StarDate

Finding your way to the other bodies of the solar system is a tough chore. They’re a long way away, they’re fairly small targets, and they’re in constant motion. So it helps to have some navigational beacons to guide you.

One of those beacons is the Sun – the brightest object in the sky. And for many spacecraft, another is Canopus, the second-brightest star in the night sky.

It’s a long way from the Sun in the sky, so tracking both objects allows a craft to triangulate its position. That provides a precise fix on its location in space.

Canopus would make a good navigational beacon for any civilization within a thousand light-years of it. That’s because it’s extremely bright – more than 10 thousand times brighter than the Sun. So even though it’s more than 300 light-years away, it outshines all the other stars except Sirius, which is less than nine light-years away.

Canopus shines so brightly because of its size and its temperature. It’s about 70 times the Sun’s diameter, and its surface is thousands of degrees hotter. The combination makes Canopus one of the most impressive stars in our part of the galaxy.

And Canopus also is a good beacon for skywatchers in the far south of the United States – south of about Little Rock. Right now, it stands just above the southern horizon about an hour and a half after sunset. It’s almost directly below Sirius, which is much higher – the brightest stars in the night sky.

Script by Damond Benningfield

Sirius, the brightest star in the night sky, arcs across the southwest on March nights. It’s low in the south at nightfall and wheels westward later on. Not only is it especially bright, it’s also especially twinkly – it shifts from blue to red to white in the blink of an eye.

Sirius is visible from most of Earth’s surface – all but the high Arctic. But the second-brightest star has a more limited range. Canopus is a stunner from the southern hemisphere, but it’s tough to see from the United States. You have to be south of about San Diego or Dallas to find it. And even then, it never climbs more than a few degrees above the horizon.

Canopus itself is much more impressive than Sirius. It’s far larger and more massive, and thousands of times brighter. But it’s also 300 light-years farther, so it can’t quite match Sirius’s luster.

Canopus is at the end of its prime phase of life, so it’s quite puffy. If it took the Sun’s place in our own solar system, it would extend all the way out to Mercury. But no one is quite sure whether it’s getting even bigger, or if it’s starting to “deflate” after going through a puffier phase. Either way, Canopus will continue to shine brightly in Earth’s night sky – even if not everyone can see it.

If you’re far enough south, look for Canopus just above the southern horizon as night falls. The star is due south about 8 p.m., almost directly below Sirius.

Script by Damond Benningfield

Our three closest celestial neighbors highlight the early evening sky tonight – the Moon and the planets Venus and Mercury. Venus is the brilliant “evening star.” Fainter Mercury stands well below the Moon. It looks like a bright star, but it’s so low in the sky that it’s easy to miss.

The Moon is the closest neighbor. It orbits Earth once every four weeks, at an average distance of less than a quarter of a million miles.

Venus and Mercury are our closest planetary neighbors. Mercury is the nearest planet to the Sun, Venus is second, and Earth is third. So Venus passes closer to Earth than any other planet – as little as 24 million miles away. Combined with its size and its unbroken cloud cover, that makes Venus the brightest object in the night sky other than the Moon.

Mercury passes as little as 50 million miles from Earth. Mars can actually come closer than that. But on average, Mercury is much closer than Mars. In fact, the average distance to Mercury and Venus is the same – about 93 million miles.

If you know the layout of the solar system, that number may sound familiar – it’s the average distance from Earth to the Sun. But it’s also the average distance to any object that stays inside Earth’s orbit.

Mercury is climbing away from the Sun as seen from Earth now, while Venus is dropping toward the Sun. They’ll pass each other in about 10 days, lining up side by side in the evening twilight.

Script by Damond Benningfield

The Grand Canyon is impressive – a multi-colored chasm that’s 275 miles long, up to 18 miles wide, and more than a mile deep. But compared to the largest canyon system on Mars, it’s like something a toddler dug in a sandbox. Valles Marineris extends a quarter of the way around the planet – almost 2500 miles from end to end. At its widest, it spans 120 miles – so far that you couldn’t see from one rim to the other. And it’s more than four miles deep.

