StarDate

The nearest star system visible to the unaided eye that has a known planet scoots across the southern sky on winter evenings. Epsilon Eridani is in the south at nightfall, although you need dark skies to see it.

The star is 10 and a half light-years away — right next door. It’s orbited by at least one planet. It’s not a good place to look for neighbors, though. The planet is a gasball similar to Jupiter, the giant of our own solar system. And it’s so far from Epsilon Eridani that it’s quite cold — not a likely haven for life.

Only a couple of other stars with known planets are closer to Earth. And both of those stars are so faint that you need a telescope to pick them out.

One is Proxima Centauri. It’s the Sun’s closest neighbor, at just 4.2 light-years. Its planet is about the same size as Earth. And it’s at the range from the star where temperatures should be just right for liquid water. But the planet is bathed in radiation and a strong wind from the star. That could strip away any atmosphere and sterilize the surface.

And late last year, astronomers reported the discovery of a planet around the second-closest star system, Barnard’s Star. The planet is about three times as massive as Earth, so it’s probably a ball of rock. It’s so far out, though, that it should be frozen solid — too cold for life like that on Earth — one more world where we’re not likely to meet any neighbors.

More about exoplanets tomorrow.

Script by Damond Benningfield

Lepus is a faint constellation with some impressive stars. The rabbit scampers below the feet of Orion, who chases it across the sky.

The rabbit’s brightest star is Arneb, from an Arabic name that means “the hare.” It’s not that much to look at. But that’s only because it’s perhaps 2200 light-years away or farther. The fact that it’s visible to the eye at all means that it must be quite impressive. In fact, it’s probably about 14 times more massive than the Sun, a hundred times wider, and perhaps 30,000 times brighter.

Arneb is quite young. Yet it’s already nearing the end of its life. In the next million years or so, it should explode as a supernova — a blast that’ll shine as brightly as billions of normal stars.

A star at the corner of the constellation is also impressive — not just for its size and brilliance, but for its color. R Leporis is one of the reddest stars around. In fact, it’s also known as Hind’s Crimson Star. That’s in honor of its discoverer, J.R. Hind, who said it looked like a drop of blood on a black field.

The color comes from carbon at its surface. The star is old and bloated, and giant bubbles of gas carry carbon from its core up to the surface. Carbon compounds absorb blue light, allowing the red to shine through.

R Leporis pulses in and out like a beating heart. When it’s at its biggest, it’s barely visible to the unaided eye. But you need a telescope to see the rich color of this amazing star.

Script by Damond Benningfield

We all know the saying: If the groundhog sees his shadow on Groundhog Day, there’ll be six more weeks of winter. If not, then it’s an early spring. In the United States, it’s a tradition that dates back almost two centuries. But it’s based on far older traditions, which were based in part on the seasons.

The oldest known celebration of what is now Groundhog Day was observed in ancient Ireland and Scotland. Known as Imbolc, it was a commemoration of a cross-quarter day.

The dates of the solstices and equinoxes were known as quarter days — they divided the year into four equal parts. At the time, though, those dates marked the middle of a season, not its beginning or end. Those were marked by the cross-quarter days, which came roughly half way between the quarter days. Imbolc marked the start of spring, and was celebrated with big feasts.

Later, the early Church developed its own cross-quarter celebration. Known as Candlemas, it marked the 40th day of Christmas — the day Jesus was presented at the Temple of Jerusalem. The event came to be celebrated with candles — hence the name.

Both commemorations included references to the weather. A cold, clear day was thought to be a sign of more winter, while a mild, cloudy day was a harbinger of an early spring.

In parts of western Europe, people began using animals as indicators of the weather. That tradition made its way to the U.S. in the 19th century — leading to Groundhog Day.

Script by Damond Benningfield

Two of the biggest and brightest stars in the galaxy flank Orion’s Belt, which is in the southeast at nightfall. Orange Betelgeuse is to the upper left of the belt, with blue-white Rigel to the lower right.

