StarDate

Ophiuchus is a little creepy. The constellation represents a man holding a snake – something most people definitely would not want to experience. Yet in one version of his story, the snake helped make Ophiuchus a great healer – so great that the gods of Olympus turned against him.

In Greece, Ophiuchus was known as Asclepius. One day, a friend was bitten by a snake and died. Asclepius then killed the snake. But another snake dropped a mouthful of herbs on the dead one, which was resurrected. Asclepius then used those same herbs on his friend. He, too, returned to life.

Armed with those magical herbs, Asclepius began healing people all over the place. That was creating a population explosion. So Zeus, the king of the gods, killed the healer with a lightning bolt. Zeus then placed both man and snake in the night sky.

Today, Asclepius is known as the father of medicine. And one of the symbols of medicine is a snake wrapped around the staff of Asclepius.

Ophiuchus is a big constellation. It’s low in the sky at nightfall, and stretches all the way from due east to due southeast. Its main pattern of stars resembles the outline of a coffee urn. The urn is on its side in early evening, but stands upright later in the night, as Ophiuchus climbs the southern sky. The head of the snake rises above Ophiuchus, with its tail below.

Script by Damond Benningfield

If you have a mechanical watch or clock, you can hear it ticking off the seconds — 86,400 of them every day.

The second has been the most basic unit of time for millennia — since long before it could even be measured. It originated in ancient Babylon. Astronomers used the number 60 as the base for keeping time and for measuring angles in the sky. It’s divisible by many other numbers, so it was easy to work with.

In this system, each smaller division was one-sixtieth the size of the larger one. So one-sixtieth of an hour became a minute. And one-sixtieth of a minute became a “second minute” — indicating that it was the second position in the list of time.

No one could really measure so small a unit of time, though, until the invention of mechanical clocks in the 16th and 17th centuries.

Not long after that, scientists realized they needed a precise definition for a second, which is a key unit for many measurements and equations. Originally, their definition was based on Earth’s rotation. But that rate isn’t constant. Hurricanes, earthquakes, and other disturbances can change it by a tiny bit.

So in 1967, they adopted a new definition. It uses the vibrations of a cesium atom that’s zapped with a laser. It’s measured with atomic clocks. So one second is the amount of time it takes an atom to “vibrate” nine billion, 192 million, 631 thousand, 770 times — the length of a single “tick” on the clock.

Script by Damond Benningfield

A day on Earth consists of 24 hours, 1,440 minutes, or 86,400 seconds. But not all days are equal. Earth’s rotation on its axis varies from day to day. Earthquakes and hurricanes, for example, can cause “hiccups” that alter the length of the day ever so slightly. It’s not nearly enough to notice. But it means that we can’t rely on Earth’s rotation to keep highly accurate time. So scientists have devised several time systems to compensate.

The basic system is known as Universal Time. But there are several versions of it. The one that’s used for everyday clocks is Universal Time Coordinated. It’s based on International Atomic Time, which keeps time with atomic clocks.

Scientists use Universal Time 1. It is based on the motions of astronomical objects and artificial satellites across the sky. A network of radio telescopes plots the positions of distant quasars, for example, with extreme precision. It tells astronomers how long it takes those objects to return to the same position in the sky — a highly accurate clock.

Astronomers also use a system known as Terrestrial Time. It figures time as though Earth were a smooth, featureless ball. That’s because clocks at different altitudes tick at slightly different rates. Adjusting them to the same altitude compensates for those differences.

Today, Terrestrial Time has drifted ahead of atomic time — by about 32 seconds.

More about time tomorrow.

Script by Damond Benningfield

Keeping time is a tough job. If you travel, you might cross several time zones – there are 38 of them around the world. Every year, most of us “spring forward” and “fall back” as we begin and end Daylight Saving Time. But not all time zones observe daylight time, further complicating things.

The starting point for the worldwide time system is zero degrees longitude. That line runs through Greenwich, England, which was home of the Royal Observatory. That line became the default for maps and other navigational standards.

