Full Moon day — the Moon appears as a fully bright circle.
New Moon day — the Moon isn't visible at all.
Growing (Shukla Paksha) or shrinking (Krishna Paksha) — a full cycle takes about a month.
The Moon's cycle only — drifts from the seasons over time.
Earth's orbit, with leap years — stays synced with seasons.
Both, with an extra month added periodically to correct drift.
Diwali and Holi follow lunar or luni-solar calendars, so their dates change each year.
Makar Sankranti, Pongal, and Vaisakhi follow a solar calendar — nearly the same date every year.
The Moon appears as a full bright circle.
The Moon isn't visible at all.
Bright portion growing / shrinking.
Based only on the Moon's phase cycle.
Based on Earth's revolution around the Sun.
Combines both, with a correction month.
A year with an extra day to stay synced with the seasons.
A human-made object launched to orbit Earth.