Both stars are popular in science fiction. They’ve appeared in dozens of books, TV shows, and other media. Betelgeuse, for example, was featured in the original “Planet of the Apes” novel. And Rigel was featured in several episodes of “Star Trek,” as well as in a series of stories by Isaac Asimov.

In reality, though, neither star would be a good home for life — or even planets. Both stars probably are less than 10 million years old, for example, so there probably hasn’t been enough time for planets to form and give rise to life at either of them.

And even if planets did form, Betelgeuse is so big that if it took the Sun’s place in our own solar system, it would extend to the asteroid belt and maybe beyond. To be habitable, a planet would have to be billions of miles away from the star.

Rigel isn’t as big as Betelgeuse, but it’s much hotter. So a planet would have to be much farther away to be habitable. And like Betelgeuse, Rigel produces a strong wind that could damage the atmosphere of a nearby planet.

And to make things even worse, time is about up for both stars. Within a couple of million years, both are likely to explode as supernovae — really bad news for any planets around these impressive stars.

Script by Damond Benningfield

Some beautiful but remote lights twinkle across the sky this evening. Sirius, the brightest star in the night sky, shines at us from almost nine light-years away. Betelgeuse, the orange shoulder of Orion, is hundreds of light-years away. And arcing across the sky, the Milky Way is the combined glow of millions of stars, many of which are farther still.

Looking at this view under a dark, moonless sky can help us appreciate the vastness of the universe. But to fully appreciate its workings, scientists also must look at the other end of the size scale — to the tiniest particles.

It’s at these scales that scientists can probe some of the mysteries of the universe. One is why the universe consists almost entirely of matter, with only a tiny bit of antimatter. The Big Bang should have created them in almost equal amounts. But there may have been an imbalance, so most of the antimatter was destroyed.

Another mystery is whether particles of gravity “jump” into hidden dimensions. If they do, that could explain why gravity is so much weaker than the other basic forces of nature.

To solve these mysteries, scientists use particle accelerators, which ram together subatomic particles at almost the speed of light. These experiments are telling us about the first moments of the universe, and the processes that shape it today — processes that work not only on the smallest scales, but across the immensity of time and space.

Script by Damond Benningfield

Venus huddles close to the Moon before and during dawn tomorrow. It’s the brightest point of light in the night sky, so you can’t miss it.

Venus moves back and forth between morning and evening skies. And because it’s so brilliant, it’s often called the morning or evening star. It’s not a star at all, of course — it’s a planet — and the closest one at that.

Venus follows a regular schedule of appearances in the sky. It’s visible in the morning for about nine months, then disappears behind the Sun for about two months. Then it’s nine months in the evening sky, followed by a week-long absence as it passes between Earth and the Sun.

These numbers are all rounded off, and they can vary depending on the precise geometry and even on the viewer’s latitude. But they add up to an average of 584 days. Five of these cycles add up to almost exactly eight years. So Venus will appear in almost exactly the same spot in the evening sky eight years from today.

Most cultures have understood for a long time that morning and evening Venus were really the same object. Even so, some of them maintained separate names for its different appearances. In Rome, for example, morning-star Venus was known as Lucifer — the bringer of light.

Whatever you call it, Venus will bring its light to the morning sky until summer. It’ll then disappear until fall — when it’ll return as the evening star.

Script by Damond Benningfield

The average surface temperature on Io, one of the big moons of Jupiter, is a couple of hundred degrees below zero. That’s a little surprising, though, when you consider Io’s claim to fame: It’s the most volcanically active body in the solar system.

Io is covered by more than 400 active volcanoes. Some of them blast plumes of gas and dust hundreds of miles high. Others produce lakes of molten rock. The temperatures of these pools can top 2,000 degrees Fahrenheit.

The heat doesn’t get spread to the rest of the surface, though, because Io has almost no atmosphere. Scientists have detected some wisps of sulfur, but they would qualify as a hard vacuum here on Earth. And what little atmosphere there is freezes out when Io passes through Jupiter’s wide shadow.

