Okay, the OP has caused me to reconsider an issue.
If we have an orange on a table, the bottom of the orange is the point which touches the table and the top of the orange is the point which is highest from the table. The same is true if you consider something like a person or a building or a tree; the bottom is the part which is closest to the ground and the top is the part which is farthest from the ground. The perspective is set by gravity; the point which is closest to the source of gravity is the bottom and the point which is farthest from the source of gravity is the top.
Now consider the Earth. The gravity of the planet itself isn’t relevant here. The source of gravity which effects Earth’s movement is the Sun. So the bottom of the Earth isn’t the south pole; it’s the point which is closest to the Sun, Earth’s source of gravity. And the top of the Earth is the point furthest from the Sun.
So the top of Earth is wherever it’s midnight and the bottom of the Earth is wherever it’s noon (taking axial tilt into account to determine the subsolar point and its opposite).
If it hadn’t been in England, the Prime Meridian probably would still have passed through somewhere or other in Europe, and pretty much anywhere in Europe would put the 180º line mostly in the Pacific.
Why are you considering the axis as along the side of the planet rather than the top/bottom like a top? Why define the top as the strongest gravitational force on the Earth? If anything, considering that gravity pulls us down and midnight is the start of the day, the antipodes to the Sun makes more sense as “the top” than your definition.
The date line doesn’t have to be at the anti-meridian. You’re assuming the discontinuity has to be at +/-12, but there’s no reason it couldn’t be at -7/-15, if for example the prime meridian was at Washington instead of London.
I’m not saying the axis runs along the side of the planet. The Earth rotates around its axis. What I’m saying is that the axis of rotation is not relevant to defining top and bottom.
To illustrate that, consider a wheel rolling along a highway. That’s rotating around its axis. But we don’t say that the axle is passing through the top and bottom of the wheel.
Defining top and bottom in relation to gravity is the standard usage. Saying we should define the top and bottom of the planet by its rotation is arguing that we should create a special usage that only applies in that one situation.
None at all. The official time on any piece of land is whatever the government of that land says it is. However, in the open ocean, not in anyone’s territorial waters, the IDL defaults to the 180th meridian based on some international agreement.
I would be interested in a cite for that, because while it’s entirely believable that there could be such an agreement, it could also be the case that the International Date Line is merely a de facto boundary between the territory of + countries and - countries. In which case the IDL wouldn’t necessarily have to be a line at all but could be discontinuous. Either possibility would be interesting.
I thought there had been such an international agreement, but on researching it, it seems there wasn’t. The open ocean zones you see on time zone maps are based on the proposals of several people, most notably Sandford Fleming, a Scottish-Canadian engineer, who proposed 24 time zones in 1876.
Does crossing the International Date Line and thereby gaining or losing a day affect legalities such as how much pay sailors have accrued, when tours of duty expire, etc.?
I think the axis is only inclined towards the direction of the sun once a year. Or twice, if you want to avoid being accused of north-hemispherism.
But isn’t the gravity with which the Sun attracts the Earth exactly set off by the centrifugal force caused by the Earth’s orbit around the sun? I don’t see how Earth’s orbit could remain stable otherwise. Therefore the Sun’s gravity force as experienced on Earth is zero and if we used your method there would be no top or bottom of the Earth at all!
All references are a choice. Scientists like to make those choices the most meaningful or useful.
Sometimes that means using a historical reference or standard, especially when the choice is a arbitrary. With rotating systems, rotation is a meaningful choice.
“Top” and “bottom” on Earth are typically defined by the gravity field. But sometimes we use those words differently.
For example, the aforementioned toy labeled a top. Or consider the lid of a canister like a Pringles can. Those type of lids are often called tops.
When discussing the geometry in astronomy, references were chosen with respect to the rotating systems and historical legacy.
The Greeks first defined the world and assigned the directions. They set a East and West by the Sun, and then put North and South in. When making maps, something has to be the top.
Because Europe and China are in the northern hemisphere, either culture that defined “up” would be prone to North, because the Sun moves East to West. Using the Sun would be awkward. Flat maps defined top and bottom.
References to the “top” and “bottom” of Earth follow from that. The globe used maps as the reference.
“Inclined to the direction of the Sun” must mean axial tilt. The Earth’s axis can never point in the direction of the sun. Maybe only Uranus gets pretty close.
That is how I understood it, but the tilt (that is why I wrote “inclined towards”, not “point in the direction of the sun”) is not always pointing towards the sun, it always points in the same sidereal direction, but as the Earth moves around the sun this direction (tilt) points towards the sun only once (or twice) a year.
OK, but I am not 100% certain how to parse that sentence. At any given moment, the Earth’s axis plus the Sun together define a plane, but what is its significance? I guess you are not talking about an equinox, because at that moment the axis is perpendicular to an imaginary line connecting the Earth and the Sun.
I don’t see how the Sun’s motion or the hemisphere of those nations would make either prone to putting north at the top of maps, and in fact, it used to be the norm on European maps to put east at the top (hence “orienting”).