StarDate

So far, the only way to get around on Mars has been on wheels. NASA has dropped four rovers onto the Red Planet, and each of them has maneuvered on six wheels. But wheels probably won’t always be the only way to move across Mars. In fact, the next Mars rover is scheduled to carry a small sidekick: a four-pound helicopter.

Flying on Mars won’t be easy. Atmospheric pressure is less than one percent of the pressure on Earth. That means there’s less “air” to support an aircraft. That hasn’t stopped people from trying, though. Various groups have proposed craft with wings — both gliders and powered craft. So far, though, none of those concepts has gone anywhere.

The helicopter, though, seems ready for flight. The tiny craft will have two rotors, stacked on top of each other. One will spin clockwise, and the other counter-clockwise. That will lift the chopper and keep it stable. The softball-sized fuselage will contain power and radio systems, and a pair of cameras.

Plans call for the helicopter to reach altitudes of more than a thousand feet, and roam up to a couple of thousand feet from the rover. Launch for the rover and its flying companion is scheduled for 2020.

And the next couple of nights are great times to view their target — the planet Mars. It looks like a bright orange star low in the southeast at nightfall. It’s close to the lower left of the Moon tonight, and a similar distance to the lower right of the Moon tomorrow night.

Script by Damond Benningfield

A test bed that’s designed to help the effort to find hidden nuclear reactors could also help reveal the hidden workings of exploding stars.

Watchman is designed to lead to bigger instruments that could detect reactors thousands of miles away. The plan calls for it to be built in a mine on the coast of England. The mine is about 15 miles from a pair of nuclear reactors. They produce huge numbers of particles called antineutrinos. These particles zip through solid matter as easily as they zip through space.

Watchman will consist of a large tank of water mixed with a special element. The tank will be lined with light detectors. Rare interactions between antineutrinos and atoms in the tank will produce double flashes of light.

But some of those flashes may be triggered by sources other than the reactors. Some types of exploding stars, for example, also produce antineutrinos.

When a heavy star reaches the end of its life, its core collapses and its outer layers blast into space as a supernova. The process creates huge numbers of antineutrinos. Watchman should be able to detect the particles from supernovae within our own galaxy, the Milky Way. That would reveal new details about how stars explode.

Since antineutrinos are the antimatter counterparts of neutrinos, Watchman might also help reveal why the universe contains so much more normal matter than antimatter — a possible cosmic discovery from a down-to-earth experiment.

Script by Damond Benningfield

The Moon bowls past Saturn the next couple of nights. The planet looks like a bright star. It’s close to the lower left of the Moon tonight, and to the right of the Moon tomorrow night.

Saturn has a huge entourage of moons of its own. More than 50 have been plotted and named, and several others are awaiting final status — more than 60 in all.

The largest is Titan, a world with a dense, cold atmosphere and lakes filled with hydrocarbons. Titan contains more than 95 percent of the mass of Saturn’s entire system of moons and rings.

Most of the planet’s moons are nothing more than big boulders — chunks of rock no more than a couple of dozen miles across. These moons follow all kinds of orbits. Some of the orbits are quite lopsided, while others are tilted at different angles. Some orbits are even backwards — the moons move in the opposite direction from Saturn’s rotation.

These little moons appear to come in groups. The members of each group have something in common — some aspect of their orbits or composition. That suggests that the members of each group share a common origin. They may be remnants of a larger moon that was blasted apart by an impact, for example.

Such impacts need not be especially powerful. A recent study found that even low-speed collisions could split a moon apart or chip off big pieces. That could result in the odd shapes and sizes of many of the moons as well — giving Saturn a large and interesting collection of moons.

Script by Damond Benningfield

Most of the action in the evening sky right now is in the south. The four brightest lights in the entire night sky are there — the Moon and the planets Venus, Jupiter, and Mars. So are the planet Saturn, and the bright stars Antares and Spica. As the Moon slides past them, it creates a beautiful new configuration every night.

But if you turn around, there’s plenty to see in the northern precincts of the sky as well.

