StarDate

The mild nights of spring are generally a good time for skywatching. Only one thing is missing: a great meteor shower. The really good showers are clustered in fall and winter, with the Perseids of August sometimes joining the list.

Although the season doesn’t offer a great shower, a pretty good one should reach its peak tomorrow night: the Lyrids. Under a dark sky, you might see a dozen or more meteors per hour between midnight and dawn. The number of meteors increases closer to dawn, as your part of Earth turns more directly into the meteor stream. And the Moon is new, so it’s not around to spoil the show.

One good thing about meteors, though, is that you don’t have to wait for a shower to see them.

A shower occurs when Earth passes through a stream of small bits of rock shed by a comet or asteroid, which happens a few times a year.

But other bits of rocky debris are scattered throughout the solar system. So on any dark night, you can see several meteors racing across the sky. And while the meteors in a shower all appear to “rain” into the sky from a common point in space, these “random” meteors can come from any direction.

So if you have a chance, look for the Lyrid meteor shower over the next few nights, and especially in the wee hours of Wednesday morning. If not, then take advantage of just about any clear, dark night to look for meteors flashing across the heavens.

We’ll talk about another meteor shower tomorrow.

Script by Damond Benningfield

On any dark night, if you can get away from city lights, you might see a dozen or more meteors blazing across the sky. These streaks of light form when space rocks vaporize as they ram into Earth’s atmosphere at high speed.

Scientists keep a close eye on meteors every night. They’ve set up networks of cameras that track them across the sky. That tells them about the origin of the meteors, and helps them track down bits of rock that fall to Earth as meteorites.

There’s a network in Australia, and several in Europe, for example. And there are several in the United States as well. CAMS, for example, is operated by the SETI Institute. It has 80 cameras just in California, and coordinates with other networks around the world.

Tracking a meteor’s path with different cameras allows scientists to plot its orbit around the Sun. That tells them where the meteor came from. It’s also allowed them to discover many new meteor showers.

A NASA network is designed to help engineers understand the risks that space rocks pose to spacecraft.

And the networks allow scientists to track down possible meteorites. Most of the rocks that hit Earth burn up in the atmosphere or fall into the oceans. But a few hit the ground. Tracking them down gives scientists a more complete picture of them – their origin, their composition, and much more.

The cameras are seeing a lot of action right now, because a meteor shower is under way. More about that tomorrow.

Script by Damond Benningfield

Not every rock on Earth is from Earth. Some of them came from asteroids, the Moon, and even Mars. In all, about 60,000 of these space rocks have been confirmed.

Meteorites have survived the fiery plunge through Earth’s atmosphere to reach the ground. Some of them had orbited the Sun on their own since the birth of the solar system. Others were blasted off the surfaces of other bodies. More than 200, in fact, came from Mars, and almost 400 from the Moon.

Meteorites fit into several broad categories. The most common are known as chondrites. They contain small pebbles of molten rock cemented together with other materials. The spheres probably formed in the early solar system, in the asteroid belt.

A second category is achondrites. They consist mainly of once-molten rock. They probably are chips off the crusts of asteroids or other layered bodies.

Another category is iron meteorites. They consist almost entirely of metals – mainly iron, with a large fraction of nickel. And the final category is a mixture of rock and metal, called stony irons.

It’s hard to tell a meteorite from an Earth rock just by looking. Some have a dark crust – a result of their fiery journey through the atmosphere. Others are magnetic. But it generally takes an expert to identify them.

Scientists study these rocks to learn about the birth and evolution of the solar system. And they’re especially keen to find meteorites that have just fallen to Earth. More about that tomorrow.

Script by Damond Benningfield

An asteroid slammed into Earth almost 800,000 years ago. It left behind many souvenirs of the collision — black blobs of glass. But the spot where it hit has remained hidden — scientists haven’t found an impact crater. A recent study, though, says that could be because the crater is buried under volcanic rock.

The impact melted millions of tons of rock and dirt and blasted them high into the sky. As this debris fell back to Earth, some of it cooled to form blobs of glass known as tektites. And the glass from this collision has been found all over the place — across Southeast Asia and Australia, in southern Africa, and even in Antarctica. In fact, the glass may be scattered across a tenth of Earth’s surface or more — the largest tektite field on the planet.

