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EarthSky | Will Betelgeuse explode in tens of years?

Betelgeuse: Orange ball of fire exploding in brilliant white, surrounded by gas and dust.
Artist’s concept of the old red supergiant star Betelgeuse as a supernova, or exploding star. Scientists have found a supernova warning sign for stars like Betelgeuse. Before exploding, these stars dim dramatically. And, in 2019, Betelgeuse did undergo a great dimming. Image via Royal Astronomical Society/ ESO/ L. Calçada/ CC BY 4.0.

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., 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.

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.

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.

Star chart of constellation Orion with stars labeled.
Betelgeuse is a beloved star. It’s a highly noticeable star in the constellation Orion the Hunter, 1 of 2 very bright stars in Orion. It marks the right shoulder of the Hunter. The other bright star is Rigel, which marks the Hunter’s left foot. Notice Betelgeuse and Rigel on either side of the short, straight row of 3 medium-bright stars. But, in Northern Hemisphere summer, Betelgeuse is behind the sun. It will emerge around late July or early August.

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!

Four panels of orange star releasing glowing gas cooling to create a dust cloud.
This artist’s concept shows how Betelgeuse belched a hot bubble of gas that then cooled into a dust cloud and temporarily blocked some of the star’s light from Earth’s point of view. Image via NASA/ ESA/ E. Wheatley (STScI).

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.

Starfield with bright, colorful stars of Orion with Sirius below over tropical trees.
View at EarthSky Community Photos. | Betelgeuse is the bright red-orange star in the upper left of this photo by Nikunj Rawal, who captured it at Gir National Park in India on November 21, 2020. Nikunj wrote: “Orion the Hunter in the late night.” Thanks, Nikunj!

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″.

Betelgeuse: A fuzzy red star, surrounded by a shell and multiple thin red arcs.
This far-infrared image from 2013 shows multiple arcs around Betelgeuse, an old red star. The arcs you see here are winds from Betelgeuse crashing against the surrounding interstellar medium, creating a bow shock as the star moves through space. Image via ESA/ Herschel Space Observatory. Read more about this image.

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

First SpaceX Starlink launch for June. Watch here

Starlink: A white and black cylindrical vehicle launches upward into a blue sky, leaving behind clouds of smoke on the brown ground.
SpaceX’s Starlink Group 2-9 launched on May 10, 2023. Image via SpaceX.

Starlink launches in 1st half of June 2023

Starlink Group 6-4: June 4, 2023, 9:56 – 13:36 UTC (5:56 a.m. – 9:36 a.m. EDT)
Falcon 9 Block 5 | Cape Canaveral, Florida | DATE/TIME MAY CHANGE

Starlink Group 5-11: June 5, 2023, 6:15 – 13:06 UTC (2:15 a.m. – 9:06 a.m. EDT)
Falcon 9 Block 5 | Cape Canaveral, Florida | DATE/TIME MAY CHANGE

Starlink Group 5-12: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

Starlink Group 5-13: DATE/TIME TBA
Falcon 9 Block 5 | Vandenberg SFB, California

Starlink Group 5-7: DATE/TIME TBA
Falcon 9 Block 5 | Vandenberg SFB, California

Starlink Group 5-8: DATE/TIME TBA
Falcon 9 Block 5 | Vandenberg SFB, California

Starlink Group 6-10: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

Starlink Group 6-11: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

Starlink Group 6-12: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

Starlink Group 6-13: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

Starlink Group 6-14: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

Starlink launches in 2nd half of June 2023

Starlink Group 6-15: DATE/TIME TBA
Falcon 9 Block 5 | Vandenberg SFB, California

Starlink Group 6-16: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

Starlink Group 6-17: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

Starlink Group 6-18: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

Starlink Group 6-20: DATE/TIME TBA
Falcon 9 Block 5 | Vandenberg SFB, California

Starlink Group 6-22: DATE/TIME TBA
Falcon 9 Block 5 | Vandenberg SFB, California

Starlink Group 6-23: DATE/TIME TBA
Falcon 9 Block 5 | Vandenberg SFB, California

Starlink Group 6-5: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

Starlink Group 6-6: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

Starlink Group 6-7: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

Starlink Group 6-8: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

Starlink Group 6-9: DATE/TIME TBA
Falcon 9 Block 5 | Cape Canaveral, Florida

You can check back here or go directly to SpaceX’s YouTube channel for a livestream of the launch. Livestreams typically begin about five minutes before liftoff.

After launch, look for a train of lights

Following every Starlink launch, the internet buzzes with people asking:

What’s that long line of lights in the sky that looks like a train?

