Nothing is the bridge between the future and the further future. Nothing is certainty. Nothing is any definition of anything.

— Peter Hammill

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Extreme exercise may help you live longer without stressing your heart

New Scientist Space - Cosmology - Thu, 05/09/2024 - 7:30pm
People who can run a mile in less than 4 minutes generally live almost five years longer than would otherwise be expected, challenging the idea that too much strenuous exercise is bad for the heart
Categories: Astronomy

Extreme exercise may help you live longer without stressing your heart

New Scientist Space - Space Headlines - Thu, 05/09/2024 - 7:30pm
People who can run a mile in less than 4 minutes generally live almost five years longer than would otherwise be expected, challenging the idea that too much strenuous exercise is bad for the heart
Categories: Astronomy

4 large incoming solar bursts could supercharge the auroras this weekend

Space.com - Thu, 05/09/2024 - 6:00pm
The NOAA has bumped up its geomagnetic storm watch for May 11 to a "rare" level as solar activity continues at high levels and at least four coronal mass ejections propel toward Earth.
Categories: Astronomy

Astronomers are on the Hunt for Dyson Spheres

Universe Today - Thu, 05/09/2024 - 4:57pm

There’s something poetic about humanity’s attempt to detect other civilizations somewhere in the Milky Way’s expanse. There’s also something futile about it. But we’re not going to stop. There’s little doubt about that.

One group of scientists thinks that we may already have detected technosignatures from a technological civilization’s Dyson Spheres, but the detection is hidden in our vast troves of astronomical data.

A Dyson Sphere is a hypothetical engineering project that only highly advanced civilizations could build. In this sense, ‘advance’ means the kind of almost unimaginable technological prowess that would allow a civilization to build a structure around an entire star. These Dyson Spheres would allow a civilization to harness all of a star’s energy.

A Civilization could only build something so massive and complex if they had reached Level II in the Kardashev Scale. Dyson Spheres could be a technosignature, and a team of researchers from Sweden, India, the UK, and the USA developed a way to search for Dyson Sphere technosignatures they’re calling Project Hephaistos. (Hephaistos was the Greek god of fire and metallurgy.)

They’re publishing their results in the Monthly Notices of the Royal Academy of Sciences. The research is titled “Project Hephaistos – II. Dyson sphere candidates from Gaia DR3, 2MASS, and WISE.” The lead author is Matías Suazo, a PhD student in the Department of Physics and Astronomy at Uppsala University in Sweden. This is the second paper presenting Project Hephaistos. The first one is here.

“In this study, we present a comprehensive search for partial Dyson spheres by analyzing optical and
infrared observations from Gaia, 2MASS, and WISE,” the authors write. These are large-scale astronomical surveys designed for different purposes. Each one of them generated an enormous amount of data from individual stars. “This second paper examines the Gaia DR3, 2MASS, and WISE photometry of ~5 million sources to build a catalogue of potential Dyson spheres,” they explain.

A Type II civilization is one that can directly harvest the energy of its star using a Dyson Sphere or something similar. Credit: Fraser Cain (with Midjourney)

Combing through all of that data is an arduous task. In this work, the team of researchers developed a special data pipeline to work its way through the combined data of all three surveys. They point out that they’re searching for partially-completed spheres, which would emit excess infrared radiation. “This structure would emit waste heat in the form of mid-infrared radiation that, in addition to the level of completion of the structure, would depend on its effective temperature,” Suazo and his colleagues write.

The problem is, they’re not the only objects to do so. Many natural objects do, too, like circumstellar dust rings and nebulae. Background galaxies can also emit excess infrared radiation and create false positives. It’s the pipeline’s job to filter them out. “A specialized pipeline has been developed to identify potential Dyson sphere candidates focusing on detecting sources that display anomalous infrared excesses that cannot be attributed to any known natural source of such radiation,” the researchers explain.

This flowchart shows what the pipeline looks like.

This flowchart from the research illustrates the pipeline the team developed to find Dyson Sphere candidates. Each step in the pipeline filters our objects that don’t match the expected emissions from Dyson Spheres. Image Credit: Suazo et al. 2024.

The pipeline is just the first step. The team subjects the list of candidates to further scrutiny based on factors like H-alpha emissions, optical variability, and astrometry.

