EarthSky | Will Betelgeuse explode in tens of years?
Betelgeuse due to explode soon?
Betelgeuse is the nearest red supergiant star to Earth. Distance estimates vary, but it’s probably within 1,000 light-years of Earth … a hop and a skip in galactic terms. Someday, Betelgeuse will explode as a supernova. When it does, it might become as bright as a full moon. It might even be visible in broad daylight! But when will Betelgeuse explode? A decade ago, this question was interesting but academic. The answer was: Maybe today. Maybe a thousand years from now. Few imagined it would be today. But now there’s been a noticeable uptick in the brightening and dimming of Betelgeuse. And a new paper – published this week (June 1, 2023) – suggests not thousands of years but “tens of years” as Betelgeuse’s explosion timescale.
The paper focuses on the concept of stellar nucleosynthesis, the process that enables stars to shine. Inside stars, simple atoms fuse to make more complex atoms, with energy as a by-product. It’s when a star’s nuclear fuel runs out, that a supernova occurs. Arxiv.org, an open-access repository, published the new study on June 1. It’s called The evolutionary stage of Betelgeuse inferred from its pulsation periods. The scientists said:
We conclude that Betelgeuse is … a good candidate for the next galactic supernova.
The first author is Hideyuki Saio from the Astronomical Institute, Graduate School of Science, at Tohoku University in Japan. The Monthly Notices of the Royal Astronomy Society has accepted the paper for publication.
It’s got people talking
Let’s be clear. The history of observations of supernovae within our own Milky Way is sketchy. But we’d surely be lucky to see any galactic supernova, much more one as nearby as Betelgeuse, in our lifetimes.
And Betelgeuse exploding in just tens of years? That’s an amazing thought, and has people talking!
But is it realistic?
Tens of years?!
What follows are a couple of tweets that have set off a new round of chatter on Twitter. The first – from Friday, June 2 – points to the “tens of years” scenario.
Yikes – serious scientific evidence that Betelgeuse might explode within “tens” of years.https://t.co/bgRqK9l97u
— Dr Jan Eldridge (@astro_jje) June 2, 2023
An almost 50% brightness increase
A second notable tweet – from @Betelbot on Twitter, which provides daily status reports on the star – is from May 18, 2023. It points to a recent almost 50% brightness increase for the star! Note that Betelgeuse is behind the sun in summer. So, until it emerges before dawn in late summer, we won’t know what it’s doing.
Now at 142% of my usual brightness! #Betelgeuse pic.twitter.com/S7TuFTcjdj
— Betelgeuse Status (@betelbot) May 18, 2023
The background buzz on Betelgeuse
Stars shine because they undergo thermonuclear fusion reactions in their interiors. Simply put, they fuse simple elements (like hydrogen) to create more complex elements (like helium), with energy as the by-product. As massive stars (eight or more solar masses) age, they run out of the simplest fuels, but progressively burn more complex fuels until ultimately their cores are made of iron … and then nuclear burning ceases. At that point, with no more fusion taking place, the high temperatures in a star’s interior drop. And that means the high pressures in the star’s interior drop too. The star begins to collapse on itself. It collapses … then rebounds in a terrific explosion, a supernova.
So, massive stars like Betelgeuse explode as Type II supernovae – collapsing rapidly and exploding violently – after they exhaust their fuel supply.
And so, when a star explodes depends on what’s going on inside the star, on how much fuel it has left, and on how close it is to collapse.
But what’s going on inside Betelgeuse?
The new online study said:
We conclude that Betelgeuse is in the late stage of core carbon burning …
And the carbon burning phase for a massive star like Betelgeuse lasts around 1,000 years. If we are “near the end” of that stage, then Betelgeuse has neared the end of its lifetime and may be about to explode, perhaps even in “tens of years.”
But are there other possibilities? Of course there are.
UniverseToday published a great story on Betelgeuse on Friday, June 2, 2023, that explains some of the science involved with drawing any conclusion about whether Betelgeuse will explode soon. The author pointed out that:
… What hasn’t attracted as much attention is the following part of the paper.
‘In fact, it is not possible to determine the exact evolutionary stage, because surface conditions hardly change in the late stage close to the carbon exhaustion and beyond,’ the researchers write. Astronomers can only see the surface, but it’s what’s happening deep inside the star that tells the tale.
The authors of the paper are really saying that according to observations, data, and modelling, Betelgeuse could explode sooner than thought. But – and this is critical – they don’t know what stage of core carbon-burning the star’s in. Carbon burning could go on for a long time, according to some of the models that fit the data.
