StarDate

In “The Martian,” when astronaut Mark Watney is stranded on the Red Planet, he turns to an old NASA mission for help. He travels to an ancient floodplain called Ares Vallis, where he grabs Mars Pathfinder. Later, he uses the parts to contact Earth and help arrange his rescue.

“The Martian” is fiction, but Pathfinder was real. The lander and rover touched down on Mars 25 years ago today, and operated for almost three months. It was the first landing on Mars in two decades, and the first rover on any other planet.

Pathfinder was designed mainly to test out new technologies for landing and operating on Mars. The craft bounced to a halt inside a cocoon of airbags, for example.

Yet Pathfinder also carried scientific instruments, on both the lander and the rover, which was named Sojourner. The rover weighed about 25 pounds and was the size of a microwave oven. In all, it traveled roughly the length of a football field.

It measured the composition of the rocks and soil, and found that liquid water had once flowed across the surface. And it demonstrated that a rover could be guided along the Martian surface, setting the stage for more-capable machines in the future.

The lander monitored the weather and snapped more than 16,000 pictures. They revealed clouds of water ice in the early morning, and dust devils twirling across the desert landscape later in the day — a quarter of a century ago.
 

Script by Damond Benningfield

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It probably doesn’t sound right on a hot summer day, but Earth is actually farthest from the Sun for the entire year about now — more than 94 million miles.

Earth’s orbit around the Sun is a bit lopsided. The average distance to the Sun is about 93 million miles. But during the year, the distance varies by about three percent in either direction.

That slight variation is known as the “eccentricity” of the orbit. The orbits of all the planets are eccentric, but by different amounts. Venus’s orbit is the least eccentric — less than one percent. Mercury’s is the most eccentric — about 20 percent.

In fact, it’s almost impossible for one body to have a perfectly circular orbit around another. Earth and the other planets of the solar system, for example, are pushed and pulled by the gravity of all the other planets. And collisions with other bodies have also skewed their orbits.

As Earth’s distance from the Sun changes, so does the amount of energy we receive from the Sun. At our closest, in January, we get about six percent more total energy than we’re getting right now.

Surprisingly, though, there’s little impact on Earth’s climate. The atmosphere and oceans store the heat and distribute it around the planet. That’s why we can have really hot days during summer here in the northern hemisphere, even though the Sun is three million miles farther than during the dead of winter.
 

Script by Damond Benningfield

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A bit of danger looms above the crescent Moon this evening: a sickle. It’s a curved pattern of stars that forms the head, mane, and heart of Leo, the lion. The handle is Regulus, the lion’s heart, to the left of the Moon. And Leo’s next-brightest star is near the middle of the sickle — looming above the Moon.

Algieba is a binary — two stars locked in orbit around each other. The system is about 130 light-years away. By astronomical standards, that’s nothing more than a hop. And the two stars are separated by about four times the distance between the Sun and Pluto.

Even so, the system still isn’t all that well understood. Astronomers know that both stars are into their final phase of life. They’ve used up the original hydrogen fuel in their cores, which has caused them to swell up. So both stars are a good bit bigger and brighter than the Sun.

Estimates for one star say it’s about 30 times wider than the Sun, although it could be even bigger. The size of the other star is even less well known — astronomers can only make a rough guess.

We do know that the better-known star has a planet. It’s about nine times the mass of Jupiter, the giant of our own solar system. It’s just a little bit farther out than Earth is from the Sun. There’s evidence of a second planet much farther out. But so far, that’s unconfirmed — one more thing to learn about a bright star system in the sickle.
 

Script by Damond Benningfield

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In the tradition of the Maori people of New Zealand, a new year is just beginning. That’s because Matariki is climbing into view in the dawn sky. It’s a time to start afresh, to celebrate those who passed on in the previous year, and to harvest the sweet potatoes and other crops.

In the western world, Matariki is known as the Pleiades. It’s a star cluster that looks like a tiny dipper. It marks the shoulder of Taurus, the bull.