368 sources survived the last cut. Of those, 328 were rejected as blends, 29 were rejected as irregulars, and 4 were rejected as nebulars. That left only 7 potential Dyson Spheres out of about 5 million initial objects, and the researchers are confident that those 7 are legitimate. “All sources are clear mid-infrared emitters with no clear contaminators or signatures that indicate an obvious mid-infrared origin,” they explain.

This pie chart shows the breakdown of the 368 sources that made it through the filter. Only 7 objects out of millions are labelled Dyson Sphere candidates. Image Credit: Suazo et al. 2024.

These are the seven strongest candidates, but the researchers know they’re still just candidates. There could be other reasons why the seven are emitting excess infrared. “The presence of warm debris disks surrounding our candidates remains a plausible explanation for the infrared excess of our sources,” they explain.

But their candidates seem to be M-type (red dwarf) stars, and debris disks around M-dwarfs are very rare. However, it gets complicated because some research suggests that debris disks around M-dwarfs form differently and present differently. One type of debris disk called Extreme Debris Disks (EDD) can explain some of the luminosity the team sees around their candidates. “But these sources have never been observed in connection with M dwarfs,” Suazo and his co-authors write.

That leaves the team with three questions: “Are our candidates strange young stars whose flux does not vary with time? Are these stars’ M-dwarf debris disks with an extreme fractional luminosity? Or something completely different?”

This figure from the research shows the seven candidates plotted on a colour-magnitude diagram. It indicates that all seven are M-dwarfs. Image Credit: Suazo et al. 2024.

“After analyzing the optical/NIR/MIR photometry of ~5 x 106 sources, we found 7 apparent M dwarfs exhibiting an infrared excess of unclear nature that is compatible with our Dyson sphere models,” the researchers write in their conclusion. There are natural explanations for the excess infrared coming from these 7, “But none of them clearly explains such a phenomenon in the candidates, especially given that all are M dwarfs.”

The researchers say that follow-up optical spectroscopy would help understand these 7 sources better. A better understanding of the H-alpha emissions is especially valuable since they can also come from young disks. “In particular, analyzing the spectral region around H-alpha can help us ultimately discard or verify the presence of young disks,” the researchers write.

“Additional analyses are definitely necessary to unveil the true nature of these sources,” they conclude.

The post Astronomers are on the Hunt for Dyson Spheres appeared first on Universe Today.

Categories: Astronomy

Video: Plunge into a Black Hole

Sky & Telescope Magazine - Thu, 05/09/2024 - 3:56pm

A new visualization from NASA takes the viewer on a one-way journey into a black hole.

The post Video: Plunge into a Black Hole appeared first on Sky & Telescope.

Categories: Astronomy

We Need to Consider Conservation Efforts on Mars

Universe Today - Thu, 05/09/2024 - 3:36pm

Astrobiology is the field of science that studies the origins, evolution, distribution, and future of life in the Universe. In practice, this means sending robotic missions beyond Earth to analyze the atmospheres, surfaces, and chemistry of extraterrestrial worlds. At present, all of our astrobiology missions are focused on Mars, as it is considered the most Earth-like environment beyond our planet. While several missions will be destined for the outer Solar System to investigate “Ocean Worlds” for evidence of life (Europa, Ganymede, Titan, and Enceladus), our efforts to find life beyond Earth will remain predominantly on Mars.

If and when these efforts succeed, it will have drastic implications for future missions to Mars. Not only will great care need to be taken to protect Martian life from contamination by Earth organisms, but precautions must be taken to prevent the same from happening to Earth (aka. Planetary Protection). In a recent study, a team from the University of New South Wales (UNSW) in Sydney, Australia, recommends that legal or normative frameworks be adopted now to ensure that future missions do not threaten sites where evidence of life (past or present) might be found.

The study was led by Clare Fletcher, a Ph.D. student with the Australian Centre for Astrobiology (ACA) and Earth and Sustainability Science Research Centre at UNSW. She was joined by Professor Martin Van Kranendonk, a researcher with the ACA and the head of the School of Earth and Planetary Sciences at Curtin University, and Professor Carol Oliver of the School of Biological, Earth & Environmental Sciences at UNSW. Their research paper, “Exogeoconservation of Mars,” appeared on April 21st in Space Policy.

