# A Quick Science Question

How would Magellan measure latitude if the sky were filled with clouds all the time? I’m thinking of measuring Coriolis effect, but I’d hate to dive into that if there’s a more obvious answer.

## 13 thoughts on “A Quick Science Question”

1. “Latitude was measured in the past either at noon (the “noon sight”) or from Polaris, the north star (assuming it is sufficiently visible above the horizon, which it may not be in the Southern Hemisphere). Polaris always stays within 1 degree of the celestial north pole. If a navigator measures the angle to Polaris and finds it to be 10 degrees from the horizon, then he is about 10 degrees north of the equator. Angles are measured from the horizon because locating the point directly overhead, the zenith, is difficult. When haze obscures the horizon, navigators use artificial horizons, which are bubble levels reflected into a sextant.”

… is what i found.

• Thanks!

But… to state my question a little more clearly, how do you determine latitude if you can’t see the sky?

2. Sheesh, thanks for being called onto a cobwebby carpet. There is a sine(lat) part of the acceleration due to coriolis but I think it would be too tiny to be measured by someone in Magellan’s age. Also, the ship would not move far enough in a short enough time for coriolis to significantly show itself over other forces. Currently, my best answer is Magellan is s.o.l.

• So far my solution is land-based, but that’s OK for my story. I’ve got the lads hauling a monstrously heavy portable Foucault pendulum which they can set up and measure the rate of precession. They also have to carry a huge tent to keep the wind off the pendulum during measurements. The weather is going to be continuously bad.

Jesse – I might have some more meteorological questions as I fiddle with this idea I mentioned a while back.

3. How far away from the poles would these folk normally wander? If their natural range is limited enough, you’d have a situation like the Mediterranean Sea — a constrained navigable area in which knowing your latitude isn’t really helpful:

And if the characters do frequently wander far enough from the poles to make latitude useful, it seems like a compass would come in handy.

It seems like this would be a really windy world, with the atmosphere handling massive heat transfer.

• It is a really windy world – I’m imagining a temperate area at the top in a relatively calm zone, surrounded by a permanent storm – they’re basically in the eye of an eternal hurricane. The storm feeds a rainforest that gives out to vast algae swamps and other primitive oxygen-producers farther south, with water from the endless rain flowing back south to where the ocean is boiling at the equator.

• Oh, to reply to your question, normally they don’t wander so far, but this is a scientific expedition to see what’s out there. The military commander of the mission also wants to see if there’s any conquering to do at the south pole. He might just be a little crazy (or is it just the heat)?

4. Focault pendulum, check. If you get tired of that, by pure serendipity I ran across this today in my January issue of scientific american:

“The geomagnetic field’s inclination varies continuously […] south pole it points straight up, whereas at the north pole it points straight down; […] halfway along it is horizontal. An ordinary compass […] cannot measure the field’s inclination, responding only to the side-to-side component. Birds can do better and probably use inclination to roughly estimate their distance from the magnetic poles.” — from the article The Compass Within pp. 48-53.

There ya go… you just need a wizard with a robin familiar who speaks, and tells him how far he “feels” he is from the poles. Then again, if you’re not writing a fantasy, then I default to my earlier best guess – s.o.l.

• Right now I’m thinking that they don’t have compasses, since they’ve never been far enough south for them to work well. The more I think about it, though, I figure that if they have a faucault’s pendulum they are probably aware of their planet’s magnetic field.

Hm… instead of northern lights, they’d have outer lights, since the lights form a ring around the pole as well.

• Why assume that the magnetic poles are closely aligned with the axis of rotation? Just for fun you could have your planet be in the midst of pole shift, with lots of poles.

• If there were something about the pole shift that created the conditions that made the expedition possible, that would be cool. Otherwise it might eat into my coincidence capital. Something to think about.

• If the magnetic pole shifted out of the polar inhabitable zone, some genius might discover the usefulness of a compass.