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How do astronomers know the age of the planets and stars?

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How do astronomers know the age of the planets and stars?

Astronomers can estimate ages for stars outside the Solar System, but not planets.
Corbis Historical via Getty Images

Adam Burgasser, University of California, San Diego

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.


How do we know the age of the planets and stars? – Swara D., age 13, Thane, India


Measuring the ages of planets and stars helps scientists understand when they formed and how they change – and, in the case of planets, if life has had time to have evolved on them.

Unfortunately, age is hard to measure for objects in space.

Stars like the Sun maintain the same brightness, temperature and size for billions of years. Planet properties like temperature are often set by the star they orbit rather than their own age and evolution.

Determining the age of a star or planet can be as hard as guessing the age of a person who looks exactly the same from childhood to retirement.

Sussing out a star’s age

Fortunately, stars change subtly in brightness and color over time. With very accurate measurements, astronomers can compare these measurements of a star to mathematical models that predict what happens to stars as they get older and estimate an age from there.

Stars don’t just glow, they also spin. Over time, their spinning slows down, similar to how a spinning wheel slows down when it encounters friction. By comparing the spin speeds of stars of different ages, astronomers have been able to create mathematical relationships for the ages of stars, a method known as gyrochronology.

A close up image of the Sun in outer space
Researchers estimate the Sun is 4.58 billion years old.
NASA via GettyImages

A star’s spin also generates a strong magnetic field and produces magnetic activity, such as stellar flares – powerful bursts of energy and light that occur on stars’ surfaces. A steady decline in magnetic activity from a star can also help estimate its age.

A more advanced method for determining the ages of stars is called asteroseismology, or star shaking. Astronomers study vibrations on the surfaces of stars caused by waves that travel through their interiors. Young stars have different vibrational patterns than old stars. By using this method, astronomers have estimated the Sun to be 4.58 billion years old.

Piecing together a planet’s age

In the solar system, radionuclides are the key to dating planets. These are special atoms that slowly release energy over a long period of time. As natural clocks, radionuclides help scientists determine the ages of all kinds of things, from rocks to bones and pottery.

Using this method, scientists have determined that the oldest known meteorite is 4.57 billion years old, almost identical to the Sun’s asteroseismology measurement of 4.58 billion years. The oldest known rocks on Earth have slightly younger ages of 4.40 billion years.
Similarly, soil brought back from the Moon during the Apollo missions had radionuclide ages of up to 4.6 billion years.

A close up image of craters on the surface of the moon.
Craters on the moon’s surface.
Tomekbudujedomek/Moment via Getty Images

Although studying radionuclides is a powerful method for measuring the ages of planets, it usually requires having a rock in hand. Typically, astronomers only have a picture of a planet to go by. Astronomers often determine the ages of rocky space objects like Mars or the Moon by counting their craters. Older surfaces have more craters than younger surfaces. However, erosion from water, wind, cosmic rays and lava flow from volcanoes can wipe away evidence of earlier impacts.

Aging techniques don’t work for giant planets like Jupiter that have deeply buried surfaces. However, astronomers can estimate their ages by counting craters on their moons or studying the distribution of certain classes of meteorites scattered by them, which are consistent with radionuclide and cratering methods for rocky planets.

We cannot yet directly measure the ages of planets outside our solar system with current technology.

How accurate are these estimates?

Our own solar system provides the best check for accuracy, since astronomers can compare the radionuclide ages of rocks on the Earth, Moon, or asteroids to the asteroseismology age of the Sun, and these match very well.

Stars in clusters like the Pleiades or Omega Centauri are believed to have all formed at roughly the same time, so age estimates for individual stars in these clusters should be the same. In some stars, astronomers can detect radionuclides like uranium – a heavy metal found in rocks and soil – in their atmospheres, which have been used to check the ages from other methods.

Astronomers believe planets are roughly the same age as their host stars, so improving methods to determine a star’s age helps determine a planet’s age as well. By studying subtle clues, it’s possible to make an educated guess of the age of an otherwise steadfast star.


Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.The Conversation

Adam Burgasser, Professor of Astronomy & Astrophysics, University of California, San Diego

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Predictive policing AI is on the rise − making it accountable to the public could curb its harmful effects

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theconversation.com – Maria Lungu, Postdoctoral Researcher of Law and Public Administration, University of Virginia – 2025-05-06 07:35:00

Data like this seven-day crime map from Oakland, Calif., feeds predictive policing AIs.
City of Oakland via CrimeMapping.com

Maria Lungu, University of Virginia

The 2002 sci-fi thriller “Minority Report” depicted a dystopian future where a specialized police unit was tasked with arresting people for crimes they had not yet committed. Directed by Steven Spielberg and based on a short story by Philip K. Dick, the drama revolved around “PreCrime” − a system informed by a trio of psychics, or “precogs,” who anticipated future homicides, allowing police officers to intervene and prevent would-be assailants from claiming their targets’ lives.