Until the 1800s, every town and village kept its own time, based on the position of the Sun. Local noon came when the Sun crossed the meridian – the line that passes from due north to due south, crossing directly overhead.

With the birth of railroads, though, that created a mess. It was impossible to know when a train was supposed to arrive or depart. So England adopted a single time zone – Greenwich Mean Time, or GMT. That soon became the standard for defining time zones around the world.

Scientists began using GMT as a way to coordinate observations made around the world. But that was confusing. Astronomical GMT began at noon. But civil GMT – the version used for everyday life – began at midnight. So in 1935, the International Astronomical Union recommended a new name for the scientific version of GMT – Universal Time.

Universal Time is still in use today – but in several forms. More about that tomorrow.

Script by Damond Benningfield

Ancient skylore is pretty tawdry. Everywhere you look, you find stories of betrayal, seduction, vanity, and even murder. Yet some skylore is a bit more uplifting — tales of love, devotion, and sacrifice.

One of those tales is told in the story of Castor and Pollux — the twins of Gemini — who are dropping down the western sky on these late spring nights.

According to one version of the story, the queen of Sparta gave birth to two sets of twins — one boy and one girl in each pair. One set was fathered by her husband. But the other set was sired by Zeus, the king of the gods.

The four children were raised together, and the two boys — one mortal, the other immortal — were inseparable. They had many adventures — they joined Jason and the other Argonauts in the search for the golden fleece, for example.

But during a fight, the mortal Castor was killed. Pollux was inconsolable. He begged Zeus to allow him to die so he could join Castor. Moved by Pollux’s love for his brother, Zeus agreed to keep them together for all eternity. They spend their time in the heavens — where they’re represented by the stars of Gemini.

The constellation is in the western sky at nightfall. Its brightest stars represent the twins themselves. They line up to the right of the Moon. Brighter Pollux is closer to the Moon, with Castor to its right.

Script by Damond Benningfield

HIP 3765 is pretty average. The yellow-orange star is about three-quarters the size and mass of the Sun, and billions of years older.

It does have one distinction, though. It lines up in such a way that any astronomers in the system could see Earth pass across the face of the Sun. From that, they could determine that Earth is in the “Goldilocks Zone” — the distance from the Sun where conditions are best suited for life. And if the folks there were outgoing, they might beam greetings our way — a “beacon” for our radio telescopes to hear.

But a study released a few months ago found that HIP 3765 is quiet. Three scans of the system found no evidence of such a beacon, or any other signal.

The study was conducted by Sofia Sheikh, a graduate student at Penn State, as part of Breakthrough Listen — the largest effort to find other civilizations to date.

This part of the project used a radio telescope in West Virginia to scan 20 stars. All of them could see Earth crossing the Sun, giving their residents a reason to try to contact us. HIP 3765 was the closest of them, at about 25 light-years. All of the stars remained silent, though, with no interstellar “howdys” beamed our way.

HIP 3765 is the only one of the stars that’s visible to the unaided eye. It’s in Pisces, the fishes, which is swimming into the early morning sky. The star is low in the east at first light, but you’ll need a starchart to pick it out.

Script by Damond Benningfield

The jewel of the northern crown caps the sky tonight. It’s high in the east at nightfall, and passes overhead a few hours later.

Alphecca is the brightest star of Corona Borealis, the northern crown — a semicircle of stars that looks like a tiara.

Alphecca actually consists of two jewels — two stars. We see them as a single point. If we could see them individually, though, one would shine pure white, the other yellow.

That’s an indication of their surface temperatures. The yellow star is about 10,000 degrees Fahrenheit — about the same as the Sun. The white star is almost twice as hot.

Surface temperature is driven by nuclear reactions deep inside the star, which create energy. The energy makes its way to the surface and shines away into space.

The rate of those reactions is driven by the star’s mass. Alphecca’s yellow star, for example, is a bit less massive than the Sun. Its gravity squeezes the core tightly enough to heat it to more than 20 million degrees. That’s a little cooler than the Sun’s core. As a result, the core produces a little less energy than the Sun, so the star is a little fainter and cooler than the Sun.