What you’re seeing is the Starlink satellites moving into a higher orbit. You can check to see if they will pass over your area using the Find Starlink website.

Growing numbers amid controversy

According to Wikipedia, as of May 2023, Starlink consists of over 4,000 mass-produced small satellites in low Earth orbit that communicate with designated ground transceivers. Overall, they provide internet access to more than 1.5 million subscribers.

Love ’em or hate ’em, these Starlink satellites are part of SpaceX’s vision for a global internet communication satellite constellation. They deliver high-speed internet service worldwide, mainly to locations where ground-based internet is unreliable, unavailable or expensive. The private company is well-known for launching batches back-to-back, several times a month, regularly lofting 60 satellites at a time. And eventually, SpaceX plans to build up to perhaps as many as 30,000.

To begin with, most thought it was exciting to see the first few Starlink satellites traveling together in the night sky. But, then more were launched, and then more. And astronomers began to worry.

Because Starlinks are bright, astronomers say they’re photobombing astronomical images. Therefore, they have the potential to interfere with the professional astronomical observations that have brought us our modern-day view of the cosmos. And although SpaceX has tried to address the issue, they remain far from what astronomers say is acceptable.

Bottom line: SpaceX’s first Starlink launch for the month is currently scheduled from Florida between 9:48 – 13:28 UTC on June 4, 2023.

Read more from EarthSky: Starlink satellites can look like a plume or train of light

Via Space Launch Schedule

Mars and the Beehive! See them together on June 1 and 2


Mars and the Beehive

On the evenings of June 1 and 2, 2023, you can spot Mars as it passes through a background star cluster known as the Beehive in Cancer the Crab. In fact, Mars appears as a big, bright ruby surrounded by tiny diamonds of distant stars.

First, to find Mars, look for brilliant Venus in the west, which at magnitude -4.3, wants to steal the show. You may also notice two bright stars strung out to one side of Venus. These are the twin stars in Gemini, Pollux and Castor. Above Venus and this duo is a bright, reddish light … that’s Mars. And if you’re in a dark-sky site or have binoculars, you can spot the smattering of stars beside the red planet.

Green line of ecliptic with Venus and Mars circled beside the Beehive cluster, also Castor and Pollux labeled.
The Beehive star cluster in Cancer the Crab gets a visit from reddish Mars on June 1 and 2, 2023. Aim your binoculars at the red planet to see the sparkling background star cluster. Bright Venus, Pollux and Castor are nearby. Read more about Mars and the Beehive below. Chart by John Goss/ EarthSky.

A closer look at the Beehive star cluster

You’ll want binoculars to get a good look at just some of the 1,000 stars in the Beehive. While you can spot the cluster with your eyes alone, they will appear as a misty patch. However, with optical aid, the true nature of this star cluster comes alive.

The stars in this cluster lie about 577 light-years distant. So when you gaze at the Beehive, think about how many planets might reside among these 1,000 stars. We already know of at least two (Pr0201b and Pr0211b).

Circle with arrow showing motion of Mars across the Beehive cluster, with red dots for Mars on 2 dates.
Binoculars will help reveal the Beehive cluster’s many stars near bright Mars. Chart by John Goss/ EarthSky.

Do you have a photo to share? Submit it at EarthSky Community Photos. We sure enjoy seeing them.

Starry sky showing Beehive cluster with reddish Mars nearyby.
View at EarthSky Community Photos. | David Hoskin of Halifax, Nova Scotia, Canada, captured this image on May 31, 2023, and wrote: “This image shows Mars approaching the Beehive Cluster, which is an open star cluster in the constellation Cancer.” Thank you, David.

Bottom line: Spot Mars and the Beehive star cluster together on June 1 and 2, 2023. You’ll want binoculars to get a good view of the starry cluster making a sparkling background for the red planet.

Want to see more night sky events? Visit EarthSky’s night sky guide

Our charts are mostly set for the northern half of Earth. To see a precise view from your location, try Stellarium Online.

A fake climate change theory is going viral on TikTok after Joe Rogan talked about it

/ TikTok videos amplify climate misinformation from Joe Rogan’s podcast. a:hover]:text-gray-63 [&>a:hover]:shadow-underline-black dark:[&>a:hover]:text-gray-bd dark:[&>a:hover]:shadow-underline-gray [&>a]:shadow-underline-gray-63 dark:[&>a]:text-gray-bd dark:[&>a]:shadow-underline-gray”>Illustration by Alex Castro / The Verge A made-up global warming theory discussed in the Joe Rogan Experience podcast is spreading on TikTok despite…

Moon analemma over Egypt’s Great Pyramids

Moon analemma: A figure 8 of moon phases in one sky over the pyramids.
View at EarthSky Community Photos. | Wael Omar in Cairo, Egypt, captured the images to create this moon analemma from April 22 to May 17, 2023. Wael wrote: “I took an image of the moon 50 minutes and 29 seconds later on successive days over almost a lunar month from the same place every day … this will result in a figure eight or infinity sign.” Thank you, Wael! Read more of what Wael had to say below, and learn more about moon analemmas.

