nm
(I read that wrong.)
Well, magnetic declination is a completely different issue. Imagine that you had a magic compass that always pointed to the geographic north pole, you will still have to continuously change your bearing in order to follow a great circle route.
Yes, many people underestimate just how much water there is - particularly in the Pacific. I’ve always found the concept of the Water hemisphere and Land hemisphere very interesting.
I wonder if the aliens came by years ago and thought “No one could live on that planet. There isn’t enough land.”
There is a way the rotation does influence our perception of the time consumed in travel: unless you cross the IDL, if travelling East a long distance, you arrive at a later numbered hour of civil time than you’d expect from just adding departure hour + flight time, and conversely if you travel West (unless you’re flying supersonic, where you can “catch up” to the rotation).
Very cool. Here’s a screenshot of my water world. The pin is Bora Bora.
Then I don’t understand what you mean by “change your bearing”. You mean something like “make a left turn”? Because that’s not how it works. The ‘curved’ path is a straight line. There’s no turning involved in following a great circle route.
I think he means change the bearing relative to magnetic north.
No, relative to geographic north, and that’s true. Most straight-line courses will change their bearing with respect to geographic north, magnetic north, or any other arbitrary reference point you put on the globe, as you continue on course.
Right. I missed the part about the compass being magical.
I don’t know how it was done back in the day, but I have an educated guess. When we make oceanic crossings, we keep a paper chart with of all of our waypoints plotted on it. For a north Atlantic crossing, we will typically have a waypoint at each fifth degree of longitude. We keep our paper chart updated with our current position in case we lose all forms of long range navigation and have to dead reckon (heading + wind = ground track) along our planned route back to landfall. Let’s say we have two waypoints along the same line of latitude and five degrees of longitude apart. The initial eastbound heading might be 088. Halfway along the leg, the heading will be 090. When we arrive at the second waypoint, our heading will be 092. Had we flown 090 the whole time, we would have ended up in the same place, but it would have taken slightly longer. So we can take the headings from the mid points of each “short” leg and use them one after another to approximate a great circle route in a crude manner. If everything goes to plan, the flight guidance computers will constantly update our heading to account for this, as well as correcting for the actual winds. Our long range nav equipment is certified to guarantee us to be within 4 nautical miles of a given point 95% of the time. In reality, the five independent nav sources on my airplane typically agree to within a few feet.
To answer your question, I would think that a once-an-hour check would be sufficient on an airplane only moving at 200-300 knots, but back then airplanes carried navigators. His whole entire job was to tell the pilot what heading to fly, so my assumption would be that he had nothing better to do than to recalculate the winds and the estimated time for the next 1 degree heading change over and over again.
That is amazing, isn’t it? I wonder why that is not the water hemisphere rather than the one I see on Wiki? That is half the globe, right?
Not really a complete hemisphere because of perspective. (You’re seeing the Earth from a finite height.) It’s close, though. You’d have to be infinitely far away to see half of a sphere. Here, I’ll zoom way out to give something approaching a true hemisphere and then scale up the resulting image. Like this. Still pretty watery.
Thanks. That’s exactly what I was looking for.
People should see this view more often. The Pacific is often underestimated in size.
There is no turning but your bearing is changing constantly. You might start out flying NW, then WNW, then W, WSW and then finish on a SW bearing. That’s pretty much the definition of a great circle route.
I believe I stumbled upon that view on day while looking for the island in Cast Away. (The filming location, not the fictional island.) It was then I realized how much was the Pacific and I started playing around to see how big I could make the ocean.
I think they needed to do it constantly, in their heads. Mental math required effort, back in the day.
Weren’t there some of those circular slide rule type devices back then to help with that?
I should have checked wikipedia first. Article on great circle navigation.