Betelgeuse: The Red Supergiant Star on Its Way to Supernova

Star Walk
7 min readApr 12, 2024
© ESO/L. Calçada

Imagine a distant star so huge and luminous that, in the last act of its life, it could outshine our Moon and be visible in daylight. Betelgeuse, a red supergiant, is just such a star. Positioned at the left shoulder of Orion, it glows with a distinctive orange-red hue and is one of the most searched-for objects in our Star Walk 2 and Sky Tonight astronomy apps. But the most thrilling aspect of Betelgeuse isn’t just its size or color; it’s the anticipation of it going supernova. In this article, you’ll learn why this star deserves your attention tonight, and what to expect from its explosion if it does happen in our lifetime.

What is Betelgeuse?

Let’s start with the scientific characteristics of Betelgeuse.

  • Official names: Betelgeuse, α Orionis, Alpha Orionis, Alpha Ori, α Ori
  • Catalog designations: 58 Ori, HR 2061, HD 39801, HIP 27989
  • Constellation: Orion
  • Star type: red supergiant
  • Right ascension: 05h 55m 10.305s
  • Declination: +07° 24′ 25.4304″
  • Apparent magnitude: variable
  • Mass: 14–19 solar masses
  • Luminosity: 7,600 to 14,000 L
  • Radius: ~640–1,021 solar radii
  • Surface temperature: 3,500 K
  • Distance from the Earth: 642.5 light-years
  • Rotation period: 36 ± 8 years

Now let’s make it easier. What is Betelgeuse, in a nutshell?

  • Red supergiant: The stars of this type are nearing the end of their lives. They are the largest stars in the Universe and expand outward into space as they age. You can learn more about the life cycles of stars in our colorful infographic.
  • Big and massive star: Betelgeuse is 20 times heavier and 1,400 times larger than our Sun. If it were at the center of our Solar System, it would extend beyond Jupiter’s orbit.
  • Distant celestial body: Betelgeuse is 650 light-years from us, which means that the light we see from Betelgeuse today began its journey in the Middle Ages. Still, it’s the closest red supergiant to our Solar System, making it an important object for scientists to study.
  • Variable star: Unlike most stars that have a constant glow, Betelgeuse gets brighter and dimmer over time. It has several cycles of changing brightness, including a major one about every 420 days, and others lasting 185 days, 230 days, and even 2,200 days. In addition, Betelgeuse has sudden brightness changes that break out of the known cycle.
  • Naked eye orange-red star: Betelgeuse is the 2nd brightest star in Orion (after Rigel), the 7th brightest star in the Northern Hemisphere, and the 10th brightest star in the entire night sky. Although its brightness is not stable, it is visible to the naked eye even at its dimmest.

Now that you’re more familiar with this majestic star, let’s move on to how you can spot it in the night sky.

How to find Betelgeuse in the sky?

To easily find Betelgeuse in the night sky, consider using an astronomy app such as Star Walk 2 or Sky Tonight. Just enter “Betelgeuse” in the search bar, select the star from the search results, and point your device at the sky. Follow the on-screen arrow until you see reddish bright Betelgeuse on the app’s sky map and in the real sky above you.

Choose the vibrant Star Walk 2 app, perfect for beginners, or opt for a more in-depth exploration of the cosmos with Sky Tonight. In either app, simply follow the on-screen arrow to find Betelgeuse from your location. © Vito Technology, Inc.

Where is Betelgeuse located?

Betelgeuse marks the left shoulder of Orion, the legendary hunter in the sky. It’s the second-brightest star in the constellation, the first being bluish Rigel, which shines brightly at the hunter’s right foot. You will find Betelgeuse above Alnitak — the first of the three stars that form the famous Orion’s Belt. Rigel is on the other side of the Belt, below the star Mintaka. Need help remembering this? Check out our captivating celestial poem on Instagram, which will guide you to the prominent stars of Orion!

Betelgeuse is a part of the asterism Winter Triangle, also known as the Great Southern Triangle. This asterism resides within the Winter Hexagon and also contains the bright stars Sirius and Procyon.

To find Betelgeuse, look in the southwestern sky if you are in the Northern Hemisphere or in the northwestern sky if you are in the Southern Hemisphere. It is best seen between latitudes 85 north and 75 degrees south of the equator.

When is Betelgeuse visible?

Betelgeuse is usually visible to most people around the Earth from September through March, with the best views in December. The star rises in the evening, from around sunset. You can find out the exact time it will be visible in your location in the Sky Tonight app and set up notifications so you don’t miss it.

Are you ready for observation? Test your skills with our stargazing quiz!

