StarDate

The Sun isn’t quite steady. It goes through an 11-year cycle of magnetic activity. When the cycle is at its peak, there are lots of sunspots and other powerful events. But no two cycles are alike. The most recent cycle, for example, was weak. And over the centuries, both weak and strong cycles tend to come in clumps.

One of the weakest “clumps” of the last millennium was the Spoerer Minimum. It may have lasted more than a century, and been the “quietest” of all the Sun’s known quiet periods.

It’s named for German astronomer Gustav Spoerer, who discovered it. It could have started as early as 1415, and lasted until about 1540, although the exact dates are uncertain.

In part, that’s because no one was counting sunspots at the time. Instead, scientists deduce what was happening on the Sun by looking at tree rings and ice cores. When the Sun is quiet, it allows more cosmic rays to enter the solar system. They interact with Earth’s atmosphere to make radioactive forms of carbon and other elements. Trees take up some of the carbon, and some of the other elements are trapped in the ice. So measuring those elements reveals how active the Sun has been over the ages.

The intensity of the solar cycle appears to have a small effect on Earth’s climate. During the Spoerer Minimum, there’s evidence that the planet was cooler than average. So studying the solar cycle can help us understand more about conditions right here on Earth.

Script by Damond Benningfield

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The next sunspot cycle will be especially quiet. Unless it’s one of the busiest on record. Two groups have come up with different predictions. It’s as though one has forecast a warm, calm spring afternoon, while the other has predicted a blizzard.

The Sun goes through an 11-year cycle of magnetic activity. At the cycle’s peak, the Sun is covered with more sunspots. These giant storms are cooler than the surrounding gas, so they look dark by comparison. At the end of each cycle, the Sun’s magnetic field flips over, starting the new cycle.

The number of sunspots varies from cycle to cycle. The most recent one, which ended last year, was unusually quiet. That’s good news for Earth’s technology. Solar storms can disrupt satellites, knock out power grids, and cause other problems.

NASA and NOAA have predicted that the new cycle will be just as tranquil as the last. But a team of American and British researchers disagrees. It predicts twice as many sunspots at the cycle’s peak. That would make it one of the strongest cycles ever seen.

The team used a method of measuring the length of a sunspot cycle that’s different from the one that’s most commonly used. According to that method, the last cycle was shorter than average — just shy of 10 years. The team’s models say that short, quiet cycles usually are followed by busy cycles. So it predicts peak rates of more than 200 sunspots at a time — a busy season for the Sun.

Script by Damond Benningfield

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A cosmic “stingray” is fading away before our eyes. A recent study found that it grew much fainter and cooler in just a couple of decades — and even lost its shape.

The Stingray Nebula is about 18,000 light-years away. It’s in the constellation Ara, which is too far south to see from most of the U.S.

The nebula is the final gasp of a dying star. The star expelled its outer layers into space, forming a rapidly expanding “bubble” of gas and dust.

The Stingray is the youngest such nebula yet seen. It began forming just a few decades ago. And in 1996, an image from Hubble Space Telescope showed a bright and colorful bubble whose outline resembled that of a stingray.

But a recent study compared that picture to one taken 20 years later. And in the more recent observation, the Stingray was only a fraction as bright. It didn’t look nearly as big, and a blue-green glow at its center had vanished.

The change probably was caused by the star’s dying core. A few decades ago, a shell of helium around the core probably ignited, causing the core to flare up. The extra energy shined on the surrounding gas and dust, causing it to glow like a neon bulb.

In the more recent image, though, the flare-up had ended, and the core had grown cooler and fainter. So there wasn’t enough energy to light up the entire nebula. The nebula is still there, expanding rapidly into space. But we just can’t see the full outline of the Stingray.

Script by Damond Benningfield

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Today is the vernal equinox — the beginning of spring in the northern hemisphere. It comes with a persistent myth: that you can balance an egg on its end on the equinoxes — and only on the equinoxes.

Like most pseudoscience, the myth invokes a few scientific terms to make it sound reasonable. Unfortunately, though, throwing in words like “equinox” and “gravity” doesn’t cleanse the smell of rotten eggs.