The film probes at hefty ethical questions: How can someone be guilty of a crime they haven’t yet committed? And what happens when the system gets it wrong?

While there is no such thing as an all-seeing “precog,” key components of the future that “Minority Report” envisioned have become reality even faster than its creators imagined. For more than a decade, police departments across the globe have been using data-driven systems geared toward predicting when and where crimes might occur and who might commit them.

Far from an abstract or futuristic conceit, predictive policing is a reality. And market analysts are predicting a boom for the technology.

Given the challenges in using predictive machine learning effectively and fairly, predictive policing raises significant ethical concerns. Absent technological fixes on the horizon, there is an approach to addressing these concerns: Treat government use of the technology as a matter of democratic accountability.

Troubling history

Predictive policing relies on artificial intelligence and data analytics to anticipate potential criminal activity before it happens. It can involve analyzing large datasets drawn from crime reports, arrest records and social or geographic information to identify patterns and forecast where crimes might occur or who may be involved.

Law enforcement agencies have used data analytics to track broad trends for many decades. Today’s powerful AI technologies, however, take in vast amounts of surveillance and crime report data to provide much finer-grained analysis.

Police departments use these techniques to help determine where they should concentrate their resources. Place-based prediction focuses on identifying high-risk locations, also known as hot spots, where crimes are statistically more likely to happen. Person-based prediction, by contrast, attempts to flag individuals who are considered at high risk of committing or becoming victims of crime.

These types of systems have been the subject of significant public concern. Under a so-called “intelligence-led policing” program in Pasco County, Florida, the sheriff’s department compiled a list of people considered likely to commit crimes and then repeatedly sent deputies to their homes. More than 1,000 Pasco residents, including minors, were subject to random visits from police officers and were cited for things such as missing mailbox numbers and overgrown grass.

YouTube video
Lawsuits forced the Pasco County, Fla., Sheriff’s Office to end its troubled predictive policing program.

Four residents sued the county in 2021, and last year they reached a settlement in which the sheriff’s office admitted that it had violated residents’ constitutional rights to privacy and equal treatment under the law. The program has since been discontinued.

This is not just a Florida problem. In 2020, Chicago decommissioned its “Strategic Subject List,” a system where police used analytics to predict which prior offenders were likely to commit new crimes or become victims of future shootings. In 2021, the Los Angeles Police Department discontinued its use of PredPol, a software program designed to forecast crime hot spots but was criticized for low accuracy rates and reinforcing racial and socioeconomic biases.

Necessary innovations or dangerous overreach?

The failure of these high-profile programs highlights a critical tension: Even though law enforcement agencies often advocate for AI-driven tools for public safety, civil rights groups and scholars have raised concerns over privacy violations, accountability issues and the lack of transparency. And despite these high-profile retreats from predictive policing, many smaller police departments are using the technology.

Most American police departments lack clear policies on algorithmic decision-making and provide little to no disclosure about how the predictive models they use are developed, trained or monitored for accuracy or bias. A Brookings Institution analysis found that in many cities, local governments had no public documentation on how predictive policing software functioned, what data was used, or how outcomes were evaluated.

YouTube video
Predictive policing can perpetuate racial bias.

This opacity is what’s known in the industry as a “black box.” It prevents independent oversight and raises serious questions about the structures surrounding AI-driven decision-making. If a citizen is flagged as high-risk by an algorithm, what recourse do they have? Who oversees the fairness of these systems? What independent oversight mechanisms are available?

These questions are driving contentious debates in communities about whether predictive policing as a method should be reformed, more tightly regulated or abandoned altogether. Some people view these tools as necessary innovations, while others see them as dangerous overreach.

A better way in San Jose

But there is evidence that data-driven tools grounded in democratic values of due process, transparency and accountability may offer a stronger alternative to today’s predictive policing systems. What if the public could understand how these algorithms function, what data they rely on, and what safeguards exist to prevent discriminatory outcomes and misuse of the technology?

The city of San Jose, California, has embarked on a process that is intended to increase transparency and accountability around its use of AI systems. San Jose maintains a set of AI principles requiring that any AI tools used by city government be effective, transparent to the public and equitable in their effects on people’s lives. City departments also are required to assess the risks of AI systems before integrating them into their operations.