A moon analemma

Maybe you’ve already heard of a sun analemma, which is a composite photo of the sun taken over the course of many months. If they’re done correctly, such composites trace out a figure-8 path. Likewise, photos of the moon can be used to create a figure-8 path in our sky, over the course of a lunar month. NASA explains how to capture a moon analemma:

On average the moon returns to the same position in the sky about 50 minutes and 29 seconds later each day. So, photograph the moon 50 minutes 29 seconds later on successive days. Over one lunation or lunar month it will trace out an analemma-like curve as the moon’s actual position wanders due to its tilted and elliptical orbit.

Wael Omar’s lunar analemma

Wael Omar explained his journey to this image:

The journey of this image was really challenging and exhausting. On top of that were the sleepless nights I went through to stay awake waiting for the scheduled time to take the image of the moon. There were also some cloudy nights, and I was a little lucky to see the moon through it when the time of the shoot came.

I used a Canon 200D camera with 18mm lens. During the last week, the images were during daytime. That’s why the moon images on these days are a little blue. They were so faint, but I could see them when I zoomed deeply on the images. Of course the details were absent, so I came up with an idea to use my GOTO mount to point to the location of the moon. (It would be impossible to see it with the unaided eye.) Then I took images with the help of my Redcat 51 scope. Finally, I put them in the same location of the moon on the 18mm lens image.

I took a vacation from work on the last two weeks to be ready for the moon images, as they were after midnight and during daytime. I exerted so much effort to image the foreground, as I climbed up a 50-meter-high building to have a clear view of the pyramids. Then I blended this view with the total analemma I imaged.

Your efforts were well worth it, Wael!

Bottom line: A moon analemma follows the path of the moon over the course of a lunar month. Thanks to Wael Omar for this stunning photo!

Media We Love: The Merlin Bird ID app

Media We Love: A gray bird sits on a fencepost with a squiggly stick in its mouth.
View at EarthSky Community Photos. | Barry Medlin in Hahira, Georgia, captured this image on May 8, 2023. He wrote: “This mockingbird was busy all day bringing in different materials for the nest in our crepe myrtle tree.” Thank you, Barry! The Merlin Bird ID app can help you identify birds in your yard. Read more in this installment of Media We Love.

Media We Love: Merlin Bird ID app

Kelly Kizer Whitt recommends the Merlin Bird ID app

On a relatively quiet Sunday evening in my neighborhood, I sat out on my porch about an hour before sunset. With the construction, lawn mowing and car sounds of the weekday finally absent, the air came alive with a chorus of birds. Using my recently downloaded Merlin Bird ID app from the Cornell Lab of Ornithology, I clicked on Sound ID and the app began recording all the tweets, chirps, caws and coos surrounding me.

I let the app run for 20 minutes, recording bird sounds the entire time. It automatically identified the birds behind the noises. As it did, it kept a running list in the window and would light up yellow beneath each bird’s name to indicate what my phone – and my ears – were hearing.

Over the 20 minutes, the app identified 15 birds. Most of them I was well-acquainted with, as they visit my bird feeders or hang out on my lawn. One of the birds, the common nighthawk, had a special half-filled circle by its name. The half circle indicates that it’s an uncommon species (apparently despite its moniker). Rare species would be indicated by a solid red circle.

It felt a bit like I was getting to know the neighbors better as I saw each new bird species pop up on the list.

My mother, who made me aware of the app, lives about 15 miles (25 km) away from me. Her location is in a forested area, and on the Monday morning after my experiment, she ran Sound ID for 10 minutes. The app counted 33 birds at her site. More than twice as many as mine!

I’m excited to try the app a couple weeks from now as I travel to the Rocky Mountains and “meet” some new birds.

More about the free app

If you want to try the app, it’s free, but it can take up a lot of storage space on your phone. When you first download the app, you’ll want to put in your location and install the “bird pack” for your region. Or – for 1.39 GB of space – you can install the bird pack for both the U.S. and Canada. I plan to travel to Canada later this summer, so I went ahead and put the bigger bird pack on my phone.

