StarDate

When the Sun rises, the rest of the universe vanishes. Scattered sunlight turns the sky blue, erasing the stars and planets from view.

The curtain of blue also hides meteors — the streaks of light formed by bits of space rock burning up as they plunge into the atmosphere. Just as many meteors flash through the daytime sky as the nighttime, including several meteor showers. And one of the most intense should be at its peak tomorrow.

The Daytime Sextantids are spawned by an asteroid. It may have split from the parent body of December’s nighttime Geminid shower, which is one of the year’s best. When Earth crosses the asteroid’s path at this time of year, though, the dayside of our planet is facing into the cloud of debris, so the meteors are washed out.

Astronomers track the meteors with radar. The meteors leave trails in the upper atmosphere that reflect radio waves. Astronomers use observations of those reflections to trace the paths of the meteors, and track down their parent asteroids.

There are two ways for the rest of us to observe the shower. You can look for the meteors in the hour or so before dawn, low in the eastern sky.

Or you can “listen” for them. A meteor’s trail reflects FM radio waves. If you have an FM radio, tune to a weak station at the low end of the band. When a meteor passes by, the signal should become louder and clearer for a few seconds — the sound of a “shooting star.”

Script by Damond Benningfield

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Earth is loosening its grip on the Moon. As a result, the Moon moves about an inch and a half farther from us every year. And the same thing is happening to the biggest moon of Saturn — but at a faster rate.

As the Moon orbits Earth, its gravitational pull on our planet creates the tides. The sloshing of the tides causes Earth to lose energy, so it spins a tiny bit slower. To keep the books in balance, the Moon gains the energy that Earth loses. That causes the Moon to move away from us.

The same process is creating a change in the orbit of Titan, one of the most intriguing worlds in the solar system. Titan is about half again as big as the Moon, and it’s blanketed by a cold, thick atmosphere. Liquid methane and ethane fill lakes and seas and carve riverbeds.

Titan’s gravity squeezes the interior of Saturn. That appears to cause Saturn to “wiggle” a bit. Saturn loses energy through the wiggle. The lost energy is transferred to Titan, making it move outward. In fact, observations by the Cassini spacecraft show that Titan is moving away from Saturn by about four inches per year. That means the big moon must have formed much closer to Saturn, and has spent the last four-and-a-half billion years gradually sneaking away.

Look for Saturn quite close to our moon this evening. It looks like a bright star, and is just above the Moon at nightfall. The brighter planet Jupiter is off to the right.

Script by Damond Benningfield

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A half-century ago today, a Soviet spacecraft parachuted to Earth with a precious cargo: a few ounces of lunar dirt. It was the first time that samples had been brought to Earth by a robotic probe.

Luna 16 had arrived at the Moon just a few days earlier, on a volcanic plain known as the Sea of Fertility. It landed during the lunar night — another first for any mission. It drilled into the powdery surface and pulled out a sample for return to Earth.

Several more Luna probes followed. The last was another sample-return mission, Luna 24, in 1976. Since then, neither the Soviet Union nor Russia has attempted a single trip to the Moon. But Russia may get back in the game over the next few years.

The Russian space agency has announced plans for a new mission — Luna 25. Plans call for it to land in a crater near the south pole. The crater floor should be in perpetual darkness, so it could contain deposits of frozen water. The lander will drill into the surface to see if it can find any of that ice.

Current plans call for a launch late next year, although the launch has been delayed several times. Luna 26 — an orbiter — would follow a year or so later. And another lander, Luna 27, would come after that — renewing a program of lunar exploration.

Look for the Moon and some bright companions this evening. The brilliant planet Jupiter is close to the upper left of the Moon, with the fainter planet Saturn farther from the Moon.

Script by Damond Benningfield

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There’s more than one way for a planet to get moons. Some moons are born with their parent planets, from the disk of debris around the young Sun. Others are born after a planet gets blasted by another one. That’s the way our own moon probably was born.

And some recent studies outline a couple of other ways.

One study looked at Pluto and its moons. The largest moon, Charon, probably was born after an impact between Pluto and another large body. And some studies say that Pluto’s four smaller moons formed from the same debris.

