StarDate

The Moon and the planet Venus – the brilliant “evening star” – put on a spectacular display tonight. They’ll be separated by the width of a couple of fingers held at arm’s length. They’ll be easy to spot not long after sunset, and they’ll remain in good view for more than two hours.

Venus and the Moon are in almost opposite “phases” tonight.

The Moon is a thin crescent – the Sun lights up only about 14 percent of the hemisphere that faces our way. It’s nighttime across the rest of that hemisphere.

That tells us that the Moon is lining up only a little way to the side of the line between Earth and the Sun. Over the next week and a half, the Moon will move farther from the Sun as it travels along its orbit. Eventually, it will line up opposite the Sun. The Sun will shine on the entire Earth-facing hemisphere, so the Moon will be full.

Venus, on the other hand, is in a “gibbous” phase – the Sun lights up two-thirds of its Earth-facing hemisphere. That tells us that Venus is on the far side of the Sun. But it’s looping over to our side, and will pass between Earth and the Sun in March. As the planet slides our way, the Sun will light up less and less of the portion we can see. Before Venus disappears in the Sun’s glare, it’ll be a thin crescent. Yet for most of that time, Venus will grow brighter, because it’ll be getting closer – setting up more beautiful encounters with the crescent Moon.

Script by Damond Benningfield

The days are continuing to get shorter here in the northern hemisphere. That provides a lot of time to get out and enjoy the night sky. But over the next few weeks, one part of that trend will head the other way: The Sun will begin to set a little later each night – even though the shortest day of the year is still weeks away.

The shortest day is the winter solstice, December 21st. So between now and then, the total length of time between sunrise and sunset will shrink. Yet the date of earliest sunset comes before the solstice.

There are a couple of reasons for that. One is Earth’s tilt on its axis. It causes the angle and location of sunrise along the horizon to change from day to day. The other reason is Earth’s lopsided orbit. It causes the Sun to return to the same point in the sky a little earlier or later in the day depending on whether we’re close to the Sun or farther away.

When you add these factors together, you find that the date of earliest sunset works its way from south to north. For the latitudes of Honolulu and Miami, the earliest sunsets happen about now. For higher latitudes, such as Denver, they’ll take place in a few days. And for cities that are even farther north, such as Anchorage, earliest sunset happens just a few days before the solstice.

To balance things out, the date of the latest sunrise comes after the solstice, working from north to south – a few more minutes of darkness before dawn.

Script by Damond Benningfield

Earth is about to catch up to Jupiter, the solar system’s largest planet. We’ll pass between Jupiter and the Sun on Saturday. As a result, Jupiter is putting on its best performance of the year. It’s in view shortly after sunset and stays in view all night. Jupiter is brightest for the year as well.

Jupiter is the fifth planet out from the Sun – about five times farther from the Sun than Earth is. At that distance, it takes almost 12 years for the planet to complete a single turn around the Sun.

Since Earth is much closer to the Sun, it zips past Jupiter every 13 months. Jupiter lines up opposite the Sun during those passages – a point called “opposition.” That’s when the two planets are closest. This week, Jupiter will be just 380 million miles away.

The combination of that proximity and the good viewing angle means that Jupiter is brightest at opposition. It’s almost always the third-brightest object in the night sky – only the Moon and the planet Venus regularly outshine it. But it’s especially bright right now – it looks like a brilliant star, shining all night long.

Look for Jupiter low in the east-northeast at nightfall. It’s between the horns of Taurus. The bull’s bright orange eye, the star Aldebaran, glows to the upper right of Jupiter. The planet climbs high across the sky during the night, and is in the west at dawn, with Aldebaran below it.

We’ll have more about Jupiter during the week.

Script by Damond Benningfield

Stars can act like they don’t want company. Radiation and “winds” of charged particles – especially from young, heavy stars – can clear away the gas and dust around them. That can prevent the birth of more stars. On the other hand, that process can squeeze the gas and dust, creating new stars.

