Arcturus in the birth chart: the guardian of the Bear

Star data

sefstars catalogue, Swiss Ephemeris 2.10.03.

Arcturus is the brightest star of the northern half of the sky, and its Greek name means "guardian of the Bear". Ptolemy gave it the nature of Mars and Jupiter. In the tropical zodiac it stands near the end of Libra, almost on the same degree as Spica, though in the sky the two are far apart.

In the sky

Arcturus belongs to the constellation Boötes. For astrology the more important fact is its latitude: it lies about 31° north of the ecliptic, so a conjunction by longitude does not bring it close to the planet in the sky. Many astrologers therefore give Arcturus more weight through parans than through a longitude conjunction.

Of all the stars in the sky, Arcturus is the fourth brightest. It is a red giant of spectral class K, and to the eye it looks a warm orange. It has roughly the Sun's mass but has already swollen: its diameter is about 25 times the Sun's. It lies about 37 light-years away.

Arcturus is also a fast mover, travelling at about 122 km a second relative to the solar system. Each year it shifts across the sky by about 2″, and among first-magnitude stars only Alpha Centauri moves faster. For the zodiac this motion hardly matters, since precession carries the star along the zodiac about 25 times faster.

Finding it from Ukraine

Arcturus is at its best on spring and early summer evenings. The Big Dipper shows the way: follow the curve of its handle until it runs into a bright orange star. Carry the same curve on and it leads to Spica. In Kyiv Arcturus climbs to about 59° above the horizon, in Odesa to about 63°, so in spring it stands high and is hard to miss.

Name and history

The name comes from the Greek for "guardian of the Bear". The image is a keeper standing watch beside the Bear.

The name first appears in Hesiod's Works and Days, where Arcturus works as a farmer's calendar. Sixty wintry days after the solstice it first rises brilliant at dusk, a sign of spring. And when rosy-fingered Dawn sees Arcturus, that is, once it shows in the morning sky, Hesiod says it is time to cut the grapes and bring them home. Aratus, in the Phaenomena, places the star beneath the belt of Boötes and calls it brighter than the rest.

In Arabic astronomy Arcturus was al-Simak al-Ramih, "the Simak with the lance", the lance being formed by neighbouring stars of Boötes. Spica was the second, "unarmed" Simak; the pair is covered on the Spica page. In early European tables the Arabic word was garbled into forms such as Aramech. The well-known line about Arcturus in the Book of Job, as Allen explained, really refers to the Great Bear rather than to this star. The name Arcturus was approved by the International Astronomical Union in 2016.

The best-known modern episode is the Chicago World's Fair of 1933, which was opened with the light of Arcturus. Four telescopes at different observatories focused the star's light onto photoelectric cells, and these switched on the fair's floodlights. The star was chosen because its distance was then put at 40 light-years, so its light had supposedly set out during the previous Chicago fair, in 1893.

Nature in the tradition

Ptolemy describes Arcturus as having the nature of Mars and Jupiter. Mars brings initiative and the will to act, Jupiter breadth and the sense of a larger purpose. Together they describe enterprise: taking the lead and starting something new.

Tradition links Arcturus with independence and with leading or teaching others. The star is generally counted among the favourable ones, and the Mars share keeps it active rather than comfortable.

Ptolemy gives the same pairing to Regulus, and comparing the two shows how the sky position shapes the reading. Regulus sits almost on the ecliptic, in the heart of the Lion, and tradition reads it through rank, authority and recognition from others. Arcturus stands high above the ecliptic, apart from the zodiac figures, and its image is a guardian rather than a king.

After Ptolemy

In the second book of Agrippa's Occult Philosophy, chapter 47 lists the fifteen Behenian stars and presents them "according to Hermes' opinion". Arcturus is eleventh on the list, straight after Spica, under the garbled Arabic name Alchameth. In chapter 31 of the same book Agrippa places Alchameth in the seventeenth degree of Libra and gives it the nature of Mars and Jupiter, which simply repeats Ptolemy. Today Arcturus stands more than seven degrees further on, near the end of the sign. For a natal chart this is historical background, not a separate source for the star's nature.

Conjunctions with planets and angles

The usual orb for a longitude conjunction is about 1°. A planet in late Libra conjoins both Arcturus and Spica; how such a double contact is read is covered on the Spica page. Two examples of how the tradition reads Arcturus itself:

• Arcturus with Mercury. Mercury is the planet of thought and speech, so the star's theme shows through ideas: a mind that prefers its own route, an interest in explaining and teaching.
• Arcturus on the Ascendant. The star's theme becomes part of how a person comes across: self-directed, ready to take the first step.

Precession and the sign

Through precession Arcturus moves along the zodiac by about 1.4° a century. Spica moves at the same rate, so the two stay paired for centuries. Arcturus is about five and a half degrees short of Scorpio, which at this rate is close to four centuries.

In celebrity charts

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

• Marion Cotillard: Mercury, orb 0°03′
• Zohran Mamdani: Sun, orb 0°04′
• Vladimir Putin: Mercury, orb 0°12′

Find fixed stars in your chart