Of course, you can also identify birds on the app through photos with their Photo ID option. You can also explore the birds in their database and sign in to create your own list of birds, essential for the true birder.

And once you’ve created a log in, you can use the same log in for things such as the Great Backyard Bird Count, Project FeederWatch and more.

Two blue and white birds face each other with beaks wide open as if shouting.
View at EarthSky Community Photos. | Diane Rains captured this photo of tree swallows in Hudson, Wisconsin, on May 12, 2023. Diane wrote: “In this photo 2 of our resident females argue over a favored nestbox. Fortunately, violence did not erupt!” Thank you, Diane!

Images from the Merlin Bird ID app

Here’s a look at what you’ll see when you download the Merlin Bird ID app. Here’s a screenshot of some of the birds the app identified in my backyard.

A visual of sound waves at top with a list of birds and an image of each below.
Here’s a peek at the list of birds the Merlin Bird ID heard in my yard. Image via Merlin Bird ID/ Kelly Kizer Whitt.

And, if you need to identify a bird you saw, they help you with a step-by-step guide.

Three smart phone screens showing steps on visual identification.
Follow the steps so that Merlin Bird ID can help you identify the bird you saw. Image via Merlin Bird ID.
Icon image showing a cartoon of a black and yellow bird flying with app name below.
The Merlin Bird Id app.

Bottom line: In this installment of Media We Love, EarthSky editor Kelly Kizer Whitt recommends the Merlin Bird ID app.

Sky measurements: Degrees, arcminutes and arcseconds

Five hands with fingers extended in various configurations, showing different widths.
Use this “handy” guide to measure degrees – or sky measurements – on the dome of the sky. Image via Used with permission.

How do you describe how far apart something is in the sky? The fact is, the handiest measuring stick for the sky’s dome is the one on the end of your arm. You can use the width of your pinky, fist and more to gauge the distance between sky objects. That comes in handy when you’re observing conjunctions between planets, or close planets and stars, or planets and stars and the moon, plus many other space objects. You’ll often find these objects described as being a certain number of degrees, arcminutes or arcseconds apart.

Use this “handy” tool for sky measurements

To begin with, from one side of the sky – or the horizon – all the way across to the other horizon measures 180 degrees, or half a circle. Therefore, from horizon to zenith, the point straight above your head, should be 90 degrees (this is assuming a flat horizon, not a hilly or mountainous region).

The general rule amateur astronomers use is that the width of your fist held at arm’s length equals about 10 degrees. You may look at your fist and the fist of a small child and wonder how both can measure 10 degrees, but the size of peoples’ fists is generally proportional to the length of their arms. Thus, a child with a small fist and small arm will measure approximately 10 degrees from their perspective, just as an adult with a larger fist and longer arm measures 10 degrees from their point of view.

If you want to do a rough check, extend your arm and fist out toward a flat horizon. Then place your other arm and fist on top of the first, and alternate, trying not to wobble, until you have counted nine fists. Your ninth fist should be pointing straight up, over your head, because the zenith is at 90 degrees.

For degrees smaller than 10, focus on just your fingers. At arm’s length, a pinky measure about 1 to 1.5 degrees, and your three middle fingers measure about 5 degrees. For larger degrees, you’ll need to stretch those fingers out. To find 15 degrees, use your index finger and pinky spread apart, and to find 25 degrees, look at the span between your pinky and thumb spread apart.

View along arm with hand with fingers extended. From pinky to index finger, measures 15 degrees of sky.
You can measure 15 degrees of sky by the span between your pinky and index finger. Image via Sharon Kizer.

The Big Dipper works for sky measurements

The Big Dipper is a good target to use in checking your hand measurements. The end two stars in the bowl, the ones that are used to find Polaris, are about five degrees apart. The top two stars in the bowl of the Big Dipper are 10 degrees apart. And finally, using the same far star in the bowl of the Big Dipper that you used for the first two tests (Dubhe, the spot at which water would pour out if it were a real dipper) plus the end star in the handle will measure 25 degrees.

Big Dipper showing relative degrees of different parts of it.
The Big Dipper can be a handy tool to measure degrees in the sky. The angle of the Big Dipper will vary by season and time of night, but it’s easy to see from most of the Northern Hemisphere. Image via NASA/ JPL/ Night Sky Network.

What about the sun and the moon?

How wide do you think the full moon looks? How many degrees would you expect it to measure? Five degrees? Two? One? Most people overestimate its size, but the full moon is a mere half degree across. How about the sun? While instinctually you might want to say the sun is larger, because its actual size is huge if put side-by-side with the moon, we know that the amount of sky the sun and moon take up is equal, a half degree.