Io is heated by an eternal tug of war between Jupiter and a couple of its other large moons. The moons pull Io into a slightly lopsided orbit. That causes Jupiter’s gravity to squeeze and stretch the moon like a child playing with a Nerf ball. That heats Io’s interior, creating reservoirs of molten sulfur and other compounds. Some of that lava punches through to the surface, creating the hellish landscape on this distant moon.

And Jupiter is near our own moon at first light tomorrow. It looks like a bright star to the lower left of the Moon. The brighter planet Venus — the “morning star” — is farther along the same line.

More about Venus and the Moon tomorrow.

Script by Damond Benningfield

The Moon is the most dominant object in the night sky. It outshines every star and planet, even when it’s a barely-there crescent. Yet the Moon isn’t limited to the night. It spends just as much time in the daytime sky. Most of us don’t notice it, though, because it’s a poor second place to the Sun.

To be fair, the Moon is never at its best when it’s in the sky at the same time as the Sun. It shines brightest when it’s full. At that moment, though, it lines up opposite the Sun. So the full Moon is just rising as the Sun sets, and just setting as the Sun rises.

And for a couple of days before and after it’s full, the Moon shares the sky with the Sun for only a little while — just before sunrise or after sunset. And for a day or two on either side of its new phase, it’s not really visible at all — during day or night.

For every phase between those extremes, though, the Moon can spend hours in the daytime sky. But the Sun can be millions of times brighter, so it fills the sky with light. Through the curtain of blue sky, the Moon looks washed out — a mere shadow of its nighttime glory. If you find it, though, it’s still a beautiful sight.

As the Sun rises tomorrow, for example, the Moon will stand in the south, with sunlight illuminating about a third of its visible hemisphere. It’ll arc low across the south and southwest during the morning, and set in the early afternoon — the champion of the night in the daytime sky.

More tomorrow.

Script by Damond Benningfield

When a dying star exhales it last breath, it’s a doozy. The star blows its outer layers of gas out into space. That surrounds the star’s core with a colorful bubble. The bubble can last for tens of thousands of years before it fades away.

One of those bubbles is on the edge of Gemini. The constellation is well up in the east as darkness falls. It’s marked by its brightest stars, the “twins” Pollux and Castor.

The Medusa Nebula is about 1500 light-years away, and it spans about four light-years. Some of the strands of gas that make up the nebula have reminded skywatchers of the snakes on the head of Medusa, one of the Gorgons of Greek mythology.

The strands have been expanding into space for thousands of years. They began their journey when their star could no longer produce nuclear reactions in its core. Gravity squeezed the dying core tighter, making it smaller and hotter. The radiation of the hotter core pushed away the layers of gas around the core. And they’re still expanding — more than 30 miles every second.

Ultraviolet light from the core “energizes” the gas in the nebula, making it glow. Different elements glow in different colors, allowing astronomers to identify them. That tells them about the original star, and about its demise.

The fate of the Medusa Nebula is shared by all Sun-like stars. So billions of years from now, the Sun will create its own nebula — a colorful bubble blown with its final breath.

Script by Damond Benningfield

The twins of Gemini climb high across the evening sky at this time of year. Pollux and Castor are well up in the east at nightfall, with Castor standing a little above its brighter “twin.”

Pollux is an orange giant — an old, bloated star that’s about 35 light-years from Earth. It has at least one planet — a world at least three times as massive as Jupiter, the giant of our own solar system.

Castor is about half again as far as Pollux. And it consists of six known stars. All of them are related — they were born from a single giant cloud of gas and dust, probably about 200 million years ago.

The sextet is split into three pairs of twins. Two sets are more fraternal than identical. One star in each pair is a good bit bigger, brighter, and heavier than the Sun. Both of their companions are smaller, fainter, and less massive than the Sun.

The stars in these pairs are so close together that they orbit each other in just a few days. With so little space between them, there’s no way for telescopes to see them as individual stars. Instead, special instruments separate the “barcodes” of the stars as they orbit each other, providing details on each star.

The third set of twins is identical. Each star is smaller and less massive than the Sun, and much fainter. And while the other two sets of twins are close to each other, these twins are so far away that it takes them thousands of years to orbit the others.

Script by Damond Benningfield