StarDate

The celestial unicorn isn’t much to look at. Monoceros fills a void between the bright constellations Orion, Gemini, and Canis Major and Canis Minor. Yet you need dark skies to see even a smattering of stars in that region. And none of them represents the horn of the unicorn. But there is an object that resembles a horn right about where the horn should be. It’s faint, though, so it shows up only in long-exposure photographs.

The Cone Nebula is at the edge of NGC 2264, a complex of young stars and giant, billowing clouds of gas and dust. Ultraviolet energy from the young stars sets the hydrogen gas in the clouds aglow. That makes much of the region shine reddish pink.

But the complex also includes clouds of colder gas and dust. Those clouds form dark streamers and blobs against the colorful background. The Cone Nebula is the most prominent, with its narrow end pointing toward the center of NGC 2264.

The nebula spans about seven light-years. That’s almost twice the distance from the Sun to its closest neighbor stars.

A hot, bright young star close to the Cone is ripping away material from its top. Yet the gas and dust deep inside the cone may remain dense and cold enough to give birth to new stars. If it does, then one day the energy from these stars will erode the cone from the inside — stripping away the unicorn’s faint “horn.”

We’ll talk about another nebula in the unicorn tomorrow.

Script by Damond Benningfield

In the mid 1860s, astronomers were just beginning to use a new tool to study the heavens. Called spectroscopy, it allowed them to split the light from an astronomical object into a rainbow of colors. Individual light and dark lines etched onto the rainbow revealed an object’s composition, motion, and more.

But a tool is worthless without a skilled practitioner to use it. And for at least two decades, British astronomer William Huggins was the master craftsman of spectroscopy.

Huggins was born 200 years ago today. By the time he was 18, he owned both a microscope and a telescope. He planned to enter Cambridge University. Instead, he had to take over his father’s business. But he continued to study science. Later, he sold the family business and built his own observatory, on Tulse Hill, near London. He lived and worked there for the next five decades.

By the early 1860s, scientists had used spectroscopy to identify the chemical elements present in the Sun. Huggins applied the same technique to other stars — and succeeded. He found that the stars are all put together much like the Sun, but their chemical composition can be quite different. Later, he measured how fast the stars are moving away from Earth.

Huggins married another astronomer, Margaret Lindsay Murray. From their observatory on Tulse Hill, they worked together on many research projects, until William’s death, in 1910.

Script by Damond Benningfield

Astronomers have discovered dozens of planets that orbit both stars in a binary system. Like Tatooine of “Star Wars” fame, that gives the planets double sunrises and sunsets. But only a handful of those planets lie in their system’s “habitable zone” — the region around the stars that are most comfortable for life. That means we haven’t yet seen a real Tatooine just yet.

One of the circumbinary systems is close to the Northern Cross — the body and wings of Cygnus, the swan — which is nosediving into the northwestern horizon at sunset. The system is just off the end of the right arm of the cross. But it’s so faint that you need a telescope to see it.

The system is known as Kepler-47. It’s more than 3,000 light-years away. And it’s perhaps the most Tatooine-like system yet seen. Its main star is about as big and as bright as the Sun. The second star is a bit smaller and a good bit fainter. The planet orbits them once every 10 months, at an average distance that’s about the same as Earth to the Sun.

The planet itself is a bit more than three times the mass of Earth, and about five times Earth’s diameter. That means it’s probably half gas and half rock and ice. That composition isn’t especially good for hosting life. But the planet could have good-sized moons, where conditions could be more comfortable. So while Kepler-47c might not be Tatooine, one of its moons could be.

Script by Damond Benningfield

Many spacecraft bounce among the planets and moons of the solar system like they’re inside an old pinball machine. They use the gravity of one object to bat them toward another. That’s like having an extra rocket booster at no extra cost.