The search for life on Mars can be traced to the late 19th and early 20th centuries when Percival Lowell made extensive observations from his observatory in Flagstaff, Arizona. Inspired by Schiaparelli’s illustrations of the Martian surface (which featured linear features he called “canali”), Lowell recorded what he also believed were canals and spent many years searching for other indications of infrastructure and an advanced civilization. During the ensuing decades, observatories worldwide observed Mars closely, looking for indications of life and similarities with Earth.

However, it was not until the Space Age that the first robotic probes flew past Mars, gathering data directly from its atmosphere and taking close-up images of the surface. These revealed a planet with a thin atmosphere composed predominantly of carbon dioxide and a frigid surface that did not appear hospitable to life. However, it was the Viking 1 and 2 missions, which landed on Mars in 1976, that forever dispelled the myth of a Martian civilization. But as Fletcher told Universe Today via email, the possibility of extant life has not been completely abandoned:

“It’s my personal belief that it is unlikely we will find evidence of extant (current) life on Mars, as opposed to evidence of past life on Mars. If we were to find extant life on Mars that could be proven to be endemic to Mars and not contamination from Earth, some think it might be found underground in lava tubes, for example, and some think the ice caps or any possible source of liquid water might be suitable places.”

Ironically, it was the same missions that discredited the notion of there being life on Mars that revealed evidence that water once flowed on its surface. Thanks to the many orbiter, lander, and rover missions sent to Mars since the turn of the century, scientists theorize that this period coincided with the Noachian Era (ca. 4.1 – 3.7 billion years ago). According to the most recent fossilized evidence, it was also during this period that life first appeared on Earth (in the form of single-celled bacteria).

Artist’s impression of Mars during the Noachian Era. Credit: Ittiz/Wikipedia Commons

Our current astrobiology efforts on behalf of NASA and other space agencies are focused on Mars precisely for this reason: to determine if life emerged on Mars billions of years ago and whether or not it co-evolved with life on Earth. This includes the proposed Mars Sample Return (MSR) mission that will retrieve the drill samples obtained by the Perseverance rover in the Jezero Crater and return them to Earth for analysis. In addition, NASA and China plan to send crewed missions to Mars by 2040 and 2033 (respectively), including astrobiology studies.

These activities could threaten the very abodes where evidence of past life could be found or (worse) still exists. “Human activities might threaten sites like this in part due to possible microbial contamination,” said Fletcher. “Evidence of life (past and extant) also has greater scientific value when in its palaeoenvironmental context, so any human activities that might damage the evidence of life and/or its surrounding environmental context pose a risk. This could be something innocuous, like debris falling in the wrong spot, or something more serious, like driving over possibly significant outcrops with a rover.”

Conservation measures must be developed and implemented before additional missions are sent to Mars. Given humanity’s impact on Earth’s natural environment and our attempts to mitigate this through conservation efforts. In particular, there have been numerous cases where scientific studies were conducted without regard for the heritage value of the site and where damage was done because of a lack of proper measures. These lessons, says Fletcher, could inform future scientific efforts on Mars:

“It’s important that we learn from what has been considered “damaging” on Earth and take this into consideration when exploring Mars. If a site is damaged beyond being able to be studied in the future, then we limit what can actually be learned from a site. When considering Mars missions cost billions of dollars and are to meet specific scientific goals, limiting the information being learned from a site is incredibly detrimental. My recommendations are that of my paper: interdisciplinary cooperation, drawing on experience and knowledge from Earth, creating norms and a code of practice (part of my PhD work), and working towards creating legislation for these issues.”

Artist’s rendition of NASA’s Dragonfly on the surface of Titan. Credit: NASA/Johns Hopkins APL/Steve Gribben

The need for exogeoconservation is paramount at this juncture. In addition to Mars, multiple astrobiology missions will travel to the outer Solar System this decade to search for evidence of life on icy moons like Europa, Ganymede, Titan, and Enceladus. This includes the ESA’s JUpiter ICy moons Explorer (JUICE) mission, currently en route to Ganymede, and NASA’s Europa Clipper and Dragonfly missions that will launch for Europa and Titan in October 2024 and 2028 (respectively). Therefore, the ability to search for extant or past life without damaging its natural environment is an ethical and scientific necessity.

“I hope this paper is very much a starting point for anyone working in Mars science and exploration, as well as anyone thinking about space policy and exogeoconservation,” said Fletcher. “My goal was to start drawing attention to these issues, and that way start a generation of researchers and practitioners focused on exogeoconservation of Mars.”

