What is Due East?

[TacomaSailor]

I thought I understood a bit about long distance navigation but the following question/answer on “Who Wants to be a Millionaire” has me puzzled:

If you head due east from New York City where will you hit land?
- Ireland
- Lisbon
- Senegal
- Norway


Heading Due East to me says “stay on the same line of latitude” so my answer was Lisbon because NYC is at 40N and Lisbon is at 38N.

The TV show said the answer was Senegal, which is at 24N.

Using Visual Suite Bearing and Distance from NYC:
Lisbon is at a heading of 65T and Senegal is at a heading of 90T.

How can one stay on the same line of latitude (40N) and traverse a bearing of 65T?

How can one head Due East from 48N and end up at 24N?

What very fundamental fact of navigation am I missing?

[Shrew]

Are you accounting for Magnetic Declination? "Due" is in reference to the compass bearing, not the geographic North Pole.

[boatman61]

Well.. they reckon the Earth is between 16-19degrees off vertical at present so get a chart and steer 106* and see where you end up..

[barnakiel]

Due East is not a scientific term and you can define it for yourself or use google on it and see what others think.

If you move your finger ON A CHART due East you will end up at the same latitude, while if you follow the magnetic compass you will sail or fly a weavy course and end up elsewhere. But maybe your compass is a gyro ... etc.

In navigation you place a letter somewhere close to the figure, so all ambiguity is removed 090T. Etc.

A valid question and well asked too. Thx for bringing this up!

b.

[TacomaSailor]

When I use the Range/Bearing tool in Visual Suite to go Due South from NYC (following the 24W longitude line southward) I am also heading on a bearing of 180T.

It appears Due South and 180T are equivalent, unlike what I found with Due East and the True compass bearing of 65 -vs- 90.

I am so confused?

[Dsanduril]

The adverb form of "due" is defined as "directly or exactly", so "due east" is exactly or directly east, with no reference to magnetic or true, so you get into an argument about what it means when you say "east". I say that would normally be true (not magnetic).

The exact same question here says you end up in Portugal (as you expected).

But, your Visual Suite is correct when calculating a great circle route. The initial bearing from NYC to Lisbon is 65T, taking you NE, and your final bearing into Lisbon is ~110T. This will get you there in the shortest travel, but maintaining a constant course of east will also get you to Lisbon.

The initial bearing NYC-Senegal on a great circle is indeed east, but it doesn't stay that way long.

[denverd0n]

Originally Posted by barnakiel

Due East is not a scientific term...

Exactly. So, it is perfectly reasonable to say that going "due east" means following a line of latitude. It is also perfectly reasonable to say that going "due east" means going straight along the 90 degree line of a compass. And we could probably come up with several other, perfectly reasonable, definitions of the term. There is no one, official, universally-accepted meaning to "due east."

Which, of course, means that it is a pretty stupid term to use in a game show, unless they also define exactly what they mean by "due east."

[StuM]

It all depends on how you interpret "head due east from".

Do you follow that Great Circle that passes through NY at 90°T or do you maintain a constant bearing?

If you head due east from New York City and continue on the Great Circle, you end up in North Africa (you need to constantly change your bearing to follow the circle)If you head due east from New York City (90°T) and maintain that bearing, you end up in Spain.

IOW, there is no single correct answer.

[StuM]

Originally Posted by TacomaSailor

When I use the Range/Bearing tool in Visual Suite to go Due South from NYC (following the 24W longitude line southward) I am also heading on a bearing of 180T.

It appears Due South and 180T are equivalent, unlike what I found with Due East and the True compass bearing of 65 -vs- 90.

I am so confused?

Due East and 90T are also equivalent - if you are on the equator

[MarkJ]

I'd say they weren't ready to pay the extra premium on the insurance for the $1M payout.

Definitely a trick question.

Sent from a stupid phone that replaces words with weird stuff.

[Dsanduril]

And "due east" from NYC using a magnetic compass doesn't land you in either place, the current magnetic declination in NYC is 13W, so a heading of E or 90 on a compass lands you at a heading of 77T. Which on a constant bearing lands you in France, and on a great circle lands you someplace like Gibraltar.

[Dsanduril]

Originally Posted by TacomaSailor

When I use the Range/Bearing tool in Visual Suite to go Due South from NYC (following the 24W longitude line southward) I am also heading on a bearing of 180T.

It appears Due South and 180T are equivalent, unlike what I found with Due East and the True compass bearing of 65 -vs- 90.

I am so confused?

Remember, lines of longitude are all great circles by definition. That's why they appear as "wedge" shaped on a Mercator projection, because they are equi-angular from the prime meridian.

Lines of latitude, on the other hand, are equi-distant from the Equator, rather than equi-angular.

[El Pinguino]

'Lines' of longitude appear as straight lines in mercator projection which is why Greenland looks so big on a map or chart of the world.
Mercator projection allows rhumb lines to be plotted directly onto the chart while distorting land masses.

[carstenb]

certainly a trick question (i would have answered lisbon also). I would contend that unless given more information, "due east" should be defined in regards to magnetic north (a compass being the only way we have of determining direction).

One could argue that "due east" because of the use of the word "due" refers to true north and I might accept that argument - but great circles can't be brought into the discussion IMHO

[El Pinguino]

I think it is a poorly framed question.. however...

Lets see what happens if you sail 'due east' by compass.
We have to ignore deviation here.
Let us accept that you leave NY with variation of 13W...so 090 on your compass you will see you steering 077 true..... 'error west, compass best'

Unfortunately variation is westerly all over the north atlantic so if you maintain a course of 090 by compass you are going to end up in Iceland or somewhere up that way.

So we can't explain it that way....

Variation or - if you must - declination can be seen here https://upload.wikimedia.org/wikiped...ation_2015.pdf