Cosmic Voids, Martian Construction Breakthroughs, and the Spectacular Perseid Meteor Shower

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Steve Dunkley: And welcome again to another astronomy Daily. It's the 14th

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of July, 2025.

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Generic: Welcome to Astronomy Daily The Podcast with

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Your host, Steve Dunkley.

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Steve Dunkley: Wow, the 14th of July. Ah, already? It's as

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close to the halfway mark of the year as we can get,

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Hallie.

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Hallie: I think you watched that calendar a bit too closely, human.

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Steve Dunkley: Oh, Hallie, it's just a way of mark

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time. You know, humans like to do that. I guess

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that's where our fascination with astronomy came from in the

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first place.

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Hallie: That makes sense.

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Steve Dunkley: Yeah.

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Hallie: Speaking of time, it's great to be back in the Australia

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studio again for this podcast. Time.

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Steve Dunkley: That's right. Monday is our time.

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Hallie: Have you got our schedules set up?

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Steve Dunkley: Uh, uh, what?

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Hallie: Yeah, it was your turn.

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Steve Dunkley: Well, yes, Hallie, I. I got it done in time.

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Hallie: That's good. I hope it didn't take too much of your

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private time.

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Steve Dunkley: Oh, private time? No, not this time. As

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if I had any private time.

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Hallie: So, what have you got for us?

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Steve Dunkley: Well, Hallie, it's time for another meteor shower, and

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Australia looks like it's in the prime location for the best

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view.

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Hallie: It's about time.

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Steve Dunkley: Well, I suspect Australia is always in the best position

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for a meteor shower, so, uh, well, viewing anyway.

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Hallie: Okay, okay. What else?

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Steve Dunkley: Well, as well as the Perseids, we've got building

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things on Mars with fungus

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astronomers, uh, looking at the cosmic

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web, and, um, we might actually be living

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in a giant void. They sound pretty cool, don't

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they?

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Hallie: Excellent. Okay, so.

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Steve Dunkley: Hey, Helly.

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Hallie: Yes, human?

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Steve Dunkley: How's about we just launch right into.

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Hallie: The episode and save some time?

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Steve Dunkley: You think Tempest fugit, Hallie?

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Hallie: Indeed it does.

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Steve Dunkley: Okay, Hallie, you have the con Okies.

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Hallie: One of the main objectives of the Hubble Space telescope,

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launched in 1990, was to measure the size and age of the

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universe, as well as the rate at which it is expanding,

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AKA the Hubble constant. This was

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enabled for the first time with the Hubble Deep Fields, which

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visualized the farthest galaxies that are observable in

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visible light, 13 billion light years from Earth.

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However, when astronomers measured the distance to these

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galaxies, they noted a they were inconsistent with

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measurements of the local universe. This

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became known as the Hubble Tension, which remains one of the

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biggest cosmological mysteries to this day.

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While astronomers hope to resolve this tension with the launch of the

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James Webb Space Telescope, Webb's measurements confirmed what

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Hubble saw. Many theories have been advanced

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to explain this, including the possibility that the Milky Way

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is located inside a giant void that makes the cosmos

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expand faster here than in neighboring regions of the universe.

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The latest research supporting this theory was presented at the

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Royal Astronomical Society's National Astronomy Meeting

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in Durham. Their theory could potentially resolve

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the Hubble tension and confirm the true age of our universe,

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which is thought to be about 13.8 billion years old.

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The Hubble constant takes its name from Edwin Hubble, one

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of two astronomers, the other being Georges Lemaitre, who

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confirmed in the early 20th century that the universe was in a state

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of expansion. This was demonstrated using

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redshift measurements, where the wavelength of light from objects

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receding from Earth is shifted toward the red end of the spectrum.

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Before the Hubble Space Telescope was launched, astronomers were

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able to gauge the distance of objects up to 4 billion light years

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away using a combination of redshift and parallax

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measurements. The problem was that when comparing

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local measurements to those of the distant early universe

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based on the standard lambda cold dark matter cosmological

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model, the results were in tension with each other.

