Let’s start with some well-known facts about the Earth – it’s the fifth-largest planet in the solar system, 70 per cent of its surface is covered in water, and it’s the only planet known to have life on it.
One lesser-known fact is that a day on Earth isn’t exactly 24 hours long.
Sure, the Earth takes about 86,400 seconds – 1,440 minutes – on average, to make a full rotation around the sun. But there are a number of factors that affect the Earth’s rotation, causing it to speed up or slow down.
“We’re all used to the idea that Earth rotates every 24 hours, but of course, nothing’s ever really that simple,” Elaina Hyde, director of the Allan I. Carswell observatory and assistant professor at York University, told CTVNews.ca in a video call.
“We’re a rocky planet with a molten core, we have an atmosphere, we have oceans – all of these things can combine with different kinds of complex motions to create effects…like what we have been seeing.”
Hyde is referring to changes in the speed of the Earth’s rotation in recent years. In 2020, scientists say the Earth sped up so much that it broke a previous record for the shortest day on Earth 28 times. The shortest of these days was recorded on July 19, when Earth rotated around the sun 1.4602 milliseconds faster than the average time of 86,400 seconds.
WHAT CAUSES THE EARTH TO SPEED UP?
When it comes to explaining why these shifts happen, Hyde says there’s no single answer. She points to natural events such as earthquakes, as well as the movement of jet streams, and rising ocean levels as a result of climate change as just a few factors that come into play. Hyde also highlights the slowing down of major ocean currents, particularly in the northern Atlantic Ocean, as having an impact as well.
Each of these activities affects the Earth’s angular momentum, she explains, or the rate at which it rotates, taking into account its massive size.
“Saying that this was due to any one cause is not statistically significant,” Hyde said. “It is a combination of effects.”
While the Earth’s rotation has since slowed down, 2021 is still predicted to be the shortest year in a decade by milliseconds, says Hyde. This may create a need for a negative leap second.
Negative leap seconds, the opposite of regular leap seconds, involve subtracting time from the Earth’s timekeeping system so that it aligns with astronomical time, or the time it actually takes the Earth to complete a rotation around the sun.
Co-ordinated universal time, or UTC, is the time standard used to adjust clocks on Earth. It’s determined using an atomic clock. These clocks calculate time based on the movement of atoms. Placing an atom under specific frequencies of radiation will cause its electrons to move between different states of energy. The amount of cycles of radiation necessary for atoms to move between both energy states amounts to a second. Since 1967, one second has been defined as “9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.”
“This clock does not depend on any external force to give you that count of time, it’s a completely independent measurement,” said Hyde. “Atomic clocks are incredibly accurate at keeping time.”
Since many factors can affect the speed at which the Earth rotates, the time it takes to complete a rotation doesn’t always align with UTC on Earth. This creates the need for an adjustment. According to the National Institute of Standards and Technology (NIST), leap seconds are added, or subtracted, when there is a difference of 0.4 seconds or more between UTC and astronomical time.
“To keep our very precise atomic clocks lined up so that we can still keep using the months and the days and the years in the calendar system we have, we have to make adjustments,” explained Hyde. “[A leap second] is basically an artificial adjustment that we make in our calendar system to bring ourselves up to date.”
According to the NIST, leap seconds have been added once every 18 months or so since 1972, making them quite common. Negative leap seconds, on the other hand, have never been implemented.
THE POSSIBILITY OF A NEGATIVE LEAP SECOND
While the Earth’s spin has slowed down since last year, it’s still spinning slightly faster than average. Research shows the average length of a day in the first half of 2021 was 0.39 milliseconds less than it was the year before. From July to September though, days were actually 0.05 milliseconds longer than the 2020 average.
“It is more usual to have the leap second going in the direction of making the day longer because that is the overall pattern that we’re expecting,” said Hyde. “But like I said, all kinds of events can cause it to go the other way, it’s just not as common though.”
Looking at the speed at which the planet is rotating now, it’s possible a negative leap second may need to be implemented within the decade. The International Earth Rotation and Reference Systems Service is responsible for that decision. But when looking at the impact this change might have on day-to-day life, Hyde insists it isn’t something to worry about, unless stock market trading is involved.