We know this without even having to check out the sun with our half-pinky measurement, because we know that during total solar eclipses the moon temporarily slips just in front of the sun, blocking all of its light for a fleeting few minutes.

Totla solar eclipse with white cornona and pink photosphere just starting to show.
Both the sun and moon measure a half degree in our sky, which becomes clear when we see the moon cover the sun during a total solar eclipse, as shown here from the August 2017 total solar eclipse. Image via Aaron Van Pelt. Used with permission.

Now about arcminutes and arcseconds

Once you have a good grasp of degrees, if you want to estimate smaller measurements, you need to know that degrees are further divided by arcminutes. There are 60 arcminutes in one degree, therefore the moon and sun are each 30 arcminutes across. Then, arcminutes can also be divided. So, 60 arcseconds make up one arcminute.

Going back to the Big Dipper, the stars at the bend of the handle are a double star system named Mizar and Alcor and are separated by just 12 arcminutes. People with good eyesight can see the two separate stars without optical aid. Stars closer than this usually require binoculars or a telescope to split. Mizar has another companion that is even closer than Alcor. Mizar’s double star is a mere 14.4 arcseconds away. Arcminutes are written with the same symbol as feet (‘) and arcseconds are written with the inch notation (“).

Star field with prominent Big Dipper stars in deep blue sky over icy lake.
View at EarthSky Community Photos. | Jim Peacock captured this photo of the Big Dipper on January 3, 2021, over the horizon of a freezing bay of Lake Superior in northern Wisconsin. Thanks, Jim! The 2 so-called Pointer Stars in the Dipper’s bowl (the 2 stars farthest from the Dipper’s handle) – used to find Polaris, the North Star – are about 5 degrees apart. The top 2 stars in the bowl of the Big Dipper are 10 degrees apart. You can easily see the 2nd star in the handle of the Big Dipper (Mizar and Alcor) is 2 stars.
Starfield with 2 bright bluish stars at center, Mizar and Alcor, and a degree ruler at the bottom.
Here are Mizar and Alcor, a naked-eye double star you can with your eye alone, the second to last star in the handle of the Big Dipper. They are 12 arcminutes apart. Image via Fred Espenak/ Used with permission.

The sun moves about 15 degrees an hour

Also, you can tell how long until the sun will set by measuring its distance from the horizon. The sun moves about 15 degrees across the sky in an hour. Moving 15 degrees an hour for 24 hours would equal 360 degrees, or a full day from sunset to sunset. (Of course, the sun is not really moving, it’s only appearing to move in the sky as Earth turns.) Remember that unless you are at the equator, the sun is not moving in a beeline toward the horizon. The sun sinks downward at an angle that gets steeper the closer you’re located to the poles .

Multiple golden sunset images with mountains and clouds watching the progress of the sun as it sets.
View at EarthSky Community Photos. | Peter Lowenstein of Mutare, Zimbabwe, captured these images on March 9, 2023, and wrote: “Twice year, a few days after the spring or before the autumn equinox, the path of the setting sun when viewed from my location almost coincides with the southern slope of Murahwa Mountain and if the weather is clear the sun appears to roll down it.” Thank you, Peter. The sun crosses 15 degrees of sky every hour, which can help you estimate how long until sunset.

Bottom line: Degrees, arcminutes and arcseconds are all useful units of measurement in astronomy. Sometimes your own hand – held at arm’s length – can help. For example, your fist held at arm’s length measures 10 degrees on the sky’s dome. Your pinky at arm’s length measures one degree.

New supernova! Closest in a decade

Supernova in M101: Grayish white swirl made of haziness and stars with small yellow arrowhead pointing at 1 clump.
View at EarthSky Community Photos. | Our friend Eliot Herman used the Utah Remote Desert Observatories to capture this image of the new supernova in M101 – the Pinwheel Galaxy – just hours after its discovery on May 19, 2023. See the bright spot by the yellow arrowhead? This is the closest supernova to us in more than a decade. Eliot commented: “There will be many weeks to watch this one evolve.” Thank you, Eliot!

A new, close supernova

A new supernova in the Pinwheel Galaxy, aka M101, is the closest to Earth in a decade. Amateur astronomer Koichi Itagaki discovered it on May 19, 2023. The supernova should continue to brighten for a few days. It should remain visible to amateur astronomers with backyard telescopes for a few months. The supernova – named 2023ixf – lies in the direction of the constellation Ursa Major, near the end of the handle of the Big Dipper.

