Vedic astrology is based on the Moon and the shifting of the Zodiacs as we view them on Earth, while Tropical astrology is based on the journey of the Sun and Earth over a year.
This is why the Vedic astrological New Year begins with Aries in April, and why Tropical Astrology starts in March as The Moon moves differently to the Sun through the Houses (and Rooms)!
A fair amount of astrologists base their understanding of Zodiacs and the Moon from a Western understanding as they base it on where the Sun and Earth are and continue through the rest of the chart even though the Moon is calculated differently in Vedic Astrology and is actually pushed forward.
There’s a lot of discourse about when a New Moon and Full Moon occurs with placements, and this is explained by understanding that it is only a New Moon when the Sun, Moon, and Earth are lined up in the same Zodiac and House in that order, and a Full Moon only occurs when the Sun, Earth, and Moon are in a line as well!
Some scholars discuss how Vedic is Sun based which is most likely a mistranslation by western scholars as Tropical Astrology focuses on the Sun as the main and it was developed from the Greek understanding of the Sky, and Vedic came from India and the focus is on the Moon as the Moon is the most important sign in your chart in Vedic Astrology.
An example of the New and Full Moon is that when Western Astrologists mention that a New Moon in Gemini is this month while the Sun is in Cancer, it is not a New Moon as the Sun and Moon are not lining up and the Moon must be completely hidden for a New Moon to occur.