Valles Marineris is named for the Mariner 9 orbiter, which discovered the canyon half a century ago. And geologists have been debating its origin ever since. They’ve wondered whether it was carved by water, ice, winds, volcanic activity, or some combination.

Today, the leading view says it began as a crack in the crust. Over millions of years, a giant volcano near the eastern end of the canyon grew larger and larger. It became so heavy that it fractured the crust. The walls of that crack then collapsed, making it wider. The wind scoured out more of the landscape. And parts of the canyon may have been eroded by water or ice – giving Mars one of the grandest canyons in the solar system.

And Mars is in grand view. It passed closest to Earth a few weeks ago, so it’s still pretty close. It looks like a bright orange star, high in the east at nightfall. Castor and Pollux, the twin stars of Gemini, line up to its left and lower left.

Script by Damond Benningfield

A stroll on Mars would be quite different from one here on Earth. It would look different, feel different, and sound different.

The surface of Mars features many of the same landforms as Earth – mountains, canyons, sand dunes, and wide-open plains. But much of the surface is coated with orange dust. A lot of it is lofted into the sky by the winds. The dust colors the sky in shades of pink and yellow.

The winds also stir up dust devils – rotating columns of dust that resemble tornadoes. They can be miles high. And dust storms can fire up across wide regions – and even cover the entire planet. The dust can be thick enough to blot out the Sun.

Clouds made of frozen water and carbon dioxide float high in the sky. Snow sometimes falls from the clouds, but most of it vaporizes before it hits the ground.

The Martian air is less than one percent as thick as Earth’s. So Mars walkers will need space suits to protect them. The suits also will protect them from the extreme cold. The average temperature on Mars is about 80 below zero Fahrenheit, and it rarely climbs above freezing. And the air is so thin that it carries little sound, so a stroll would be silent.

Mars walkers would feel a difference as well. The surface gravity on Mars is just three-eighths as strong as Earth’s. So a person who weighs 150 pounds on Earth would tip the scales at just 57 pounds on Mars – making for a bouncy stroll across the Red Planet.

Script by Damond Benningfield

Vomitoxin is as nasty as the name suggests. It’s produced by fungus that grows in damp conditions on corn, wheat, and other grains. It can cause an upset stomach for anything that eats it – animal or human. But it helped geologists work out the history of a meteorite from Mars, which was born in its own wet conditions.

The Lafayette meteorite was discovered more than a century ago. No one kept a record of the date, but it probably was found in 1919. A student at Purdue University in Indiana was fishing when he saw a rock splash into the mud. He fished it out and gave it to the university. Scientists thought it was an Earth rock, so they tossed it in a drawer.

Someone pulled it out in 1931, and realized it was a space rock. Decades later, it was identified as a bit of Mars. It had been blasted into space 11 million years ago.

To confirm its history on Earth, scientists studied the contaminants it picked up here. They found high levels of vomitoxin. Indiana had suffered an outbreak of the fungus that causes it in 1919 – likely confirming the story of the meteorite’s fall to Earth.

Recently, scientists studied the minerals in the rock. They found that it was born in wet conditions 742 million years ago. That suggests there was liquid water on Mars fairly recently – evidence preserved in a rock that splashed to Earth.

Mars is high in the east at nightfall, and looks like a bright orange star.

Script by Damond Benningfield

Water covers more than 70 percent of the surface of Earth. It’s the only world in the solar system with liquid water on its surface. But that hasn’t always been the case. Water once filled rivers and lakes on Mars. And it might have filled an ocean that covered a third of the planet.

If the ocean existed, it filled a large basin in the northern hemisphere. Today, the elevation of that region is thousands of feet lower than average – a good “bowl” for holding water.

Parts of the bottom of the bowl are covered with sediments that are hundreds of feet thick. They could have been deposited by winds or some other mechanism, but water is considered the most likely culprit. Some of the landforms there resemble underwater canyons seen on Earth. And there are features that look like a shoreline.

