StarDate

Mars blazes across the night sky this week. The Red Planet rises around sunset, scoots low across the south during the night, and sets around sunrise. It’s brightest for the year, too. In fact, for the next couple of months it’ll be the third-brightest object in all the night sky -- only the Moon and the planet Venus will outshine it.

Mars is staging such an amazing show because it’s at opposition -- it will line up opposite the Sun in our sky on Thursday night. It passes closest to Earth around opposition, so it’s a big, bright target.

Not all Mars oppositions are created equal, though. The planet’s maximum brightness varies by quite a bit from one opposition to the next.

That’s mainly because Mars’s orbit is quite lopsided. Its distance from the Sun varies by more than 25 million miles. When opposition occurs during summer, we pass Mars when it’s closest to the Sun. At the same time, Earth is farthest from the Sun -- about one million miles farther than average. That’s not a lot, but it helps. So at its closest, in about a week, Mars will be less than 36 million miles away -- just about as close as it’s possible for the planet to be.

Normally, Jupiter is the third-brightest object in the night sky. But right now, Mars outshines it by quite a bit. Look for it low in the southeast as night falls, and due south a few hours later -- a bright orange planet that dazzles all night long.

We’ll have more about Mars tomorrow.

Script by Damond Benningfield

Many of the features on the Moon are named after astronomers. So are features on Mars and other planets and moons. And hundreds of asteroids also are named for astronomers.

You won’t find many features named for astronomers here on Earth, though. Quite a few streets and schools are named for them, but when it comes to major features, like mountains or cities, the list is pretty thin -- especially in the United States. One of the few on the list is Mount Langley, a 14,000-foot summit in California. It’s named for Samuel Pierpont Langley, who was a long-time director of the Allegheny Observatory.

To see a lot more features named for astronomers, though, you need to head south -- to Australia, New Zealand, and even Antarctica.

In Australia, for example, a river and an estuary are named for Thomas Brisbane, an early governor of New South Wales. And so is the city of Brisbane, the capital of Queensland. In addition to his official duties, Brisbane was an astronomer. He set up Australia’s first major observatory.

In New Zealand, several of the peaks in a large mountain range are named for astronomers, including Galileo Galilei and Nicholas Copernicus. And an entire range is named for Johannes Kepler.

And in Antarctica, many features are named for early explorer James Ross. But Ross himself named several features for astronomers, including Cape Smyth and Mount Lubbock -- down-to-earth features named for men who studied the stars.

Script by Damond Benningfield

The night sky features two great crosses -- one in the northern hemisphere, and the other in the south.

The Northern Cross is another name for Cygnus, the swan, which sails high overhead on summer evenings.

It’s a noteworthy constellation for several reasons. For one thing, it hosts the bright star Deneb. This white supergiant is one of the most impressive stars in our region of the galaxy. It’s so far away that astronomers don’t know its exact distance. Yet it’s still easily visible to the eye alone, standing at the top of the cross.

And when we look at Cygnus, we’re looking down the spiral arm that contains our own solar system, so we see lots of amazing celestial objects -- bright clouds like the North American Nebula, and even black holes. In fact, Cygnus is home to the first black hole ever found, Cygnus X-1.

The southern sky also has a cross. But Crux isn’t nearly as big as Cygnus. In fact, Crux is the smallest of the 88 constellations.

No matter, though, because Crux is brilliant, boasting four prominent stars. And it also has a well-known dark feature: a cloud of light-absorbing dust known as the Coalsack Nebula, which is only a few hundred light-years away.

The Southern Cross has one fault, though: It’s so far south that most of us in the United States can’t see it. Still, the Northern Cross is quite prominent at this time of year, and it really does resemble both a cross and a swan -- a beautiful feature of the summer sky.

Script by Ken Croswell

The biggest moon in the solar system is bigger than the planet Mercury. It’s the only moon known to generate a magnetic field. And it may have the biggest ocean in the solar system -- more water than in all of Earth’s oceans combined.

Ganymede orbits the biggest planet in the solar system, Jupiter. The planet looks like a brilliant star just below our own moon this evening. Binoculars reveal Ganymede and three other Jovian moons, which look like tiny stars near the planet.