Countdown to a Betelgeuse supernova

As beautiful as Betelgeuse is to observe, the main question on many people’s minds is when it will go supernova. If it happens soon, it will be one of the greatest astronomical events in history! A Betelgeuse supernova will shine as brightly as a half-Moon and will be visible during the day for several months. A sight that no one will miss. But scientists still don’t agree on the date when it will happen.

When will Betelgeuse go supernova?

For years, scientists have said that Betelgeuse could go supernova sometime in around 100,000 years. But in 2023, a new groundbreaking research, titled “The evolutionary stage of Betelgeuse inferred from its pulsation periods”, was published. Led by Hideyuki Saio from the Astronomical Institute, Graduate School of Science at Tohoku University in Japan, this research suggests that Betelgeuse could go supernova much sooner — within a few decades after the exhaustion of the star’s core carbon fuel. The research suggests that Betelgeuse is currently in the late stage of core carbon burning, and its core will exhaust the carbon fuel in less than 300 years. After that, anytime within a few decades, a supernova will occur.

However, the scientists themselves admit it’s hard to know exactly where Betelgeuse is in its life cycle because the star’s surface doesn’t change much in the late stages when carbon is running out. The astronomers can only see the star’s surface, but what’s happening deep inside the star tells the real story. So, we’re not sure if Betelgeuse is almost done burning its carbon fuel and might go supernova within a few hundred years or even decades, or if it’s still uncertain and could happen anytime between tomorrow and 100,000 years from now.

What would happen if Betelgeuse exploded?

Massive stars like Betelgeuse explode as Type II supernovae, collapsing rapidly and violently after they use up all their fuel. However, for it to pose a threat to the Earth, the supernova would need to occur within 160 light-years of us, and Betelgeuse is about four times that distance away. Still, a supernova could have unexpected effects on the Earth. For instance, many animals use the Moon for navigation and may be confused by an unusual light source. Even astronomers would face challenges. Observing the night sky is already difficult when the Moon is bright, and a Betelgeuse supernova would make it even harder.

But despite the challenges, a Betelgeuse supernova would be an incredible event to witness. The last time a nearby star went supernova was in 1604. While stars explode regularly in the universe, most are too far away to see without powerful telescopes. Betelgeuse would be the closest supernova ever observed by humans.

When Betelgeuse explodes, it will shine as brightly as the half-Moon for over three months. People would be able to see it in the daytime sky for about a year, and it would remain visible to the naked eye at night for several years as it gradually fades. Astronomers predict that we would receive advance warning of the explosion, with instruments on the Earth detecting neutrinos or gravitational waves generated by the event up to a day in advance. Just imagine people all around the world staying up to watch Betelgeuse, eagerly awaiting the spectacular light show and cheering when it finally begins.

The Great Dimming of Betelgeuse in 2019–2020

All the buzz about Betelgeuse going supernova started in 2019 when the star suddenly dropped to about 40% of its usual brightness before gradually returning to normal by early 2020. For a while, there was a theory that the star was about to explode, and there was indeed an explosion…just not the one we expected.

By analyzing data from observatories, including NASA’s Hubble Space Telescope, scientists found that Betelgeuse experienced a surface mass ejection in 2019. The star spewed a huge chunk of its surface material into space, forming a dust cloud that temporarily obscured the star’s light.

In late 2019, Betelgeuse ejected material from its surface, which cooled into a cloud of dust and blocked the star’s light from reaching the Earth. This event is known as the Great Dimming. © NASA, ESA, Elizabeth Wheatley (STScI)

While similar events happen on our Sun all the time, Betelgeuse’s ejection was about 400 billion times more massive, and the chunk the star spewed into space was probably several times the mass of our Moon.

So, in reality, Betelgeuse didn’t actually dim during the Great Dimming. It just looked that way because we were looking through a cloud of stellar debris.

Monitoring Betelgeuse’s brightness

The light variations of Betelgeuse are not fully understood yet, so it’s a source of dedicated study. And the good news is that you can get involved! As an amateur observer, you can join the AAVSO Photoelectric Observing Program and contribute your observations of Betelgeuse’s changing brightness to the International Database. You can also check out other members’ observations and see how Betelgeuse looks from different locations at different times. Who knows, maybe your observations will help researchers better understand the nature of this captivating red supergiant.

Betelgeuse: not yet a supernova, but still a celestial gem

Betelgeuse is a stunning orange-red star that you can spot with the naked eye in the constellation Orion. There’s a chance it could go supernova in our lifetime, but that’s just a possibility, and the exact date is unknown. So, for now, let’s appreciate its current beauty while hoping for an even greater celestial show. With the user-friendly apps Star Walk 2 and Sky Tonight, locating Betelgeuse in the sky is a breeze. Take a moment to admire this amazing star!

Text Credit: Vito Technology, Inc.



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