The last supernova in M101 was in 2011. Andy Howell, an astronomer at the University of California, Santa Barbara, explained on Twitter that the 2011 explosion resulted from a white dwarf that underwent a thermonuclear supernova. Andy said that the new supernova is most likely from a different cause, from a core collapse of a massive star at the end of its life. While observers won’t be able to see this supernova with the unaided eye, amateurs should be able to catch it backyard telescopes. As Andy said:

… this new supernova will increase in brightness over the coming days. You should be able to see it with backyard telescopes, for a few months, though it will just be a point of light.

White chart with black dots showing shape of Ursa Major.
Star chart for Ursa Major. M101 is in red on the left near the Big Dipper’s handle. Image via Wikimedia Commons/ IAU/ Sky and Telescope.

How close is the closest in a decade?

M101 is 21 million light-years away. So even though it just appeared to us on Earth Friday, it occurred 21 million years ago. And even though it’s the closest in a decade, it’s still quite far away. In fact, for a supernova to have an effect on Earth, it would have to be within 50 light-years of our planet. You can rest assured that the new supernova won’t harm Earth. Instead, we get to watch a relatively rare event as scientists gather information on the new supernova.

Supernova before-and-after image

Supernova photo gallery

A collage of six whitish spirals, together with foreground stars.
View larger. | Eliot Herman of Tucson, Arizona, using the Utah Remote Observatory, made this collage illustrating the evolution of Supernova 2023ixf on May 22, 2023. Eliot wrote: “Supernova 2023ixf in M101 is rising in brightness in the three days since its discovery. Supernova 2023ixf was discovered on May 19th, and these images are a series showing how its brightness is rising from day one through three after discovery. All images were captured with iTelescope T68 and are 11 x 90 sec. (color) and 7 x 120 sec iTelescope T11.” As Eliot reflected upon this event, he told us in an e-mail: “I hope the denizens of nearby M101 planets, ducked 21 million years ago, they might have gone the way of the dinosaurs… we will never know, but it is sobering to think every time we see fireworks, there might be mass extinctions in its wake, all a roll of the cosmic dice.” Thank you, Eliot!

For the supernova images, each photographer chooses their own orientation. Therefore, you can see the supernova in various locations, such as in the 2, 11, 5, or 8 o’clock positions, for example. That’s because there is no standard way to capture a galaxy (there’s no “up” in space).

A circular, telescopic field-of-view with a dozen faint stars.
View at EarthSky Community Photos. | Greg Redfern in Fremont, California, captured this telescopic image of Supernova 2023ixf in only half-a-second, On May 21, 2023. Greg wrote: “Supernova 2023ixf is so bright it could be imaged in just 500 milliseconds with my Unistellar eVscope 2! Pretty amazing!” Thank you, Greg!
Two large, bluish spiral clouds, together with foreground stars.
View at EarthSky Community Photos. | Paul Macklin in Bloomington, Indiana, made this 4-day comparison of Supernova 2023ixf before its discovery and after. Paul wrote: “This image captures the new supernova SN 2023ixf in Messier 101, just before and after its appearance, from an Indiana backyard. On May 16, 2023, the supernova was not visible in a 5 hour integrated exposure. On May 20th, it was clear as a brilliant white star even in 3-minute exposures. I tried to process and crop both ‘before’ and ‘after’ as similarly as possible. The left image is 5 hours of 3-min exposures; the right is 6 hours of 3-min exposures; both nights without filter.” Thank you, Paul!
Large, whitish spiral cloud, together with a multitude of foreground stars.
View at EarthSky Community Photos. | Richard Edmonds near Flagstaff, Arizona, captured this telescopic image of Supernova 2023ixf On May 20, 2023. Richard wrote: “It was late. I had been shooting M51 and M63 when around 11:45 I decided to try for M101. I had not heard about the supernova but was just trying to capture one more galaxy before calling it a night. I noticed dew forming on my telescope and finder tube, so I increased the ISO from 1600 to 3200 to shorten exposure time even though this would increase the camera noise level. This was a lucky move because, after the fourth frame, my auto guider was losing track due to dew on its optics. I had to quit at five frames.” Thank you, Richard!
Large, whitish spiral cloud, together with foreground stars.
View at EarthSky Community Photos. | Orlando Montes in Charles City, Iowa, captured this telescopic image of galaxy Messier 101 on May 19, 2023, showing the then newly discovered supernova 2023ixf. Orlando wrote: “Coincidentally, I was capturing M101 the very same night that the supernova was discovered!” Thank you, Orlando!

