Sagittarius
Sagittarius, the Archer, sits in the southern summer sky where the Milky Way runs thickest. The center of our galaxy lies in this direction, so it's packed with nebulae and star clusters.
| Latin name | Sagittarius |
|---|---|
| Abbreviation | Sgr |
| Brightest star | Kaus Australis (mag 1.8) |
| Best seen | Summer–early autumn evenings (Northern Hemisphere) |
| Astrological dates | November 22 – December 21 |
| Sun actually passes | December 18 – January 19 |
| Stars used by Planetica | 2,208 |
How to find it
Sagittarius is visible in the evening sky from July to September and climbs highest in the south in the early evening in August. Even then it stays fairly low above the southern horizon, so a dark spot with an open view to the south is best. It's also known as the Archer.
First find Antares, the red star of Scorpius, and the S-shaped tail, then look to their left (east). About eight stars of 2nd–3rd magnitude form the shape of a teapot. This "Teapot" asterism is practically the emblem of Sagittarius. Its spout points west (toward Scorpius), and its handle faces east. From a dark site, the Milky Way seems to rise like steam from the Teapot's spout.
The six stars of the Teapot's handle and lid form a small dipper, known in English as the "Milk Dipper." In Korea and elsewhere in East Asia it was called the Southern Dipper (南斗六星), a counterpart to the Big Dipper in the north. To picture the centaur with his bow, imagine the Teapot as his body.
The myth: the archer centaur
Sagittarius shows a centaur, human from the waist up and horse below, drawing his bow. His arrow points straight at Antares, the heart of neighboring Scorpius, and one interpretation says he is keeping watch on the scorpion that killed Orion.
Stories differ on who the archer is. Some say he's the wise centaur Chiron, but Chiron is usually identified with Centaurus in the southern sky. So one ancient Greek tradition named Crotus, son of the god Pan and companion of the Muses, as the figure of Sagittarius. Crotus is said to have invented archery, and the Muses asked Zeus to place him in the sky.
In the East Asian 28 lunar mansions, the Southern Dipper is the Dipper mansion (斗宿), and the stars near the Teapot's spout are the Winnowing Basket (箕宿). In old tales, the Southern Dipper was said to govern life and the Big Dipper death.
Main stars
| Name | Apparent magnitude | Distance (approx., ly) | Notes |
|---|---|---|---|
| Kaus Australis (Epsilon) | 1.8 | ~140 | The brightest star in Sagittarius, at the bottom right of the Teapot. |
| Nunki (Sigma) | 2.0 | ~230 | A blue-white star in the Teapot's handle. |
| Ascella (Zeta) | 2.6 | ~90 | At the bottom of the handle; a binary of two stars orbiting each other. |
| Kaus Media (Delta) | 2.7 | ~350 | An orange giant on the spout side of the Teapot. |
| Kaus Borealis (Lambda) | 2.8 | ~78 | The star at the top of the Teapot's lid, marking the upper end of the bow. |
West of the Teapot's spout, about 26,000 light-years away, lies the center of the Milky Way, home to Sagittarius A*, a supermassive black hole about 4 million times the mass of the Sun. An image of its shadow was released in 2022. Nearby are showpieces visible even in binoculars, including the Lagoon Nebula (M8), the Trifid Nebula (M20), the Omega Nebula (M17), and the bright globular cluster M22.
Birthday sign dates: two different answers
In astrology, Sagittarius runs from November 22 to December 21. But during that period, the real Sun is passing through Scorpius and Ophiuchus. The Sun is actually inside the boundaries of Sagittarius from about December 18 to January 19, about 33 days. So people born December 18–21 are Sagittarius both in astrology and in the real sky.
The first reason the dates differ is precession. Earth's axis wobbles like a spinning top over a cycle of about 26,000 years, moving the equinox and solstice points by about 1 degree every 72 years. The astrological signs divide the ecliptic into 30-degree slices from the vernal equinox point based on the reference of about 2,000 years ago, so the roughly one month of drift since then remains. As a result, the Sun at the December solstice, which was in Capricornus about 2,000 years ago, is now in Sagittarius.
The second reason is that the constellation boundaries set by the International Astronomical Union (IAU) in 1930 cover different areas. In particular, Ophiuchus squeezes in just before Sagittarius. The dates can vary by about a day from year to year.
In Planetica
If your birthday's astrological sign is Sagittarius, Planetica places your planetary system next to a real star inside the Sagittarius constellation. The candidates are the 2,208 stars in the HYG catalog that lie within about 3,000 light-years of Earth and inside the IAU boundaries of Sagittarius. Since it faces the galactic center, this part of the sky is crowded with stars.
One of them is picked at random, and your system settles about 1–6 light-years from it. "Twin systems" from people with the same name and birthday all sit in Sagittarius, but each next to a different star.
Planetica also shows which constellation the Sun was really in on your birthday. For example, someone born on December 5 is a Sagittarius in astrology, but on that day the Sun was actually in Ophiuchus. Someone born on December 20, on the other hand, gets Sagittarius for both.
Fun facts
- Rukbat, the Alpha star of Sagittarius, is only magnitude 4.0, far from the brightest star in the constellation.
- Sagittarius contains 15 Messier objects, more than any other of the 88 constellations.
- Today, the Sun is in Sagittarius at the December solstice.
Other constellations
Create your own planetary system
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