“It’s not going to be a big effect for anyone,” she said. “But if you are interested in high-frequency trading or any kind of computational activities that take place multiple times a second, please make sure to keep up with these atomic clocks when they make the adjustment.”
This is as simple as going online and staying up to date with atomic clocks such as this one.
Still, there’s no guarantee that a negative leap second will need to be applied just yet. While it may be easy to plot out the Earth’s rotation over the long term, these kinds of measurements are tougher to predict in the short-term, says Hyde.
“It’s much more difficult because we don’t know exactly when earthquakes are going to appear all over Earth, we don’t know exactly how much water is going into the oceans due to climate change there’s a lot of unknowns,” she said. “Earth is an unpredictable system by nature. So making very, very precise predictions…is hard.”
The drifting giant A68 iceberg released billions of tons of fresh water in South Georgia ecosystem – MercoPress
Scientists monitoring the giant A68a iceberg from space reveal that a huge amount of freshwater was released as it melted around the sub-Antarctic island of South Georgia. An estimated 152 billion tons of freshwater – equivalent to 20 x Loch Ness or 61 million Olympic sized swimming pools, entered the seas around the sub-Antarctic island of South Georgia when A68a melted over three months in 2020/2021, according to a new study published this month by the British Antarctic Survey.
In July 2017, A68a calved off the Larsen-C Ice Shelf on the Antarctic Peninsula and began its epic three-and-a-half year, 4.000 km journey across the Southern Ocean. At 5719 square kilometers – about a quarter the size of Wales – it was the biggest iceberg on Earth when it formed and the sixth largest on record. Around Christmas 2020, the berg received widespread attention as it drifted worryingly close to South Georgia, raising concerns it could harm the island’s fragile ecosystem.
A team from Center for Polar Observation and Modeling and BAS used satellite measurements to chart the iceberg’s area and thickness change throughout its life cycle. The authors show that the iceberg had melted enough as it drifted to avoid damaging the sea floor around South Georgia by running aground. However, a side effect of the melting was the release of a colossal 152 billion tons of fresh water in close proximity to the island – a disturbance that could have a profound impact on the island’s marine habitat.
For the first two years of its life, A68a stayed close to Antarctica in the cold waters of the Weddell Sea and experienced little in the way of melting. However, once it began its northwards journey across the Drake Passage it traveled through increasingly warm waters and began to melt. Altogether, the iceberg thinned by 67 meters from its initial 235 m thickness, with the rate of melting rising sharply as the berg drifted around South Georgia.
Laura Gerrish, GIS and mapping specialist at BAS and co-author of the study said, “A68 was an absolutely fascinating iceberg to track all the way from its creation to its end. Frequent measurements allowed us to follow every move and break-up of the berg as it moved slowly northwards through an area called ‘iceberg alley’, a route in the ocean which icebergs often follow, and into the Scotia Sea where it then gained speed and approached the island of South Georgia very closely.”
If an iceberg’s keel is too deep it can become grounded on the sea floor. This can be disruptive in several different ways; the scour marks can destroy fauna, and the berg itself can block ocean currents and predator foraging routes. All of these potential outcomes were feared when A68a approached South Georgia. However, this new study reveals that it collided only briefly with the sea floor and broke apart shortly afterwards, making it less of a risk in terms of blockage. By the time it reached the shallow waters around South Georgia, the iceberg’s keel had reduced to 141 meters below the ocean surface, shallow enough to avoid the seabed which is around 150 meters deep.
Nevertheless, the ecosystem and wildlife around South Georgia will certainly have felt the impact of the colossal iceberg’s visit. When icebergs detach from ice shelves, they drift with the ocean currents and wind while releasing cold fresh melt-water and nutrients as they melt. This process influences the local ocean circulation and fosters biological production around the iceberg. At its peak, the iceberg was melting at a rate of 7 meters per month, and in total it released a staggering 152 billion tons of fresh water and nutrients.