The process is known as feedback. And it’s the subject of a mission that’s set to launch this month from Antarctica – aboard a giant balloon. ASTHROS is scheduled to reach altitudes of almost 25 miles, and stay aloft for three to four weeks.

NASA launches a dozen or more scientific balloon missions every year. Missions this summer, launched from Sweden, studied the Sun, cosmic rays, and black holes.

Antarctica is an especially good site for balloons. The air is cold and dry, which is good for observing the universe. And high-altitude winds circle around the south pole, allowing a payload to land fairly close to the launch site.

The telescope aboard ASTHROS features a main mirror that’s eight feet across. It’s coated with nickel and gold, allowing it to gather forms of infrared light that are impossible to see from the ground. Its instruments will split the light into its individual wavelengths. That will reveal the composition of gas and dust between the stars, and how that material is moving. From that, astronomers will create 3D maps of regions where new stars are being born – helped or hindered by stellar feedback.

Script by Damond Benningfield

Ann Hodges was taking a nap on her sofa when she did something that other people just sing about: She caught a falling star. Or to be more accurate, a falling star caught her. It left a big bruise on her hip and turned her into a media celebrity – 70 years ago today.

The “falling star” was an eight-and-a-half-pound meteorite – a cosmic rock that had been orbiting the Sun. It was part of a larger rock that plunged into the atmosphere on November 30th, 1954, creating a streak of light that was visible across three states.

The rock exploded while it was still high in the air. One fragment took aim at a house near the Comet Drive-In Theater in Sylacauga, Alabama. It blasted through the roof, bounced off the floor and a radio, and smacked into Hodges. The story made national headlines, and Life magazine published a picture of Hodges and her bruise.

Reports of meteorites hitting buildings or cars aren’t that rare. Neither are stories of meteorites landing near people. But it is rare for a meteorite to actually hit a person. There are accounts of meteorites killing people in some old records in China and elsewhere, but scientists haven’t confirmed those reports. The Alabama impact was easy to document because scientists could see the bruise, the meteorite, and the hole in the roof.

Today, the meteorite is on display in the Alabama Museum of Natural History – a “falling star” that caught a sleeping person.

Script by Damond Benningfield

Tachyons are a bit, well – tacky. These hypothetical particles would travel faster than light. They’ve never been detected, but scientists keep on studying them. The particles have implications for everything from the age of the universe to time travel.

Tachyons were proposed many decades ago. They were named from a Greek word that means “quick” or “swift.” Many studies have dismissed them entirely. One objection is that faster-than-light particles could go back in time – a violation of the laws of physics.

Other studies treat tachyons as something you can think about mathematically, but not in reality. But still others say the particles could be real. One recent study, for example, says tachyons must have been involved in the creation of matter in the early universe.

Another study says tachyons could make up “dark matter” – matter that produces no detectable energy, but exerts a gravitational pull on the visible matter around it. Decades of searches for dark matter have come up empty. The study also says that tachyon dark matter would eliminate the need for dark energy, which is causing the universe to accelerate faster as it ages. And that would change the age of the universe – to about eight billion years, not 13.8 billion, as generally accepted.

More studies are needed to determine whether any of these ideas are correct – allowing these “tacky” particles to stick around at least a while longer.

Script by Damond Benningfield

We’re a long way from developing warp drive – a way to travel faster than light. But scientists have an idea of what the end of a warp trip might sound like – a short, high-frequency “chirp” in the form of gravitational waves.

The laws of gravity say that warp drive isn’t impossible. A ship could enfold itself in a “bubble” of spacetime. The drive would “squeeze” the spacetime ahead of the ship, and expand the spacetime behind it. As seen by an outside observer, that would allow the ship to move faster than light. There are all kinds of problems to solve, but perhaps future generations can make it so.

Researchers in Europe recently checked out some of the physics of warp bubbles. As they wrote in their paper, they wanted to “explore strange new spacetimes – to boldly simulate what no one has seen before.” So they created computer models to probe the signals a starship might create when it either “engaged” or dropped out of warp.