Its first appearance in the dawn sky has been a key moment for many cultures. In parts of Central and South America, that first glimpse has been used to forecast the weather and its impact on the crops.

It served the same role for the Maori . If the stars in the cluster looked sharp and clear, then a good harvest was considered likely. If they were fuzzy, though, it was a sign of a bad harvest.

The timing of the ceremonies varied from tribe to tribe. Most common, though, was to start at the Moon’s last-quarter phase after Matariki’s first appearance, and continue until new Moon. That put the new year’s festival in late June or early July. Beginning this year, the celebration is a national holiday in New Zealand. It was celebrated on June 24th.

From here in the U.S., the Pleiades is low in the eastern sky at dawn. It’s above Venus, the brilliant “morning star.” It’ll stand a little higher each day as the bull continues its annual journey across the night sky.
 

Script by Damond Benningfield

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Planet Earth doesn’t keep very good time. On average, it makes one complete turn on its axis relative to the Sun every 86,400 seconds. But that rate can vary by a fraction of a second. And that’s one reason the world timekeeping organization occasionally adds a “leap second” to the clock. The first one was tacked on 50 years ago today.

There are many reasons that the Earth clock doesn’t always tick at the same rate. The sloshing of the tides slows things down, although very slowly. The rotation of the core and sloshing motions in molten rock below the crust are among the other causes. So are earthquakes and big storms, which can cause a change of perhaps a few thousandths of a second per day. They can either speed things up or slow them down. But since scientists have been tracking it, the net has been a slowdown.

There’s also a slight difference in how clocks based on Earth’s rotation and atomic clocks tick off the seconds — a difference that adds up.

So to try to keep everything synchronized, scientists introduced leap seconds. When needed, they’re usually added at the end of June or December. There have been 27 so far.

But for some areas of science, business, and other fields, that extra second has been a problem. So there are proposals to do away with it. That would allow timekeeping systems based on different clocks to drift apart — ticking off their own good time.
 

Script by Damond Benningfield

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A pair of tiny rainbow-like splashes of color sometimes flanks the rising or setting Sun like dogs attending their master. Perhaps that’s why these displays are known as sun dogs.

Regardless of the name, sun dogs faithfully maintain the same distance from the Sun: roughly 22 degrees — twice the width of your fist held at arm’s length. They’re sometimes accompanied by fainter halos that completely encircle the Sun.

Both sun dogs and halos are created by flat ice crystals with six sides. They’re found in thin clouds that pass between the Sun and the viewer. The crystals act as tiny prisms, bending the sunlight. Different colors are bent at different angles, so red appears on the inside, closest to the Sun, and blue on the outside, farthest from the Sun.

The ice crystals that form a halo line up in random directions. As a result, a halo usually is faint and white, with little or no color.

The crystals that form a sun dog, on the other hand, flutter through the clouds like leaves falling from a tree. That makes most of them line up parallel to the horizon. That provides more prisms to bend and split the light, producing brighter and more colorful displays.

Larger crystals wobble more as they descend. That spreads their light across a wider area, producing a larger splotch of color “dogging” the Sun.
 

Script by Damond Benningfield

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One of the biggest volcanic eruptions in the solar system yet seen was at its hottest 25 years ago today. The peak temperature reached almost 3,000 degrees Fahrenheit — far hotter than any eruption ever seen on Earth.

Pillan Patera is on Io, a moon of Jupiter. Io is about the same size as our own moon. But while the Moon is pretty much dead, Io is the most active body in the solar system, with hundreds of active volcanoes. They’re powered by a gravitational tug-of-war between Jupiter and some of its other moons, which melts the rock below Io’s surface. The molten rock forces its way out through giant volcanoes.

Pillan Patera is one of Io’s bigger volcanoes — 45 miles wide. And from about May to September of 1997, it staged a massive eruption. The plume of ash climbed about 90 miles high. As the ash fell back, it covered an area as big as Iowa.