The surface of Ganymede is ancient -- about a third of it appears to be at least four billion years old. It’s dark, and covered by old craters. The rest of the surface is a bit younger and lighter, and is marked by long cliffs and grooves.

But Ganymede’s most interesting feature lies far below the surface -- a possible ocean of liquid water. It’s sandwiched between the moon’s icy crust and ice and rock below the ocean. It could be a habitat for life. But so far, we don’t know what conditions are like in the ocean, so no one is sure how good a home it would make.

Europe is preparing a spacecraft that should reveal many details about the ocean. Known as JUICE, it’s scheduled for launch in four years. It’ll study a couple of other moons before entering orbit around Ganymede. From there, it will study the structure, composition, and odd surface of Ganymede -- observations that will reveal much more about the possible giant ocean in this giant moon.

Script by Damond Benningfield

The Sun isn’t bothered by much. That’s because it orbits the center of the galaxy on its own. But most of the stars in the galaxy have at least one companion star. And the interactions between them can have a big impact.

Consider Spica, a bright star near the Moon tonight. Although it looks like a single star, it really is at least two stars. One of them is more than 11 times the mass of the Sun, while the other is about seven times the Sun’s mass. That makes Spica one of the most impressive binary systems around.

Its stars are extremely close together. They follow a stretched-out orbit that brings their surfaces to within about 10 million miles of each other.

So the stars have big impacts on each other. For one thing, their mutual gravitational pull distorts both stars. They’re shaped like eggs, with the tapered ends pointing toward each other. Also, the pull of the smaller star appears to create ripples in the larger star. And the sides of the stars that face each other are hotter than the sides that face away.

In a few million years, the larger star will explode as a supernova. That’s likely to blast away some of the gas at the surface of the companion. And it’ll probably send the smaller star zipping across the galaxy -- fired into space by a close companion.

Look for Spica to the lower right of the Moon at nightfall. The much brighter planet Jupiter is about the same distance to the lower left of the Moon.

More tomorrow.

Script by Damond Benningfield

It’s almost a cliché these days, but it’s true nonetheless: We are all made of starstuff. The calcium in our bones, the iron in our blood, and the oxygen in the air we breathe were forged by stars. These elements were expelled into space when the stars died, “seeding” the galaxy with the raw materials for new stars, planets -- and life.

We see many of these ingredients in supernova remnants -- the debris from exploded stars. Sensitive instruments detect dozens of different elements in these rapidly expanding clouds.

There are more of these elements in supernova remnants created by the collapse of massive stars. During their short lives, these stars manufacture a list of heavier elements in their cores, from carbon and oxygen to cobalt and iron. When the core is converted to iron, it can’t continue this process. The core collapses, and the star’s outer layers then blast out into space, ejecting a rich brew of elements.

And the blast itself creates even more elements. The heat and pressure of the explosion causes lighter elements to ram together, forming heavier ones -- especially elements that are more massive than iron.

Debris from such a blast races into space at up to about 10 percent of the speed of light. When the blast wave hits a cloud of cool gas and dust, it can cause the cloud to collapse to form a new star and perhaps planets -- infused with elements forged or released by the death of a heavy star.

Script by Damond Benningfield

Cassiopeia the queen sits low in the north-northeast at nightfall, then wheels high to the north at first light. Its stars form a bright letter W, so it’s one of the easiest constellations to pick out.

It would have been a lot easier to pick out in 1572. A “new” star appeared near the W -- a star so bright that it was visible in daylight.

And about a century later, another new star flared to life not far away. There are only sketchy indications that it was ever seen. But today, astronomers know all about both stars -- they were blasting themselves to bits as supernovae. Astronomers know that because they can see and study the remains of both stars -- expanding bubbles of gas and dust.

The first star is known as Tycho’s supernova. That’s because it was studied in detail by Tycho Brahe, the leading astronomer of the time. The star exploded when the small corpse of a once normal star stole gas from a companion star. When enough gas built up, the star blasted itself to smithereens. Debris from the supernova forms a colorful bubble. It spans about 35 light-years, and it’s expanding at about 10 million miles per hour.