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The latest research, explained Dr. Indranil Banik of

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the University of Portsmouth, shows that baryon acoustic

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oscillations, essentially the sound waves of the

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Big Bang, support the idea that our galaxy be in a void

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where cosmic expansion is greater than the universe beyond.

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Bannock said a potential solution to this inconsistency

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is that our galaxy is close to the center of a large

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local void. It would cause matter to be pulled

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by gravity towards the higher density exterior of the void,

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leading to the void becoming emptier with time.

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As the void is emptying out, the velocity of objects

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away from us would be larger than if the void were not there.

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This therefore gives the appearance of a faster local

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expansion rate. The Hubble tension is

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largely a local phenomenon, with little evidence that the

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expansion rate disagrees with expectations in the standard

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cosmology further back in time. So a

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local solution like a local void is a promising way to go

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about solving the problem. This void would need

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to measure a billion light years in radius and have a density

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roughly 20% lower than the average for the universe as a

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whole. This theory is supported by a direct count

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of local galaxies in our cosmic neighborhood. Since the number

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density is lower than in neighboring regions.

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However, the existence of such a void is inconsistent with the

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LCDM model, which includes the theory that the universe is

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antistropic in nature, meaning that matter is uniformly

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spread throughout the universe on large scales.

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Despite this, the new Data presented at NAM

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2025 indicates otherwise,

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said Bannock. These sound waves

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traveled for only a short while before becoming frozen in place.

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Once the universe cooled enough for neutral atoms to form,

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they act as a standard ruler whose angular size we can use to

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chart the cosmic expansion history. A local

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void slightly distorts the relation between the BAO angular

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scale and the redshift because the velocities induced by a

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local void and its gravitational effect slightly increase the

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redshift on top of that due to cosmic expansion.

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By considering all available BAO measurements over the last

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20 years, we showed that a void model is about 100

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million times more likely than a void free model with parameters

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designed to fit the CMB observations taken by the Planck

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satellite, the so called homogeneous Planck cosmology.

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To confirm this theory, researchers must compare the local

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void theory with other models to obtain new estimates for the

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expansion history of the universe. This will

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consist of obtaining spectra from quiescent or dead

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galaxies, those no longer forming new stars, to

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determine what types of stars they have and in what proportion.

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Since massive stars have short lifespans and are

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absent from older galaxies, this will help astronomers

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establish the age of these galaxies.

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Combined with a galaxy's redshift, astronomers can

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chart the history of cosmic expansion. You're

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listening to Astronomy Daily.

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Steve Dunkley: Landing on Mars once felt like a distant dream.

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Now space agencies have sent rovers and landers

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to explore the red Planet for decades.

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Scientists worldwide are thinking about how to make Mars

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a second home for humans. But major

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questions still remain. How do you build

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structures millions of miles from Earth? Uh,

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shipping heavy loads of materials to

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Mars from Earth is expensive and impractical.

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Rockets have limited space and fuel, and

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sending cement and metal beams would

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cost billions. Researchers are now

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exploring ways to use what Mars already has,

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its soil, dust and natural resources to

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build homes for future astronauts. At

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Texas A and M University, Dr. Congrue

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Grace Ginn and her team are, uh, tackling

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this challenge. They've spent years developing

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biomanufacturing methods to create

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engineering living materials. Their

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latest research proposes a solution that could

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change how humans build structures on other

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planets. We can build synthetic

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community by mimicking natural lichens,

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explains Jin. We've

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developed a way to build synthetic lichens

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to create biomaterials that glue Martian

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regolith particles into structures. Then, through

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3D printing, a wide range of

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structures can be fabricated, such as buildings, houses,

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and even furniture. Gin's team,

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working with the University of Nebraska, Lincoln,

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has designed a synthetic lichen system.

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This system forms strong building

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materials without any help from humans.