So, basically, we’re back to square one. Betelgeuse might explode tomorrow. It might explode in “tens of years.” Or it might explode in a thousand years.
But why did Betelgeuse dim in 2019?
In late 2019, Betelgeuse sparked excitement around the world when it began dimming noticeably. Astronomers now refer to this event as the Great Dimming of Betelgeuse. As it was happening, many believed (and hoped!) the big event – the explosion of this relatively nearby star – was close at hand.
Of course – although Betelgeuse since regained brightness, then dimmed again, now brightened again, and so on – it has not exploded yet.
So why did it dim?
Analyzing data from NASA’s Hubble Space Telescope and several other observatories, astronomers concluded that the bright red supergiant star Betelgeuse quite literally blew its top in 2019. Betelgeuse lost a substantial part of its visible surface and produced a gigantic Surface Mass Ejection (SME). This is something never before seen in a normal star’s behavior.
Our sun routinely blows off parts of its tenuous outer atmosphere, the corona, in an event known as a coronal mass ejection (CME). But the Betelgeuse SME blasted off 400 billion times as much mass as a typical CME!
Read more: Betelgeuse is recovering from blowing its top
So, the Great Dimming of Betelgeuse in 2019 was apparently caused by a cloud of hot gas, expelled by the star, that temporarily blocked some of the star’s light.
Clearly, some game is afoot at Betelgeuse!
Will its supernova destroy Earth?
Whenever Betelgeuse does blow up, our planet Earth is too far away for this explosion to harm, much less destroy, life on Earth. Studies indicate we’d have to be within 160 light-years of a supernova for it to harm us. And Betelgeuse is perhaps four times this distance.
Instead, anyone alive on Earth when Betelgeuse does finally explode will see an amazingly beautiful sight in the night sky – a very, very, very bright star.
And professional astronomers will be happy to have an exploded Betelgeuse so close. They’ll be able to study the star post-supernova.
Meanwhile, amateur astronomers and casual stargazers will enjoy the explosion, too. But the many who enjoy seeing Betelgeuse as Orion’s bright red star will dearly miss it when it’s gone!
Betelgeuse in the night sky
At mid-northern latitudes, around the first of every year, Betelgeuse rises around sunset. The star is prominent on January and February evenings.
By the beginning of March, this star is due south in early evening. By mid-May, it is briefly visible in the west after sunset. Betelgeuse is traveling behind the sun in early summer, but it returns to the east before dawn by about mid- to late July. Certainly, by early August, you can see Betelgeuse in Orion in the east before sunrise, where the constellation is known as the ghost of the summer dawn.
The star Betelgeuse has a distinctive muted orange-red color. It’s ideal for convincing non-believers that stars do, in fact, come in colors.
Stars designated as Alpha are typically brightest in their constellations. But Betelgeuse is Alpha Orionis, despite the fact that it’s fainter than Orion’s other bright star, Rigel.
Betelgeuse is the 10th-brightest star in the sky overall, and it’s the 7th-brightest star visible from most of the U.S., Canada, Europe and the majority of the Northern Hemisphere.
Pop culture, history and mythology
Remember the movie Beetlejuice? This star’s name is similar to that.
The proper names of many bright stars are Arabic in origin. This fact reflects the dominance of Arabic astronomers and astrologers during Europe’s Dark Ages. The name Betelgeuse is derived from an Arabic phrase that is usually translated as The Armpit of the Giant. Of course, the Giant refers to Orion, but – rather than an armpit – some authors see Betelgeuse as representing a hand or sometimes a shoulder. While it is not entirely clear what the name means, Betelgeuse marks the right shoulder of Orion in many old star maps.
In the ancient myths, Orion is most often associated with a giant, a warrior, a hunter, a god or some other anthropomorphic or animal figure, so it is not surprising that most depictions of Betelgeuse have an anatomical connection. The Sanskrit name signified an arm, too, for example, although it likely was really the leg of a stag. In parts of Brazil, Betelgeuse was seen as the hind leg of a caiman (crocodilian) or the foreleg of a turtle. On the other hand, in ancient Japan, Betelgeuse was considered to be part of the rim of a ceremonial drum. In Peru, it was one of four vultures about to devour a criminal.
The position of Betelgeuse is RA 05h 55m 10.3053s, dec +07° 24′ 25.4″.
