In The Lord of the Rings, Appendix E, Tolkien discusses the tengwar runes that are used in compass roses.
The names of the letters most widely known and used were 17 n, 33 hy, 25 r, 10 f: númen, hyarmen, rómen, formen=west, south, east, north (cf. Sindarin dûn or annûn, harad, rhûn or amrûn, forod). These letters commonly indicated the points W, S, E, N even in languages that used quite different terms. They were, in the West-lands, named in this order, beginning with and facing west; hyarmen and formen indeed meant left-hand region and right-hand region (the opposite to the arrangement in many Mannish languages).
The Lord of the Rings - Appendix E - "Writing and Spelling" - "Note"
As you can see, the directions began with West, and then South and North corresponded with the meanings for right hand side and left hand side.
We can see some related instances to this in Tolkien's writing:The main compass direction is West. This is the direction of Valinor, and Númenor, and has extreme spiritual and cosmological significance.
eldar ataformaiti epetai i hyarma ú ten ulca símaryassen úsië, an cé mo quernë cendelë númenna, ve senya i hyarma tentanë Melcorello ar cé mo formenna tentanes Amanna
The Elves were ambidexters; consequently, the left hand was not to them evil in their imaginations. On the contrary. For if one turned the face westwards as was usual, the left hand pointed away from Melkor (in the North), and if northwards, it pointed towards Aman (the Blessed Land).
The Nature of Middle-earth, Part 2, Chapter 3, "Eldarin Hands, Fingers and Numerals" (and also Vinyar Tengwar No. 49.)
As to how anyone would know which way West was, we can look at the etymology of the words. Númen, "West", is associated with sunset, and Rómen, "East", is associated with sunrise.The elvish words for West and East are also related to the motion of the Sun. Númen, "West", is associated with sunset, and Rómen, "East", is associated with sunrise.
[Númenor] is a construction from the Eldarin base √NDU 'below, down; descend'; Q. núme 'going down, occident'; númennúmen 'the direction or region of the sunset' +nóre 'land' as an inhabited area. I have often used Westernesse as a translation.
September 1965 Letter to Dick Plotz - Letters of JRR Tolkien #276
- andúnë ‘sunset, west’ in Andúnië, to which corresponds in Sindarin annûn, cf. Annúminas, and Henneth Annûn ‘window of the sunset’ in Ithilien. The ancient root of these words, ndu, meaning ‘down, from on high’, appears also in Quenya númen ‘the way of the sunset, west’ and in Sindarin dûn ‘west’, cf. Dúnedain. Adûnaic adûn in Adûnakhôr, Anadûnê was a loan from Eldarin speech.
- rómen ‘uprising, sunrise, east’ (Quenya) in Rómenna. The Sindarin words for ‘east’, rhûn (in Talath Rhúnen) and amrûn, were of the same origin.
The Silmarillion - Appendix "Elements in Quenya and Sindarin Names"
With West as the main compass direction, North and South follow as Right and Left.
The names of the letters most widely known and used were 17 n, 33 hy, 25 r, 10 f: númen, hyarmen, rómen, formen=west, south, east, north (cf. Sindarin dûn or annûn, harad, rhûn or amrûn, forod). These letters commonly indicated the points W, S, E, N even in languages that used quite different terms. They were, in the West-lands, named in this order, beginning with and facing west; hyarmen and formen indeed meant left-hand region and right-hand region (the opposite to the arrangement in many Mannish languages).
The Lord of the Rings - Appendix E - "Writing and Spelling" - "Note"
[Quenya:] eldar ataformaiti epetai i hyarma ú ten ulca símaryassen úsië, an cé mo quernë cendelë númenna, ve senya i hyarma tentanë Melcorello ar cé mo formenna tentanes Amanna
[English:] The Elves were ambidexters; consequently, the left hand was not to them evil in their imaginations. On the contrary. For if one turned the face westwards as was usual, the left hand pointed away from Melkor (in the North), and if northwards, it pointed towards Aman (the Blessed Land).
The Nature of Middle-earth, Part 2, Chapter 3, "Eldarin Hands, Fingers and Numerals" (and also Vinyar Tengwar No. 49.)
- North points towards the Big Dipper
- South points to the sun
- West points to the Pelóri, the Mountains of Valinor (see this painting of Mount Taniquetil, made just one year earlier)
- East points to the Gates of Morn, where the sun emerges from every morning, (described in the Book of Lost Tales as "a great arch ... all of shining gold and barred with silver gates")