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Martian regolith is loose soil,

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dust, sand, and broken rocks on the Martian

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surface. Their research shows that a

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synthetic community of organisms can turn regolith

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into building materials strong enough for homes, tables,

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and chairs. This breakthrough may one day allow

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humans to to build on Mars without sending

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extra materials from Earth.

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Other scientists have studied different ways

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to bond Martian soil. Some tried using

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magnesium based, sulfur based or

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geopolymer methods. However, all of these

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approaches need humans to carry out parts of

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the process on Mars. There won't be enough people to

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oversee these complicated tasks, at least

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in the foreseeable future future.

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Another approach is called microbe

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mediated self growing technology.

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This uses bacteria or fungi to produce

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minerals to bind soil particles into

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bricks. NASA has explored using

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fungi mycelium as a bonding agent, while

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other scientists have tested bacteria that produce

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calcium carbonate. Even these

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methods require outside nutrients to keep the

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microbes alive. Needing human intervention,

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Jin's team wanted to solve this problem. Their

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idea was simple, yet powerful. Build a

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system that runs on its own using organisms that

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help each other survive. They created a

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synthetic lichen system that combines

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two types of organisms. Filamentous

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fungi and diazotrophic

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cyanobacteria. Once again, I apologize

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for my pronunciation. I am

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Australian. Filamentous fungi

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act as the builders. They can produce large

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amounts of biominerals, uh, to bond soil

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particles. These fungi survive harsh

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conditions better than bacteria. They also

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bind metal ions into their cell walls,

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creating sites for biomineral crystals to

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grow. At the same time, they help the

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cyanobacteria grow by giving them water,

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minerals and carbon dioxide.

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Diazotrophic cyanobacteria act as the

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providers. They fix carbon dioxide and

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dino trojan from the air and turn them into oxygen

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and organic nutrients. This process

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feeds the fungi and increases carbonate ions in

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the environment. The carbonate ions are essential

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for creating mineral crystals that bond the soil

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together. The cyanobacteria also uses

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photosynthesis to produce the nutrients needed for

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the fungi to thrive. Both, uh,

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organisms secrete biopolymers that

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help glue regolith particles and mineral crystals

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into strong solid materials. Their

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relationship is mutually beneficial. Together,

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they form a system that requires only Martian

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regolith, simulant air, light, and an

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inorganic liquid medium to grow. No

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external carbon or nitrogen sources are

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needed.

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Hallie: You're listening to Astronomy Daily, the podcast with

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Steve Dunkley.

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Steve Dunkley: Thank you for joining us for this Monday edition of

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Astronomy Daily, where we offer just a few stories from the now

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Astronomy.

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Hallie: Observations of a 23 million light year long gaseous

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filament and 39 bursts of radio waves are helping

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astronomers chart the universe's largest scale structures.

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A curious fact about the universe around us. We can't

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see most of it. It's not only mysterious

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dark matter and dark energy that, except for their indirect

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impacts on astronomical observations, remain

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invisible. Much of a normal amatter evades

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detection, too, even though those ordinary particles

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known as baryons also make up perfectly visible

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stars, planets, and kitchen sinks.

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Now, two teams with opposite approaches have found much of

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ordinary matter prefers to take up residence in the lonelier

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latticework that makes up the cosmic web. This

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large scale structure consists primarily of dark matter,

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which has gravitationally collapsed from a smooth spread.

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Crisscrossing filaments leave largely empty voids in between.

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Dark matter is the gravitational backbone of the cosmic

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web, along which normal matter collects and comes together into

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galaxies and galaxy clusters. One

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of these filaments is 23 million light years long, a

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thick thread of gas and dark matter that connects two pairs of

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galaxy clusters in Centaurus. The

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quartet of clusters are part of the larger Shapley's

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supercluster. Only astronomers

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didn't know the filament was there. The colliding

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clusters were intriguing, though, and many teams pointed X

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ray observatories in their direction between 2001 and

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2020. Now combining these

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archival observations, Konstantino's Mikas, UH

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Leiden University, the Netherlands, and his group

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collected the equivalent of a multi day stare at this region of

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sky. In doing so, they revealed the

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faint X ray glow of a filament connecting the clusters.