If taken correctly, these measures can effectively open the black box, dramatically reducing the degree to which AI companies can hide their code or their data behind things such as protections for trade secrets. Enabling public scrutiny of training data can reveal problems such as racial or economic bias, which can be mitigated but are extremely difficult if not impossible to eradicate.

Research has shown that when citizens feel that government institutions act fairly and transparently, they are more likely to engage in civic life and support public policies. Law enforcement agencies are likely to have stronger outcomes if they treat technology as a tool – rather than a substitute – for justice.The Conversation

Maria Lungu, Postdoctoral Researcher of Law and Public Administration, University of Virginia

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Note: The following A.I. based commentary is not part of the original article, reproduced above, but is offered in the hopes that it will promote greater media literacy and critical thinking, by making any potential bias more visible to the reader –Staff Editor.

Political Bias Rating: Center-Left

The article provides an analysis of predictive policing, highlighting both the technological potential and ethical concerns surrounding its use. While it presents factual information, it leans towards caution and skepticism regarding the fairness, transparency, and potential racial biases of these systems. The framing of these issues, along with an emphasis on democratic accountability, transparency, and civil rights, aligns more closely with center-left perspectives that emphasize government oversight, civil liberties, and fairness. The critique of predictive policing technologies without overtly advocating for their abandonment reflects a balanced but cautious stance on technology’s role in law enforcement.

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Worsening allergies aren’t your imagination − windy days create the perfect pollen storm

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theconversation.com – Christine Cairns Fortuin, Assistant Professor of Forestry, Mississippi State University – 2025-05-05 07:45:00

Windy days can mean more pollen and more sneezing.
mladenbalinovac/E+ via Getty Images

Christine Cairns Fortuin, Mississippi State University

Evolution has fostered many reproductive strategies across the spectrum of life. From dandelions to giraffes, nature finds a way.

One of those ways creates quite a bit of suffering for humans: pollen, the infamous male gametophyte of the plant kingdom.

In the Southeastern U.S., where I live, you know it’s spring when your car has turned yellow and pollen blankets your patio furniture and anything else left outside. Suddenly there are long lines at every car wash in town.

A car covered in yellow. Someone drew a smiley face with the words 'LOLLEN,' with LOL underlined.
On heavy pollen days, cars can end up covered in yellow grains.
Scott Akerman/Flickr, CC BY

Even people who aren’t allergic to pollen – clearly an advantage for a pollination ecologist like me – can experience sneezing and watery eyes during the release of tree pollen each spring. Enough particulate matter in the air will irritate just about anyone, even if your immune system does not launch an all-out attack.

So, why is there so much pollen? And why does it seem to be getting worse?

2 ways trees spread their pollen

Trees don’t have an easy time in the reproductive game. As a tree, you have two options to disperse your pollen.

Option 1: Employ an agent, such as a butterfly or bee, that can carry your pollen to another plant of the same species.

The downside of this option is that you must invest in a showy flower display and a sweet scent to advertise yourself, and sugary nectar to pay your agent for its services.

A bee noses into a white flower.
A bee enjoys pollen from a cherry blossom. Pollen is a primary source of protein for bees.
Ivan Radic/Flickr, CC BY

Option 2, the budget option, is much less precise: Get a free ride on the wind.

Wind was the original pollinator, evolving long before animal-mediated pollination. Wind doesn’t require a showy flower nor a nectar reward. What it does require for pollination to succeed is ample amounts of lightweight, small-diameter pollen.

Why wind-blown pollen makes allergies worse

Wind is not an efficient pollinator, however. The probability of one pollen grain landing in the right location – the stigma or ovule of another plant of the same species – is infinitesimally small.

Therefore, wind-pollinated trees must compensate for this inefficiency by producing copious amounts of pollen, and it must be light enough to be carried.

For allergy sufferers, that can mean air filled with microscopic pollen grains that can get into your eyes, throat and lungs, sneak in through window screens and convince your immune system that you’ve inhaled a dangerous intruder.

Tiny flowers on a live oak tree.
When wind blows the tiny pollen grains of live oaks, allergy sufferers feel it.
Charles Willgren/Flickr, CC BY

Plants relying on animal-mediated pollination, by contrast, can produce heavier and stickier pollen to adhere to the body of an insect. So don’t blame the bees for your allergies – it’s really the wind.

Climate change has a role here, too

Plants initiate pollen release based on a few factors, including temperature and light cues. Many of our temperate tree species respond to cues that signal the beginning of spring, including warmer temperatures.