Bottom line: Betelgeuse is due to explode as a supernova someday, although maybe not soon on a human timescale. When it does explode, it’ll be bright enough from our earthly vantage point to shine during the day. But it’s far enough away that Earth won’t be in any danger.
Source of “tens of years” paper: The evolutionary stage of Betelgeuse inferred from its pulsation periods
Read more: Colors of Betelgeuse in a star collage
Vega is a bright bluish star on May evenings
Vega shines brightly on May evenings
Look for Vega tonight. It’s the 5th brightest star in our sky. If you’re in the Northern Hemisphere, you’ll find beautiful, bluish Vega easily, simply by looking northeastward at mid-evening in May. Vega is so bright that you can see it on a moonlit night.
From far south in the Southern Hemisphere, you can’t see Vega until late at night in May. That’s because Vega is located so far north on the sky’s dome. Vega will reach its high point for the night around three to four hours after midnight, at which time people in the Southern Hemisphere can see Vega in their northern sky. As seen from mid-northern latitudes, Vega shines high overhead at this early morning hour.
Because it’s the brightest star in the constellation Lyra the Harp, Vega is sometimes called the Harp Star. Like all stars, Vega rises some four minutes earlier each day as Earth moves around the sun. So Vega will adorne our evening sky throughout the summer and fall.
It’s visible most nights from mid-northern latitudes
Although Vega is considered a late spring or summer star, it’s actually so far north on the sky’s dome that – from mid-latitudes in the Northern Hemisphere – you can find it at some time during the night, nearly every night of the year.
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Bottom line: If you’re in the Northern Hemisphere, Vega is easy to identify in its constellation Lyra at this time of year. Just look northeast in the evening hours for a bright, bluish star above the northeastern horizon.
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Spica, the bright beacon of Virgo, is 2 stars
Spica is a close double star
The star Spica – aka Alpha Virginis – is the brightest star in the constellation Virgo the Maiden. From a distance of about 250 light-years away, Spica appears to us on Earth as a lone bluish-white star in a quiet region of the sky. But Spica consists of two stars and maybe more. In fact, the pair are both larger and hotter than our sun, and they’re separated by only 11 million miles (less than 18 million km). Plus, they orbit their common center of gravity in only four days.
Earth is 93.3 million miles (150 million km, or 1 astronomical unit aka AU) from our sun. Spica’s two stars are only .12 AU from each other, a small fraction of the Earth-sun distance.
And the two stars in the Spica system are individually indistinguishable from a single point of light, even with a telescope. Only the analysis of its light with a spectroscope – an instrument that splits light into its component colors – revealed the dual nature of this star.
Hot, hot, hot
Spica’s two stars are so close, and they orbit so quickly around each other, that their mutual gravity distorts each star into an egg shape. It’s thought that the pointed ends of these egg-shaped stars face each other as they whirl around.
The pair of stars are both dwarfs, brightening near the end of their lifetimes.
Spica is one of the hottest 1st-magnitude stars. The hottest of the pair is 22,400 Kelvin (about 40,000 F or 22,000 C). That’s blistering in contrast to the sun’s 5,800 Kelvin (about 10,000 F or 5,500 C). This star might someday explode as a supernova.
The light from Spica’s two stars, taken together, is on average more than 12,100 times brighter than our sun’s light. Their estimated diameters are 7.8 and four times our sun’s diameter.
Also, Spica is one of several bright stars that the moon can occult (eclipse). Furthermore, based on observations of how the star’s light is extinguished when the moon passes in front, some astronomers think that it may not just be a spectroscopic binary star. Instead, they feel that there may be as many as three other stars in the system. In that case, Spica would not be a single or even a double star, but a quintuple star!
How to find Spica
The best evening views of Spica come from northern spring to late northern summer, when this star arcs across the southern sky in the evening. So in the month of May, as seen from the Northern Hemisphere, you’ll find Spica in the southeast in early evening. Then, from the Southern Hemisphere, Spica is closer to due east. From all of Earth in May, as night passes, Spica appears to move westward. Spica rises earlier each evening so that – by the end of August – Spica can be viewed only briefly in the west to west-southwest sky as darkness falls.
At least there’s a fool-proof way to find Spica, using the Big Dipper as a guide. Scouts and stargazers remember this trick with the saying: Follow the arc to Arcturus, and speed on (or drive a spike) to Spica.