“This is a huge amount of melt water, and the next thing we want to learn is whether it had a positive or negative impact on the ecosystem around South Georgia. Because A68a took a common route across the Drake Passage, we hope to learn more about icebergs taking a similar trajectory, and how they influence the polar oceans,” said Anne Braakmann-Folgmann, a researcher at CPOM and PhD candidate at the University of Leeds’ School of Earth and Environment, and lead author of the study.
The journey of A68a has been charted using observations from five different satellites. The iceberg’s area change was recorded using a combination of Sentinel-1, Sentinel-3, and MODIS imagery. Meanwhile, the iceberg’s thickness change was measured using CryoSat-2 and ICESat-2 altimetry. By combining these measurements, the iceberg’s area, thickness, and volume change were determined.
Tommaso Parrinello, CryoSat Mission Manager at the European Space Agency pointed out that “Our ability to study every move of the iceberg in such detail is thanks to advances in satellite techniques and the use of a variety of measurements. Imaging satellites record the location and shape of the iceberg and data from altimetry missions add a third dimension as they measure the height of surfaces underneath the satellites and can therefore observe how an iceberg melts.”
Observing the Disintegration of the A68A Iceberg from Space is published in the journal Remote Sensing of Environment at https://doi.org/10.1016/j.rse.2021.112855.
Are the northern lights caused by 'particles from the Sun'? Not exactly – Phys.org
What a spectacle a big aurora is, its shimmering curtains and colorful rays of light illuminating a dark sky. Many people refer to aurora as the northern lights (the aurora borealis), but there are southern lights too (the aurora australis). Either way, if you’re lucky enough to catch a glimpse of this phenomenon, it’s something you won’t soon forget.
The aurora is often explained simply as “particles from the Sun” hitting our atmosphere. But that’s not technically accurate except in a few limited cases. So what does happen to create this natural marvel?
We see the aurora when energetic charged particles—electrons and sometimes ions—collide with atoms in the upper atmosphere. While the aurora often follows explosive events on the Sun, it’s not quite true to say these energetic particles that cause the aurora come from the Sun.
Earth’s magnetism, the force that directs the compass needle, dominates the motions of electrically charged particles in space around Earth. The magnetic field near the surface of Earth is normally steady, but its strength and direction fluctuate when there are displays of the aurora. These fluctuations are caused by what’s called a magnetic substorm—a rapid disturbance in the magnetic field in near-Earth space.
To understand what happens to trigger a substorm, we first need to learn about plasma. Plasma is a gas in which a significant number of the atoms have been broken into ions and electrons. The gas of the uppermost regions of Earth’s atmosphere is in the plasma state, as is the gas that makes up the Sun and other stars. A gas of plasma flows away continuously from the Sun: this is called the solar wind.
Plasma behaves differently from those gases we meet in everyday life. Wave a magnet around in your kitchen and nothing much happens. The air of the kitchen consists overwhelmingly of electrically neutral atoms, so it’s quite undisturbed by the moving magnet. In a plasma, however, with its electrically charged particles, things are different. So if your house was filled with plasma, waving a magnet around would make the air move.
When solar wind plasma arrives at the earth it interacts with the planet’s magnetic field (as illustrated below—the magnetic field is represented by the lines that look a bit like a spider). Most of the time, plasma travels easily along the lines of the magnetic field, but not across them. This means that solar wind arriving at Earth is diverted around the planet and kept away from the Earth’s atmosphere. In turn, the solar wind drags the field lines out into the elongated form seen on the night side, called the magnetotail.
Sometimes moving plasma brings magnetic fields from different regions together, causing a local breakdown in the pattern of magnetic field lines. This phenomenon, called magnetic reconnection, heralds a new magnetic configuration, and, importantly, unleashes a huge amount of energy.
These events happen fairly often in the Sun’s outer atmosphere, causing an explosive energy release and pushing clouds of magnetized gas, called coronal mass ejections, away from the Sun (as seen in the image above).
If a coronal mass ejection arrives at Earth it can in turn trigger reconnection in the magnetotail, releasing energy that drives electrical currents in near-Earth space: the substorm. Strong electric fields that develop in this process accelerate electrons to high energies. Some of these electrons may have come from the solar wind, allowed into near-Earth space by reconnection, but their acceleration in the substorm is essential to their role in the aurora.