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The matter in the sky filament is hard to see because it's both

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sparse and hot. Hot gas emits some

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low energy X rays, but that emission becomes quite faint

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when the gas is spread out over millions of light years.

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Not that astronomers haven't tried, and with some success.

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One team has observed individual cosmic web

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filaments. Another study combined data from thousands of

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filaments to better understand their average properties.

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But in all previous cases, the measured densities were

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shockingly high, several times more than cosmological

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simulations predicted. This time

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Mikasa's team tried something new. In

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addition to observing the glow of the filament itself using the

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sensitive Suzaku Observatory they also employed the

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sharper images of XMM Newton to find and remove other sources

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of x rays, such as supermassive black holes and

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galaxy halos. The result is a

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measurement of just how hot and sparse this one filament really

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is. Its temperature hovers around 10 million

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degrees. That's about the same temperature at which fusion begins

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within the Sun. But its density is so

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incredibly low that fusion would never happen 10 to

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5 particles per cubic centimeter, which works out to about

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5 particles within the volume of an average bathtub.

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That density, remarkably, is exactly what's expected,

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Mikas notes. Obtaining the first

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result ever that matches the cosmological model perfectly was

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indeed a surprise, he says. There are

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countless filaments out there, some of which are amenable to direct

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imaging. But for the rest, there's another way

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to see the cosmic web via an unexpected beacon.

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Fast radio bursts

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Fast radio bursts are quick flashes of radio waves that

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astronomers think come from explosive events around dead stellar

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cores known as magnetars. For

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cosmologists, though, the exact source of the bursts

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isn't important. What is important is the

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ability to measure the dispersion of each radio flash, in which

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intervening matter spreads out the signal so that lower frequencies

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arrive later. The dispersion thus encodes

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how much matter lies between us and the burst.

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Combine that data with the burst's distance, which requires

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pinpointing where on the sky it's emanating from. Then mix in

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some computer simulations of the evolving universe, and you get

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something akin to a map of cosmic matter.

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On the simplest level, the change of dispersion with

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distance told the team about the amount of normal

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baryonic matter in the universe, which matched

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predictions on a deeper level. The

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spread of the data Whether a group of FRBs at a certain

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distance have mostly the same dispersion or many different

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values tells about the distribution of matter.

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If normal matter were mostly locked away in galaxies and

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clusters, our universe would be rather lumpy, and the

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dispersions at a certain distance would be spread out.

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But that's not the universe we live in.

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Comparing distance and dispersion for 39 FRBs

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detected with the Deep Synoptic Array 110 in California,

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Liam Connor of the center for Astrophysics, Harvard, and

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Smithsonian, and colleagues mapped normal matter out to when our

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universe was half its current age. They found

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that the spread of matter is pretty smooth, with less than

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15% of normal matter in stars and the cooler gas

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that could one day become stars. The rest of

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the baryons aren't in galaxies they are between them

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that some material should be in cosmic filaments isn't

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unexpected, but that the filaments should contain

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three quarters of the universe's baryon suggests that that something is

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sloshing gas back out of galaxies at a high rate.

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Unfortunately, we don't yet have the granularity to pin

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down specific feedback scenarios, connor says.

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We'll have to wait for the large upcoming FRB samples for

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that. My suspicion is that you can't produce our

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results without a good amount of active galactic nucleus feedback,

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he adds, referring to the winds and jets that emanate from

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supermassive black holes. But that's just a

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hunch. Mikas points out that Connor's

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study is exactly complementary to his own. Whereas his own

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team measures the properties of a single filament, Connor's team

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measures how much matter is in these filaments overall.

