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Since time immemorial, humans around the world have gazed up in wonder at the night sky. The starry night sky has not only inspired countless works of music, art, and poetry but has also played an important role in timekeeping, navigation and agricultural practices in many traditions.

For many cultures, the night sky, with its stars, planets and the Milky Way, is considered just as important a part of the natural environment as the forests, lakes and mountains below. Countless people around the world gaze at the night sky: not only amateur and professional astronomers, but also casual observers who enjoy looking up at the stars to contemplate our place in the cosmos.

However, the night sky is changing. Not only is ground-based light pollution increasing rapidly, but growing numbers of satellites and space debris in orbit around Earth are also impacting the night sky.

Earlier research showed that satellites and space debris may increase the overall brightness of the night sky. In a new paper in Nature Astronomy, my colleagues and I applied this knowledge to predicting the performance of a major astronomical sky survey. We found this phenomenon may make the survey 7.5 percent less efficient and US$21.8 million (roughly Rs. 180 crore) more expensive.

A brighter sky

As a cultural astronomer, I am interested in the role of the night sky in cultural traditions around the world. In particular, I am interested in how light pollution and increasing satellite numbers affect different communities.

The number of satellites in orbit is growing rapidly. Since 2019, the number of functional satellites in orbit has more than doubled to around 7,600. The increase is mostly due to SpaceX and other companies launching large groups of satellites to provide high-speed internet communications around the world.

By the end of this decade, we estimate, there may be 100,000 satellites in orbit around the Earth. Collisions that generate space debris are more likely as space fills with new satellites. Other sources of debris include the intentional destruction of satellites in space warfare tests.

Increasing numbers of satellites and space debris reflect ever more sunlight towards the night side of Earth. This will almost certainly change the appearance of the night sky and make it harder for astronomers to do research.

One way satellites impact astronomy is by appearing as moving points of light, which show up as streaks across astronomers’ images. Another is by increasing diffuse night sky brightness. This means all the satellites that are too dim or small to be seen individually, as well as all the small bits of space debris, still reflect sunlight, and their collective effect is to make the night sky appear less dark.

Hard times for astronomers

In our research, we present the first published calculations of the aggregate effects of satellites and space debris in low-Earth orbit on major ground-based astronomy research facilities.

We looked at the effect on the planned large-scale survey of the night sky to be carried out at the Vera Rubin Observatory starting in 2024. We found that, by 2030, reflected light from objects in low-Earth orbit will likely increase the diffuse background brightness for this survey by at least 7.5 percent compared to an unpolluted sky.

This would diminish the efficiency of this survey by 7.5 percent as well. Over the ten-year lifetime of the survey, we estimate this would add some $21.8 million (roughly Rs. 180 crore) to the total project cost.

Brighter night skies mean longer exposures through telescopes are needed to see distant objects in the cosmos. This will mean that for projects with a fixed amount of observing time, less science will be accomplished, and there will be increased competition for telescope access.

In addition, brighter night skies will also reduce the detection limits of sky surveys, and dimmer objects may not be detected, resulting in missed research opportunities.

Some astrophysical events are rare and if researchers are unable to view them when they occur, there might not be an opportunity to easily see a given event again during a survey’s operational period. One example of faint objects is near-Earth objects – comets and asteroids in orbits close to Earth. Brighter night skies make it more likely such potentially hazardous objects may remain undetected.

A dramatic and unprecedented transformation

Increases in diffuse night sky brightness will also change how we see the night sky with the unaided eye. As the human eye cannot resolve individual small objects as well as a telescope can, an increase in satellites and space debris will create an even greater increase in the apparent brightness of the night sky. (When using a telescope or binoculars, one would be able to make out more of the dimmer satellites individually.) The projected increase in night sky brightness will make it increasingly difficult to see fainter stars and the Milky Way, both of which are important in various cultural traditions. Unlike “ground-based” light pollution (which tends to be the worst near large cities and heavily populated areas), the changes to the sky will be visible from essentially everywhere on Earth’s surface.

Our models give us a conservative lower limit for a likely increase in night sky brightness. If numbers of satellites and space debris continue to grow at the expected rate, the impacts will be even more pronounced.

As we note in our paper, “we are witnessing a dramatic, fundamental, and perhaps semi-permanent transformation of the night sky without historical precedent and with limited oversight”. Such a transformation will have profound consequences for professional astronomy as well as for anyone who wishes to view an unpolluted night sky.


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SpaceX Aims to Break Launch Record With 170 Orbital Liftoffs Planned for 2025

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SpaceX Aims to Break Launch Record With 170 Orbital Liftoffs Planned for 2025

By 2025, SpaceX is aiming to launch at a record pace: 170 orbital missions, nearly one every other day. Should we hit our goal, it would best the company’s annual record of 134 launches set in 2023. Anne Mason, SpaceX’s director of national security space launch, announced the ambitious goal during a media call on May 28. Mason emphasised the growing normalcy of this rapid cadence while previewing the upcoming GPS III SV08 satellite mission for the U.S. Space Force, currently slated for liftoff on Friday, May 30.