Here’s the basic outline of the tale: At the equinox, the Sun stands directly above the equator at noon. That part is true. So there’s a special gravitational “balance” that doesn’t exist at other times of the year. That part isn’t true. This balance allows you to stand a raw egg on its end, which can’t be done on any other date. And that part is absolutely rotten.

It may well be true that more eggs are balanced on end on the March equinox than at any other time of year. If so, it’s only because more people give it a try then.

It’s easy to disprove this tale by trying to stand an egg on end on different days of the year. It’s not easy at any time; the egg’s interior is a thick liquid, so it doesn’t want to sit still. But with a little patience it can be done. It’s easier to accomplish if the egg has a rough shell and it’s sitting on a rough surface. But many people have done it with smooth eggs on glassy surfaces. Just keep trying, and eventually you’ll get the egg-xact formula — no matter what the date.

Script by Damond Benningfield

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Winter is about to meet its end. Spring arrives in the northern hemisphere in the wee hours of tomorrow morning.

That moment is known as the vernal equinox. And over the centuries, it’s played a central role in the development of the calendar.

In fact, people discovered the length of the year — and even the concept of the year — by following the rhythms of the seasons. Spring brought new life to the world after the dark winter, so it became the most important seasonal marker. Indeed, the period between vernal equinoxes defined the length of the year. This period is known as the tropical year, and it lasts 365 days, 5 hours, 48 minutes, and 45 seconds.

That extra dab of time beyond 365 days has given calendar makers fits. It’s forced them to add extra days, and even to revamp the entire calendar.

In ancient Rome, for example, the astronomer Sisogenes recommended adding an extra day every fourth year. Julius Caesar accepted the idea and instituted a new calendar in 46 B.C.

That worked for a while. But by the 16th century, the calendar had slipped out of sync with the equinox by about 11 days. That was a particular problem for Christians, who used the equinox to calculate the date of Easter. So Pope Gregory XIII made one more change: He dropped three leap years from every four centuries.

We still use the Gregorian calendar today — a calendar that’s calibrated by the vernal equinox.

Script by Damond Benningfield

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Gale Crater is dry, cold, and quiet. But the Martian feature hasn’t always been that way. More than three and a half billion years ago, for example, heavy rains produced massive flooding — perhaps leaving the crater warm and wet for centuries.

For the last eight years, the Curiosity rover has been crawling around the crater and on the flanks of the tall mountain at its center.

The rover has photographed rock formations in the crater. Some are mostly buried below the sand. They include giant “waves” — formations that are three stories tall and longer than a football field. They probably formed during heavy flooding.

Scientists who analyzed the rover’s findings outlined a possible scenario:

More than three and a half billion years ago, an asteroid slammed into Mars. It blasted frozen carbon dioxide and methane into the atmosphere. That warmed the entire planet. Clouds then dumped massive amounts of rain, which began filling Gale Crater and pouring down the sides of its mountain. That created torrents of water up to 75 feet deep, moving at more than 20 miles per hour.

The floods may have lasted just a few days. But the warm, wet conditions could have hung around for a lot longer — making Gale Crater one of the most interesting spots on Mars.

Look for Mars above the Moon this evening. It looks like an orange star. The true star Aldebaran — which is also orange — is about the same distance to the upper left of the Moon.

Script by Damond Benningfield

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Three spacecraft arrived at Mars last month. It took them almost seven months to get there. But there may be a faster way to reach Mars in the decades ahead — especially for missions that carry people: spaceships powered by nuclear engines.

NASA and other agencies studied nuclear engines for a couple of decades. They built test models, and were ready to build an engine to fly in space when the project shut down, in the 1970s. But there’s been renewed interest in recent years. In 2019, NASA received $125 million to study the technology again.

Nuclear thermal propulsion would use a small amount of uranium to heat the engine’s fuel — probably liquid hydrogen. The hydrogen would expand and shoot out into space through a rocket nozzle. Improvements since earlier testing could make it possible to use a less-enriched form of uranium, which would be safer and easier to handle.

