Starlit Chart

Birth chart guide

Placidus vs Whole Sign: why your houses change

Two charts can agree on a planet's zodiac sign and disagree on its house. Signs locate planets along the zodiac; houses divide the chart relative to a birth time and place. Different rules for those divisions can give the same planet a different house label.

What each system divides

Whole Sign makes the entire rising sign House 1, starting at that sign's 0° boundary. The next sign is House 2, and so on: twelve equal 30° houses. The Ascendant remains at its actual degree inside House 1.

Placidus uses divisions of the time a zodiac degree takes to travel above and below the horizon. Its first cusp is the Ascendant, its tenth is the Midheaven, and its houses generally have unequal widths. A sign can span more than one house, or sit inside a house without being on a cusp.

What Starlit Chart actually uses

Our default is Placidus when the birth time is known. At an absolute latitude at or above 66° north or south we use Whole Sign. We also fall back to Whole Sign if the Placidus calculation does not converge below that threshold. The 66° cutoff is our engine's conservative rule, not the exact position of the polar circle.

Our free form has no house-system switch. Without a birth time, neither system is calculated: there is no Ascendant and no house assignment. See the unknown-time guide before treating a noon chart as a timed one.

Same fictional birth, two divisions

Jordan, May 14, 1991 at 7:40 AM in Denver, Colorado (America/Denver; 39.73915° N, 104.9847° W). This is a demonstration from our engine, not a customer chart. The resolved instant is 1991-05-14T13:40:00.000Z. The second wheel applies Whole Sign to the same Ascendant and planet longitudes for illustration; it is not a new calculator setting.

Fictional Denver chart: PlacidusBirth chart wheel. Sun in Taurus, Moon in Taurus and Rising sign Gemini. Also Mercury in Aries, Venus in Cancer, Mars in Cancer, Jupiter in Leo, Saturn in Aquarius, Uranus in Capricorn (retrograde), Neptune in Capricorn (retrograde), Pluto in Scorpio (retrograde) and North Node in Capricorn (retrograde). The 12 houses are shown.123456789101112ASCMC23°28°27°6°23°6°6°13°R16°R18°R20°R
Placidus: House 1 starts at 23°21' Gemini.
Fictional Denver chart: Whole Sign demonstrationBirth chart wheel. Sun in Taurus, Moon in Taurus and Rising sign Gemini. Also Mercury in Aries, Venus in Cancer, Mars in Cancer, Jupiter in Leo, Saturn in Aquarius, Uranus in Capricorn (retrograde), Neptune in Capricorn (retrograde), Pluto in Scorpio (retrograde) and North Node in Capricorn (retrograde). The 12 houses are shown.123456789101112ASCMC23°28°27°6°23°6°6°13°R16°R18°R20°R
Whole Sign: House 1 starts at 0°00' Gemini.

The planetary positions and Rising degree stay the same. The dividing lines and some house labels change. Neither layout proves a personality interpretation is scientifically correct.

When comparing two calculators

First match date, recorded local time, birthplace and known-time status. Then check the house system and zodiac convention: our chart is tropical. A different time zone conversion or a rounded time can move angles and cusps as well. Do not choose whichever result sounds more flattering as proof of calculation accuracy.

Source

Astrodienst's Swiss Ephemeris technical documentation lists house systems and explains why Placidus cannot be calculated beyond the polar circle. Its library uses a different fallback; Starlit Chart's Whole Sign fallback is described above. We use our own engine rather than that library.

Try your own details

Get your free birth chart. The form asks for your name, date and birthplace, plus your recorded time if known. No email is needed to see your chart. The optional full reading costs $37; start with the free result and its uncertainty notes.

For entertainment and self-reflection. Calculating astronomical positions does not validate astrology's personality claims or predict events.

Reviewed October 13, 2026.