Regulus – The Brightest Star in Leo
Regulus is the brightest star in the constellation Leo. Use Sky Tonight to find Regulus in the sky, learn when to observe it, and check when to see Regulus near the planets and the Moon. Here, you’ll learn some facts about this star.
Contents
- Regulus (Alpha Leonis) – key star facts
- Where is Regulus in the sky?
- When is Regulus visible?
- Fun facts
- What is the star Regulus: Conclusion
Regulus (Alpha Leonis) – key star facts
- Official name: Regulus, Alpha Leonis, Alpha Leo, α Leo
- Alternative names: Cor Leonis, Lion’s Heart, Basiliskos, Qalb al-Asad, Kabeleced, Rex
- Catalog designations: 32 Leonis, HIP 49669, HR 3982, HD 87901, TYC 833-1381-1
- Constellation: Leo
- Star type: class B7 V main-sequence star
- Right ascension: 10 h 08 m 21.2 s
- Declination: +11° 58′ 06.3″
- Apparent magnitude: 1.4
- Mass: 3.8 solar masses
- Luminosity: 316.2 L
- Radius: 4.35 solar radius
- Surface temperature: 12,460 K
- Distance from the Earth: 79.3 light-years
- Rotation period: 16 hours
Regulus star system
Although Regulus appears to be a single star, it’s actually a system of four stars that are organized into two pairs. The first pair, known as Regulus A, consists of the blue main sequence star of the spectral type B8 and a presumed main sequence white dwarf. The blue star is visible to the naked eye, and its partner has never been directly observed. Astronomers predicted its existence using spectroscopic analysis.
If you have a small telescope with at least 50x magnification, you can spot the third star in the Regulus system, called Regulus B. It’s a cool orange dwarf star that belongs to the spectral type K2 V. Regulus B has its own companion, Regulus C, which is a red dwarf of the spectral type M4V. You’ll need a powerful telescope to catch a glimpse of Regulus C.
Where is Regulus in the sky?
Regulus is the 21st brightest star in the sky. It resides within the constellation Leo and is one of the three bright stars making up the Spring Triangle, a recognizable asterism. The star has an apparent magnitude of 1.4, which means it’s easily visible to the naked eye without any telescopes or binoculars.
So, if you’re looking for a new celestial object to explore and show off to your friends, Regulus is a great choice. Now let’s discover how to locate this stunning star in the sky above you.
How to find Leo’s brightest star – the Sickle of Leo
A classic way to find Regulus in the night sky is to look at it in relation to other celestial objects. Regulus is part of the asterism called the Sickle of Leo, which resembles a backward question mark. To locate Regulus, start by searching for the Sickle in the band of the sky where you see the Moon and the planets (near the ecliptic).
If you live in the Northern Hemisphere, you can also use the famous Big Dipper, the asterism of Ursa Major, to locate the star. Draw an imaginary line between the two stars, called Megrez and Phad, on the inner (closest to the handle) edge of the Big Dipper’s bowl. Then extend this line about eight times downwards, and you’ll arrive at Regulus, the brightest star in that direction. Keep in mind that planets also move nearby, so if you don’t want to mix up Regulus with Venus, read our article on how planets and stars differ.
How to find Leo’s brightest star – Sky Tonight
Exploring the night sky is exciting, and it can also be very easy with a proper astronomy app like Sky Tonight. With this free app, you can find Regulus in a few simple steps:
- Open the app’s search bar and type “Regulus.”
- Tap the blue target button to the right of the matching result. The app will show you the star's position on the sky map.
- Tap the blue compass button at the bottom right of the screen. The app will use your device’s location to align the screen image with the real sky above you.
- Move your device following the white arrow until you see Regulus on the screen and in the real sky.
In addition to bright Regulus, Sky Tonight offers thousands of other celestial objects to explore. Watch our video tutorials to get the most out of this app.
When is Regulus visible?
Regulus can be seen in the sky for most of the year, except for a brief period from early August to early September when the star is too close to the Sun. Starting from mid-September, you can spot Regulus in the morning sky. Then, around mid-February, it transitions to the night sky. Regulus is visible from both the Northern and Southern hemispheres. Note that the star’s home constellation Leo appears upside down in the southern latitudes.
