Our planet’s north magnetic pole is on a journey across the top of the world. But it’s slowing down. Over the past five years, it’s put on the brakes – its position has changed much more slowly than over the previous couple of decades.
Earth’s magnetic field acts like a giant bar magnet, with north and south poles. The poles aren’t tied to the geographic poles – they wander.
The north magnetic pole was discovered in 1831. At the time, it was centered over northwestern Canada. It moved farther south, then made a big turn, toward Siberia. In all, it’s moved almost 700 miles since it was discovered.
For a couple of decades, it was moving at more than 30 miles per year. More recently, though, it’s slowed to about 22 miles a year – the biggest slowdown ever recorded. Scientists are trying to understand why.
The magnetic field is generated by motions of molten rock in Earth’s outer core. Those motions produce electric currents, which create the magnetic field. So the changing position and rate of motion are telling us something about what’s going on deep inside our planet.
The change in the magnetic pole has important practical implications as well as scientific ones. GPS, aircraft, the military, and others use magnetic north for navigation. So maps of Earth’s magnetic field are updated every few years to show the change in the pole’s location – keeping everyone headed in the right direction.
Script by Damond Benningfield
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2:14
Moon in Balance
The full Moon achieves a sort of celestial balance tonight. It’s passing across Libra, the balance scales – a symbol of justice. But the proper names of the constellation’s brightest stars have nothing to do with balance, justice, or anything similar. Instead, the names mean “the claws” – of nearby Scorpius, the scorpion.
Originally, the stars did belong to Scorpius. But thousands of years ago, they were severed from the scorpion and placed in a new constellation.
As night falls, one of the claws stands to the upper left of the Moon. Called Zubenelgenubi, it represents the southern claw. It’s the second-brightest star of Libra, and it’s about 75 light-years away.
Like many of the stars in the night sky, Zubenelgenubi is deceiving. To the eye alone, it looks like a single point of light. Scan it with binoculars, though, and you’ll see two stars. They appear to be moving through space together, so they might be orbiting each other. But they’re so far apart that it takes the light from each star a month to reach the other one. At that separation, they might not be held together by gravity – their close appearance might be just a coincidence.
Each of the two stars is actually a binary in its own right. In both cases, the stars are so close together that even giant telescopes can’t see them as individual stars. But we see the “fingerprints” of two stars in the light from each half of the southern claw.
Script by Damond Benningfield
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2:14
NSF at 75
As World War II wound to an end, President Franklin Roosevelt asked his top scientific advisor a question: How could the type of research that helped win the war be applied to peacetime? The advisor suggested a new agency to support basic research at colleges and universities. It took a few years to work out the details. But 75 years ago today, President Harry Truman signed the law establishing that agency: the National Science Foundation.
Over the decades, its mission has expanded into many fields, from chemistry and physics to computers and materials science.
The list also includes astronomy. NSF established the first national observatories in 1956 – optical telescopes in Arizona, and radio telescopes in West Virginia. Today, NSF-supported facilities span the globe. They include observatories that no one was even dreaming of when the agency started. They hunt for the ghostly particles known as neutrinos, and listen for gravitational waves from merging black holes and neutron stars.
NSF also is a partner in the Vera Rubin Observatory, which is scheduled to take its first peek at the universe this summer. Its giant telescope will scan a wide slice of the sky every night. It will discover exploding stars, asteroids, and other objects. It will map the Milky Way Galaxy. And it’ll provide new information about dark energy and dark matter – basic research that will teach us much more about the universe.
Script by Damond Benningfield
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2:14
Cecilia Payne
The star Spica, which is quite close to the Moon tonight, is quite different from the Sun. It consists of two stars, not one. Both stars are many times bigger and heavier than the Sun. And their surfaces are tens of thousands of degrees hotter, so the stars shine blue-white.
On the other hand, the Sun and Spica are made of almost exactly the same ingredients: mainly hydrogen and helium, with only a smattering of heavier elements. That composition was figured out by an astronomer who was born 125 years ago tomorrow, in England.
Cecilia Payne caught the astronomy bug when she saw a lecture by Arthur Eddington, one of the world’s leading astronomers. She started her education in England, then finished in the United States. She earned a Ph.D. in 1925. And her doctoral thesis shook up the field. Decades later, in fact, Otto Struve, the first director of McDonald Observatory, called it the most brilliant thesis ever written in the field.
Astronomers already had the techniques for measuring what stars are made of. Their work led them to believe that stars contain the same mixture of elements as Earth. But Payne used a new way to analyze the readings, taking into account the charge of atoms. She concluded that stars were made mainly of hydrogen and helium – elements formed in the Big Bang.
By a few years later, just about everyone accepted her analysis – completely changing our concept of the stars.
Script by Damond Benningfield
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2:14
Granulation
The surface of the Sun is like a pot of boiling water. Millions of bubbles of hot gas churn across it, constantly rising and falling. But the bubbles are a little bigger than those on your stovetop.
The bubbles are known as granules. They form as energy from deep inside the Sun works its way to the surface. That heats the gas in the Sun’s top layer, forming bubbles. As they reach the surface, their gas cools and drops back into the Sun. This non-stop activity creates an easy-to-see pattern of bright blobs – the hot gas – with dark lanes between them – the cooler gas.
The size of the granules varies from about a hundred miles to more than a thousand – big enough to swallow Texas. And each granule lasts for no more than about 20 minutes.
A recent study said the granulation changes a bit during the Sun’s 11-year cycle of magnetic activity. Just after the peak of the cycle, there are slightly more granules than average, but they’re a little smaller than average.
Other stars are so far away that we can’t see the granulation on most of them. But several types of observations confirm that they, too, are boiling away. Astronomers have seen granulation on a few stars. The stars are much bigger than the Sun. And they’re late in life, so they’re undergoing big changes. The granules on those stars are tens of millions of miles across – dozens of times the diameter of the Sun – giant bubbles of hot gas on giant stars.
Script by Damond Benningfield
New Zealand