Matariki is a heliacal tradition
As Earth moves around the Sun throughout the year, our vantage point from which we look at the night sky changes as little as almost one degree of arc per day.
Some celestial objects are on the same line of sight as the Sun. These are mostly the stars from the zodiacal constellations. They are a band of stars that are about 8 degrees each side of the path of the Sun (the ecliptic) and of course our planets and Moon.
The Pleiades are in the zodiacal constellation of Taurus. For about two months a year, any stars from the zodiacal band disappear behind the glare of the Sun. For the Pleiades, this happens between approximately the 15th of April and 15th of June.
Just after mid-June, the star cluster the Pleiades reappears on the eastern horizon and is visible for a short amount of time in the pre-dawn sky, very close to the Sun. They will be visible 4 minutes earlier every day and further and further from the Sun.
Before the 15th of June, as observed from Aotearoa, The Pleiades are not visible in the morning sky with the naked eye.
Matariki will still be in the sky after sunrise, but the Sun washes out the light from all other objects in the sky. The heliacal rising of Matariki lasts for about a month, during which time the New Year is also observed.
The heliacal rising of the stars of Matariki, combined with the sighting of the Moon, marks the beginning of the Māori New Year.
Even though Matariki is heralded by the Sun (Tamanui Te Rā), the New Year (Te Tau Hou), is calculated by the phases of the Moon (Marama).