Look for the Big Dipper
First, look for the Big Dipper in the northern sky. It’s highest in the evening sky in the northern spring and summer. Notice that the Big Dipper has a bowl and a long, curved handle. Follow the arc of the Dipper’s handle outward, away from the Dipper’s bowl. The first bright star you come to is orange Arcturus. Then drive a spike (or speed on) along this curving path. And the next bright star you come to is Spica.
Spica shines at magnitude 1.04, making it the brightest light in Virgo. In fact, it’s the 15th-brightest star visible from anywhere on Earth. It’s virtually the same brightness as Antares in the constellation Scorpius, so sometimes Antares is listed as the 15th and Spica as the 16th brightest.
History and mythology of Spica
The name Spica is from the Latin word for “ear” (of grain). The general connotation is that Spica refers to an “ear of wheat.” Indeed, the star and the constellation Virgo itself were sometimes associated with the Greek goddess of the harvest, Demeter.
There are many names and stories for Spica’s constellation – Virgo – in mythology, and by association with Spica as well. Fewer stories refer to Spica independently. Many classical references refer to Virgo’s stars as a goddess or with some association with wheat or the harvest, since the sun passes through Virgo in the fall. In Greece and Rome she typically was Astraea, the very personification of Justice; or Persephone, daughter of Demeter. In Egypt, Virgo was identified with Isis, and Spica was considered her lute bearer. In ancient China, Spica was a special star of spring known as the Horn.
One Arabic name was Azimech, derived from words meaning Defenseless One or Solitary One. This title may be in reference to Spica’s solitary status with no other bright stars nearby. But Spica is not the most solitary star. That honor goes to Fomalhaut, sometimes called the Autumn Star.
Spica’s position is RA: 13h 25m 12s, dec: -11° 09′ 41″
Bottom line: Spica is the brightest star in Virgo. Spica is at least two stars orbiting extremely close together, distorting each other into egg shapes.
Virgo? Here’s your constellation
Find the Keystone in Hercules, and M13
Use Vega to locate the Keystone in Hercules
In late spring, from mid-northern latitudes, you can easily find the brilliant star Vega in the eastern sky at dusk and nightfall. The brilliant blue-white star Vega acts as your guide star to the Keystone, a wedge-shaped pattern of four stars in the constellation Hercules.
Look for the Keystone asterism – star pattern – to the upper right of Vega. Or hold your fist at arm’s length, it’ll easily fit between Vega and the Keystone.
Also, you can locate the Keystone by using Vega in conjunction with the brilliant yellow-orange star Arcturus. The Keystone is found about 1/3 of the way from Vega to Arcturus, the two brightest stars to grace the Northern Hemisphere’s spring and summertime sky. From mid-northern latitudes this time of year, Arcturus is found quite high in the eastern sky at nightfall and evening. Then, by late evening, Arcturus will have moved high overhead.
Use the Keystone to find M13
Furthermore, the Keystone is your ticket to find a famous globular star cluster in Hercules, otherwise known as the Hercules cluster, aka Messier 13 or M13.
Most likely, you’ll need binoculars to see the Hercules cluster. Although sharp-eyed people can see it with the unaided eye in a dark, transparent sky. But through binoculars, this cluster looks like a dim smudge or a somewhat fuzzy star. However, a telescope begins to resolve this faint fuzzy object into what it really is, a great big, globe-shaped stellar city populated with hundreds of thousands of stars!
Then, later in the evening, the Keystone and the Hercules cluster swing high overhead after midnight, and are found in the western sky before dawn.
Photos of M13 from EarthSky Community Photos
Bottom line: Let the bright star Vega guide you to a famous star pattern in Hercules – called the Keystone – and then to the Hercules cluster, aka M13, a famous globular star cluster.
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Polaris â the North Star â is part of the Little Dipper
Don’t wait for it to set
The North Star or Pole Star – aka Polaris – is famous for holding nearly still in our sky while the entire northern sky moves around it. That’s because it’s located very close to the north celestial pole, the point around which the entire northern sky turns. Although it’s a common belief, Polaris is not the brightest star in the nighttime sky. In fact, it’s only the 48th brightest star. But you can find it easily, and, once you do, you’ll see it shining in the northern sky every night from Northern Hemisphere locations.
Polaris marks the spot that is due north. As you face Polaris and stretch your arms sideways, your right hand points due east, and your left hand points due west. Then, an about-face from Polaris steers you due south.
A star to steer by
In a dark country sky, even when the full moon obscures a good deal of the starry heavens, the North Star is relatively easy to see. That fact has made this star a boon to travelers throughout the Northern Hemisphere, both over land and sea. So finding Polaris means you know the direction north.