A lot of research has zeroed in on Southeast Asia as the site of the impact — especially Laos and Cambodia. That includes the recent study. It places the impact in southern Laos.

Researchers say several bits of evidence support that idea. The chemistry of the tektites suggests the impact took place in a volcanic region, for example. Rocks near the site were smashed by a close impact. And the region’s gravitational field reveals a possible crater below the rocks. It measures about 10 miles across.

If that’s correct, then the asteroid slammed into a region that was already paved with volcanic rock. Fresh eruptions after the impact covered up the crater — hiding a cosmic scar.

Script by Damond Benningfield

The oldest bits of material on Earth weren’t born here. Instead, they were born around dying stars — hundreds of millions of years before the formation of the Sun, Earth, and the rest of the solar system.

The objects are solid grains a few millionths of an inch across. They formed from material expelled from dying stars. They blew through the galaxy until they reached the cloud of gas and dust that was giving birth to the solar system. They combined with other materials in that cloud to form a space rock.

That rock — or a part of it — fell to Earth in 1969. It plunged through the atmosphere, then shattered when it hit the ground, in Australia. More than 200 pounds of debris were recovered.

Scientists at the Field Museum in Chicago recently studied some of that debris. They used acid to dissolve the stuff that formed inside the solar system, leaving the grains from beyond it. They measured different forms of certain elements inside the grains. The ratio of those elements — especially neon — told them how long the grains had been in space. And that gave them a rough age for the grains.

More than half of the grains were older than the solar system — some by a billion years or more. And the oldest one could pre-date the solar system by three billion years.

Astronomers can learn about the conditions in which our solar system was born from these ancient relics — the oldest solid particles on Earth.

More about rocks from space tomorrow.

Script by Damond Benningfield

One of the goals of the missions to Mars is to find signs of life. Some of the best signs to date are periodic “burps” of methane – a compound that can be produced by living organisms. But the burps aren’t common – and they’re hard to see.

In June, for example, the Curiosity rover detected the heaviest concentration of methane yet seen – more than 20 parts per billion. That’s dozens of times higher than the average level. But two spacecraft in Mars orbit passed above Curiosity within hours – and didn’t “sniff” a thing.

Here on Earth, most of the methane in the atmosphere is produced by life – from bacteria to people. So methane on Mars could be produced by life as well. But it also could be produced by chemical reactions in the rocks, or by volcanoes.

Several methane outbursts have been seen over the years – by orbiters, telescopes on Earth, and especially by Curiosity.

Some of the rover’s detections have also been seen by Mars orbiters. But the one in June wasn’t. That might be because Curiosity was looking at night, the orbiters during the day. Sunlight destroys methane, so it might have disappeared by the time the orbiters rolled into view.

Scientists are trying to pinpoint where the methane is coming from. That should help them figure out whether it’s produced by life on the Red Planet.

Mars teams up with the Moon at first light tomorrow. It looks like an orange star above the Moon. Saturn and Jupiter line up to their upper right.

Script by Damond Benningfield

The Moon is rolling past a trio of bright planets in the early morning sky this week. Tomorrow, Saturn will stand above the Moon. Brilliant Jupiter is to the upper right, with orange Mars to the lower left.

Such a lineup is possible because the Moon and planets are all close to the ecliptic – the Sun’s path across the sky. The alignment isn’t quite perfect, though. The orbit of each body is tilted a bit with respect to the ecliptic, so each of them can appear a little above or below that path.

Right now, Jupiter and Saturn sit almost directly atop the ecliptic. Mars is a degree or so south of it, with the Moon a couple of degrees farther.

The Moon sometimes passes directly between Earth and one of the planets. In fact, it passed in front of Mars just a couple of months ago, blocking the planet from view. Because of the different angles of the orbits, though, such “coverups” don’t happen every time the Moon passes by a planet. Most of the time there’s just a close encounter, as there is with Saturn tomorrow.

The Moon sometimes covers the Sun as well, creating an eclipse. And that’s where the word “ecliptic” comes from. Eclipses can happen only when the Moon is crossing the Sun’s path. If the Moon covers the Sun, it’s a solar eclipse. And if the Moon passes through Earth’s shadow, it’s a lunar eclipse — all made possible by passages across the ecliptic.