But the new study pushes the impact down a generation. It suggests that Charon was hit by a large ball of ice and rock. That blasted a cloud of small particles into orbit around Charon and Pluto. Within a few hundred years, much of that material clumped together to make the other moons.

The giant planet Neptune, on the other hand, may have stolen some of its moons. A study simulated what might happen if Neptune plunged close to another giant planet — something that was possible in the early solar system.

Neptune could have stolen some of the other planet’s moons. Neptune’s gravity, and perhaps collisions with smaller bodies, would have sculpted the final orbit of a moon like Triton, Neptune’s biggest. Moons that are farther out would have followed elongated orbits — like Nereid, Neptune’s third-largest moon.

So there are many ways for a planet to acquire moons — some easy, and some violent.

Script by Damond Benningfield

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The Sun rises in the east and sets in the west. That’s common knowledge. But it’s also a bit imprecise. Unless you live along the equator, the Sun rises due east and sets due west only twice a year — at the equinoxes. The rest of the time, it can swing well north and south of those points.

And today is the autumnal equinox — the beginning of autumn in the northern hemisphere.

The sunset and sunrise points change because Earth is tilted on its axis — which is also why we have seasons. At the summer solstice, in June, the north pole is tilted most directly toward the Sun. The northern hemisphere gets lots of sunlight, so it’s the start of summer. And at the winter solstice, in December, the south pole tips sunward, so the southern hemisphere is in the light.

On the equinoxes, the Sun appears to stand directly above the equator. So there’s roughly equal sunlight north and south of it.

Over the course of a year, then, the Sun moves north and south along the horizon — farthest north in summer, farthest south in winter. And on the equinoxes, it’s between those extremes. So it rises due east and sets due west.

As we head toward the winter solstice, in December, the Sun will move ever southward. How much it will move depends on your latitude. It makes a much more dramatic swing for those at higher latitudes. So those in Spokane and Duluth will see the Sun move more than those in Miami and San Antonio — a motion caused by the changing seasons.

Script by Damond Benningfield

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Apollo astronauts brought about 840 pounds of lunar rocks and dirt back to Earth. Most of those samples are locked away in laboratories and vaults, while a few more are displayed in museums.

Many other moonrocks are simply scattered across the ground. It’s possible that you’ve walked past one, or even picked one up. But it takes an expert — and one of those laboratories — to confirm its origin.

These moonrocks are meteorites — bits of the Moon blasted into space when an asteroid slammed into the lunar surface. Some of the debris from such an impact enters Earth’s atmosphere. Pieces that are big enough hit the ground.

Scientists have cataloged hundreds of lunar meteorites. But it’s not easy. Most lunar meteorites look like Earth rocks. So it takes a detailed analysis to confirm their lunar origin.

Scientists examine the rock’s chemical and mineral composition. They look for evidence that it’s been zapped by cosmic rays, which are blocked by Earth’s atmosphere. And they look at the ratios of different forms of certain elements, which are different for the Moon than for Earth or other bodies.

Lunar meteorites tend to be found where all meteorites are common — deserts where there are few Earth rocks — places where pieces of the Moon can hide in plain sight.

And the Moon itself is in plain sight this evening. It’s in the southwest at nightfall, with the bright star Antares, the heart of the scorpion, to its lower left.

Script by Damond Benningfield

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For most of its life, a star like the Sun looks a bit drab — it’s a bright, glowing orb that doesn’t change much. At the very end, though, the star puts on a spectacular show. It expels its outer layers of gas into space, forming a colorful bubble that can be sculpted into many different shapes. The bubble can last for thousands of years before it dissipates and fades from sight.

One of the best-known examples stands high in the southeast as darkness falls, in Vulpecula, the fox.

The bubble is known by several names. The most evocative is the Dumbbell Nebula; seen through a telescope, it resembles a hand weight like you’d use at the gym.

The best measurements say the nebula is more than 1200 light-years away. The distance could be off by a couple of hundred light-years in either direction, though.

For most of its life, the star was like the Sun, steadily burning through the nuclear fuel in its core. Now, though, it can no longer sustain the nuclear reactions, so it’s shut down.