Studies have found that pollen seasons have intensified in the past three decades as the climate has warmed. One study that examined 60 location across North America found pollen seasons expanded by an average of 20 days from 1990 to 2018 and pollen concentrations increased by 21%.

That’s not all. Increasing carbon dioxide levels may also be driving increases in the quantity of tree pollen produced.

Why the Southeast gets socked

What could make this pollen boost even worse?

For the Southeastern U.S. in particular, strong windstorms are becoming more common and more intense − and not just hurricanes.

Anyone who has lived in the Southeast for the past couple of decades has likely noticed this. The region has more tornado warnings, more severe thunderstorms, more power outages. This is especially true in the mid-South, from Mississippi to Alabama.

A map showing windiest events in the Southeast are over Alabama and Mississippi.
Severity of wind and storm events mapped from NOAA data, 2012-2019, shows high activity over Mississippi and Alabama. Red areas have the most severe events.
Christine Cairns Fortuin

Since wind is the vector of airborne pollen, windier conditions can also make allergies worse. Pollen remains airborne for longer on windy days, and it travels farther.

To make matters worse, increasing storm activity may be doing more than just transporting pollen. Storms can also break apart pollen grains, creating smaller particles that can penetrate deeper into the lungs.

Many allergy sufferers may notice worsening allergies during storms.

The peak of spring wind and storm season tends to correspond to the timing of the release of tree pollen that blankets our world in yellow. The effects of climate change, including longer pollen seasons and more pollen released, and corresponding shifts in windy days and storm severity are helping to create the perfect pollen storm.The Conversation

Christine Cairns Fortuin, Assistant Professor of Forestry, Mississippi State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Note: The following A.I. based commentary is not part of the original article, reproduced above, but is offered in the hopes that it will promote greater media literacy and critical thinking, by making any potential bias more visible to the reader –Staff Editor.

Political Bias Rating: Centrist

The content is a scientific and educational article focusing on the biology of pollen, its effects on allergies, and the influence of climate change on pollen production. It presents factual information supported by research studies and references, without taking a partisan stance. While it acknowledges climate change as a factor, the discussion remains grounded in scientific observation rather than political opinion, leading to a neutral, centrist tone.

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The Women’s Health Initiative has shaped women’s health for over 30 years, but its future is uncertain

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theconversation.com – Jean Wactawski-Wende, Professor of Public Health and Health Professions, University at Buffalo – 2025-05-02 07:44:00

Jean Wactawski-Wende, University at Buffalo

Women make up more than 50% of the population, yet before the 1990s they were largely excluded from health and medical research studies.

To try to help correct this imbalance, in 1991 the National Institutes of Health launched a massive, long-term study called the Women’s Health Initiative, which is still running today. It is the largest, longest and most comprehensive study on women’s health ever conducted in the U.S. It also is one of the most productive studies in history, with more than 2,400 published scientific papers in leading medical journals.

On April 20, 2025, the Department of Health and Human Services told the study’s lead investigators it plans to terminate much of the program’s funding and discontinue its regional center contracts. On April 24, after pushback from the medical community, HHS officials said the funding had been reinstated. But the reversal was never officially confirmed, so the study’s lead investigators – including me – remain concerned about its future.

I am a public health researcher who has studied chronic disease prevention in women for nearly 40 years. I have been centrally involved with the Women’s Health Initiative since its inception and currently co-direct one of its four regional centers at the University at Buffalo.

The project’s findings have shaped clinical practice, prevention strategies and public health policies across the U.S. and the world, particularly for older women. In my view, its loss would be a devastating blow to women’s health.

An imperative to invest in women’s health

The Women’s Health Initiative was established in response to a growing realization that very little medical research existed to inform health care that was specifically relevant to women. In the U.S. in the 1970s, for example, almost 40% of postmenopausal women were taking estrogen, but no large clinical trials had studied the risks and benefits. In 1985 an NIH task force outlined the need for long-term research on women’s health.

Launched by Bernadine Healy, the first woman to serve as director of the NIH, the Women’s Health Initiative aimed to study ways to prevent heart disease, cancer and osteoporosis.

The hands of an older woman and a caregiver, clasped
About 42,000 women ages 78 to 108 remain active participants in the Women’s Health Initiative.
Frazao Studio Latino/E+ via Getty Images

Between 1993 and 1998, the project enrolled 161,808 postmenopausal women ages 50 to 79 to participate in four randomized clinical trials. Two of them investigated how menopausal hormone therapy affects the risk of heart disease, breast cancer, hip fractures and cognition. Another examined the effects of a low-fat, high-fiber diet on breast and colorectal cancers as well as heart disease. The fourth looked at whether taking calcium plus vitamin D supplements helps prevent hip fractures and colorectal cancer.