Further Reading: Space Policy

The post We Need to Consider Conservation Efforts on Mars appeared first on Universe Today.

Categories: Astronomy

I Am Artemis: Lauren Fisher

NASA - Breaking News - Thu, 05/09/2024 - 3:22pm
Fisher stands in front of the launch vehicle stage adapter for NASA’s SLS (Space Launch System) rocket. The hardware will be used for the agency’s Artemis III mission that will land astronauts on the lunar surface. Fisher works with a number of teams across the agency and believes her background in music education has been an asset to her work as an engineer: “Teaching skills help you look at things from a different perspective and helps with understanding how others might approach a situation – all very helpful when I’m working with teams.”

Not many music majors get to be hands-on with building a Moon rocket, but Lauren Fisher has always enjoyed the unusual.

Now a structural materials engineer at NASA’s Marshall Space Flight Center in Huntsville, Alabama, Fisher works on a key adapter for NASA’s SLS (Space Launch System) rocket for the first crewed missions of NASA’s Artemis campaign.

Manufactured at Marshall by NASA, lead contractor Teledyne Brown Engineering, and the Jacobs Space Exploration Group’s ESSCA contract, the cone-shaped launch vehicle stage adapter partially encloses the rocket’s interim cryogenic propulsion stage and connects it to the core stage below and the Orion stage adapter above. The launch vehicle stage adapter also protects avionics and electrical devices from extreme vibration and acoustic conditions during launch and ascent.

Fisher and the thermal protection system team develop and apply the spray-on foam that acts as insulation and protects the adapter and all its systems from the extreme pressures and temperatures it’ll face during flight. The thermal protection system for the component, unlike other parts of the rocket, is applied by hand using a spray gun. When first applied, the insulation is yellow, but after time and exposure to the Sun, it turns orange.

“We’re taking the same stuff someone might use to insulate their attic, except making it for cryogenic atmospheres, and spraying it all over a giant piece of hardware that will help launch us to the Moon,” Fisher said. “With my work for NASA’s Space Launch System rocket, I get to play with foam and glue. I like to call it arts and crafts engineering!”

Although engineering runs in her family, Fisher initially graduated from University of Southern Mississippi with a Bachelor of Arts in music performance and an interest in music education. She developed an interest in carbon-based polymers, and decided to go back to school, completing a chemical engineering degree with a polymeric materials track from the University of Alabama in Huntsville. Her new degree led to an opportunity to work for the thermal protection system team at Marshall.

When Fisher isn’t in the office, she likes travelling to unusual places and checking items off her self-described “Bizarre Bucket List.” Recently, she went to Punxsutawney, Pennsylvania, to watch the famous groundhog predict an early spring.

Being part of the Artemis Generation is incredibly inspiring for Fisher, who takes pride in her work supporting the first three Artemis missions, including Artemis II, the first crewed mission under Artemis, in 2025.

“I’m literally building the hardware that will send the first woman to deep space,” Fisher says. “Watching our rocket take shape, I’m like ‘you see that thing? I did that; that’s mine. See that one? My team did that one. We did that, and see this?’” She beams with pride. “You can do that, too. Just being a part of the generation that’s changing the workforce and changing the space program — it gives me goosebumps.”

NASA is working to land the first woman, first person of color, and its first international partner astronaut on the Moon under Artemis. SLS is part of NASA’s backbone for deep space exploration, along with the Orion spacecraft and Gateway in orbit around the Moon and commercial human landing systems, next-generational spacesuits, and rovers on the lunar surface. SLS is the only rocket that can send Orion, astronauts, and supplies to the Moon in a single launch.

Categories: NASA

Invisible 'dark radiation' may explain a big problem with dark energy

New Scientist Space - Cosmology - Thu, 05/09/2024 - 3:00pm
Surprising recent measurements hint that the universe isn’t expanding in the way we had thought, and it could be explained by still-theoretical dark radiation
Categories: Astronomy

Invisible 'dark radiation' may explain a big problem with dark energy

New Scientist Space - Space Headlines - Thu, 05/09/2024 - 3:00pm
Surprising recent measurements hint that the universe isn’t expanding in the way we had thought, and it could be explained by still-theoretical dark radiation
Categories: Astronomy

Sierra Space's 1st Dream Chaser space plane aces key tests. Next stop: Florida launch site.