We’ll have more about this early morning lineup tomorrow.

Script by Damond Benningfield

APOLLO 13: Okay, Houston, we’ve had a problem here. CAPCOM: This is Houston, say again, please. 13: Houston, we’ve had a problem.

Perhaps no line in the history of the space program is better known than that one. Fifty years ago today, while more than halfway to the Moon, the crew of Apollo 13 — Jim Lovell, Fred Haise, and Jack Swigert — was in big trouble.

LOVELL: It looks to me, looking out the hatch, that we are venting something. We are venting something out into space.

An oxygen tank had exploded, damaging other systems and shutting down the mothership’s fuel cells. Without them it had no power — and no way to keep the crew alive. Flight director Gene Kranz prepped his team in Mission Control for the challenge:

KRANZ: Okay, now, let’s everybody keep cool. We got the LM still attached, the LM spacecraft’s good, so if we need to get back home we’ve got a LM to do a good portion of it with. So let’s solve the problem, but let’s not make it any worse by guessing.

Within an hour of the explosion, the astronauts were prepping their lunar lander, Aquarius, to serve as a lifeboat. They fired its main engine to put them on a path that would take them behind the Moon, then straight back to Earth. Over the following three and a half days, they relied on its power and engines to keep them alive and on course. And they relied on hundreds of engineers and technicians on the ground to solve problems and work out procedures.

The astronauts were cold, thirsty, and miserable for much of the journey, but they made it home — surviving a famous problem in space.

Script by Damond Benningfield

NGC 6946 is the galactic equivalent of the Fourth of July – the source of a whole lot of fireworks. Over the last century or so, it’s produced more supernovas than any other galaxy. And surveys have revealed almost 200 possible supernova remnants – the remains of stars that exploded in the last few thousand years. So NGC 6946 is also known as the Fireworks Galaxy.

The galaxy is a beautiful spiral, like our home galaxy, the Milky Way. But it’s probably less than half the Milky Way’s diameter, with only a fraction as many stars. Yet it’s giving birth to many more stars than the Milky Way is.

Many of those stars are hot and massive. They burn out quickly, then explode as a supernova, shining brighter than billions of “normal” stars.

Supernovas are rare, though. On average, the Milky Way creates about one per century. And none has been seen here in four centuries. NGC 6946, on the other hand, has produced 10 of them since 1917.

And one other star in the galaxy should have exploded but didn’t. It was the type of star that ends its life as a supernova. Over the last decade it brightened a bit, then vanished. Only a small blob of infrared light remains. The star could have collapsed to form a black hole. The infrared light could come from material falling into it – more fireworks from the Fireworks Galaxy.

NGC 6946 is in the northeast before dawn, to the left of Deneb, the bright star at the tail of the swan.

Script by Damond Benningfield

The Moon is the biggest single object in the night sky that’s visible to the eye alone. But many objects that are too faint to see are much bigger. An example is a nebula in the constellation Vela. It spans about 16 times the width of the Moon – almost the size of your fist held at arm’s length. And it’s getting bigger all the time.

The Vela Supernova Remnant is 800 light-years away. It was born about 11,000 years ago as seen from Earth, when a supergiant star exploded, blasting its outer layers into space.

As those layers ram into surrounding clouds of gas and dust, they glow. If you look across the entire spectrum – from radio waves to X-rays – the nebula looks like a mound of billowing clouds.

When the star exploded, the outer layers were expelled at up to a few percent of the speed of light. So over the millennia, the nebula has inflated to a diameter of more than a hundred light-years. And it’s still expanding – at more than two million miles per hour.

That rate is one way in which astronomers determine when the star exploded. Another is the star’s dead core, called a neutron star. It spins rapidly, emitting pulses of energy with each turn. Measuring how quickly it’s slowing down gives a rough estimate of when the neutron star formed – telling us when a massive star died.

The Vela Supernova Remnant is in Vela, the sails, which hugs the southern horizon at nightfall. The nebula is big but faint, so you need a good telescope to see it.

Script by Damond Benningfield