Betelgeuse：The Red Supergiant Star in Orion

Betelgeuse is the second brightest star in the constellation of Orion, and is usually the tenth brightest star in the entire night sky. I say usually because Betelgeuse is a variable star. Its brightness changes over time, and in fact, over the past few years, it has continued to surprise astronomers with dramatic dimming events in which it becomes noticeably fainter to the naked eye. But even in areas with light-polluted skies, this star can easily be spotted as the red Let's take a quick moment to acknowledge the variation in how to say this star name before the comments combust. If you're wondering why it sounds different than the way in which you learned, welcome to astronomy. There's more than one way to pronounce this star. I've heard Betelgeuse, Betelgeuse, and Betelgeuse as pronunciations coming from both professional and amateur astronomers, and even the International Astronomical Union acknowledges that there's no single correct way to pronounce a constellation name. Many star names have traveled through Arabic, Greek, Latin, and modern languages for centuries, and along the way, pronunciations get creatively reshaped. How we say them reflects where we're from, and how we're taught, not whether we're right. I'm here to talk about the science of the stars, not to settle pronunciation arguments. Star names come from many languages and traditions, so variations are expected. The universe is big enough for more than one pronunciation. Now let's turn back to the science of this star. Betelgeuse is a red supergiant, a massive star nearing the end of its life. If it were placed at the center of our solar system, its outer layers would extend beyond the orbit of Jupiter. Its radius is roughly 700 to 1,000 times that of the Sun, making it one of the largest stars visible to the naked eye. Betelgeuse is often compared to the other bright star in Orion called Rigel. Both these stars are in similar stages of their life, but Betelgeuse is farther along in its evolution. It's larger in size, it has a cooler surface temperature, and it's fusing elements in its outer shells. That cooler temperature is what gives Betelgeuse its striking color, a deep orangish-red glow that's easily visible to the eye. The color especially comes through when taking long-exposure photos of Orion. Massive stars like Betelgeuse have reached a very advanced stage of stellar evolution. In its core, it has already exhausted most of the hydrogen and helium, and it has moved on to fusing heavier elements like carbon and oxygen. This is like the last leg of its life. Eventually, it will run out of fuel entirely, and when it does, fusion will stop and gravity will win. As the core collapses, the star will erupt as a supernova, sending its outer layers rushing outward into space. When this happens, Betelgeuse will brighten so much that it may be visible during the day, even for weeks or months. After the explosion, all that remains may be either a neutron star or possibly a black hole depending on the mass of the star. In 2019, Betelgeuse drew worldwide attention when its brightness dropped dramatically. This event, now known as the Great Dimming, sparked speculation that the star might be about to explode. But Betelgeuse eventually returned to its normal brightness. Astronomers discovered that the dimming was caused by a massive release of gas from the star's surface. As this material drifted outward, it cooled and formed a cloud of dust that temporarily blocked some of the star's light from reaching Earth. Astronomers now think Betelgeuse is not a single star, but part of a binary system. For decades, it was suspected that it might have a companion, but the constant changes in brightness made it difficult to confirm. This small companion is thought to be a main-sequence star orbiting deep within the main star's vast outer envelope. This makes it extremely difficult to detect against the supergiant's intense glow. Nicknamed Betel Buddy and sometimes called Sea Warha, it may help explain these long-standing cycles of dimming and brightening. When astronomers classify stars, they are plotted on the Hertzsprung-Russell diagram, which shows the relationship between temperature, luminosity, and color. Betelgeuse sits far above the main-sequence band, in the upper-right region where cool, highly luminous supergiants reside. Its position reflects its enormous size and relatively low surface temperature. The best way to find Betelgeuse is to learn to recognize Orion. This constellation is visible from both hemispheres, but it will appear upright or upside-down depending on where you live on Earth. Here is the Southern Hemisphere view and the Northern Hemisphere view. Betelgeuse marks Orion's shoulder, which is opposite of Rigel at the foot. So when you look at photos of Orion, try to nulcate it. You should notice the color difference between the two. Rigel shines bluish-white, while Betelgeuse glows an orange-red color. That contrast makes them easy to tell apart. And as you look at different images, take a moment to practice spotting the difference between these two main stars. If you'd like to learn more about Rigel, the other brightest star in Orion, I have a whole separate video about it. It truly is a fascinating four-star system that's also a supergiant. Let's look at Betelgeuse using Stellarium, a free online planetarium tool. You can use this either on your computer or download an app for your phone. And I usually type in the constellation I'm looking for and toggle different features on and off. You can also put your own location in so you can see what Orion looks like from your part of the world. You can also search stars by their names, such as Betelgeuse, and zoom in and out to see what is around it and the different characteristics of this particular star. This program is one of my favorite ways to study the sky, especially during the winter time when much of the sky is covered with clouds because of the cold weather. But when it is clear outside, I'm sure to go outside, I just bundle up and get the right clothing on, and the night sky is worth it during this time of year. There's just so much to see. Meanwhile, observers near the equator or in the southern hemisphere get to enjoy Orion under warmer skies. Betelgeuse is one of the most intriguing stars in our sky. It's a red supergiant nearing the end of its life, and astronomers estimate it could explode as a supernova sometime within the next 100,000 years. And because it is hundreds of light-years away, it's even possible that that explosion has already happened. Its light simply hasn't reached Earth yet. This star is a reminder that the night sky is active and evolving. So let me know in the comments, can you spot Betelgeuse? Have you ever noticed the color contrast between the stars and the surrounding area? And what stories about this star were told from where you live? As you continue to learn about the night sky, whenever you're able to, try to seek out darker skies. The universe has so much more to show us when we step away from the city lights. Thank you so much for watching, and as always, keep looking up.