The white star is heavier than the Sun, so its core is twice as hot as the Sun’s. So the star’s nuclear engine runs at a faster rate, producing far more energy. That makes the surface hotter, too. And it makes the star shine far brighter than the Sun — lighting up the jewel of the northern crown.

Script by Damond Benningfield

A quartet of similar worlds huddles low in the western sky at sunset the next few evenings – the Moon, two planets, and an asteroid.

The Moon is quite low in the sky this evening. It’s also the thinnest of crescents – the Sun illuminates less than two percent of the lunar disk. So it’s a bit of a challenge to find.

The planet Venus is close above it – the brilliant “evening star.” The fainter planet Mercury is a little higher still. And the asteroid is Vesta, to the left of Mercury. You need strong binoculars or a telescope to pick it out.

All four of these objects are “differentiated” – they’re made of distinct layers. At the center is a solid metallic core. There’s a mantle of rock around the core, wrapped in a crust of volcanic rock.

Vesta is the smallest body in the solar system to have such a layered structure – it’s just 325 miles in diameter. A research team recently learned more about Vesta’s history by studying pieces of the asteroid – meteorites found in Antarctica. They revealed that Vesta was volcanically active for at least 30 million years after its birth – longer than expected for such a small body. Vesta might have had oceans of molten rock just below its surface. They helped keep it warm for a long time. And that helped build Vesta’s layered structure.

Again, look for this quartet low in the west right after sunset. The Moon will have climbed above the other three bodies tomorrow evening, enhancing the view.

Script by Damond Benningfield

Storms on the Sun can have unpleasant consequences. They can damage satellites, force airlines to reroute flights, and even cause power blackouts. And for some marine mammals, they could be deadly.

Dolphins and whales occasionally strand themselves on the beach. Biologists say there are many possible causes: injury, disease, human-made sounds, and others. And in recent years, they’ve even found a possible link between strandings and solar activity.

Dolphins and whales may use Earth’s magnetic field to navigate. Solar storms can change the contours of the field. So researchers have suggested the storms may “scramble” the navigation system – like passing a bar magnet near a compass.

A recent study, though, says the problem isn’t changes in the magnetic field. Instead, it may be bursts of radio waves from the storms.

Researchers looked at 35 years of strandings of grey whales. They eliminated whales that were sick or injured, or that might have been confused by sonar or other loud sounds. They then compared the remaining strandings to changes in Earth’s magnetic field, and to outbursts of radio waves.

The results showed no relationship between strandings and changes in the magnetic field. But there was a relationship with the radio bursts. In fact, the whales were more than four times as likely to strand during those outbursts. So storms on the Sun can be bad news for these beautiful creatures.

Script by Damond Benningfield

Most stars don’t change much over time scales that we can see. Instead, the changes play out over millions or billions of years. But one star is undergoing dramatic changes over scales of decades. That’s allowing astronomers to watch it evolve in real time.

T Ursae Minoris is in Ursa Minor, the little bear. As night falls, it’s above the Little Dipper

The star is nearing the end of its life. As a result, the nuclear reactions in its core aren’t stable. That causes changes in the star’s outer layers. And those changes create cycles in the star’s brightness.

Until about 40 years ago, it had one main cycle, which lasted a bit more than 10 months. Since then, though, that period has dropped to about six and a half months. And another cycle has emerged. It lasts about three and a half months.

A recent study concluded that the second period showed up thanks to a “helium flash.” A shell of helium around the star’s core suddenly ignited, converting the helium to carbon.

Comparing the two cycles allowed researchers to compile a complete dossier on the star. They found that it was born 1.2 billion years ago. It’s 1.7 times the mass of the Sun, and almost 300 times the Sun’s diameter.

Overall, the star is getting smaller and fainter. But things should turn around in about 50 years, when the star will start getting bigger and brighter. And within a hundred thousand years, it’ll blow away its outer layers, leaving only its dead core – the final phase for a star that’s changing in a hurry.

Script by Damond Benningfield