In response, the star’s outer layers began streaming into space more than 10,000 years ago. The gas left the star in waves and clumps, producing shells of gas with embedded “knots” that can be heavier than Earth.

Although the core is no longer producing nuclear reactions, it continues to shine because it’s extremely hot. Its energy causes the escaping outer layers to glow, setting the Dumbbell ablaze with color — a brilliant final act for a star.

Script by Damond Benningfield

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A fox carries a goose high across the sky this evening. You need dark skies to pick them out, and a vivid imagination to “see” them.

The constellation Vulpecula stands high in the southeast at nightfall. It’s near the middle of the Summer Triangle, which is defined by the stars Vega, Deneb, and Altair.

Johannes Hevelius created the constellation more than three centuries ago. His original name for it was Vulpecula cum Anser — fox with goose. He showed it as a fox holding a goose in its jaws.

Perhaps the fox later ate the goose, or perhaps the goose escaped and flew away. Whatever the reason, the name was shortened to just Vulpecula — the fox. The goose is still remembered, though, in the name of the constellation’s brightest star — Anser. It’s not much to look at. In fact, you need dark skies to see the star at all.

The star itself is actually pretty impressive. It’s a red giant — a dying star that’s puffed up like a giant balloon. But its distance of 300 light-years dulls its luster.

One of Vulpecula’s claims to fame is the first pulsar. When it was discovered more than a half-century ago, there was a brief hope that it might be a signal from another civilization. But follow-up work showed that it was the crushed, rapidly spinning core of a dead star — an impressive discovery in its own right.

Another dying star has created another impressive object in Vulpecula: the Dumbbell Nebula. We’ll have more about that tomorrow.

Script by Damond Benningfield

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The planet known as TrES-2b sounds like it should glow like wild. It’s only about three million miles from its parent star — much closer than Mercury is to the Sun. And its night side may sizzle at almost 3,000 degrees. Yet the planet appears to be the darkest yet seen — darker than charcoal.

TrES-2b is named for the project that discovered it — the Trans-Atlantic Exoplanet Survey. The planet orbits a star that’s a near twin to the Sun — it’s the same size, mass, and temperature. It’s about 750 light-years away.

TrES-2b is a giant ball of gas. It’s bigger and heavier than Jupiter, the giant of our own solar system. And it’s “locked” so that the same hemisphere of the planet always faces the star, just as the same side of the Moon always faces Earth. Powerful winds may carry some of the daytime heat to the nightside.

TrES-2b appears to reflect no more than one percent of the light from its star. By comparison, the Moon, which is quite dark, reflects about 10 percent of the sunlight that hits it.

The planet may be so dark because the heat prevents bright clouds from forming in its atmosphere. Or dark, heavy compounds in the atmosphere may absorb light — leaving TrES-2b in the dark.

The TrES-2 system is high overhead at nightfall, at the edge of Draco, the dragon. The star is too faint to see without a telescope. But it’s near one of the wingtips of Cygnus, the swan, which soars high across the sky in early evening.

Script by Damond Benningfield

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When it comes to making planets, star systems may not waste much time. A recent study says that planets may form in less than a million years — the blink of an eye in the lifetime of a star.

Planets form when bits of debris around a newborn star stick together. Chunks of ice and rock can merge to form bodies the size of Earth or bigger. Bodies that are far away from the star can then sweep up huge amounts of leftover gas and dust. That makes giant planets, such as Jupiter and Saturn in our own solar system.

Observations of star systems that are as young as one million years, though, have shown a dearth of the dust grains needed to make Jupiter-sized planets. That could mean that such systems won’t give birth to giant planets — or that they already have.

In a recent study, astronomers used arrays of radio telescopes in New Mexico and Chile to study especially young star systems in Perseus. The systems are no more than a half-million years old — mere infants. The astronomers found that the systems contain plenty of dust for making planets. That suggests that giant planets can form in a million years or less — the blink of an eye.

Perseus is climbing into the evening sky this month. Tonight, it’s in good view, in the northeast, by about 10:30. It rises a few minutes earlier each night, providing plenty of time to enjoy one of the highlights of the autumn sky.

Tomorrow: a “hot coal” of an exoplanet.

Script by Damond Benningfield

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