing it straight out without the momentum of his turns behind it. By flying around the moon before heading out, our ship is like the discus, and our momentum comes from the Moon’s gravitational strength.

But you’d better have finished your phone call before you get around the other side of the moon, because as soon as you do, your call is going to drop. That’s because the moon is now between you and the communications devices on earth and in orbit around it. This blackout happens because radio waves move in a straight line; if there’s something between the sender and the receiver, the signal is blocked.  It’s why we keep communication satellites in orbit around the earth. The orbiting satellites give ‘line-of-sight’ access to our ground communications, so we can talk to anyone on earth regardless of our own line of sight on the surface of the earth.

In a little less than an hour, we’ll be around the other side of the moon and travelling toward our next destination. In the next lesson, we’ll visit Venus and examine what makes it such a beautiful but dangerous place, and then it’s on to Mercury and a close pass by the star at the centre of our neighbourhood!