In Makemson I find inspiration:

"Whanui, Great Space, as Vega was known to the Maori, was a whetu-rangatira, 'a star of high rank', being exceeded in brightness only by Sirius and Canopus among the fixed stars. Seen rising on the northern horizon in March Vega governed the time of digging the valuable sweet potato crop and also provided suitable omens for a lean or fat season as the case might be.

A Maori sage explained the function of Vega as follows:

Another important star is Whanui, whose address to the people is, 'O friends! Here am I, Whaka-koro-ngata. Awake and rise! Seize your spades and to work! Store the crops in the pits; then turn to rejoicing and sing your chants of joy; for all women and children are now joyful. There is naught to disturb their happiness!'

The office of Vega in providing the sweet potato was explained by a curious story. In one version Vega was the father of the tuber while Pani-tinaku was the mother. Pani was the wife of Rongo-maui, a young relative of Whanui's. When Whanui refused to part with his sweet potato children and bestow them on mankind, Rongo-maui stole them away and transported them to earth. After that Whanui sent the boon of kumara to men each year, but he made them suffer for Rongo-maui's theft by afflicting them with three kinds of caterpillar which preyed on the sweet potato vines.

If Vega at rising appeared to move slowly it was a sign of tau kai, a fat season: if the star appeared to move quickly 'as though borne forward on the wind', there would ensue a season of scarcity.

During the ninth month, February-March, under the guidance of the star Altair - Poutu-te-rangi, Pillar-of-Heaven - pits were dug in readiness for storing the sweet potatoes which would be removed from the ground the moment Whanui made his appearance in the northeastern sky before dawn."

On Easter Island sweet potatoes were planted beginning in February (though also, it seems, in September):

The explanation of Tehetu'upú as related to 'a lot of stones (pu)' suggested in Barthel 2 is interesting. I have instead imagined the month name to mean Te Hetu'u Pú = The Star Hole, i.e. the season when sun is making himself ready for going. He will of course return next year, but that is another 'generation'.

The main month for planting sweet potatoes is Vaitu nui. When sun goes 'into the earth' also the sweet potatoes should follow him down.

But Vaitu nui lies at the beginning of the journey of the kuhane (Nga Kope Ririva and Te Pu Mahore). This implies that the kuhane is landing around autumn equinox, when the sweet potatoes and the sun is going into the earth. The location of Vinapu further on (between Te Kioe Uri and Te Piringa Aniva) at winter solstice is in agreement. The year begins beyond autumn equinox in Vaitu nui.

The calendar starts, however, with He Anakena, and Anakena is at the other end of the kuhane journey. If autumn equinox lies before (or at the beginning of) Vaitu nui, then the end of summer must be at He Anakena.

The geography, furthermore, indicates Poike in the extreme east as the point where sun makes his turnaround from growing (following the southern coast in the same direction as the moon and the kuhane) to waning (going towards the west).

Although it is easy to draw the conclusion that we must go straight north from Vinapu to find the opposite of winter solstice it is wrong. We must move with the kuhane until we come to the end of the 1st half of the year = the end of the island in the east.

The south coast is longer than the north coast, which explains why there are 8 months from Nga Kope Ririva to Poike. The north coast has 4 months only.