The first gravity assist took place 50 years ago today. Mariner 10 flew past Venus, the next planet in toward the Sun. It used Venus’s gravity to help it reach Mercury, the closest planet to the Sun. That made Mariner 10 the first probe to explore two planets beyond Earth. It eventually flew past Mercury three times.

Today, gravity assists are common. A spacecraft might use many of them during its mission. The Juno spacecraft, for example, is using the gravity of Jupiter’s big moons to allow it to explore some of the other moons. And later this year, a mission called JUICE will use the gravity of Earth and the Moon to help push it toward Jupiter. Once there, it, too, will get gravitational kicks from Jupiter’s big moons to help it explore the Jovian system.

There’s no way for a craft to carry enough propellant to do that kind of maneuvering on its own. So without help from the planets and moons, we’d know a whole lot less about the many worlds of the solar system.

Venus, the planet that provided the first helping hand, is the brilliant “morning star.” It’ll stand well to the lower left of the Moon at dawn tomorrow, and closer to the Moon on Wednesday.

Script by Damond Benningfield

One of the most amazing achievements in astronomy in recent decades is the discovery of planets in other star systems — 5,000 of them and counting. And many of those systems are a long way off — hundreds of light-years.

Consider a binary system in Lynx. The faint constellation is in the northeast at nightfall, to the upper right of the Big Dipper. The system has the science fiction-sounding name XO-2. It’s named for the project that discovered the planets. The system is almost 500 light-years away.

Both stars — XO-2N and XO-2S, for north and south — are about the same size and mass as the Sun. The stars are hundreds of billions of miles apart — almost five thousand times the distance from Earth to the Sun.

Each star has two known or suspected planets. The planets of the south star are pretty close in, so they orbit the star in a few weeks or months. One of them is about a third the mass of Jupiter, the giant of our own solar system. The other is a little more massive than Jupiter.

XO-2 North has one confirmed planet and another possible one. The confirmed planet, which is about two-thirds the mass of Jupiter, takes less than three days to orbit the star. The possible world is almost twice Jupiter’s mass, and it takes at least 17 years to circle the star.

Astronomers continue to look for more planets around these distant stars.

Script by Damond Benningfield

The Moon has a giant companion at dawn the next couple of days. Make that two giants. The star Antares is close to the lower left of the Moon tomorrow, and about the same distance to the upper right of the Moon on Monday.

About half way between those appearances, the Moon will pass directly between Earth and Antares. As seen from much of Asia, the scorpion's brightest star will disappear behind the Moon.

Such a disappearing act is known as an occultation. And over the past couple of centuries, occultations helped astronomers learn a lot about Antares.

During one in 1819, for example, one astronomer saw that the light from Antares faded in steps — one drop, followed a few seconds later by a second one. That showed that Antares consists of two stars.

Precise timing of how long it takes the two stars to vanish and reappear reveals the apparent sizes of both stars. Astronomers combine that with measurements of the system's distance — about 550 light-years. That allows them to calculate the true sizes of the stars. The smaller star is more than four million miles in diameter — more than 1600 times the diameter of the Moon. And the main star is almost 600 million miles across — roughly 270 thousand times the width of the Moon.

The Moon will occult Antares every month this year. That'll give astronomers chances to learn even more about this pair of giant stars.

Script by Damond Benningfield

The Juno spacecraft is scheduled to visit one of the most dangerous regions of the solar system tomorrow. It'll fly less than a thousand miles from Io, one of the big moons of Jupiter. That's where Jupiter's radiation belts are strongest. Without the heavy shielding Juno carries for its electronics, the craft probably wouldn't survive.

Io is a little bigger than our own moon. More important, it's the most active body in the solar system, with more than 400 volcanic features.

Io's biggest volcanoes belch ash and gas up to 300 miles high. Jupiter's powerful magnetic field strips electrons from many of the atoms in those plumes. That creates a mixture of charged atoms and free electrons. They spread out along Io's orbit, forming a wide "doughnut" around Jupiter. Any spacecraft that flies through the doughnut gets zapped. So it has to be shielded to keep it alive.

