StarDate Billy Henry

The head of the serpent slithers into the early evening sky this month, with its tail twisting along a bit later.



Serpens is the only constellation that’s split apart. The two halves are separated by Ophiuchus, the serpent bearer. The snake’s head rises first. It’s in the east and southeast at nightfall, marked by a serpentine trail of faint stars. The tail, which is below Ophiuchus, climbs into view about an hour later.



The brightest of the stars of Serpens is Unukalhai — an Arabic name that means “the serpent’s neck.” The star also is known as Alpha Serpentis, indicating its ranking as the constellation’s leading light.



The star is in the final stages of life. It converted the hydrogen fuel in its core to helium, causing the core to shrink and get hotter. That triggered the next round of nuclear reactions, with the helium being converted to carbon and oxygen.



The changes in the core have caused the star’s outer layers to puff up like a balloon. That’s made the star about 14 times wider than the Sun. The expansion also made the star’s surface much cooler, so it shines yellow-orange.



In time, all the reactions in the star’s core will stop, and the outer layers will puff out into space. For a while, that expanding cloud will form a colorful bubble. As the bubble cools and dissipates, though, only the star’s dead core will remain — depriving the serpent of its bright neck.



More about the serpent tomorrow.



Script by Damond Benningfield

Aiello del Friuli is a village in northern Italy, about 75 miles from Venice. It’s home to about 2200 residents and more than a hundred sundials — so many that it’s known as the “village of sundials.” It hosts a sundial festival every year, in late May.



The village began earning the nickname in 1994. A resident created a sundial and hung it on the side of his house. It was more than just a pointer and some numbers, though — it was a work of art. So others in the village asked him to make sundials for their homes. He obliged. And before long, other artists got into the act.



Today, the sundials are spread all across town. There are more than 20 in a plaza next to a museum, but they’re in all the neighborhoods as well. Like the original, many of the sundials are mostly two-dimensional and are displayed on building walls. But some are more three-dimensional — globes, bowls, and other shapes mounted on their own.



The sundials follow many artistic themes. Some have religious or historic significance. Others depict nature or agriculture, or have a more abstract quality. And the bounty keeps on growing. The annual festival includes a contest for the best sundial created during the previous year.



All of the sundials also do a job: They track the time as the Sun crosses the daytime sky in the “village of sundials.”



Tomorrow: the head of the serpent wriggles into the evening sky.



Script by Damond Benningfield

Black holes are the darkest objects in the universe — they produce no light at all. Yet they power some of the brightest objects. Known as quasars, these beacons can outshine entire galaxies of hundreds of billions of stars. In fact, the brightest one seen so far emits more light every minute than the Sun will produce in its entire 10-billion-year lifetime.



A black hole’s gravity is so powerful that nothing can escape from it — not even light. But before anything disappears into the black hole, it enters a disk that spirals around the black hole at a good fraction of the speed of light. That creates friction, which heats the material to millions of degrees. The disk emits enormous amounts of radiation, so it shines brightly at many wavelengths.



Quasars are disks around supermassive black holes in the hearts of galaxies. And the brightest one yet seen is truly a monster. It encircles a black hole that appears to be about 17 billion times the mass of the Sun. The black hole is gulping the equivalent of a star as massive as the Sun every day. That creates a disk that’s hundreds of millions of miles across. It shines thousands of times brighter than our entire Milky Way Galaxy.



We see the quasar as it looked more than 12 billion years ago — not long after the birth of the universe. So by now, it’s probably shut down — turning off one of the most brilliant lights we’ve ever seen.



Script by Damond Benningfield

Stars like the Sun aren’t massive enough to become black holes when they die. But there’s a possible exception to that rule: if the star is born with a small black hole inside it. The idea was first proposed by Stephen Hawking. And it’s supported by a recent study.



Normally, a star like the Sun just isn’t massive enough to collapse to make a black hole.



But the universe might be sprinkled with black holes created in the Big Bang. Such black holes could be just about any mass — from almost nothing, to as heavy as a star.



Such a black hole could be incorporated into a newly forming star. There, it would slowly “eat” the star from the inside. Over time, that process could account for some of the star’s energy production. But the black hole might reach a tipping point where it would gobble the rest of the star — converting the whole thing into a black hole.



Measuring the vibrations at the surfaces of Sun-like stars might reveal the presence of black holes inside them — eating them from the inside.



The new study says that a black hole up to about one millionth of the Sun’s mass could be at work inside the Sun today. If it’s there, within a hundred million years it could cause the Sun to drop to about half of its current brightness. The Sun then would puff up to many times its current size, and shine brighter for billions of years. After that, it would collapse to form a black hole.



More about black holes tomorrow.



Script by Damond Benningfield

Our brains can see things that aren’t there. They connect points and shapes to create “pictures.” So we might see a dragon in some puffs of clouds, “canals” on the surface of Mars, or a scorpion in the stars.



One of the most persistent pictures is the “man in the Moon” — a face created from features on the lunar surface. Stories about the man in the Moon — or, in some cases, the woman in the Moon — go back centuries, from cultures around the planet.



In China, for example, the face represented the goddess Chang’e. She was stranded on the Moon after taking too much of a potion that made her immortal. In Germany, the man was a giant who poured water from the Moon to create high tides. And in parts of Europe, the man was banished to the Moon after he stole from a neighbor or worked on the Sabbath.



Today, inns and pubs from Tokyo to the Isle of Wight are called Man in the Moon. It’s been the title of several books. And in the first science-fiction movie, in 1902, a rocket from Earth slammed into the man’s “eye,” with messy results.



The features that make up the man’s face are a combination of dark, smooth volcanic plains, and lighter areas that are more jumbled. You can look for the face yourself the next couple of nights because the Moon is full. And it has a bright companion: The star Antares is to the lower left of the Moon this evening, but almost touching the Moon tomorrow night.



Script by Damond Benningfield

The Moon is in a sort of cosmic balance tonight. It’s passing through Libra, the balance scales — the only constellation of the zodiac that doesn’t represent a living thing.



But the scales are associated with two living things — Virgo, which represents a goddess, and Scorpius, the scorpion. In various cultures of the Mediterranean, the stars of Libra were attached to one or both of those figures.



In ancient Babylon, the stars represented a scale held by Shamash, the Sun god. He was also the god of truth and justice. The scales helped him maintain a “balance” on Earth and in the heavens.



And there may have been an astronomical reason for thinking of the stars of Libra as “in balance.” Until about 2700 years ago, the Sun passed across those stars at the fall equinox — a time when day and night are roughly the same length — they’re in balance.



Libra also was identified as the claws of the scorpion, which is on the opposite side of the constellation. The names of Libra’s brightest stars still reflect that heritage: Zubeneschamali, the northern claw, and Zubenelgenubi, the southern claw, which is quite close to the Moon tonight.



The Greeks maintained the connection to both the gods and the scorpion. Libra wasn’t depicted as a separate constellation until a couple of thousand years ago, in Rome. Yet it maintains the links to its heritage — the scales of justice, and the claws of the scorpion.



Script by Damond Benningfield