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Astronomers Caught Betelgeuse Just Before it Started Dimming and Might Have Seen a Pressure Wave Rippling Through its Atmosphere – Universe Today



A couple of years ago, Betelgeuse generated much interest when it started dimming. That caught the attention of astronomers worldwide, who tried to understand what was happening. Was it about to go supernova?

Evidence showed that dust was the most likely culprit for the red supergiant’s dimming, though there are still questions. A new study shows that the star was behaving strangely just before the dimming.

The optical dimming that Betelgeuse—or Alpha Orionis—exhibited in late 2019 and early 2020 was unprecedented. Betelgeuse often undergoes periodic optical dimming, which happens in timescales of ~300-500 days and ~2000 days. But the Great Dimming, as it came to be known—when the star dimmed to about two-thirds of its normal brightness— was the faintest that the star had become in almost 200 years of observations.

Researchers got to work generating possible explanations for the dimming. Some hypothesized that dust caused the dimming, others hypothesized that a reduction in photosphere temperature caused it, and some thought both played a role.

Astronomers continued studying it, and evidence showed that temperature decrease alone couldn’t be the culprit. Episodic mass loss was proposed as the cause, paired with a rise in large grain dust in the line of sight. Others argued that large inhomogeneities in the photosphere caused the dimming. Another suggested a critical shift in Betelgeuse’s pulsation dynamics caused the Great Dimming. If feedback from UT readers is any indication, there’s still confusion around the cause of the dimming event.

Betelgeuse, as seen by the Hubble Space Telescope. Credit: NASA
Betelgeuse, as seen by the Hubble Space Telescope. Credit: NASA

But there were really two dimming events, and that’s helped create some of the confusion. The scientific community has settled on dust as the cause of the first dimming. “We know the first dimming event involved a dust cloud,” said Dr. Meridith Joyce from The Australian National University in 2020.

According to Dr. Joyce, the second dimming event had a different cause: “We found the second smaller event was likely due to the pulsations of the star.”

Now a new paper presents observations of Betelgeuse just before the Great Dimming. Its title is “SPATIALLY RESOLVED OBSERVATIONS OF BETELGEUSE AT ?7 MM AND ?1.3 CM JUST PRIOR TO THE
GREAT DIMMING.” The Astrophysical Journal will publish it, but for now, it’s available on the pre-press site The authors are Dr. Lynn D. Matthews of MIT’s Haystack Observatory and Andrea Dupree from the Harvard and Smithsonian Center for Astrophysics. The paper is based on observations of Betelgeuse with the Karl G. Jansky Very Large Array.

“Our measurements suggest recent changes in the temperature and density structure of the
atmosphere,” the authors write. The star’s photosphere “… is ~20% dimmer than in previously published
observing epochs between 1996–2004.” This is … lower than previously reported temperatures at comparable radii and >1200 K lower than predicted by previous semi-empirical models of the atmosphere.”

Betelgeuse is known for pulsating, as it swells and shrinks symmetrically. These are Hubble images of the star from 1998 and 1999. Image Credit: NASA/ESA/Hubble
Betelgeuse is known for pulsating, as it swells and shrinks symmetrically. These are Hubble images of the star from 1998 and 1999. Image Credit: NASA/ESA/Hubble

The researchers also found that the measured brightness temperature was cooler than expected and that there were “… no obvious signatures of giant convective cells or other surface features.” The star’s brightness profile was also more complex than a uniform elliptical disk (A uniform elliptical disk is a tool astrophysicists use to characterize the mean properties of a star.) Their observations were from about six weeks before ultraviolet measurements found increases in electron density in Betelgeuse’s southern hemisphere, coupled with a large-scale outflow.

So what does all that mean?

“We discuss possible scenarios linking these events with the observed radio properties of the star, including the passage of a strong shock wave.”

Researchers in the astrophysical community have postulated that a shock wave could’ve caused the Great Dimming. A 2021 paper found that Betelgeuse’s photosphere experienced successive shock waves in February 2018 and January 2019, with the initial shock amplifying the second one. Other research showed that a shock wave passed through the southwestern portion of Betelgeuse’s chromosphere between 2019 September and November. Since the photosphere is under the chromosphere, it’s reasonable to think that the two shock waves are related.

This diagram of a star's layers shows how the photosphere is below the chromosphere. The photosphere is the lowest layer of a star's atmosphere and also the lowest observable layer. Image Credit: ESA
This diagram of a star’s layers shows how the photosphere is below the chromosphere. The photosphere is the lowest layer of a star’s atmosphere and the lowest observable layer. Image Credit: ESA

The researchers say they can’t conclude that their observations are directly responsible for the Great Dimming, even though their data suggests “… recent changes in the density and/or temperature structure of the atmosphere…” But a large-amplitude shock or pressure wave passing through Betelgeuse’s atmosphere could cause changes in density and temperature.

