What it is
The Moon sign is the zodiac sign the Moon was in at the moment you were born. The Moon moves quickly — it changes sign roughly every two and a half days — so unlike the Sun sign, your birth date alone is not always enough. If you were born on a day the Moon changed signs, the birth time decides it.
In astrological tradition the Moon stands for the inner weather: how you respond before you think, what soothes you, how you care for others and want to be cared for. Where the Sun describes what you reach toward, the Moon describes what you retreat to.
Because the Moon is so fast, it is also the most personal fast-moving point in a chart. Two people born the same week share a Sun sign; their Moon signs may differ completely.
Why it matters for daily reflection
Most of daily life happens at Moon level: irritation before coffee, the urge to call someone, the restlessness at nine in the evening. A Moon sign gives you a frame for those small movements. A Cancer Moon may notice that a bad day gets better after cooking for someone; a Gemini Moon may notice that it gets better after talking it through.
The point is not that the sign causes the feeling. The point is that naming a tendency makes it easier to catch in the act — and to ask whether it is serving you today.
In Lunara
Your natal Moon sign is part of the basic chart in Lunara's free tier. Each day, Lunara reads today's Moon — its sign and phase — against your birth chart to compose one personal Signal, so the relationship between the sky's Moon and your own Moon is at the heart of the daily loop. The Moon sign needs no birth time unless the Moon changed sign on your birthday.