Algol in the birth chart: the fixed star of the Gorgon's head

Star data

sefstars catalogue, Swiss Ephemeris 2.10.03.

Algol is a star in Perseus that medieval authors counted among the most difficult in the sky. Ptolemy's star catalogue, the Almagest, lists it among the stars of the Gorgon's head, and its Arabic name means "the demon's head". Today it sits near the end of Taurus, and astrologers still look for it in any chart with a planet or an angle in the last degrees of that sign.

In the sky

Algol belongs to the constellation Perseus and lies well north of the ecliptic, more than 20° away from it, so the Moon and planets never pass over it. It is not among the brightest stars in the sky. Its light is not constant, which sets it apart.

Algol is an eclipsing binary. Two stars orbit each other, and when the fainter one passes in front of the brighter, the combined light drops. This happens roughly once every 2.9 days.

What kind of star it is

Algol is about 90 light-years away and is the nearest eclipsing binary to us. Most of the time it shines at about magnitude 2.1. During an eclipse it fades to about 3.4, more than three times fainter, and the whole dip from start to finish takes about ten hours, so the change can be followed with the naked eye over one evening.

The system has three known stars. The brighter star of the eclipsing pair is a hot blue-white star, its partner a cooler subgiant, and a third star circles the pair further out. The pair has long puzzled astronomers: the less massive star is the more evolved one, which should not happen if both formed together. The usual explanation is that the partner was once the heavier star, swelled first and passed most of its mass to its neighbour.

Discovery of the variability

In Europe the changes in Algol's light were first noted scientifically by the Italian astronomer Geminiano Montanari, in the years before 1672. In 1783 the English astronomer John Goodricke reported the period to the Royal Society and suggested that a large body circling the star regularly passes in front of it. The idea was confirmed in 1889, when Hermann Carl Vogel found shifts in Algol's spectrum showing that it moves in an orbit.

There is also an older and more debated claim. In 2015 the Helsinki researchers Lauri Jetsu and Sebastian Porceddu analysed an Egyptian calendar of lucky and unlucky days, the Cairo papyrus 86637 from the late second millennium BC, and found in it a cycle of about 2.85 days, which they link to Algol. Not everyone accepts this reading, and it remains a hypothesis.

Finding it from Ukraine

Algol is a star of autumn and winter evenings. From October to February it stands high in the eastern and then the southern sky, and in December it passes almost overhead late in the evening. Perseus lies between Cassiopeia and the Pleiades, and Algol marks the Gorgon's head that the hero holds in his hand.

At the latitude of Kyiv and further north Algol is technically circumpolar: it never sets, although at its lowest point it barely clears the northern horizon. In the south of the country, around Odesa, it sets for a short time each day.

The name

The name comes from the Arabic for "the demon's head". It continues the Greek picture of the constellation, where these stars mark the head of the Gorgon. In astrological writing this picture shaped the star's meaning more than any physical fact.

Ptolemy's own description is "the bright one of those in the Gorgon's head", and Hipparchus and Pliny, according to Allen, even treated the Gorgon's stars as a separate constellation, the Head of Medusa. Algol is the official name approved by the International Astronomical Union.

The myth behind the image is old. Hesiod in the Theogony already tells how Perseus cut off the head of Medusa, and how Chrysaor and the winged horse Pegasus sprang from her blood. In Ovid's Metamorphoses Perseus carries the head with him and turns his enemies to stone by holding it up.

Nature in the tradition

In the Tetrabiblos Ptolemy gives the stars of Perseus, Algol among them, the nature of Jupiter and Saturn. Saturn stands for weight, limits and endurance, Jupiter for expansion and authority. Together they suggest something heavy that also grows large.

The pairing itself is not what makes Algol feared. Ptolemy gives the same two planets to the bright stars of Orion apart from its shoulders, Rigel among them, and Rigel has no such reputation. The difference lies in the image: a star in a demon's head was always going to be read more darkly than the foot of a hunter.

Allen, writing in 1899, notes that astrologers held it to be the most unfortunate and dangerous star in the sky. Much of that reputation was written with the Gorgon myth in mind. The same image opens Cornelius Agrippa's list of fifteen Behenian stars: the chapter in the second book of his Three Books of Occult Philosophy begins with "the head of Algol".

Many modern astrologers read Algol differently. Instead of a source of misfortune they see a theme of intensity: strong feelings, a capacity to face what others avoid, and the question of how that force is handled.

Conjunctions with planets and angles

A planet or angle within about 1° of Algol is treated as a contact; the orb section explains why the tolerance is so tight. Because Algol lies far from the ecliptic, a conjunction by longitude does not mean the two are close in the sky.

Two examples show how the tradition reads it:

• Algol with the Moon. The Moon describes feelings and the body's rhythms, so the star's intensity is read through emotional life: strong reactions, deep attachments, a need to learn how to hold them.
• Algol on an angle. On the Ascendant or MC the star's theme becomes visible to others. Older authors read this as a sign of a turbulent life; modern ones more often speak of a forceful presence that does not go unnoticed.

Precession and the sign

Through precession Algol moves along the zodiac by about 1.4° a century. It is now in the last degrees of Taurus, about three and a half degrees, or roughly two and a half centuries, short of Gemini. Tables from the early twentieth century put it more than a degree earlier, so a planet that sits on Algol by an old book may already be out of orb.

The next star of this section along the zodiac is Alcyone, the brightest of the Pleiades, at the very start of Gemini.

In celebrity charts

Conjunctions within 1° to the planets from the Sun to Saturn and to the chart angles.

• Zendaya: IC, orb 0°49′

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