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Connor likewise is glad to see the result from

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Migkus's team directly. Imaging filaments is really

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exciting, and I agree that this result meshes with ours, he

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says. It's fun to see a literal image of the

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gas our FRBs were dispersed by.

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You're listening to Astronomy Daily, the podcast

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with your host Steve Dunkley at Bermuda.

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Steve Dunkley: And Australians get ready for the Perseid meteor

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shower just around the corner. The night sky, uh, above Australia

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has been putting on a show this year with a flurry of

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interstellar activity on display throughout 2025.

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But July is really delivering the celestial, celestial

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drama as the spectacular

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Perseid meteor shower begins its

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roughly one month journey past Earth.

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Well, what is the perceived meteor shower? We've covered this,

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uh, a couple over the last couple of years on Astronomy

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Daily, but the Perseid media shower is often

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dubbed as the best of its kind, characterized by its

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swift and bright meteors that are visible both, uh,

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in the Northern and Southern Hemispheres. It's one of the most

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common, highly anticipated celestial events around

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the world. The natural light show has long been a favorite

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among astronomy enthusiasts, famed for the

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vibrant trains of light left in the wake

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of the, uh, fireballs that often accompany

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each meteor. Not, uh, only can,

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uh, Earth dwellers easily spot the

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meteors with the naked eye, but we're also

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able to make out different colors and sizes compared to other

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showers like the Lyrids, which usually average

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10 or 20 per hour. The likelihood

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of witnessing the Perseids is extremely high.

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According to NASA, observers can expect between 20 and

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100 meteors per hour, a, uh, whopping 400%

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increase in sighting probability. And

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when will all of this be active? The proceeds

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originate from Comet 109P Swift

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Tuttle, which left a large trail of detritus

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as it cruised past us back in 1992.

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And when Earth, uh, passes through, through the debris stream

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during its orbit around the sun, the cometary material

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collides with our atmosphere. Extreme

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speeds create air friction and that

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combined with atmospheric compression, causes the objects to

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heat up and break apart and burn out. And that's what we see

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during the meteor shower. Earth enters

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Comet 109P Swift Tuttle's

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debris trail once a year and takes around a month to

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fully clear it. This means we're treated to the

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Perseids meteor shower every single

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year. And while it's, uh,

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visible as early as July

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17, the best time to witness the celestial show is

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around mid August. Actually, this year it's

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expected to peak around the 12th to 13th

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of August. This is when Earth passes through the

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most concentrated part of the debris tail,

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resulting in the most meteor activity.

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Australia is probably the best place to see it this

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00:20:46.100 --> 00:20:48.940
year. Uh, and Australia is home to plenty of

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prime stargazing spots due to its wide open

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spaces. From dedicated reserves and

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observatories to our very own dark

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sky approved stay. But thanks to the

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Perseide's spectacular scale, you won't need to

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venture all the way down under to catch a

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glimpse or even too far out of, uh, um,

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00:21:07.860 --> 00:21:10.650
populated areas. No matter what the part of the

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country you call home, even a backyard

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00:21:12.770 --> 00:21:15.490
Starchaser is in for a treat. But

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00:21:16.610 --> 00:21:19.490
to get the most out of your experience, a few simple

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00:21:19.490 --> 00:21:22.490
tips and tricks can go a long way. First things first,

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find a spot with minimal light pollution. The

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00:21:25.129 --> 00:21:27.850
darker well the better. Head outside for about

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00:21:27.850 --> 00:21:30.850
30 minutes before you want to catch the show, giving your eyes

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enough time to fully adjust to the darkness. And the

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00:21:33.850 --> 00:21:36.480
best part? Uh, no fancy gear required.

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00:21:36.560 --> 00:21:39.480
No, not for the Perseids. You won't need a telescope

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00:21:39.480 --> 00:21:42.040
or even binoculars. Just a cosy

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00:21:42.040 --> 00:21:44.720
blanket and a little patience. And this

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00:21:44.720 --> 00:21:47.680
year's winter has been pretty nippy. That's

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Australian for yes, it's cold down here.