They found that a collapsing warp bubble could produce a quick burst of gravitational waves – “ripples” in spacetime. They’d be at a frequency that current detectors couldn’t hear – but future detectors might. In fact, the waves might be detectable from millions of light-years away – far enough to encompass our entire galaxy and several others – the signal of a faster-than-light trip through the cosmos.

More about faster-than-light travel tomorrow.

Script by Damond Benningfield

We can’t travel to other stars yet – and maybe we never will. But other residents of the solar system can tour the galaxy. At the same time, former residents of other star systems can visit our own. In fact, the Sun and its close neighbors might even swap planets.

Astronomers discovered a new comet earlier this year. They found that the comet had passed close to the giant planet Saturn a couple of years ago. Saturn’s gravity had given the comet a strong enough kick to escape the solar system and head for interstellar space. Another comet was ejected, in 1980, by the even bigger planet Jupiter.

Over the past decade, we’ve seen two asteroids from other star systems pass close to the Sun. They were moving fast enough to barrel through the solar system and keep on truckin’.

We might even get visits from planets. A recent study found that there are two gravitationally stable zones on the outskirts of the solar system – up to 3.8 light-years from the Sun. If a “rogue” planet – one that doesn’t orbit another star – drifted through one of these zones, it might be captured by the Sun. But the Sun’s grip wouldn’t be very strong. So if another star got close enough – say, Alpha Centauri, our closest neighboring system – it might pull the planet away. In fact, the two systems could even swap the planet back and forth – extending its tour of the galaxy.

More about traveling between stars tomorrow.

Script by Damond Benningfield

The next total eclipse of the Sun is almost two years away. But astronomers will watch many “total eclipses” between now and then. Known as occultations, they occur when one astronomical object passes in front of another, blocking the more distant one from view. The most frequent “blocker” is the Moon. And early tomorrow it’ll block out Spica, the brightest star of Virgo.

Spica is just two degrees from the ecliptic, which is the Sun’s path across the sky. The Moon moves five degrees to either side of the ecliptic, allowing it to cover the bright star. And they’re going through a series of occultations now. Tonight’s event is the last one visible from the United States this year.

Spica consists of two heavy stars that orbit each other once every four days. Occultations have helped astronomers decipher the system’s multiple personality, and learn some of its details.

The main star, Spica A, is more than 11 times the mass and seven times the diameter of the Sun. Because it’s so massive, within a few million years the star will blast itself to bits as a supernova. Spica B is no slouch, either. But it’s not quite heavy enough to become a supernova. Instead, it will cast its outer layers into space more gently, leaving behind a small, hot corpse.

Spica and the Moon climb into view just a couple of hours before dawn. The occultation will be visible across most of the country. The exact timing depends on your location.

Script by Damond Benningfield

The Alpha Persei cluster is a family of more than 500 stars, spanning almost 150 light-years. All of the stars were born at the same time, from the same giant cloud of gas and dust.

Tens of millions of years ago, the family was a lot bigger. Alpha Persei was one of several dozen clusters born in the same nursery. The clusters have all gone their own way. But a recent study supports the idea that they were born together.

Astronomers used observations from the Gaia space telescope. It’s measuring the motions and other details of billions of stars. The astronomers looked at stars in more than 270 young clusters within a few thousand light-years of Earth. The observations allowed the researchers to “rewind” the motions of the clusters. They found that, about 30 million years ago, more than half of the clusters congregated in three “super” clusters. The groups are named for their brightest members – in this case, the Alpha Persei cluster.

The scientists estimated that the three groups have spawned more than 200 massive stellar explosions. The supernovas carved bubbles and shells of gas that span hundreds or thousands of light-years.

The Alpha Persei cluster is near the star Alpha Persei, the brightest star of Perseus. They’re in the northeast at nightfall. Under dark skies, the cluster is visible to the eye alone – a bright member of a scattered family of star clusters.

Script by Damond Benningfield