Pillan Patera also belched hot lava — enough every minute to fill the Empire State Building. The lava eventually covered an area twice the size of Rhode Island, creating a huge dark spot.

The volcano hasn’t done much since then. In fact, the lava field has just about disappeared — paved over by other volcanoes on this active moon.

Jupiter is high in the southeast at dawn, and looks like a bright star. Binoculars reveal its four largest moons, which look like tiny stars near the planet. The quartet includes Io — a small world with a volcanic attitude.
 

Script by Damond Benningfield

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Heber Curtis didn’t set out to become an astronomer. In fact, he wasn’t interested in astronomy at all. At the University of Michigan, he studied classical languages. And he taught Greek and Latin at both high school and college levels. Yet Curtis eventually became one of the leading astronomers of his time. And he took part in one of the most famous events in astronomy history: the Great Debate.

Heber Curtis, 1918

There, he took part in several expeditions to view solar eclipses. And for five years, he led the observatory’s station in Chile. Mostly, though, he studied “nebulae” — objects other than stars or planets.

At the time, their nature was poorly understood. Some astronomers thought that all of them were motes of matter inside our own galaxy. That meant the Milky Way made up the entire universe. On the other hand, Curtis and others thought that some of the nebulae were separate galaxies of stars outside the Milky Way.

In 1920, Curtis and Harlow Shapley debated the subject in Washington, D.C. Most observers thought Shapley won. In the end, though, Curtis was proven right — greatly expanding the universe.

Curtis directed several observatories during the remainder of his career. He died in 1942 — an astronomer who knew his Latin.
 

Script by Damond Benningfield

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A star that shows us what the Sun will look like billions of years from now arcs high across the sky at this time of year. The star has passed the end of its “normal” lifetime and is well toward its final act.

Anser is the brightest star of Vulpecula, the fox. The star’s name means “the goose.” It comes from the constellation’s original name, the fox and goose.

The star is a red giant. That means it’s old and bloated, and  looks dull orange. It’s used up the original hydrogen in its core, converting it to helium. Now, it’s fusing the hydrogen in a thin layer around the core.

In response to that, the star’s outer layers have puffed up. The star is more than 40 times wider than the Sun, and more than 400 times brighter.

But Anser’s mass is almost exactly the same as the Sun’s. Since the way a star ages is determined mainly by its mass, that means Anser should have aged at about the same rate as the Sun will. The best estimates say that Anser is more than 11 billion years old, versus four and a half billion for the Sun. So when we look at Anser, we’re seeing what the Sun will look like in six or seven billion years: an old, bloated star at the end of its life.

Anser is in the east as night falls. Despite its size and brightness, it’s so far away that it looks quite faint. In fact, you need pretty dark skies to see it — streetlamps or other bright lights will wash it out, leaving the goose hidden in the glare.
 

Script by Damond Benningfield

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Sometime in the next decade or two, a balloon could soar through the clouds of Venus, searching for evidence of life. Or a skimmer that looks like a manta ray might zoom along with the planet’s high-altitude winds, circling Venus in just a few days.

Both ideas received funding earlier this year to help develop the concepts. There’s no guarantee that either will ever fly — only that they’ll get a look.

The balloon would spend several days bobbing between altitudes of about 30 and 40 miles. It would sample the atmosphere below the clouds, and gather as much as a gram of material inside the clouds. Research in recent years has suggested that microscopic organisms could live there, even though the clouds are made of sulfuric acid. The sample container would rocket to a rendezvous with an orbiter for the trip to Earth.

The manta-ray concept is known as BREEZE. It, too, would be an inflatable craft. It would stay at about the same altitudes as the balloon. But it would alter its shape to ride along with the high-level winds. Its instruments would measure the composition of the atmosphere, the planet’s weak magnetic field, and details about the winds. And it would use radar to map the surface — from high above the surface of Venus.

Look for Venus at dawn tomorrow. It’s the brilliant “morning star,” close to the right of the crescent Moon. The fainter planet Mercury is to the lower left, just above the horizon.
 

Script by Damond Benningfield

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