Best of all, you can readily find Polaris by using the prominent group of stars known as the Big Dipper, called the Plough in the United Kingdom, which may be the Northern Hemisphere’s most famous star pattern. To locate Polaris, all you have to do is to find the Big Dipper pointer stars Dubhe and Merak. These two stars outline the outer part of the Big Dipper’s bowl. Simply draw a line from Merak through Dubhe, and go about five times the Merak/Dubhe distance to Polaris.
This clock runs backward
The Big Dipper, like a great big hour hand, goes full circle around Polaris in one day. More specifically, the Big Dipper circles Polaris in a counterclockwise direction in 23 hours and 56 minutes. Although the Big Dipper travels around Polaris all night long, the Big Dipper pointer stars always point to Polaris on any day of the year, and at any time of the night. Polaris marks the center of nature’s grandest celestial clock!
It’s part of the Little Dipper
By the way, Polaris is famous for more reasons than one. It’s famous for hardly moving while the other stars wheel around it. And it’s famous for marking the end of the Little Dipper‘s handle. The Little Dipper is tougher to spot in the night sky than the Big Dipper. But if you use the Big Dipper’s pointer stars to locate Polaris, you’ll be one step closer to seeing the Little Dipper.
Its height in the sky depends on your location
As you travel northward, Polaris climbs higher in the sky. If you go as far north as the North Pole, you’ll see Polaris directly overhead.
As you travel south, Polaris drops closer to the northern horizon.
If you get as far as the equator, Polaris sinks to the horizon.
South of the equator, Polaris drops below the northern horizon.
History of Polaris
Polaris hasn’t always been the North Star and won’t remain the North Star forever. For example, a famous star called Thuban, in the constellation Draco the Dragon, was the North Star when the Egyptians built the pyramids.
But Polaris is a good North Star because it’s the sky’s 48th brightest star. So it’s noticeable in the sky. It served well as the North Star, for example, when the Europeans first sailed across the Atlantic over five centuries ago.
And Polaris will continue its reign as the North Star for many centuries to come. It will align most closely with the north celestial pole – the point in the sky directly above Earth’s north rotational axis – on March 24, 2100. The computational wizard Jean Meeus figures Polaris will be 27′ 09″ (0.4525 degrees) from the north celestial pole at that time (a little less than the angular diameter of the moon when at its farthest from Earth).
Meanwhile, there is no visible star marking the celestial pole in the Southern Hemisphere. What’s more, the Southern Hemisphere won’t see a pole star appreciably close to the south celestial pole for another 2,000 years.
Trusting Polaris with their lives
At one time in human history, people literally depended on their lucky stars for their lives and livelihood. Luckily, they could trust the Big Dipper and the North Star to guide them. People could sail the seas and cross the trackless deserts without getting lost. When slavery existed in the United States, people escaping slavery counted on the Big Dipper to show them the North Star, lighting their way to the free states and Canada.
While being honored as the North Star, Polaris enjoys the title of Lodestar and Cynosure as well.
Polaris is a triple star
The single point of light that we see as Polaris is a triple star system, or three stars orbiting a common center of mass. The primary star, Polaris A, is a supergiant with about six times the mass of our sun. A close companion, Polaris Ab, orbits 2 billion miles from Polaris. You are unlikely to ever see this star, because it is too close to Polaris.
Much farther away, near the top of this illustration, is the third companion, Polaris B. Polaris B, magnitude 8.7, is located approximately 240 billion miles from Polaris A. This translates to 18.4 arcseconds, and you can split these two stars in a small telescope. This split is always a hit at public star parties. The two companion stars are the same temperature as Polaris A but are dwarf stars.
Star bright, 48th star I see tonight
Astronomers estimate Polaris’ distance at 434 light-years. Considering the distance, Polaris must be a respectably luminous star. Polaris is a yellow supergiant star shining with the luminosity of 1,260 suns.
And it varies in brightness, too!
Polaris is a variable star. In the past, it had varied between magnitudes 1.86 and 2.13 every four days. In recent decades, this variability decreased from 10% to 2%, then it went back up to 4% variability. Astronomers are not sure why this happened. It’s the type of variable star known as a Cepheid variable star, a class of stars that astronomers use to figure distances to star clusters and galaxies.