Space.com - Thu, 05/09/2024 - 3:00pm
Sierra Space's first Dream Chaser space plane has finished rigorous environmental testing in Ohio and is being prepped for the journey to its Florida launch site.
Categories: Astronomy

Spitzer Space Telescope Captures Galactic Snack

NASA Image of the Day - Thu, 05/09/2024 - 2:09pm
This image of the Andromeda galaxy uses data from NASA’s retired Spitzer Space Telescope. Multiple wavelengths are shown, revealing stars (in blue and cyan), dust (red), and areas of star formation.
Categories: Astronomy, NASA

Spitzer Space Telescope Captures Galactic Snack

NASA - Breaking News - Thu, 05/09/2024 - 2:07pm
NASA-JPL/Caltech; image processing by IPAC/Robert Hurt

This image, released on May 9, 2024, from NASA’s retired Spitzer Space Telescope shows streams of dust flowing toward the supermassive black hole at the heart of the Andromeda Galaxy. These dust streams can help explain how black holes billions of times the mass of our Sun can satiate their big appetites but remain “quiet” eaters.

Read on to learn how data from Spitzer helped shed light on how some black holes consume gas and dust.

Image Credit: NASA-JPL/Caltech

Categories: NASA

NASA's Nancy Grace Roman Telescope will hunt for tiny black holes left over from the Big Bang

Space.com - Thu, 05/09/2024 - 2:07pm
Primordial black holes left over from the Big Bang and no wider than a dime could be a prime target for NASA's Nancy Grace Roman Telescope after it launches in 2026.
Categories: Astronomy

'Star Wars: Tales of the Empire' review: A gorgeous but ultimately uneven set of stories

Space.com - Thu, 05/09/2024 - 2:00pm
Lucasfilm Animation's second Star Wars anthology series often wows, but neither the tales chosen nor the structure feel like a good fit for the format.
Categories: Astronomy

Arizona, New York Students to Hear from NASA Astronauts Aboard Station

NASA - Breaking News - Thu, 05/09/2024 - 1:56pm
(March 26, 2024) — Five NASA astronauts wear eye-protecting specs in anticipation of viewing the April 8 solar eclipse from the International Space Station’s cupola. Credits: NASA

Students from Arizona and New York will have separate opportunities next week to hear from astronauts aboard the International Space Station.

At 12:10 p.m. EDT on Tuesday, May 14, NASA astronauts Jeanette Epps and Tracy C. Dyson will answer prerecorded student questions from Sunnyside Unified School District in Tucson, Arizona, in partnership with the TRiO Upward Bound Program, PIMA Community College, Desert Vista Campus. Participating students are first-generation college bound students from underserved communities, and this opportunity is intended to help spread awareness of Science, Technology, Engineering, and Math (STEM) careers and inspire students to pursue related degrees.

The space-to-Earth call will stream live on NASA+, NASA Television, the NASA app, and the agency’s website.

Media interested in covering the Arizona event should RSVP no later than 5 p.m. on Friday, May 10, by contacting Danny Pacheco at dapacheco@pima.edu or 520-286-7771.

At 11:40 a.m. on Thursday, May 16, NASA astronaut Jeanette Epps will answer prerecorded student questions from P.S. 28 The Thomas Emanuel Early Childhood Center in Corona, New York, in partnership with the New York Hall of Science. Following the live event, the center will host 200 first and second grade students for a one-hour interactive “Living in Space” learning opportunity.

Media interested in covering the New York event should RSVP no later than 5 p.m. on Tuesday, May 14, by contacting Nicole Casamento at ncasamento@nysco.org or 917-302-9242.

The space-to-Earth call will air live on NASA+, NASA Television, the NASA app, and the agency’s website.

For more than 23 years, astronauts have continuously lived and worked aboard the space station, testing technologies, performing science, and developing skills needed to explore farther from Earth. Astronauts living aboard the orbiting laboratory communicate with NASA’s Mission Control Center in Houston 24 hours a day through SCaN (Space Communications and Navigation) Near Space Network.

