What is a natal chart?

A natal chart is a map of the Solar System as seen from one place at one moment. You supply three facts: a birth date, a clock time, and a geographic location. From those inputs a calculator derives each planet’s ecliptic longitude, the degree that was rising in the east (the Ascendant), and a twelve-house division of the local sky. SideraChart is that calculator: tropical zodiac, Placidus houses by default, positions from a VSOP87-class ephemeris via astronomy-engine.

The chart is a diagram of accents, not a verdict. Each planet is a function. Each sign is a style of that function. Each house is a department of life where the function shows up. Aspects are the angular distances between those functions. Read together they tell you which parts of the chart are loud. They do not tell you whether to change jobs, leave a relationship, or take a medical decision.

Date sets which day of the Earth’s orbit you were born on, which is enough for the Sun and the slow planets to land in the correct sign. Time converts civil clock time to Universal Time with the IANA timezone rules that were in force on that date, including historical daylight-saving. Place supplies latitude and longitude so the local horizon — and therefore the Ascendant and the house cusps — can be computed.

If the time is unknown, you still get planetary signs. You do not get a reliable Ascendant or a house system. SideraChart lets you mark time as unknown and then draws planets only. Guessing noon and treating the houses as fact is worse than an honest gap. If a birth certificate has a time, use it; if relatives disagree by half an hour, treat the Ascendant as provisional.

Planets (Sun through Pluto, plus the Moon) sit on the ecliptic. The sign is which 30° slice of the tropical zodiac that longitude falls in. The house is which local sector that longitude falls in once the Ascendant is known. A planet in Aries in the tenth house is not the same statement as a planet in Aries in the fourth: same style, different department.

Aspects are the named angles between two longitudes: conjunction (0°), sextile (60°), square (90°), trine (120°), opposition (180°). SideraChart draws those five with orbs of 8° for conjunction and opposition, 6° for square and trine, and 4° for sextile. Tighter orbs read louder. The wheel’s coloured lines and the table under it show the same contacts.

A natal chart is not a daily horoscope column written for twelve Sun signs. It is not Vedic or sidereal astrology, which measures from a star-based zero point about 24° away from the tropical equinox today. It is not Chinese astrology. SideraChart does not compute those systems and does not use Swiss Ephemeris.

It is also not a personality quiz that outputs a type. Two people with the same Sun sign can have different Moons, different rising signs, different house emphasis and different aspect patterns. If you only know the Sun, you have one coordinate. The chart is the rest of the coordinate system.

SideraChart resolves the birthplace to latitude and longitude, converts local clock time to Universal Time, then reads apparent tropical longitudes from astronomy-engine (VSOP87-class). The tropical zodiac starts at the March equinox, which is the Western convention. Sidereal longitudes are not shown. Houses default to Placidus because most published Western texts assume it; Whole Sign is available when you need equal signs from the Ascendant’s sign.

Placidus divides time of ascension, so houses are uneven, and it becomes unreliable above roughly 66° latitude. For polar births, Whole Sign is the more honest grid. Planetary longitudes are computed either way. Save the chart if you want the written report and the daily cabinet; the public calculators stay free without an account.

Start with the Big Three: Sun, Moon and rising. Then read occupied houses, then the tightest aspects. Empty houses are rooms without a planet sitting in them, not missing organs. The PNG of the wheel is a snapshot; the tables are the instrument. Numbers first, then the written layer.

If you later compare the natal chart with today’s sky, that is transits — a different article. SideraChart’s cabinet stores those daily overlays at noon in the natal timezone so the day’s note stays stable. None of that rewrites the natal chart. The natal chart is the baseline you keep; transits are weather against it.