Seeing Polaris in a telescope during the day
Since Polaris hardly moves, this makes it easy to see in the daytime. Set your telescope on Polaris in the early morning, before dawn. Focus sharply on it. Turn off your clock drive, if you have one, and keep your telescope stationary. Come back just after sunrise and look for it again. It should still be in your field of view, having moved about 30 arcminutes in the past three hours.
What’s the RA today?
In the year 2000, Polaris’ position was RA: 2h 31m 48.7s, dec: +89° 15′ 51″. Due to precession, since this star is so close to the celestial north pole, its Right Ascension (RA) can change quickly. Presently it is sitting at about 03h 00m. Here is a graph showing how the RA of the star changes over the next century.
The view of Polaris you will never see: the Integrated Flux Nebula
Just when you think you have seen it all … maybe you have. Because this next bit will blow your mind, and you will never visually see it. Below we see an image of Polaris, which is several images stacked to bring out the contrast. Those are not clouds in our atmosphere. They are not clouds between us and Polaris. They are clouds well beyond Polaris, illuminated by the light of our galaxy. These clouds are called the Integrated Flux Nebula. I am not making this up: see here.
Bottom line: Polaris is the North Star; the entire northern sky wheels around it. But it’s not the brightest star in the sky. In fact, Polaris ranks only 48th in brightness.
Read more: Does Mars have a North Star?
Read more: Does the North Star ever move?
Arcturus, the brightest star of the northern sky
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Arcturus is a red giant star located only 36.7 light-years away. It’s the 4th-brightest star in the sky and the brightest one in the northern half of the sky. Look for it on spring evenings in the Northern Hemisphere by arcing to Arcturus from the Big Dipper‘s handle.
Arcturus is the alpha star of a cone-shaped constellation called Boötes the Herdsman. It’s far enough north on the sky’s dome that – for Northern Hemisphere observers – it’s visible during some part of the night throughout most of the year. There’s an easy mnemonic for identifying this brilliant orange star. Just remember the phrase follow the arc to Arcturus and then spike to Spica.
First, locate the Big Dipper in the northern sky. Notice that the handle of the Big Dipper is a curve or arc. Extend this curve past the end of the Big Dipper’s handle, and you’ll reach Arcturus.
A lonely bright star
You might notice sparkling orange Arcturus passing high overhead on late spring evenings. In summer, Arcturus is high in the sky shortly after dark. Autumn observers need to look early because it sets by mid-evening. In winter, the best time to observe it is in the wee hours before dawn.
Unlike most of the bright stars in the nighttime sky, Arcturus has no bright neighbors. It commands the sky in the springtime and reigns the heavens until the Summer Triangle takes over the eastern sky.
Our chart below shows the constellation Boötes as you stand facing east on spring evenings. Seeing a Herdsman in these stars might be difficult, but the constellation is easy to imagine as a kite.
Arcturus is the brightest star north of the celestial equator
What does that mean? Imagine that Earth’s equator projected onto the sky. This line above Earth’s equator is the celestial equator. It divides the sky into northern and southern hemispheres, just as Earth’s equator does for Earth. The three brightest stars of the sky – Sirius, Canopus and Alpha Centauri – are south of the celestial equator.
Meanwhile, Arcturus is the brightest star in the northern part of the sky. It is only marginally brighter than the Northern Hemisphere’s second-brightest star, Vega. Some people believe that Polaris, the North Star, is the brightest star in the sky because it is famous. But it’s quite faint, only about the 50th brightest star.
Visible during daytime
In 1635, less than three decades after the invention of the telescope, Jean-Baptiste Morin of France observed Arcturus in the daytime with the telescope. This was the first time that any star, besides the sun and a rare supernova, had been seen telescopically during daylight hours. You can go one step further and observe Arcturus with the unaided eye during the daytime. Here is an account from 1911 of how you can do this.
History and mythology of Arcturus
Arcturus’ constellation Boötes the Herdsman is sometimes pictured as guarding the Great Bear, or Ursa Major, which contains the Big Dipper asterism. We sometimes hear Arcturus called the Bear Guard.
In China, Arcturus’ constellation is also called the Dragon. In some classical Greek stories, Boötes was Icarus, who flew too close to the sun. Passing directly over the Hawaiian islands, Arcturus was a particularly important navigational star to the islands’ indigenous inhabitants and other Polynesians.
The translation may be questioned, but Arcturus is among the few stars mentioned in the Bible. (“Which maketh Arcturus, Orion and Pleiades, and the chambers of the south” – Job 9:9, KJV, and “Canst thou bring forth Mazzaroth in his season? or canst thou guide Arcturus with his sons?” – Job 38:32, KJV.)