A Chinese rover recently added to the discussion. Scientists reported that it found evidence of a shoreline, plus other contours that could have been part of an ocean. Their analysis showed that the ocean could have formed almost 3.7 billion years ago. It continued filling up for about 200 million years. After that, the water froze, etching a shoreline. The ice then evaporated or seeped into the ground. Some of it might still be there, below a thick layer of dust.

Despite the new evidence, the idea of an ocean isn’t settled. Scientists may need an even closer look to confirm that an ocean once covered much of the surface of Mars.

Script by Damond Benningfield

Most of the little moons of Jupiter and Saturn are oddballs. Their orbits are stretched out and tilted at odd angles. And some of them orbit in the opposite direction from the planets’ major moons. A study last year proposed that Jupiter and Saturn captured those moons thanks to a passing star.

Researchers used computers to study the orbits of many objects in the Kuiper Belt – a broad region beyond the realm of the planets. Many of their orbits are odd as well.

The work showed that all of those orbits could be explained by a close approach by a star billions of years ago. The star would have been a little less massive than the Sun. And it would have passed about 10 billion miles from the Sun – a bit more than a hundred times the distance from Earth to the Sun.

That would have taken the star near the edge of the Kuiper Belt. The star’s gravity would have stirred up the millions of objects in that region – chunks of ice and rock that can be quite large. In fact, the largest member of the belt is Pluto.

Many objects were kicked out of the solar system. But others would have been kicked toward the Sun. Some of them might have been captured by the giant outer planets – especially Jupiter and Saturn – giving both worlds big entourages of odd moons.

Jupiter itself is high in the sky at nightfall. It looks like a brilliant star. Binoculars reveal its large moons – but the odd little ones remain hidden.

Script by Damond Benningfield

A young star cluster trots along with the Dog Star, Sirius – the brightest star in the night sky. They’re in the south-southeast at nightfall, and due south by about 9 p.m. The cluster stands directly below Sirius at that hour. Under dark skies, it’s just visible to the eye alone as a small, hazy patch of light.

Messier 41 is about 2300 light-years away. And it’s about 25 light-years across. That volume is packed with hundreds of stars – as many as eight hundred, according to some estimates. By comparison, the same volume of space around the Sun contains only a few dozen stars.

That means the skies of any planets in the cluster would be packed with bright stars – especially in the middle of the cluster, where the stars are jammed together. Some of the stars there are bigger and brighter than the Sun. Some of them are still in the prime of life, but a few are already near the end. They’ve puffed up to giant proportions, so they shine hundreds of times brighter than the Sun.

The Sun probably was born in a similar type of cluster. But the Sun and its sibling stars have all gone their own ways – pulled away from each other by the gravity of the galaxy’s other stars and gas clouds.

The Sun has been around for four and a half billion years. But the stars of M41 are only about 200 million years old. So there hasn’t been enough time for the galaxy to rip apart this family of young stars.

Script by Damond Benningfield

When a sea turtle hatches, it heads toward the light. Under natural conditions, that means the ocean. But if the beach is near a bright city, it might head inland, where it can be nabbed by a predator, hit by a car, or die of exhaustion.

Baby turtles aren’t the only sea creatures affected by artificial light. Among its many impacts, the light can throw off the reproductive cycles of corals and others, make it harder for fish to hide from predators, and endanger beds of kelp by providing extra light for the urchins that feed on them.

Much of the life in the oceans depends on the light of the Moon and stars – even at depths of hundreds of feet. But the glow of coastal cities, oil rigs, and passing ships can throw things out of whack.

Corals, for example, time their spawning by the phases of the Moon. But artificial lights disrupt the timing, endangering coral reefs. Microscopic organisms move up and down in the water as the light changes to find food or avoid predators. But that cycle is disrupted by artificial lights as well.

Depending on how clear the water is, the light can penetrate anywhere from a few feet to more than a hundred feet. And bluer light, which is produced by modern LEDs, goes deeper than redder light.

Some coastal cities limit outdoor lightning, or build barricades to shield the beaches and the water close to shore – making life a little safer for baby sea turtles and other marine creatures.

Script by Damond Benningfield