The most obvious example is the Big Dipper — the brightest stars of Ursa Major, the great bear. August nights are especially good for viewing the dipper. That’s because it looks like it’s just about to dip into a well for a cool drink. It’s in the northwest at nightfall, with the handle to the upper left and the bowl to the lower right.

At the same time, another easy-to-see star pattern is low in the northeast: Cassiopeia the queen. Its stars form a distinctive letter W. It rotates high across the north later on.

And between the W and the dipper, look for perhaps the most famous individual star in all the night sky: the North Star, Polaris. It’s about the same brightness as the leading lights of the dipper. Because there are no other bright stars around it, though, it looks a bit weak and forlorn.

To find Polaris, line up the stars at the outer edge of the dipper’s bowl. Then follow that line to the upper right until you come to the first moderately bright star: the North Star — the hub of the night sky.

Script by Damond Benningfield

Antares, the heart of the scorpion, is the 11th brightest star that’s visible from most of the United States. But if we could line up those stars at the same distance, Antares would zoom way up the list.

How bright a star looks depends on two things. First is its true brightness — how much light it beams out into space. And Antares is quite high in that category. It’s hundreds of times the diameter of the Sun, so it’s quite bright — it radiates about 10,000 times more visible light than the Sun does.

The other factor is distance. Among those 11 brightest stars, the distance ranges from about nine light-years up to about 850. There’s a good bit of uncertainty among the farthest stars, but even so, we know they’re a long way off. Antares, for example, probably is about 550 to 600 light-years away. That makes it appear fainter than many of the other stars on the list.

When astronomers compare true brightness, they use a number called absolute magnitude. It’s how bright the star would look at a distance of 10 parsecs — about 33 light-years. On that scale, the brightest of those 11 stars would shine more than 10,000 times brighter than the faintest. And Antares would rank third, looking more than 300 times brighter than it is now — even brighter than Venus, the brilliant “evening star.”

Look for bright orange Antares to the lower left of the Moon as darkness falls tonight, and to the lower right of the Moon tomorrow night.

Script by Damond Benningfield

It’s been a year since American skies were darkened by a total solar eclipse. Astronomers are still studying their observations of it. And it might take a while before they know if they saw anything new.

That wasn’t the case for an eclipse that took place 150 years ago tomorrow. One astronomer quickly realized that he’d discovered something unexpected: a new element in the Sun’s atmosphere. But it did take a while for most other astronomers to accept it.

Pierre Janssen was a professor at the University of Paris. He traveled to India to observe the eclipse of August 18th, 1868.

Only a few years earlier, another physicist had found that you could identify the elements in the atmosphere of the Sun and other stars by breaking their light into its individual wavelengths. For the Sun, astronomers thought the only way to make it work was to look at filaments of gas around the Sun during an eclipse.

When Janssen looked at those filaments, he detected the “fingerprint” of an unknown element. Later, a British scientist found the same element when he looked at the un-eclipsed Sun. They submitted their papers on the same day, so they share credit for the discovery.

That element later was named helium, after the Greek name for the Sun. It wasn’t found on Earth until many years later. Yet it’s the second-most-abundant element in the universe, so it makes up a large fraction of the Sun — the first element discovered beyond our own planet.

Script by Damond Benningfield

One of the big moons of Jupiter may be an ideal place to cool off on a hot summer afternoon — it appears to be shooting a spray of cold water out into space. That provides more confirmation that an ocean lies below the moon’s icy crust — a possible home for life.

Europa is a bit bigger than our own moon. But the two worlds are nothing alike. The surface of Europa consists of ice. It’s divided into large plates and rafts. That arrangement resembles the ice that floats atop the oceans here on Earth. That suggests that the ice on Europa also floats atop an ocean. If so, it could have all the ingredients for life.

What’s more, Hubble Space Telescope has seen evidence of water squirting into space from Europa, possibly spraying through cracks in the crust.

And earlier this year, a team reported more evidence of water plumes. The scientists recently looked through 20-year-old observations by the Galileo spacecraft, which orbited Jupiter. And they found some unusual readings: a blip in the magnetic field, and some odd radio waves. Those readings came as Galileo flew through one of the possible plumes reported by Hubble. And they matched models of what the craft should see if it flew through a spray of water.

