Aquarius
Aquarius covers a wide stretch of the southern autumn sky. It depicts the youth Ganymede holding a water jar, with a stream pouring from the jar toward Fomalhaut in Piscis Austrinus.
| Latin name | Aquarius |
|---|---|
| Abbreviation | Aqr |
| Brightest star | Sadalsuud (mag 2.9) |
| Best seen | Autumn evenings (Northern Hemisphere) |
| Astrological dates | January 20 – February 18 |
| Sun actually passes | February 16 – March 11 |
| Stars used by Planetica | 2,041 |
How to find it
Aquarius is visible in the evening sky from September to November and is highest in the south in the early evening in October. It's a large constellation, but most of its stars are faint, 3rd–4th magnitude, so it's hard to find from the city and you'll need a dark site.
Two signposts help. One is the Great Square of Pegasus, high in the autumn sky; the other is Fomalhaut (in Piscis Austrinus), a lone, bright 1st-magnitude star near the southern horizon. The wide area between them, southwest of the Square, is Aquarius.
The easiest part of Aquarius to recognize is the "Water Jar" asterism. East of the Alpha star Sadalmelik, four 4th-magnitude stars cluster in a small Y or pinwheel shape: the jar that Ganymede holds. From there, faint stars zigzag south toward Fomalhaut, forming the stream of water. This region is full of water-themed constellations, including Cetus, Pisces and Piscis Austrinus, and is sometimes called "the Sea."
The myth: cupbearer to the gods
In Greek mythology, Aquarius is Ganymede, a prince of Troy, said to be the most beautiful of all mortals. Zeus took notice of him, turned into a great eagle, and snatched Ganymede while he was tending sheep on Mount Ida, carrying him off to Olympus. There, Ganymede was given the job of pouring the divine drink at the gods' banquets. Zeus is said to have consoled the Trojan king for the loss of his son with a gift of splendid horses.
The eagle that carried Ganymede away is identified with Aquila, home of Altair, and Aquila does indeed lie in the sky northwest of Aquarius. The water pouring from the jar is pictured being drunk by the fish of Piscis Austrinus. One of Jupiter's large moons is also named Ganymede after him.
In the East Asian 28 lunar mansions, the stars of Aquarius span the Girl (女宿), Emptiness (虛宿) and Rooftop (危宿) mansions. Sadalsuud is the determinative star of Emptiness, and Sadalmelik of Rooftop.
Main stars
| Name | Apparent magnitude | Distance (approx., ly) | Notes |
|---|---|---|---|
| Sadalsuud (Beta) | 2.9 | ~540 | The brightest star in Aquarius, a yellow supergiant. |
| Sadalmelik (Alpha) | 2.95 | ~520 | A yellow supergiant that looks like Sadalsuud's twin, right next to the Water Jar. |
| Skat (Delta) | 3.3 | ~160 | A white star in southern Aquarius, near Ganymede's legs. |
| Sadachbia (Gamma) | 3.85 | ~160 | One of the four stars that make up the Water Jar. |
Aquarius is home to the Helix Nebula (NGC 7293), about 650 light-years away. It's one of the closest planetary nebulae to Earth, and in photos it looks like a giant eye, earning it the nickname "the Eye of God." It's large and faint, though, so you'll need a dark sky. With a telescope you can also find the globular cluster M2 and NGC 7009, the Saturn Nebula, a planetary nebula that looks like Saturn.
Birthday sign dates: two different answers
In astrology, Aquarius runs from January 20 to February 18. But for most of that period, the real Sun is in Capricornus. The Sun actually passes through the Aquarius constellation from about February 16 to March 11, about 24 days.
The first reason for the difference is precession. Earth's axis wobbles like a spinning top over a cycle of about 26,000 years, so the vernal equinox point moves west along the ecliptic by about 1 degree every 72 years. The astrological signs divide the ecliptic evenly into 30-degree slices from the equinox point based on the sky of about 2,000 years ago, so they're now about a month out of step with the real constellations.
The second reason is the constellation boundaries set by the International Astronomical Union (IAU) in 1930. Each constellation covers a different width of the ecliptic, so the time the Sun spends in each also differs. The dates can vary by about a day from year to year.
In Planetica
If your birthday's astrological sign is Aquarius, Planetica places your planetary system next to a real star inside the Aquarius constellation. The candidates are the 2,041 stars in the HYG catalog that lie within about 3,000 light-years of Earth and inside the IAU boundaries of Aquarius.
One of them is chosen 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 Aquarius, 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 February 5 is an Aquarius in astrology, but on that day the Sun was actually in Capricornus.
Fun facts
- TRAPPIST-1, a red dwarf about 40 light-years away that was revealed in 2017 to host seven Earth-sized planets, is also in Aquarius.
- The Eta Aquariid meteor shower in early May comes from dust left by Halley's Comet. In late July you can also catch the Delta Aquariids.
- The vernal equinox point will cross from Pisces into Aquarius around the year 2600. The popular phrase "the Age of Aquarius" is tied to this idea.
Other constellations
Create your own planetary system
Enter a name and a birthday to get a one-of-a-kind planetary system, placed next to a real star in your birthday constellation.