In the last two blog, Ahab and Ernest looked closely at charts, as well as longitude and latitude [link to blog post]. This lesson, Ahab continues by looking at the compass and the magnetism of the North Pole.
“So, Ernest, whilst the kettle boils, give me a quick re-cap of the main points you have learnt so far”.
“Right… well… latitude are hoops going around the earth, longitudes are semi-circle that run from pole to pole, a chart is a map of the sea and you also taught me about a three-point fix and course-to-steer” Ernest replied.
“Great! It’s all sinking in then?”
“But can we sail now?”
“Soon, Ernest, soon, there are few a few other things I want to talk about first before we set off into the big blue yonder. Mainly the compass and a small anomaly that confuses many people” said Ahab, juggling the hot tea Ernest had just given him.
“Oh yeah. What’s that?”
“Magnetic north and true north”.
Ahab knew that the silence meant Ernest was desperately trying to figure how there could be two norths. “But, there is only one North Pole,” said Ernest pointing in what he hoped was the direction of north. It wasn’t but it wasn’t far off.
“What’s this?” asked Ahab, brandishing a compass before Ernest.
“Great! What does it do?”
“It points in the direction you are facing, so north, east, south and west.”
“And how does it work?” At this question, Ernest looked slightly more confused. “Ummm…”
“Think Ernest. What is it about the poles that make them special, the north and the south?”
“Magnetic! They are magnetic!” Triumphant, Ernest opened the chocolate covered biscuits and thought he was onto a winner with this lesson.
“Is that true or magnetic north it points to?” asked Ahab, reaching over for the biscuits before Ernest scoffed the lot. “Be careful, that could be a trick question”.
“No idea. I didn’t know there was two.”
“Right, listen carefully because I’ll be asking you questions,” said Ahab. Drawing a deep breath, he started on the explanation of the difference between true north and magnetic north.
“Magnetic north you have identified as the one that the compass points to but that is not the North Pole. The place where all the flags are where people risk life and limb crossing the vast open white landscape is the North Pole and that is known as true north.
Magnetic north is, as you quite rightly say, the place where the compass points and that is not the same place. Magnetic north moves and that means we need to bear that in mind when we use our compass.
But don’t worry, the concept of true or geographic north and magnetic north can be confusing but I can guide to a fantastic geography website to read some more”.
“So, which north do we use when we sail. Do we head to that one or that one?” asked Ernest flaying his arms in all directions.
“Drink up and I’ll tell you…”