As per a Space.com report, Mason noted that in 2020, SpaceX had launched just 25 times — a monthly average of two. The step to a flying cadence on at least a virtually daily basis emphasises the impact of operational efficiency and reusability of Falcon rockets. With the bigger and more powerful Falcon Heavy making the other two launches, the Falcon 9 executed 132 of 134 launches in 2023. Both rely on reusable first stages that have become central to SpaceX’s high-volume, low-cost access to orbit.

Mason pointed out that SpaceX currently produces an expendable Falcon upper stage every two and a half days, a crucial factor in sustaining high output. Roughly two-thirds of the company’s orbital flights in 2024 supported Starlink, its low Earth orbit satellite internet constellation, which now includes over 7,500 active spacecraft. This year, 48 of the 64 launches already completed — all via Falcon 9 — were Starlink deployments.

SpaceX will have to increase its daily launch rate from 0.43 to about 0.47 if it is to meet the 170-launch target. The number does not include suborbital Starship test flights, which are not regarded as orbital missions. The company has flown three such Starship tests in 2025 so far, with four conducted last year. Starship remains under development for long-term Mars colonisation goals and future deep space missions.

The continued growth of SpaceX’s launch rate reflects the company’s dominance in commercial and government spaceflight. Mason credited the milestone not only to technological advances but also to the team’s consistent performance. “This cadence was unimaginable five years ago,” she mentioned, “and yet, here we are.”

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Scientists Capture Plasma Streams, Coronal Raindrops in Sharpest-Ever View of Sun’s Corona

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Scientists Capture Plasma Streams, Coronal Raindrops in Sharpest-Ever View of Sun’s Corona

In a landmark achievement for solar astronomy, scientists have unveiled the most detailed view ever of the sun’s corona — its superheated outer atmosphere — revealing bizarre, never-before-seen plasma features including delicate “raindrops” and a snaking, high-speed plasma stream. Captured using a cutting-edge adaptive optics system named Cona, installed at the Goode Solar Telescope (GST) in California, the new footage offers unmatched clarity of phenomena long obscured by Earth’s turbulent atmosphere. The images, coloured to represent hydrogen-alpha light, show cooler plasma tracing the sun’s magnetic fields in mesmerising loops and arcs.

Sharpest Solar Views Yet Reveal Coronal Rain, Racing Plasmoid, and Twisting Prominences

As per researchers at NJIT’s Centre for Solar-Terrestrial Research, the adaptive optics allow the 1.6-metre telescope to reach its theoretical resolution limit of 63 kilometres. Among the findings is the sharpest view yet of coronal rain — narrow filaments of plasma falling back to the solar surface along magnetic field lines, some just 20 kilometres wide. Unlike Earth’s rain, these plasma threads arc and loop in response to the sun’s magnetism. Another striking discovery is the observation of a fast-moving ‘plasmoid’ — a stream of plasma racing across the corona at nearly 100 kilometres per second.

The footage also captured a rapidly reconfiguring solar prominence—plasma loops anchored to the sun’s surface, twisting and dancing under magnetic tension. Scientists believe such observations could illuminate the mechanisms behind coronal mass ejections and solar flares, major drivers of space weather. Researchers note that the sun’s surface appears soft and “fluffy” due to short-lived plasma jets called spicules, whose origins remain mysterious.

The team’s findings were published Tuesday, May 27, in the journal Nature.

Study co-author Philip Goode mentioned that “This marks the beginning of a new era in solar astronomy.” Researchers now hope to implement similar technology in larger instruments such as the Daniel K. Inouye Solar Telescope in Hawaiʻi. 

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MIT Study Reveals Why Roman Concrete Lasts Thousands of Years

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MIT Study Reveals Why Roman Concrete Lasts Thousands of Years

Ancient Roman structures have always been a major attraction for both common people and researchers. The durability of those magnificent architectural feats like the Pantheon of Rome has made researchers curious about how they are standing tall nearly after two thousand years of the height of the Roman empire. While The longevity of these structures can be attributed largely to Roman concrete, question still prevails about the speciality and the materials used in the concrete itself. 

Ingredients of Roman concrete

According to the study published in the journal Science Advances, an international team of researchers led by the Massachusetts Institute of Technology (MIT) found that not only are the materials slightly different from what we may have thought, but the techniques used to mix them were also different.

One key ingrediant was pozzolan, or ash. The Romans used ash from the volcanic beds of the Italian city Pozzuoli and shipped it all over the empire. The silica and alumina in the ash react with lime and water in a pozzolanic reaction at ambient temperatures, resulting in a stronger, longer lasting concrete.
Another key ingredient is lime clasts, or small chunks of quicklime.

These clasts give Roman concrete its self-healing capability. Concrete weathers and weakens over time, but water can infiltrate its cracks and reach the clasts. When they react with the water, the clasts create crystals called calcites that fill in the cracks.

Difference with modern day cement

The high-temperature kiln process used today to make modern day Portland cement, grinds all materials into fine powder. It eliminates the lime clasts which results into the lack of the self-healing properties of Roman cement.

The Romans utilized a method known as hot mixing, which involves combining quicklime with pozzolan, water and other ingredients and then heating them up. The MIT team found that this method helps unlock the lime clasts’ self-healing abilities, and can result in faster setting than cement made with a quicklime-water solution called slaked lime.

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