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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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Earth’s Spin to Speed Up Briefly, Causing Shorter Days This Summer

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Earth’s Spin to Speed Up Briefly, Causing Shorter Days This Summer

Reports indicate that for three days this summer – July 9, July 22 and August 5 – Earth’s rotation will speed up slightly, trimming 1.3 to 1.5 milliseconds off each day. Imperceptible in everyday life, this shift underscores how the Moon’s position influences our planet’s spin. For reference, the shortest day on record was July 5, 2024, lasting 1.66 milliseconds less than 24 hours. Over billions of years Earth’s rotation has slowly lengthened, but recent data show speedups. Scientists say monitoring these tiny changes is important for understanding Earth’s dynamics and timekeeping.

Causes of Faster Spin

According to timeanddate.com, the shortest-ever recorded day was on July 5, 2024, which was 1.66 milliseconds shy of 24 hours. The acceleration is largely driven by the Moon’s gravity. On those dates (July 9, July 22 and August 5), the Moon will lie far north or south of Earth’s equator, weakening its tidal braking on our planet’s spin. As a result, Earth rotates a bit faster – like spinning a top held at its ends. Seasonal shifts in mass distribution also affect rotation. Richard Holme of the University of Liverpool notes that summer growth and melting snow in the Northern Hemisphere move mass outward from Earth’s axis, slowing the spin in the same way an ice skater slows by extending her arms.

Timekeeping and Technology

Shifts in day length are handled by precise timekeeping. The International Earth Rotation and Reference Systems Service (IERS) monitors Earth’s spin and adds leap seconds to keep Coordinated Universal Time (UTC) in sync with solar time. Normally a second is added when Earth’s rotation slows, but if the spin-up trend continues, scientists have floated a “negative leap second” – removing a second – to realign clocks.

Dr. Michael Wouters of Australia’s National Measurement Institute says this fix would be unprecedented, and notes that even if a few seconds accumulated over decades, it would likely go unnoticed. Dr. David Gozzard of the University of Western Australia points out that GPS satellites, communications networks and power grids rely on atomic clocks synced to nanoseconds, and that millisecond-scale changes in Earth’s rotation are easily absorbed by these systems.

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James Webb Telescope Spots Rare ‘Cosmic Owl’ Formed by Colliding Galaxies

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James Webb Telescope Spots Rare ‘Cosmic Owl’ Formed by Colliding Galaxies

NASA’s James Webb Space Telescope has captured the “Cosmic Owl,” a startling owl-faced pair of colliding ring galaxies. This double-ring structure is exceptionally rare: ring galaxies account for just 0.01% of known galaxies, and two colliding rings is almost unheard of. The JWST image provides an exceptional natural laboratory for studying galaxy evolution. Models suggest the galactic clash began roughly 38 million years ago, meaning the owl-like shape could persist for a long time. A team led by Ph.D. student Mingyu Li of Tsinghua University in China announced the finding.

Spotting the ‘Cosmic Owl’

According to Mingyu Li, the first author of the new study , he and his team found the Owl by combing through public JWST data from the COSMOS field. The twin ring galaxies jumped out thanks to JWST’s infrared imaging. Each ring is about 26,000 light-years across (a quarter of the Milky Way), and each harbors a supermassive black hole at its core – one of the Owl’s eyes.

JWST images show the collision interface – the Owl’s beak – ablaze with activity. ALMA observations find a huge clump of molecular gas there – the raw fuel for new stars – being squeezed by the impact. Radio observations show a jet from one galaxy’s black hole slamming into the gas. Li notes the shockwave-plus-jet have ignited an intense starburst, turning the beak into a stellar nursery.

Rarity and Significance

Ring galaxies are extremely rare (≈0.01% of all galaxies), so finding two in collision is unheard of. Another team independently identified the same system and called it the “Infinity Galaxy”. Li says this event is an exceptional natural laboratory for studying galaxy evolution. In one view, researchers can see black holes feeding, gas compressing and starbursts happening together.

Li points out the collision’s shockwave and jet have triggered an intense starburst in the beak. He says this may be a crucial way to turn gas into stars rapidly, which could help explain how young galaxies built up their mass so quickly. Simulations will clarify the precise collision conditions needed to produce such a rare twin-ring “owl” shape.

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MIT Develops Low-Resource AI System to Control Soft Robots with Just One Image

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MIT Develops Low-Resource AI System to Control Soft Robots with Just One Image

The use of conventional robots for industry and hazardous environments is easy for the purpose of control and modelling. However, these are too rigid to operate in confined places and uneven terrain. The soft bio-related roots are better adapted to the environment and manoeuvring in inaccessible places. Such flexible capabilities would need an array of on-board sensors and spacious models which are tailored to each robot design. Having a new and less resource-demanding approach, the researchers at MIT have developed a far less complex, deep learning control system that teaches the soft, bio-inspired robots to follow the command from a single image only.

Soft Robots Learn from a Single Image

As per Phys.org, this research has been published in the journal Nature, by training a deep neural network on two to three hours of multi-view images of various robots executing random commands, the scientists trained the network to reconstruct the range and shape of mobility from only one image. The previous machine learning control designs need customised and costly motion systems. Lack of a general-purpose control system limited the applications and made prototyping less practical.

The methods unshackle the robotics hardware design from the ability to model it manually. This has dictated precision manufacturing, extensive sensing capabilities, costly materials and reliance on conventional and rigid building blocks.

AI Cuts Costly Sensors and Complex Models

The single camera machine learning approach allows the high-precision control in tests on a variety of robotic systems, adding the 3D-printed pneumatic hand, 16-DOF Allegro hand, a soft auxetic wrist and a low-cost Poppy robot arm.

As this system depends on the vision alone, it might not be suitable for more nimble tasks which need contact sensing and tactile dynamics. The performance may also degrade in cases where visual cues are not enough.

Researchers suggest the addition of sensors and tactile materials that can enable the robots to perform different and complex tasks. There is also potential to automate the control of a wider range of robots, together with minimal or no embedded sensors.

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