Combined with the other evidence, they strongly suggest that Europa has a vast ocean hidden beneath its icy crust.

And Jupiter appears near our moon tonight. The planet looks like a brilliant star to the lower left of the Moon.

Script by Damond Benningfield

To the eye alone, Spica is one of the 15 brightest stars in the night sky. It’s about 2,000 times brighter than the Sun, and it looks white with a hint of blue.

When you look at Spica with special instruments, though, it’s even more impressive. It consists of two stars, not one. Both are much bigger and heavier than the Sun. And when you add up all wavelengths of light, they shine about 20,000 times brighter than the Sun.

Most of that energy is in the ultraviolet — wavelengths that are much too short for the human eye. Spica’s two stars produce so much of it because their surfaces are tens of thousands of degrees hotter than the Sun.

In fact, the type of energy a star emits depends almost entirely on its surface temperature. And so does the star’s color. To the eye alone, the hottest stars look blue. But they emit huge amounts of ultraviolet. The coolest stars look orange or red. They emit huge amounts of infrared light — wavelengths that are too long for the human eye.

Stars in the middle of the temperature scale shine white or yellow. They emit most of their light at visible wavelengths. So with a star like the Sun, we see most of the energy it produces — light that’s at just the right wavelengths for the human eye.

And Spica is in good view this evening, below the Moon. They’re flanked by two bright planets. Jupiter, the giant of the solar system, is to the upper left, with Venus, the “evening star,” to the lower right.

Script by Damond Benningfield

Until Nicolaus Copernicus demonstrated otherwise, most people thought Earth was the center of the universe. And that wasn’t an unreasonable idea. The Sun, Moon, and stars all appear to circle around us, so it looks like we’re right in the middle of things.

The only problem was the planets. Some of them periodically reverse direction across the sky. And Venus and Mercury don’t go all the way across the sky. They climb part of the way into the morning sky, then double back into the evening sky. That’s hard to explain if everything is circling around Earth.

The explanation, of course, is that they don’t circle around Earth — and neither does anything else except the Moon. The planets all orbit the Sun. Some of them are outside Earth’s orbit, so they swing all the way across the sky. But Mercury and Venus lie inside Earth’s orbit, so they have a limited motion across the sky.

And in fact, Venus is at the limit of that motion over the next few nights. It’s farthest from the Sun for its current “evening star” appearance — about 45 degrees. By the end of the week, it’ll start sliding toward the Sun.

Because of the angle at which Venus sets at this time of year, though, it doesn’t look very far from the Sun. It’s quite low in the west as night falls; tonight, it’s below the crescent Moon. The planet doesn’t drop straight down toward the horizon. Instead, it slides along the horizon as it descends — a world that orbits the Sun, not Earth.

Script by Damond Benningfield

The Moon slides past a trio of bright lights the next few evenings: two planets and a star. The planets are especially bright, so you won’t have any trouble picking them out, even from a light-polluted city.

The first of the Moon’s companions is also the brightest. It’s Venus, the brilliant “evening star.” It’s off to the left of the Moon tonight, and will be even closer below the Moon tomorrow night.

As it leaves Venus behind, the Moon will cozy up to the star Spica, which is well to the upper left of Venus. It’s not nearly as bright as the two planets. Even so, it’s one of the brighter stars in the night sky. And its proximity to the planets, and to the Moon, will make it pretty easy to pick out.

Companion number three will be the planet Jupiter, to the upper left of Spica.

Jupiter usually is the third-brightest object in the night sky, after the Moon and Venus. Right now, though, it has slipped to fourth position. In part, that’s because Jupiter itself is near the bottom of its range in brightness. But it’s also because Mars is shining especially bright right now, so it’s temporarily moved ahead of Jupiter. In fact, you can see Mars low in the southeast, looking like an orange star. But the king of the planets will reclaim its usual spot in a few weeks.

So keep your eye on the southwestern quadrant of the sky the next few evenings, as the Moon passes by Venus, Spica, and Jupiter.

More about the Moon and Venus tomorrow.

Script by Damond Benningfield