Nakshatra
The Moon’s path divided into 27 mansions of 13°20′ each. The Moon covers about 13° a day, so it usually crosses one mansion per day.
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Enter on My MapJyotisha measures the sky against where the stars actually are. The slow wobble of the Earth’s axis (precession) is subtracted with a value called the ayanamsa, so a birthday that reads as one Western sign often lands one sign earlier here. This page uses the Lahiri ayanamsa of the Indian national calendar.
The Moon’s path divided into 27 mansions of 13°20′ each. The Moon covers about 13° a day, so it usually crosses one mansion per day.
The zodiac divided into twelve. The tradition leans on the Moon’s rashi rather than the Sun’s, so that is asked for first.
The lunar day: the gap between Moon and Sun cut into 12° steps, fifteen while the Moon waxes and fifteen while it wanes.
They simply fix their starting point differently. The West pins 0° to the spring equinox; India keeps it on the stars. The two are about 24° apart today, which usually shifts the sign by one.
Yes, for nakshatra and rashi. When the Moon crosses into the next mansion during that day there are two candidates, and both are shown rather than one being chosen for you. Pada, tithi, yoga, karana and lagna need the time.
The ascendant is the sign rising on the eastern horizon at that moment, so it depends on where you stood. The same clock time in another city gives a different sign.
These results are a calculation within a traditional symbolic system; they do not determine character or the future.