1933 Century of Progress Exposition in Chicago
One interesting story about Arcturus relates to the 1933 Century of Progress Exposition in Chicago. Its promoters wanted a flashy way to open the show, so they decided to have the light from Arcturus start the show. At 9:15 pm on May 27, 1933, four telescopes located in different observatories captured the light from Arcturus and focused it into photoelectric cells. The photocells in turn worked as the switch that turned on the main spotlights to open the exhibition. It’s a good thing it wasn’t cloudy!
There had also been a World’s Fair in Chicago in 1893, 40 years before the 1933 show. At the time, astronomers thought that Arcturus was 40 light-years away. If so, that light left Arcturus at the end of the 1893 fair and traveled for 40 years through space like an Olympic torch bearer, to open the 1933 show.
The promoters of Chicago’s World’s Fair had a great idea, but today’s astronomers place the distance to Arcturus at just less than 37 light-years. Maybe it should have been used for the groundbreaking ceremony!
Arcturus is large and old
Arcturus is most likely considerably older than our sun. When the sun evolves to become a red giant, it will be a star much like Arcturus is now.
Arcturus’ diameter is roughly 25 times greater than our sun. Because of its larger size, Arcturus radiates more than 100 times the light of our sun, in visible light. If you consider infrared and other frequencies in the electromagnetic spectrum, Arcturus is about 200 times more powerful than the sun. Its mass is slightly greater than that of our sun.
The reddish or orange color of Arcturus signifies its temperature, which is about 7,300 degrees Fahrenheit (around 4,000 degrees Celsius). That makes it several thousand degrees cooler than the surface of the sun.
Flying south to the winter sky
The bright orange star Arcturus is especially noteworthy for its large proper motion, or sideways motion, on the dome of Earth’s sky. Only Alpha Centauri – our sun’s nearest neighbor among the stars – has a higher proper motion among the 1st-magnitude, or bright, stars in our stellar neighborhood. And of course, the large proper motion of Alpha Centauri stems from the fact that it’s so close to us.
In the meantime, what does the proper motion of Arcturus tell us?
It tells us that Arcturus is moving at a tremendous speed (122 km/s or 76 miles/s) relative to our solar system. Arcturus is thought to be an old star. It appears to be moving with a group of at least 52 other such stars, known as the Arcturus stream or Arcturus moving group. Scientists believe these stars were not originally part of the Milky Way but came from a dwarf satellite galaxy whose stars have now become assimilated into the Milky Way.
Gone in 150,000 years!
From the vantage point of Earth, Arcturus is rapidly moving in a southerly direction at a rate of 3.9 arcminutes per century. It’s now at about its closest point to Earth. As it moves away it will vanish from visibility to the unaided eye when it reaches the Carina-Vela border in about 150,000 years.
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The position of Arcturus is RA: 14h 15 m 39.7s, dec: +19° 10′ 56″
Bottom line: The 4th-brightest star in all the sky is Arcturus, a brilliant orangish star that’s easy to find in Northern Hemisphere spring skies with the aid of the Big Dipper.
Mars in 2023: Still bright in April and May
Mars sometimes appears bright in our sky and sometimes appears faint. In early 2023, Mars appeared as bright as the sky’s brightest stars. By June 2023, Mars will start to fade dramatically in brightness and appear close to the sunset. By October, November and December, 2023, Mars will be lost from our view … behind the sun.
Mars in 2023
Opposition for Mars last fell on December 8, 2022. That’s when our planet Earth last flew between Mars and the sun. As 2023 began, Mars was still bright. But it’s fading now – and appearing in the sky for fewer hours of the night – as Earth races ahead in our smaller, faster orbit around the sun.
How to see Mars in the sky: In April and May 2023, Mars will be in the western evening sky. Mars has faded in brightness and now blends in with the other 1st-magnitude stars. That is, it still appears as one of the brightest stars in our sky. The moon will sweep past Mars on May 24. Mars will be edging toward the famous Beehive star cluster. See the charts below.
Constellations in April and May 2023: Mars is in front of the constellation Gemini this month. It’ll cross the border between Gemini and Cancer in mid-May.
Note: Mars reaches opposition only about every 26 months, or about every two Earth-years. So Mars alternates between appearing bright and faint in our sky. It was bright in late 2022 and early 2023. But by about June 2023, Mars will start to fade dramatically in brightness. It’ll disappear in the sunset glare around October 2023. It’ll pass behind the sun on November 18. It’ll come back into view, in the east before sunrise, in early 2024.