Women could participate in just one or in multiple trials. More than 90,000 also took part in a long-term observational study that used medical records and surveys to probe the link between risk factors and disease outcomes over time.

Clarifying the effects of hormone therapy

Some of the most important findings from the Women’s Health Initiative addressed the effects of menopausal hormone therapy.

The hormone therapy trial testing a combination of estrogen and progesterone was set to run until 2005. However, it was terminated early, in 2002, when results showed an increased risk in heart disease, stroke, blood clotting disorders and breast cancer, as well as cognitive decline and dementia. The trial of estrogen alone also raised safety concerns, though both types of therapy reduced the risk of bone fractures.

After these findings were reported, menopausal hormone therapy prescriptions dropped sharply in the U.S. and worldwide. One study estimated that the decreased use of estrogen and progesterone therapy between 2002 and 2012 prevented as many as 126,000 breast cancer cases and 76,000 cardiovascular disease cases – and saved the U.S. an estimated US$35 billion in direct medical costs.

Reanalyses of data from these studies over the past decade have provided a more nuanced clinical picture for safely using menopausal hormone therapy. They showed that the timing of treatment matters, and that when taken before age 60 or within 10 years of menopause, hormones have more limited risk.

Defining clinical practice

Although the Women’s Health Initiative’s four original clinical trials ended by 2005, researchers have continued to follow participants, collect new data and launch spinoff studies that shape health recommendations for women over 65.

Almost a decade ago, for example, research at my institution and others found in a study of 6,500 women ages 63 to 99 that just 30 minutes of low to moderate physical activity was enough to significantly boost their health. The study led to changes in national public health guidelines. Subsequent studies are continuing to explore how physical activity affects aging and whether being less sedentary can protect women against heart disease.

Bone health and preventing fractures have also been a major focus of the Women’s Health Initiative, with research helping to establish guidelines for osteoporosis screening and investigating the link between dietary protein intake and bone health.

One of the Women’s Health Initiative’s biggest yields is its vast repository of health data collected annually from tens of thousands of women over more than 30 years. The data consists of survey responses on topics such as diet, physical activity and family history; information on major health outcomes such as heart disease, diabetes, cancer and cause of death, verified using medical records; and a trove of biological samples, including 5 million blood vials and genetic information from 50,000 participants.

YouTube video
The Women’s Health Initiative set out to prevent heart disease, cancer and osteoporosis in menopausal women.

Any researcher can access this repository to explore associations between blood biomarkers, disease outcomes, genes, lifestyle factors and other health features. More than 300 such studies are investigating health outcomes related to stroke, cancer, diabetes, eye diseases, mental health, physical frailty and more. Thirty are currently running.

What does the future hold?

In addition to data amassed by the Women’s Health Initiative until now, about 42,000 participants from all 50 states, now ages 78 to 108, are still actively contributing to the study. This cohort is a rare treasure: Very few studies have collected such detailed, long-term information on a broad group of women of this age. Meanwhile, the demographic of older women is growing quickly.

Continuing to shed light on aging, disease risk and prevention in this population is vital. The questions guiding the project’s ongoing and planned research directly address the chronic diseases that Health Secretary Robert F. Kennedy Jr. has announced as national priorities.

So I hope that the Women’s Health Initiative can continue to generate discoveries that support women’s health well into the future.The Conversation

Jean Wactawski-Wende, Professor of Public Health and Health Professions, University at Buffalo

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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The post The Women’s Health Initiative has shaped women’s health for over 30 years, but its future is uncertain appeared first on theconversation.com



Note: The following A.I. based commentary is not part of the original article, reproduced above, but is offered in the hopes that it will promote greater media literacy and critical thinking, by making any potential bias more visible to the reader –Staff Editor.

Political Bias Rating: Centrist

The article provides an overview of the Women’s Health Initiative, highlighting its impact on women’s health research and its potential future challenges due to funding cuts. The tone of the piece is factual and focused on the scientific and health-related aspects of the initiative, without promoting a particular political ideology. It mentions the Department of Health and Human Services’ decision to cut funding and subsequent reversal, but it does so in a neutral manner, detailing the concerns of those involved without attaching a political agenda. The article maintains an academic, objective perspective on a health policy issue, which does not lean toward any political bias.

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