The magnetic field also funnels many of the electrons toward Jupiter's magnetic poles. The electrons produce radio waves. Juno recorded some of those waves during earlier encounters, and It'll listen again this time. The observations will tell scientists more about Jupiter's magnetic field. That helps them learn what's happening inside the planet.

Jupiter is high in the southwest at nightfall. It looks like a brilliant star — a beautiful world encircled by a deadly ring.

Script by Damond Benningfield

Almost a century ago, astronomers split the celestial sphere into 88 constellations. Most of them — the famous ones — date from ancient times. But 14 of them — none of which is famous — were created by a single man, in the 18th century.

Nicolas Louis de La Caille was a French astronomer. In 1751, he set up an observatory in South Africa to study the stars of the southern hemisphere. Over the following year, he cataloged about 10,000 stars. Later, he used those stars to draw constellations in parts of the sky that weren’t visible from most of Europe.

He called one of them Mons Mensa — table mountain. It honored a feature near La Caille’s observatory. He named all the others for scientific instruments, such as the telescope and microscope, or artist’s tools, such as the painter’s easel.

One of those constellations is Fornax, the furnace, which is quite low in the south as night falls.

Originally, La Caille called it Fornax Chemica, after a small heater that was used for chemistry experiments. Another astronomer shortened the name a few decades later.

Fornax isn’t much to look at — at least not with the eye alone. It contains only one modestly bright star, Alpha Fornacis. But a telescope reveals many treasures within its borders. That includes some beautiful individual galaxies, plus a giant cluster of galaxies — fiery visions in the celestial furnace.

Tomorrow: a close look at a fiery moon.

Script by Damond Benningfield

Spica is one of the brighter stars in the night sky, so it’s always easy to pick out. But it’s especially easy to find tonight, because it huddles especially close to the Moon. They climb into good view after midnight, and remain in view the rest of the night.

Spica looks like a single pinpoint. In reality, it’s a system of two massive stars. They’re so close to one another that their light blurs together.

The stars orbit each other once every four days. They’re just a few million miles apart. But their orbit is a bit lopsided, so the distance changes. And the two stars rotate at different rates. The larger star spins almost three times faster than its slightly smaller companion.

If given enough time, the stars would come into better synchronization. Their orbit would become more circular. And they’d spin at such a rate that the same hemisphere of each star would always face the other.

The key to that is “if given enough time.” The larger star is so massive that it’s destined to explode as a supernova. And given its age — about 12 million years — the “boom” probably isn’t too far away.

Before the star explodes, it’s likely to blow a lot of gas into space, decreasing its mass. That’ll change the stars’ orbit. And when it does explode, it’ll lose most of its mass, changing the orbit even more. It’s even possible that the two stars will go their separate ways — ending a close pairing of massive stars.

Script by Damond Benningfield

Astronomers have been studying the star cluster Messier 36 for almost four centuries. Yet they still aren’t sure about its details. There’s disagreement about its distance, its age, and the number of stars it contains.M36 is in Auriga the charioteer. The constellation is high in the eastern sky this evening. Its brightest star is Capella, one of the brighter stars in the night sky. M36 is one of four clusters to the lower right of Capella that are visible through binoculars.Estimates of the cluster’s distance vary by hundreds of light-years, with an average of about 4,000. Star counts place its population at up to 200 stars. And estimates of its age range from about 15 million to 30 million years.One recent study favored the lower age. In fact, it found several stars that are no more than 200 thousand years old. That suggests that even more stars could be born there in the future.As with many other details, though, there’s some uncertainty — it’s not confirmed that the infant stars are part of M36. They’re inside a small cloud of cold, dark gas and dust. It’s on the cluster’s edge. So it could be part of M36, or it could be a separate structure that happens to be close by.So it’s going to take more studies — and more years — to lock down the details of Messier 36.Tomorrow: synchronizing a close pair of stars. Script by Damond Benningfield