These particles are then funneled by the magnetic field towards the atmosphere high above the polar regions. There they collide with the oxygen and nitrogen atoms, exciting them to glow as the aurora.
Now you know exactly what causes the northern lights, how do you optimize your chances of seeing it? Seek out dark skies far from cities and towns. The further north you can go the better but you don’t need to be in the Arctic Circle. We see them from time to time in Scotland, and they’ve even been spotted in the north of England—although they’re still better seen at higher latitudes.
Websites such as AuroraWatch UK can tell you when it’s worth heading outside. And remember that while events on the Sun can give us a few days warning, these are indicative, not foolproof. Perhaps part of the magic lies in the fact that you need a little bit of luck to see the aurora in all its glory.
Are the northern lights caused by ‘particles from the Sun’? Not exactly (2022, January 21)
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Hubble telescope spots a black hole fostering baby stars in a dwarf galaxy – Space.com
Black holes can not only rip stars apart, but they can also trigger star formation, as scientists have now seen in a nearby dwarf galaxy.
At the centers of most, if not all, large galaxies are supermassive black holes with masses that are millions to billions of times that of Earth’s sun. For instance, at the heart of our Milky Way galaxy lies Sagittarius A*, which is about 4.5 million solar masses in size.
Astronomers have previously seen giant black holes shred apart stars. However, researchers have also detected supermassive black holes generating powerful outflows that can feed the dense clouds from which stars are born.
Black hole-driven star formation was previously seen in large galaxies, but the evidence for such activity in dwarf galaxies was scarce. Dwarf galaxies are roughly analogous to what newborn galaxies may have looked like soon after the dawn of the universe, so investigating how supermassive black holes in dwarf galaxies can spark the birth of stars may in turn offer “a glimpse of how young galaxies in the early universe formed a portion of their stars,” study lead author Zachary Schutte, an astrophysicist at Montana State University in Bozeman, told Space.com.
In a new study, the scientists investigated the dwarf galaxy Henize 2-10, located about 34 million light-years from Earth in the southern constellation Pyxis. Recent estimates suggest the dwarf galaxy has a mass about 10 billion times that of the sun. (In contrast, the Milky Way has a mass of about 1.5 trillion solar masses.)
A decade ago, study senior author Amy Reines at Montana State University discovered radio and X-ray emissions from Henize 2-10 that suggested the dwarf galaxy’s core hosted a black hole about 3 million solar masses in size. However, other astronomers suggested this radiation may instead have come from the remnant of a star explosion known as a supernova.
In the new study, the researchers focused on a tendril of gas from the heart of Henize 2-10 about 490 light-years long, in which electrically charged ionized gas is flowing as fast as 1.1 million mph (1.8 million kph). This outflow was connected like an umbilical cord to a bright stellar nursery about 230 light-years from Henize 2-10’s core.
This outflow slammed into the dense gas of the stellar nursery like a garden hose spewing onto a pile of dirt, leading water to spread outward. The researchers found newborn star clusters about 4 million years old and upwards of 100,000 times the mass of the sun dotted the path of the outflow’s spread, Schutte said.
With the help of high-resolution images from the Hubble Space Telescope, the scientists detected a corkscrew-like pattern in the speed of the gas in the outflow. Their computer models suggested this was likely due to the precessing, or wobbling, of a black hole. Since a supernova remnant would not cause such a pattern, this suggests that Henize 2-10’s core does indeed host a black hole.
“Before our work, supermassive black hole-enhanced star formation had only been seen in much larger galaxies,” Schutte said.
In the future, the researchers would like to investigate more dwarf galaxies with similar black hole-triggered star formation. However, this is difficult for many reasons — “systems like Henize 2-10 are not common; obtaining high quality observations is difficult; and so on,” Schutte said. However, when the James Webb Space Telescope hopefully comes online in the near future, “we will have new tools to search for these systems,” he noted.
Schutte and Reines detailed their findings in the Jan. 19 issue of the journal Nature.
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