Pre-discovery images

Large, whitish spiral cloud, together with foreground stars.
View at EarthSky Community Photos. | Dorothy Willilams in Fremont, California, captured this telescopic image of galaxy Messier 101 on May 12, 2023, one week before the discovery of Supernova 2023ixf. Dorothy wrote: “This image was taken on May 12 around 11:00 pm. There is a faint smudge where the supernova was found on May 19. The smudge may or may not show the pre-supernova before it became bright enough to be found.” Thank you, Dorothy!

Did you capture an image of the supernova you’d like to share with us? You can submit it to EarthSky Community Photos.

Bottom line: An amateur astronomer discovered a new supernova in M101 – the Pinwheel Galaxy – on May 19, 2023. The supernova will continue to brighten for a couple days and be visible to amateurs in backyard telescopes for a few months.

Mount St. Helens’ 1980 eruption still causing destruction

Mount St. Helens in the northwestern United States had an immense eruption on today’s date – May 18 – in the year 1980. It’s since often been declared the most disastrous volcanic eruption in U.S. history. This year, 2023, is its 43rd anniversary. And, just days before the anniversary – on May 14, 2023 – current warming temperatures released a debris flow, made from leftover eruptive material, that rushed down South Coldwater Creek and took out a bridge on the lone park road, State Highway 504, also known as Spirit Lake Highway. In addition, the destruction cut off access and power to the Johnston Ridge Observatory, located at the end of State Highway 504, in the heart of Mount St. Helens’ blast zone. The USGS assured people online that, while the debris flow was large enough to trigger seismographs, there was:

no volcanic unrest associated with this debris flow.

The local Fox12 news station in Oregon reported that 11 people and a dog had to be rescued by helicopter after the landslide. Cowlitz County officials estimated the landslide at about 200 yards (183 m) wide and 10 feet (3 m) deep, with a foot of water running over the entrance road.

The Johnston Ridge Observatory still lists its status as unreachable, as of May 18, 2023.

Mount St. Helens erupted on May 18, 1980


On May 18, 1980, Mount St. Helens underwent a catastrophic and deadly eruption, triggering the largest landslide ever recorded. Earlier in the year, thousands of small earthquakes, venting steam, and a growing bulge protruding 450 feet (137 m) indicated that magma was rising in the volcano. Then, at 8:32 a.m. local time, a 5.1-magnitude earthquake rocked the mountain, triggering the huge landslide and lateral blast that collapsed the volcano’s northern face. Hot pressurized magma erupted, and the ash plume reached a towering height of 80,000 feet (15 miles, 24 km), before blanketing the surrounding region. A Unites States Geological Survey (USGS) geologist described the destructive blast:

It completely destroyed an area of 230 square miles [595 square kilometers] in a matter of five to nine minutes. It essentially killed everything within that area.

Altogether, 57 people, including volcanologist David A. Johnston and photojournalist Reid Blackburn, were killed during the May 18, 1980, eruption at Mount St. Helens. Later, the Johnston Ridge Observatory in Toutle, Washington, was named for the late volcanologist.

The dense forest that covered the slopes of the volcano was reduced to ash inside an area known as the inner blast zone, which extended about 6.2 miles (10 km) from the summit. Additionally, trees farther away from the inner blast zone were also damaged by the searing heat. The total extent of the devastated forested area is known as the blowdown zone.

Lahars – mudflows carrying debris from volcanic eruptions – formed rapidly from the melting ice and snow on Mount St. Helens’s flanks. The massive lahars created in the 1980 eruption damaged homes, roads and bridges in nearby communities.

Over the past decades, however, this area has slowly rebounded with life.

Before, during and after photos

Snowcapped mountain with water in foreground.
Mount St. Helens photographed 7 years prior to the 1980 eruption. Image via U.S. Forest Service/
Gray and black cauliflower-like clouds over volcano.
Photograph of Mount St. Helens taken during the May 18, 1980, eruption. Image via Oman/ Combs/ National Park Service.
Snowcapped mountain with crater at summit, smoke plume from the center, clouds behind, and a reflection in the foreground water.
Mount St. Helens photographed 2 years after the 1980 eruption. Image via Lyn Topinka/ USGS.
Logs beside large toppled trucks.
Massive lahars swept timber, trucks and any debris in its path with it down the mountainside at Mount St. Helens on May 18, 1980. Image via D. Olson/ National Park Service.
Mountainous area covered in fallen logs.
This aerial view of timber blowdown is from June 8, 1980, after it was leveled by the Mount St. Helens eruption. Image via USGS/
Satellite image view of a white volcano at top right with some lakes at bottom and forests around them.
Mount St. Helens on April 20, 2015. Read more about this image at NASA Earth Observatory. Image via NASA Earth Observatory.