The best time to observe Regulus is from late March to May, when the star rises the highest above the horizon.
Here's a list of upcoming celestial events involving Regulus. Check out the Sky Tonight calendar to see how they'll look in the sky from your location, and set reminders so you don’t miss any of them.
November 22: Regulus near the Moon
On November 22, at 20:48 GMT (3:48 p.m. ET), Regulus (mag 1.4) will be located at a distance of 2°42′ from the Moon. The Moon will be in its last quarter phase, so the duo will be perfectly visible to the naked eye in a dark sky. In addition, reddish Mars will shine in the neighboring constellation Scorpius.
December 20: Regulus near the Moon
On December 20, at 05:37 GMT (12:37 a.m. ET), Regulus (mag 1.4) will be located at a distance of 2°30′ from the Moon. Our natural satellite will be 77% illuminated. The pair will be easily visible to the naked eye. In addition, reddish Mars will shine in the neighboring constellation Scorpius.
January 16, 2025: Regulus near the Moon
On January 16, at 14:57 GMT, Regulus (mag 1.4) will be located at a distance of 2°24′ from the Moon. Our natural satellite will be two days after the Full Moon phase, so it will look almost fully illuminated. The pair will be visible to the naked eye.
February 12, 2025: Regulus near the Moon
On February 12, at 23:21 GMT, Regulus (mag 1.4) will be located 2°18′ from the Moon. Our natural satellite will be in the Full Moon phase, which may make Regulus a little more difficult to spot, as the moonlight will outshine the nearby objects. However, the pair should be visible to the naked eye on a clear night.
Fun facts
The Little King Star
Remember we mentioned the Great Kings at the beginning of this article? Well, there are several reasons for this. First, Regulus means “little king” in Latin. Second, it belongs to the constellation Leo, and lions are often referred to as the “kings of animals.” Many other historical names for Regulus emphasize its royal significance as well.
The Greeks called the star Kardia Leontos, and the Latin name for it was Cor Leonis. In Arabic, it was referred to as Qalb al-Asad. All three of these names carry the same meaning: “the heart of the lion.” Interestingly, King Richard I of England was famously called Lionheart, too. And that’s not all! As early as 3000 B.C., Regulus was known for its majestic nature. Babylonian astronomers called it Sharru, meaning “the King.” The Persians called it Miyan, meaning “the Center,” and considered it one of the four Royal Stars. In India, the star was known as Maghā, which means “the Mighty.” Won’t you look now at Regulus with even greater respect and admiration?..
Media star
Not only ancient people paid attention to Regulus. The star can be found in popular television series such as Babylon 5 and Star Trek, as well as in computer games like BattleTech, the Frontier series, and Descent: FreeSpace. Additionally, J.K. Rowling’s “Harry Potter” series fans may recall the character Regulus Black. He was the brother of Sirius Black, Harry's godfather, whose name was a reference to the brightest star in the sky.
Fast-spinning, egg-shaped
Did you know that not all stars are perfectly round? Take, for instance, Vega, which is flattened at the poles. Well, guess what? Our esteemed Regulus is even more interesting — it’s egg-shaped! This peculiar form is a result of Regulus’ rapid rotation. The star completes one full spin on its axis approximately every 16 hours. In comparison, our own Sun takes a leisurely 27 days to complete a single rotation.
Scientists have calculated that if Regulus were to spin just 10% faster, it would tear itself apart. Still, there’s no need to worry about the well-being of our Little King. The researchers assure us that nothing within the star system could cause Regulus to speed up to such a dangerous extent.
Friends with the Moon and planets
Staying close to the ecliptic, Regulus often meets the Sun, the Moon, and the planets. Sometimes one of these objects blocks Regulus from our view – astronomers call this event an “occultation.” Regulus is most often occulted by the Moon, but sometimes by planets as well. For example, on October 1, 2044, Regulus will be occulted by Venus. Save the date!
What is the star Regulus: Conclusion
Now you know how to find Regulus in the night sky and marvel at the “Little King” by yourself. You can locate the star with the Big Dipper as a guide, or make things simpler with the user-friendly Sky Tonight astronomy app. Whichever method you choose, we hope you have clear skies and enjoy a successful stargazing experience! Happy observing!
