Billie Eilish was born at 11:30 in the morning on 18 December 2001 in Los Angeles. That gives a Sagittarius Sun, an Aquarius Moon and Pisces rising. The Sun was close to its highest point in the sky, in the 10th house, and Venus sits almost on the Midheaven, so the most public part of the chart is also the most crowded.
A birth just before noon puts the Sun near the top of the chart, and here it's at 26° Sagittarius in the 10th house, the house of calling, reputation and the work the world sees. Sagittarius brings honesty, appetite for meaning and a refusal to stay small. Mercury in early Capricorn shares the 10th house, giving the voice a dry, exact, grown-up edge.
The Sun also lies directly across from the North Node, less than a tenth of a degree from exact. The Node points at growth, and in Gemini in the 4th house it asks for roots: family, home and the private ground everything else stands on.
Venus, the planet of beauty, love and art, is in Sagittarius less than two degrees from the Midheaven. When Venus sits on the highest point of a chart, what someone makes and how they look at beauty tends to become the thing they're known for. Uranus makes a close, friendly sextile to the same point, which adds a streak of the unexpected to that public image.
The Moon is in Aquarius in the 12th house, the most inward part of the chart: dreams, solitude, and what happens out of sight. Uranus and Mars are in the 12th house too. That's a feeling life that's independent and unusual, and that does its best work in private before it's shared. A flowing trine from the Moon to Saturn gives those feelings a steady frame.
Pisces was rising at 17°, so the first impression is soft, perceptive and a little dreamlike. The ruler of Pisces is Jupiter, retrograde in Cancer in the 4th house, which ties the whole chart back to home and family once again. By the modern ruler, Neptune, it's in Aquarius in the 11th house, among friends, collaborators and the wider crowd.