The authors are cautious and inconclusive, but they do point out that the pressure wave they observed could’ve caused Betelgeuse’s Great Dimming. “Such an event may be linked to a largescale mass ejection from the star that has been postulated as an explanation for the steep decline in optical magnitude associated with the Great Dimming.”

There’s no question that Betelgeuse will explode as a Type IIP supernova, likely in the next 100,000 years or so. It’s the 10th brightest star in the night sky and is giving astronomers an opportunity to study intensely the behaviour of a star as it approaches its cataclysmic end.

The familiar constellation of Orion. Orion's Belt can be clearly seen, as well as Betelgeuse (red star in the upper left corner) and Rigel (bright blue star in the lower right corner) Credit: NASA Astronomy Picture of the Day Collection NASA
The familiar constellation of Orion. Orion’s Belt can be clearly seen, as well as Betelgeuse (red star in the upper left corner) and Rigel (bright blue star in the lower right corner). Credit: NASA Astronomy Picture of the Day Collection NASA

This study won’t be the final word on Betelgeuse and its dynamic behaviour. The star is still up there, anchoring the Orion the Hunter’s right shoulder. Generations and generations of astronomers are bound to keep watching it.

If humanity lasts long enough, our distant descendants will get to watch it explode.


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NASA will launch the CAPSTONE mission on Monday, June 27 –



Rocket Lab's Electron rocket sits atop the launch pad at Launch Complex 1 in New Zealand for a rehearsal before the CAPSTONE launch.

A small satellite is preparing to pave the way for something much greater: a fully grown lunar space station. NASA’s CAPSTONE satellite is scheduled to launch on Monday and then travel to a unique lunar orbit on the Pathfinder mission Artemis programwhich seeks to return humans to the moon later this decade.

capstone He rides aboard Rocket Lab’s Electron rocket, which will take off from the private company’s Launch Complex 1 in Mahia, New Zealand. Rocket Lab made headlines in May using a helicopter to catch a falling booster missile. CAPSTONE is scheduled to launch at 6 AM ET on June 27 with live coverage starting an hour earlier. You can watch the event in the agency website or ApplicationOr, you can watch it on the live stream below.

NASA Live: The official broadcast of NASA TV

About a week after the CAPSTONE mission, the probe’s flight will be available through NASA Eyes on the solar system Interactive 3D visualization of data in real time.

The Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE) mission will send a microwave-sized satellite into near corona orbit (NRHO) around the moon. The satellite will be the first to sail its way around this unique lunar orbit, testing it for the planned date Moon Gatea small space station intended to allow a permanent human presence on the moon.

NRHO is special in that it is where the gravitational force of the Moon and Earth interact. This orbit would theoretically keep the spacecraft in a “beautiful gravitational spot” in a near-stable orbit around the Moon, according to to NASA. Therefore NRHO is ideal because it will require less fuel than conventional orbits and will allow the proposed lunar space station to maintain a stable line of communication with Earth. But before NASA builds its gateway into this highly elliptical orbit, the space agency will use CAPSTONE — which is owned and operated by Colorado-based Advanced Space — to test its orbital models.

Artist’s concept of CAPSTONE.
GIF: NASA/Daniel Rutter

Six days after launch from Earth, the upper stage of the Electron rocket will launch the CAPSTONE satellite on its journey to the Moon. The 55-pound (25-kilogram) cube vehicle will perform the rest of the four-month solo journey. Once on the moon, CAPSTONE will test the orbital dynamics of its orbit for about six months. The satellite will also be used to test spacecraft-to-spacecraft navigation technology and unidirectional range capabilities that could eventually reduce the need for future spacecraft to communicate with mission controllers on Earth and wait for signals from other spacecraft to relay.

NASA is systematically putting together the pieces for the agency’s planned return to the Moon. The The fourth and final rehearsal for the space agency’s Space Launch System (SLS) went wellpaving the way for a possible launch in late August.

more: This small satellite linked to the moon can make a path to the lunar space station

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Astronaut view of New Zealand's North Island –



Today’s Image of the Day from NASA Earth Observatory features the North Island of New Zealand. The photo was captured as the International Space Station (ISS) approached the southernmost extent of its prograde 51.6 degree orbit. 

From this vantage point – and with the perfect weather conditions – astronauts can get a clear view of the North Island of New Zealand, according  to ESA.

“Looking towards the northwest, the astronaut photographer captured the mottled-green island that separates the Tasman Sea from the South Pacific Ocean. On the other side of Cook Strait, South Island peeks out from beneath the cloud cover,” reports ESA.

“Seven bays surround the North Island and define its distinctive shape. The inland landscape includes grasslands (lighter green areas), forests (darker green areas), volcanic plateaus, and mountain ranges formed from sedimentary rocks.”

Lake Taupō, located in the center of the North Island, is a crater lake inside a caldera formed by a supervolcanic eruption. The lake borders the active volcano Mount Ruapehu, which has the highest peak in New Zealand. 