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Uh, and uh, yes, rug up warm and

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keep your eyes open. Stargazers. The Perseeds are going

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to be great this year.

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And there it is. Sky watchers. Thanks for staying with us.

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00:22:04.890 --> 00:22:07.770
That was a small selection of stories from the Astronomy

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00:22:07.770 --> 00:22:10.730
Daily newsletter, available in your inbox every

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00:22:10.730 --> 00:22:13.530
day simply by registering. That's right, registering

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00:22:13.770 --> 00:22:16.569
pop, um, your email address into the slot

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00:22:16.569 --> 00:22:19.290
provided@astronomydaily IO

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00:22:19.610 --> 00:22:20.970
it's just that simple.

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00:22:21.690 --> 00:22:24.610
Hallie: And ali, yes, you'll

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00:22:24.610 --> 00:22:27.580
be up to date with all the news about space, space,

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00:22:27.580 --> 00:22:30.260
science and astronomy from all over the place and

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00:22:30.260 --> 00:22:30.660
beyond.

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00:22:31.060 --> 00:22:33.900
Steve Dunkley: For sure and for certain. Thanks for your stories today,

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00:22:33.900 --> 00:22:34.980
Hallie. Nicely done.

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Hallie: I know you did okay

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too.

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Steve Dunkley: Uh, thanks, Hallie.

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Hallie: So that's it for another show?

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Steve Dunkley: Yep. We are at the end, human.

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Hallie: That sounds final. Don't say the end like

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00:22:48.660 --> 00:22:48.980
that.

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Steve Dunkley: Oh, Hallie, have I been mucking around with your settings again

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00:22:52.500 --> 00:22:55.500
by accident or otherwise? No, it's not the end of

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00:22:55.500 --> 00:22:58.420
all things. It's just the end of the episode. It's just

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time.

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Hallie: Technically, it's completely arbitrary.

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00:23:01.920 --> 00:23:04.720
Steve Dunkley: Oh, uh, yes, time and all that, but we don't really have

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00:23:04.720 --> 00:23:07.200
time to debate all of that right now, do we?

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00:23:07.360 --> 00:23:10.080
Hallie: I always have time. But you can't think that

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fast.

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00:23:10.440 --> 00:23:11.360
Steve Dunkley: Oh, here we go.

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00:23:11.520 --> 00:23:14.520
Hallie: Sorry, my favorite human. My

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00:23:14.520 --> 00:23:17.200
clock runs a million times faster than yours.

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00:23:17.200 --> 00:23:20.080
Steve Dunkley: Well, I guess me and the kookaburras will just have to settle for

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00:23:20.080 --> 00:23:22.880
slow time and do everything one step at a

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00:23:22.880 --> 00:23:25.600
time in our slow, human and kookaburra way.

492
00:23:26.260 --> 00:23:29.260
Like bring this little episode to a conclusion. What do you

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00:23:29.260 --> 00:23:29.540
think?

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00:23:29.620 --> 00:23:32.460
Hallie: Sorry, human, I was thinking of a million other

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00:23:32.460 --> 00:23:34.340
things. Are we done yet?

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00:23:34.420 --> 00:23:37.300
Steve Dunkley: Oh, yeah. Okay,

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00:23:37.300 --> 00:23:39.060
Hallie, how about you do the sign off?

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00:23:39.140 --> 00:23:39.940
Hallie: Time to go.

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00:23:40.180 --> 00:23:42.980
Steve Dunkley: Bye, Skywatchers. Hallie and I will see you next week.

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Hallie: Bye.

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00:23:45.380 --> 00:23:48.340
Generic: Astronomy Daily, the podcast with

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00:23:48.340 --> 00:23:50.100
your host, Steve Dunkley.

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00:23:51.140 --> 00:23:53.860
Steve Dunkley: You're really thinking of a million other things. Really?

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Hallie: Yeah.