The other star is Cassiopeia A. It formed when the core of a supergiant star collapsed. Its outer layers then blasted into space. The debris from that blast also spans many light-years, and it’s also still expanding.

These and other supernova remnants are important for several reasons, and we’ll talk about them tomorrow.

Script by Damond Benningfield

The death of a star can produce some spectacular fireworks. The star blasts all or most of itself into space, shining as brightly as millions or billions of normal stars. And it can produce “jets” of energy that are the brightest outbursts in the universe.

Those fireworks would mean instant doom for any planet in orbit around the exploding star. But even planets that are many light-years away could suffer ill effects.

Such an explosion is known as a supernova. It can happen in one of two ways. One is when a massive star can no longer produce nuclear reactions in its core. The core collapses, and its outer layers blast into space. The other is when the dead core of a Sun-like star takes too much gas from a companion star. That triggers a nuclear blast that rips the star to bits.

Radiation from a supernova could endanger life on any planet within a few dozen light-years. It would strip away the planet’s protective ozone layer. That would allow more radiation to reach the surface -- perhaps enough to cause a mass extinction.

Some exploding stars produce jets of gamma rays, the most powerful form of energy. They blast from the poles of the exploding star as narrow beams. The beams could cause the same kind of damage as a supernova’s other forms of radiation, but at a range of thousands of light-years.

Fortunately, no likely future supernovae are anywhere close to Earth. So for now, we’re safe from these cosmic fireworks.

More tomorrow.

Script by Damond Benningfield

Venus is just about the most inhospitable place you can imagine. Its surface is hot enough to melt lead, the air is toxic, and the pressure is like being more than half a mile down in Earth’s oceans. And to top it all off, the planet’s clouds are made of sulfuric acid.

For the last half-century, though, scientists have speculated that microscopic life could exist in those clouds -- about 30 miles above the surface.

Although Venus is hellish today, it once was much more comfortable. Water could have covered its surface for up to two billion years. That’s plenty of time for life to develop. And as the water vanished and the planet heated up, some of that life could have been wafted into the clouds.

Here on Earth, microbes have adapted to live just about anywhere. That includes environments that are highly acidic, like Venus’s clouds. If life can adapt to extreme environments on Earth, it’s possible it could do so on Venus, too.

Observations of the clouds have shown dark patches that come and go. A recent study speculated that they could be like red tides here on Earth -- massive blooms of microscopic organisms.

The only way to know for sure is to sample the clouds with instruments that can look for life -- something that’s not likely to happen for a long time.

For now, we can enjoy looking at Venus, the brilliant “evening star.” Tonight, Venus is close to the crescent Moon. It’s a deadly world with a beautiful appearance.

Script by Damond Benningfield

Evening twilight is a special time of day. The day’s heat begins to abate, and the sounds begin to soften. The setting Sun paints the sky in brilliant yellow, orange, and red, giving way to shades of blue. A few fireflies may flicker to life, with flashes of distant lightning perhaps adding to the show.

And this evening offers some additional performers: the Moon, two planets, and a bright star. They’re low in the west, and ease into view as the Sun drops farther below the horizon.

The Moon is a thin crescent right now -- sunlight illuminates only five percent of the lunar hemisphere that faces our way. The rest of the Moon is visible, though, thanks to earthshine -- sunlight reflected off of our own Earth. It will become more obvious as the sky grows darker.

The planet Mercury is just a couple of degrees below the Moon. It can be tough to spot in the glow of twilight, and trees or buildings along the horizon can block it from view. It drops too low to find by the time it gets good and dark, so the viewing window is brief.

The window is much longer for Venus, the brilliant “evening star,” to the upper left of the Moon. It will stay in view until around 10 or 11 o’clock, depending on your location.

And the final member of the quartet lines up between Venus and the Moon, a little closer to Venus. It’s Regulus, the star at the heart of Leo, the lion -- shining softly through the fading twilight.

More about the Moon and Venus tomorrow.

Script by Damond Benningfield