Leo
Leo is the signature constellation of spring nights. With a lion's head shaped like a backward question mark and the bright star Regulus, it's one of the few constellations that actually looks like its animal.
| Latin name | Leo |
|---|---|
| Abbreviation | Leo |
| Brightest star | Regulus (mag 1.4) |
| Best seen | Spring evenings (Northern Hemisphere) |
| Astrological dates | July 23 – August 22 |
| Sun actually passes | August 11 – September 16 |
| Stars used by Planetica | 1,984 |
How to find it
Leo is best seen in the evening sky from March to May. In early April it stands high in the south after dusk, perfect for observing.
A famous way to find it uses the Big Dipper. The two stars at the end of the Dipper's bowl are the "Pointers" used to find Polaris; extend the line through them in the opposite direction from Polaris and you'll reach Leo.
Leo's head and mane are a curve of stars shaped like a backward question mark, also called the Sickle. At the bottom end of the Sickle's handle shines a bright white star, Regulus, the Lion's heart. Moving your eye east from the Sickle, three stars form a right triangle: the Lion's hindquarters and tail. The star at the tip of the tail, Denebola, forms the "Spring Triangle" with Arcturus in Boötes and Spica in Virgo. Connect the Sickle and the triangle and you get the side view of a crouching lion.
The myth: the Nemean Lion
In Greek mythology, Leo is the fearsome lion that lived in the valley of Nemea. Its hide was so tough that neither arrows nor swords could pierce it, and it terrorized the people, killing villagers and livestock.
Hercules was ordered to kill this lion as the first of his Twelve Labors. When his arrows bounced off its hide, he drove the lion into its cave with his club and strangled it with his bare hands. Then he skinned it using the lion's own claws, since no weapon could cut the hide, and wore the pelt like armor. That's why Hercules often appears in paintings and sculptures wearing a lion skin over his head. The lion is said to have later risen into the sky as a constellation.
In ancient Chinese astronomy, Regulus and the stars of the Lion's head belonged to a long asterism called Xuanyuan (軒轅).
Main stars
| Name | Apparent magnitude | Distance (approx., ly) | Notes |
|---|---|---|---|
| Regulus (Alpha) | 1.4 | ~79 | A blue-white star that spins so fast its equator bulges outward. It sits almost exactly on the ecliptic. |
| Denebola (Beta) | 2.1 | ~36 | A white star at the tip of the Lion's tail. Its name means "the lion's tail." |
| Algieba (Gamma) | 2.0 (combined) | ~130 | A beautiful double star that splits into two golden stars in a telescope. |
| Zosma (Delta) | 2.6 | ~58 | The top corner of the triangle that marks the hindquarters. |
| Epsilon Leonis | 3.0 | ~250 | A yellow giant at the top end of the backward question mark. |
Below the Lion's hind legs is the "Leo Triplet" (M65, M66 and NGC 3628), three galaxies that fit in a single field of view. They are about 35 million light-years away and look like faint smudges in a small telescope. Nearby are more galaxies such as M95, M96 and M105.
Birthday sign dates: two different answers
In astrology, Leo runs from July 23 to August 22. But in the first part of that period, the real Sun is in Cancer. The Sun actually passes through the Leo constellation from about August 11 to September 16, about 37 days.
There are two main reasons the dates differ. The first is precession. Earth's axis slowly wobbles over a cycle of about 26,000 years, moving the vernal equinox point by about 1 degree every 72 years. The astrological signs are a system that divides the ecliptic evenly into 30-degree slices from the equinox point, based on the reference of about 2,000 years ago, so they now differ from the real constellations by nearly a month.
The second is the constellation boundaries set by the International Astronomical Union (IAU) in 1930. Real constellations vary widely in size, so the Sun spends different amounts of time in each. Leo is on the large side, so the Sun stays a fairly long time. The dates can vary by about a day from year to year.
In Planetica
If your birthday's astrological sign is Leo, Planetica places your planetary system next to a real star inside the Leo constellation. The candidates are the 1,984 stars in the HYG catalog that lie within about 3,000 light-years of Earth and inside the IAU boundaries of Leo.
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 Leo, but each next to a different star, so they never overlap.
Planetica also shows which constellation the Sun was really in on your birthday. For example, someone born on August 1 is a Leo in astrology, but on that day the Sun was actually in Cancer.
Fun facts
- The Leonid meteor shower arrives every year around November 17–18. It's caused by dust from Comet Tempel–Tuttle, and in 1833 an incredible meteor storm with tens of thousands of meteors an hour was recorded.
- Regulus means "little king" in Latin, a name given by Copernicus.
- Regulus lies so close to the ecliptic that it is fairly often hidden by the Moon or a planet.
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.