Of the Swordsman and the Mariner by Fuin  

… a loremaster’s notes on the stars and Dagor Dagorath

The loremasters reckoned that Dagor Dagorath would come upon Arda in winter, when Menelmacar, the Swordsman, looms high in the sky, a prophecy of hope amidst ruin set into the stars.

But alas, he who brings hope to others may yet not feel it in his own heart. Thus some also said that Varda Elentári bade Telumendil, Lover of the Heavens walk by the Swordsman's side—a companion to guide him on the path of stars stretching from horizon to horizon.

Of Eärendil the Mariner the loremasters told that he would gather lights about him to shine alongside the Silmaril upon his brow like the links of a chain in the sky. As a gleaming front line they should stand against Melkor's darkness.

Five stars soaring side by side would be seen by mortal Men: Elemmírë to the left of Eärendil's Light, and to his right red Carnil and bright Alcarinquë and Lumbar adorned with rings. But by the Eldar and those scholars of Men who gaze at the night sky through great lenses revealing the secrets of the depths of Eä, seven stars are seen, for faint Luinil and Nénar up high in the heavens cannot be perceived by Men's eyes alone.

Eärendil and his star-guardians would then fight Melkor in the heavens, and they would cast him down to the ground. This would mark the beginning of Dagor Dagorath.

Then, on the plains of Valinor, Light will meet Darkness in the Last Battle, until Túrin Turambar with his reforged black blade shall slay Melkor. This will be the end of Dagor Dagorath.

Thereupon, the Silmarils shall be broken and the Light of the Trees renewed, and joy shall return to all hearts in the year-long celebration of victory.