The state of the volcano today

Now, Mount St. Helens stands as an 8,363-foot (2,550-m) high stratovolcano located in Skamania County, Washington, some 1,300 feet (396 m) shorter than before its 1980 eruption. Moreover, it is the most active volcano in the Cascade Range, which runs along the northwestern coast of North America. The Cascade Range is part of the Pacific Ring of Fire. Indeed, Mount St. Helens is still considered one of the most dangerous volcanoes in the United States.

Also, since 1980, Mount St. Helens has continued to experience periodic earthquakes and volcanic eruptions, but not to the same extent of that seen in 1980. The Cascades Volcano Observatory continually monitors activity at Mount St. Helens.

Bottom line: Mount St. Helens volcano exploded in a cataclysmic event on May 18, 1980, killing 57 people and dramatically altering the landscape. Then, in 2023, leftover debris from the 1980 eruption flowed down a creek and destroyed a bridge on the only road in to the observatory.

View more Mount St. Helens eruption videos

Read more: View from space: Life reclaims Mount St. Helens

Read more: What is the Ring of Fire?

Jurassic-age giant reptile was twice as big as killer whale

Giant reptile: Large gray beast with long tail and 2 fins swimming beside a person for scale.
This giant reptile of the Jurassic age – the pliosaur – was twice the size of a killer whale. Megan Jacobs, an author of the study, also created this artist’s concept of the pliosaur. Additionally, a human has been added for scale. Image via University of Portsmouth/ Megan Jacobs.

Giant reptile swam in Jurassic seas

Scientists examining fossils at Abingdon County Hall Museum in England came upon four large vertebrae from the Jurassic age. Initially, these fossils came from an excavation at the River Thames Valley in Oxfordshire. They are in a clay deposit that dates to the Late Jurassic, some 152 million years ago. The scientists, led by David Martill and Megan Jacobs of the University of Portsmouth, identified them as closely related to pliosaurs. Then, on May 10, 2023, they announced that these large bones indicated that pliosaurs could have been as large as 47 feet (14.3 meters). As Martill said:

It’s wonderful to prove there was indeed a truly gigantic pliosaur species in the Late Jurassic seas.

The scientists published their peer-reviewed research in the journal Proceedings of the Geologists’ Association on May 10, 2023.

What are pliosaurs?

Generally speaking, pliosaurs are prehistoric reptiles that were similar to plesiosaurs, a common marine reptile of the time period. However, pliosaurs had a bigger, elongated head with a shorter neck. Also, they sported four flippers and a short tail to help them paddle and maneuver through the seas.

The team used topographic scans to calculate a size range for pliosaurs of 32 to 47 feet (9.8 and 14.3 meters). Indeed, as you can see from the chart, this length would put them in the range of today’s whale sharks and larger.

Shadowed images of marine life such as sharks and the pliosaur compared by size.
This chart compares the size of marine life we are familiar with today and the prehistoric reptile known as a pliosaur. These giant sea creatures lived in the Late Jurassic age. Image via University of Portsmouth/ Proceedings of the Geologists’ Association/ David Martill.

Pliosaurs ruled the seas

Martill describes these prehistoric reptiles:

We know these pliosaurs were very fearsome animals swimming in the seas that covered Oxfordshire 145-152 million years ago. They had a massive skull with huge protruding teeth like daggers, as big – if not bigger than – a T. rex, and certainly more powerful.

But, despite it living in the Jurassic age and the comparison with a T. rex, Martill cautioned:

Please do not call it a dinosaur. That would be like calling a mouse cattle or a cat an elephant.

So, these prehistoric reptiles were larger than scientists previously thought and were dominant in Jurassic seas. As Martill said:

They were at the top of the marine food chain and probably preyed on ichthyosaurs, long-necked plesiosaurs and maybe even smaller marine crocodiles, simply by biting them in half and taking chunks off them. We know they were massacring smaller marine reptiles because you can see bite marks in ichthyosaur bones in examples on display in The Etches Collection in Dorset.

Bottom line: Scientists have discovered that giant reptiles of the Jurassic period – known as pliosaurs – could have been up to 47 feet in length.

Source: A truly gigantic pliosaur (Reptilia, Sauropterygia) from the Kimmeridge Clay Formation (Upper Jurassic, Kimmeridgian) of England

Via University of Portsmouth

Read more: 2 killer whales slaughter 17 sharks in 1 day

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