Important research and technology investigations taking place aboard the International Space station benefits people on Earth and lays the groundwork for other agency missions. As part of NASA’s Artemis campaign, the agency will send astronauts to the Moon to prepare for future human exploration of Mars. Inspiring Artemis Generation explorers and ensuring the United States will continue to lead in space exploration and discovery.

See videos and lesson plans highlighting space station research at:

https://www.nasa.gov/stemonstation

-end-

Gerelle Dodson
Headquarters, Washington
202-384-4861
gerelle.q.dodson@nasa.gov

Sandra Jones 
Johnson Space Center, Houston
281-483-5111
sandra.p.jones@nasa.gov

Share Details Last Updated May 09, 2024 LocationNASA Headquarters Related Terms
Categories: NASA

NASA Invites Media to Arizona Simulated Artemis Moonwalking Site  

NASA - Breaking News - Thu, 05/09/2024 - 1:12pm
NASA astronaut Kate Rubins (right) takes a photo of NASA astronaut Andre Douglas (left) as he raises an American flag during a simulated moonwalk in a rock yard at NASA’s Johnson Space Center. Credit: NASA/Josh Valcarcel

Media are invited to interact with the NASA team members practicing Artemis moonwalking operations Saturday, May 18, in the San Francisco Volcanic Fields near Flagstaff, Arizona. NASA’s in-person only event includes an opportunity to speak with subject matter experts and view various hardware stations.

The activities are the fifth in a series since April 2022 of simulated moonwalks for Artemis Generation astronauts and teams planning for future exploration of the lunar surface. The full training will take place Monday, May 13, through Monday, May 20, with NASA astronauts Kate Rubins and Andre Douglas serving as the crew.

There are four simulated moonwalks and six advanced technology runs scheduled for this set. The media day schedule includes (all times MST):

  • 2:30 p.m.: Arrival
  • 2:45 p.m.: Local overview news conference and demonstrations
  • 3:30 p.m.: Walk through stations and speak to subject matter experts

Reporters interested in attending must request accreditation by 5 p.m. CDT, Wednesday, May 15, by contacting Victoria Ugalde at 281-483-5111 or victoria.d.ugalde@nasa.gov.

Teams continue to evolve astronaut training, and crew will wear mockup spacesuits as they test hardware, capabilities, and technologies to conduct operations in a simulated lunar environment for the Artemis III mission and beyond.

Through Artemis, NASA will send astronauts – including the first woman, the first person of color, and the first international partner astronaut – to explore the Moon for scientific discovery, technology evolution, economic benefits, and to build the foundation for crewed missions to Mars. Mission simulations on Earth help prepare humans for the challenges of deep space exploration and journeying farther into the cosmos.

Learn more about NASA’s Artemis campaign:

https://www.nasa.gov/artemis/

-end-

Kathryn Hambleton
NASA Headquarters, Washington
301-286-0213
kathryn.hambleton@nasa.gov

Victoria Ugalde
NASA Johnson Space Center, Houston
281-483-5111
victoria.d.ugalde@nasa.gov

Share Details Last Updated May 09, 2024 LocationNASA Headquarters Related Terms
Categories: NASA

James Webb Space Telescope chief scientist Jane Rigby receives highest US civilian award

Space.com - Thu, 05/09/2024 - 12:50pm
Last week, the chief scientist of the James Webb Space Telescope, Jane Rigby, was awarded the 2024 Medal of Freedom.
Categories: Astronomy

Gargantuan sunspot 15-Earths wide erupts with another colossal X-class solar flare (video)

Space.com - Thu, 05/09/2024 - 12:41pm
A sunspot so big it rivals the gigantic sunspot responsible for the Carrington Event in 1859 has unleashed another X-class solar flare. Watch the eruption here and find out how to see the sunspot for yourself.
Categories: Astronomy

Game theory shows we can never learn perfectly from our mistakes

New Scientist Space - Cosmology - Thu, 05/09/2024 - 12:10pm
An analysis of a mathematical economic game suggests that even learning from past mistakes will almost never help us optimise our decision-making – with implications for our ability to make the biggest financial gains
Categories: Astronomy

Game theory shows we can never learn perfectly from our mistakes

New Scientist Space - Space Headlines - Thu, 05/09/2024 - 12:10pm
An analysis of a mathematical economic game suggests that even learning from past mistakes will almost never help us optimise our decision-making – with implications for our ability to make the biggest financial gains
Categories: Astronomy