“The volcanic nature of the island arises from its location on the tectonic plate boundary between the Indo-Australian and Pacific Plates,” says ESA. “This plate boundary is part of the vast Pacific Ring of Fire, and leads to significant geothermal activity and earthquakes in the region. Additional volcanoes, including Egmont Volcano (Mount Taranaki), also dot the North Island landscape.”

Image Credit: NASA Earth Observatory

By Chrissy Sexton, Staff Writer

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Artemis 1 moon mission could launch as soon as late August –



NASA officials have declared the Artemis 1 moon rocket’s most recent “wet dress rehearsal” a success and are hopeful the mission can get off the ground as soon as late August.

The Artemis 1 stack — a Space Launch System (SLS) rocket topped by an Orion capsule — is scheduled to roll back to the Vehicle Assembly Building (VAB) at NASA’s Kennedy Space Center (KSC) in Florida on July 1, where the massive vehicle will undergo repairs and preparations for its coming launch. 

Artemis 1, the first launch for the SLS, will send an uncrewed Orion on a roughly month-long mission around the moon. The mission has experienced several delays, and most recently the rocket’s certification to fly has been held up by incomplete fueling tests — a key part of the wet dress rehearsal, a three-day series of trials designed to gauge a new vehicle’s readiness for flight. 

Related: NASA’s Artemis 1 moon mission explained in photos 

The Artemis 1 stack first rolled from the VAB to KSC’s Pad 39B in mid-March, to prep for a wet dress rehearsal that began on April 1. But three separate attempts to fill the SLS with cryogenic propellants during that effort failed, sending the stack back to the VAB for repairs on April 25. The most recent wet dress try, which wrapped up on Monday (June 20), didn’t go perfectly, but NASA has deemed it good enough to proceed with preparations for launch.

Operators were able to fully fuel SLS for the first time, bringing the launch simulation much further along than any of the attempts in April. A leak from the core stage’s engine cooling system “umbilical” line was detected during Monday’s fueling test, but mission managers determined that the deviation didn’t pose a safety risk and continued with the simulation’s terminal count. That ended up being the right decision, Artemis 1 team members said.  

Mission operators were able to run a “mask” for the leak in the ground launch sequencer software, which permitted computers in mission control to acknowledge the malfunction without flagging it as a reason to halt the countdown, according to Phil Weber, senior technical integration manager at KSC. Weber joined other agency officials on a press call Friday (June 24) to discuss the plans for Artemis 1 now that the wet dress is in the rear view mirror.

The software mask allowed the count to continue through to the handoff from the mission control computers to the automated launch sequencer (ALS) aboard the SLS at T-33 seconds, which ultimately terminated the count at T-29 seconds. 

“[ALS] was really the prize for us for the day,” Weber said during Friday’s call. “We expected … it was going to break us out [of the countdown] because the ALS looks for that same measurement, and we don’t have the capability to mask it onboard.” 

It was unclear immediately following the recent wet dress if another one would be required, but mission team members later put that question to rest.

“At this point, we’ve determined that we have successfully completed the evaluations and required work we intended to complete for the dress rehearsal,” Tom Whitmeyer, deputy associate administrator for Common Exploration Systems at NASA headquarters, said on Friday’s call. He added that NASA teams now have the “go ahead to proceed” with preparations for Artemis 1’s launch.

Before it can be rolled back to the VAB, however, the stack will undergo further maintenance at Pad 39B, including repairs to the quick-disconnect component on the aft SLS umbilical, which was responsible for Monday’s hydrogen leak. 

There’s also one more test technicians need to perform at the pad. Hot-firing the hydraulic power units (HBUs), part of the SLS’ solid rocket boosters, was originally part of the wet dress countdown but was omitted when the countdown was aborted. Those tests will be completed by Saturday (June 25), according to Lanham. Following the hot-fire tests, operators will then spend the weekend offloading the HBUs’ hydrazine fuel.

Once back in the VAB, NASA officials estimate it’ll take six to eight weeks of work to get Artemis 1 ready to roll back to Pad 39B for an actual liftoff. Cliff Lanham, senior vehicle operations manager at KSC, outlined some of the planned maintenance on Friday’s call. 

Related: NASA’s Artemis program of lunar exploration

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Among other tasks, technicians will perform standard vehicle inspections, hydrogen leak repairs, “late-stow” for the payloads flying on Orion, and software loads to the SLS core stage and upper stage. They will also install flight batteries.

“Ultimately, we want to get to our flight termination system testing,” Lanham said. “Once that’s complete, we’ll be able to perform our final inspections in all the volumes of the vehicle and do our closeouts.”

After that work is complete, the Artemis 1 stack will roll out from the VAB once again, making the eight to 11-hour crawl back to Pad 39B on July 1. Whitmeyer said on Friday that the late-August launch window for Artemis 1, which opens on Aug. 23 and lasts for one week, is “still on the table.”

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