Why Time and Location Change the Result
Your sun sign only depends on the date - the sun spends about a month in each zodiac sign, so it's stable across an entire birthday. The moon moves much faster, changing signs every two to two-and-a-half days, so its position depends on the specific date and, near a sign boundary, the time of day. The rising sign moves fastest of all - roughly one degree every four minutes, a full sign every two hours - and it isn't about a planet's position at all, but about which point of the zodiac was crossing the horizon at your exact birth location. That's why it needs both a precise time and a precise place, while the other two don't.
Frequently Asked Questions
How accurate is this birth chart calculator?
Sun and moon sign results are accurate to well within a degree, which is more than enough to place them correctly except in the rare case of being born within an hour or two of a sign change - the tool flags that when it happens. The rising sign depends on precise astronomical formulas for sidereal time and the ascendant, and is accurate as long as the birth time and coordinates entered are accurate.
Do I need to know my exact birth time?
Only for the rising sign, which changes roughly every two hours and is highly sensitive to birth time - even a few minutes of error can shift it into a neighboring sign. Sun and moon signs are far less time-sensitive; a birth date alone is enough for the sun sign, and a date plus a rough time is enough for the moon sign in most cases.
Why does my rising sign need a birth location but my moon sign doesn't?
The moon and sun's zodiac positions at a given moment are the same no matter where on Earth you're standing. The rising sign is different: it's defined by which point of the zodiac is crossing your local eastern horizon at your birth moment, which depends entirely on your latitude and longitude as well as the time.
Is my birth information stored or sent anywhere?
No. Every calculation on this page runs in your browser using JavaScript - nothing about your birth date, time, or location is transmitted, logged, or stored anywhere, including by this site.
What if I don't know my exact birth time?
Check "I don't know my exact birth time" and the calculator will still give you a sun sign and an approximate moon sign based on midday on your birth date. Your rising sign can't be calculated without a time, since it depends on the exact moment the sky was facing at your birth location.