Such an engine could be two or three times more efficient than a chemical engine, which powers today’s rockets. That could cut travel times to Mars and other planets. And it could provide other benefits as well, as promised in this NASA promotional film from the ’60s:

AUDIO: Lower overall weight. Larger payloads. Shorter travel time. These are the chief advantages of nuclear propulsion. The technology needed to build a nuclear rocket is well advanced. It will be available when this nation determines its next great objective in space.

Script by Damond Benningfield

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The rings around the planet Uranus are young. And like most youngsters, they’re pretty active.

Uranus is the third-largest planet in the solar system, and the seventh planet from the Sun. This evening, it appears close to the upper right of the Moon. Through binoculars, it looks like a small star with a hint of blue green.

The planet’s rings are so faint that they were discovered only about four decades ago. Most of them are made of small pebbles, although a few are made of dust. The rings probably are less than 600 million years old — about one-seventh the age of Uranus itself.

The brightest and densest ring is the Epsilon ring. Its orbit is a little off-center, so the width of the ring varies. The section that’s closest to Uranus is only about 20 miles wide. But as the particles in the ring move away from the planet, the ring spreads out to about 60 miles wide. It’s held in check by the gravity of two small moons — one on the inside edge of the ring, and the other on the outside.

The Delta ring looks wavy. That may indicate that it, too, is held in check by a tiny moon. The moon may create the waves as it moves past the ring particles.

Two outer rings were discovered in the early 2000s. One of them is fairly blue, suggesting it’s made mainly of ice. The ice particles may be chipped off the surface of a nearby moon when it’s hit by other space rocks — adding fresh ice to one of Uranus’s dynamic rings.

Script by Damond Benningfield

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Julius Caesar gave us the basic calendar we use today. It’s so good that it’s required only one revision in two millennia — a tweak to the number of leap years. Caesar also gave us perhaps the most famous date in the calendar: the Ides of March. In modern times, that date is known as March 15th.

The Ides of March was immortalized in William Shakespeare’s play “Julius Caesar.” In it, a soothsayer warns the Roman leader to “beware” the Ides. Caesar ignores the advice and visits the Senate — where he’s promptly assassinated. The play, of course, is based on fact. Caesar really was murdered in the Senate on the Ides of March.

The Roman calendar didn’t number the days of the month as we do now. Instead, days were reckoned in relation to three key points: the Kalends, which marked the start of the month; the Nones, which came on the 5th or 7th, depending on the month; and the Ides, which came on the 13th or 15th. The other days were counted backwards from these dates.

In every month, the Ides was the day on which rents and other debts were due. And the Ides of March held special significance. For much of Roman history, the year began in March, not January. The Ides of March was a time of feasting and other celebrations. An early feast, for example, honored a goddess of the new year.

So enjoy the Ides of March — a famous date from the early Roman calendar.

Script by Damond Benningfield

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In the science-fiction stories of a few decades ago, there was a definite way to crash a nasty computer: get it to calculate the value of pi. Since pi is an “irrational” number, it never ends — the number of digits just goes on and on and on.

Pi is the ratio of a circle’s circumference to its diameter. Although it doesn’t have an exact value, it’s approximated as 3.14. And since today is 3.14 on the calendar — the 14th day of the third month — it’s Pi Day.

Scientists, mathematicians, and others have been using pi for millennia. It applies not only to circles, but to spheres, cones, cylinders, and other objects. It makes it possible to calculate surface area, volume, and other measurements. That’s handy for astronomers as they study stars and planets.

The concept of pi has been around for thousands of years. Egyptian architects used it to build the pyramids of Giza, for example. Their work was based on measurements. Mathematicians began calculating the value of pi around 2,000 years ago.

The name “pi” was first used in the 1600s. And it didn’t become popular until the following century. It was picked because it was the first letter of the Greek word “perimetros,” which means perimeter or circumference.

Over the centuries, scientists have calculated the value of pi with ever greater precision. And supercomputers have allowed them to add even more digits. So far, the record is about 31 trillion — with no end in sight.

Script by Damond Benningfield

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