First part of May: Mars in Gemini
May 22-23 evenings: Moon will pass Venus, Castor, Pollux and Mars
May 24 evening: Moon will visit Mars and the Beehive
View from above the solar system, April and May 2023
Sometimes, Mars is faint
Mars was in our evening sky for much of 2021. But, around October, the red planet disappeared from our sky for a time. Its superior conjunction – when it was most directly behind the sun as seen from Earth – was October 8, 2021. Then, some weeks afterwards – as both Earth and Mars moved in their respective orbits around the sun – Mars returned to our sky as a faint red dot in the east before sunrise. To be sure, it remained inconspicuous throughout the early months of 2022.
Sometimes, Mars is bright
Mars steadily brightened in the first half of 2022, first as a morning object. But later, during the second half of 2022, Mars shone as a bright red ruby in the evening sky. Ultimately, it reached opposition – when Earth flew between Mars and the sun – on December 8, 2022.
Indeed, Mars’ dramatic swings in brightness (and its red color) are why the early stargazers named Mars for their God of War.
Sometimes the war god rests. And sometimes he grows fierce! In fact, these changes are part of the reason Mars is so fascinating to watch in the night sky.
Want to follow Mars? Bookmark EarthSky’s monthly night sky guide.
Mars isn’t very big
To understand why Mars varies so much in brightness in Earth’s sky, first realize that Mars isn’t a very big world. Indeed, it’s only 4,219 miles (6,790 km) in diameter, making it only slightly more than half Earth’s size (7,922 miles or 12,750 km in diameter).
On the other hand, consider Mars in contrast to Jupiter, the biggest planet in our solar system. Jupiter is 86,881 miles (140,000 km) in diameter. As an illustration, more than 20 planets the size of Mars could be lined up side by side in front of Jupiter. Basically, Jupiter always looks bright, because it’s so big.
Not so for little Mars, however. Rather, its extremes in brightness have to do with its nearness (or lack of nearness) to Earth.
Future Martian oppositions
So, when is the next opposition of Mars? The next time Mars will appear at its brightest for that two-year period in our sky? You guessed it. In January 2025! Check out the chart on this page that lists all oppositions of Mars from 1995 to 2037.
Mars appears as a reddish light in the sky and, therefore, is often called the Red Planet. Other obvious red dots in the sky are reddish-orange Aldebaran and the famous red supergiant Betelgeuse. So, it is fun to compare Mars’ color and intensity of red with that of Aldebaran or Betelgeuse.
Surface temperature is what determines the colors of the stars. The hottest stars are blue and the coolest stars are red. In fact, from hottest to coolest, the colors of stars range from blue, white, yellow, orange and red. And while the colors of stars might be hard to detect, some stars – like Aldebaran and Betelgeuse – are noticeably colorful.
On the other hand, Mars appears red for a different reason. It’s red because of iron oxide in the dust that covers this desert world. Iron oxide gives rust and blood its red color. Rovers on Mars sampled the Martian dust and determined it contains three colors: reds, browns and oranges. So those three colors are what you may see when you gaze upon Mars.
Do you see red when you look at Mars, Aldebaran and Betelgeuse? Are they the same color? Do you see any other colors of stars?
Bottom line: Mars is still bright, but it’s destined to fade in brightness and appear for fewer hours of the night … See Mars while you can! Charts for April and May 2023 here.
Moon and Mars! Fav photos of December 7 occultation
Photos of bright Mars in 2018, from the EarthSky community
Photos of bright Mars in 2020, from the EarthSky community
Alpha Centauri, the star system closest to our sun
Our closest stellar neighbors are the 3 stars that are the Alpha Centauri system. They lie just over 4 light-years away (25 trillion miles or 38 trillion km).
The post Alpha Centauri, the star system closest to our sun first appeared on EarthSky.
Acrux is the brightest star in the Southern Cross
You have to go far south on Earth’s globe to see the Southern Cross constellation. Bluish Acrux, aka Alpha Crucis, is its brightest star.
The post Acrux is the brightest star in the Southern Cross first appeared on EarthSky.
Planet-observing is fun and easy: Top tips here
Get our top tips for planet-observing, from the innermost and elusive Mercury out to faint blue Neptune and everything in between.
The post Planet-observing is fun and easy: Top tips here first appeared on EarthSky.