StarDate

Some of our nearest neighbors are a bit shy. Even though they’re practically on our doorstep, they’re so faint that you can’t see them without a telescope. That includes the second-closest star system of all, Barnard’s Star. It’s low in the east as night falls. Without a telescope and a star chart, though, you’d never know it’s there.

Indeed, just finding the closest stars is a lot harder than you might think.

If every star were equally powerful, the closest stars would look the brightest, and they’d be the easiest to spot. But that’s not the case. There’s a huge range in stellar brightness. And most stars are quite faint — just a fraction as bright as the Sun.

That’s certainly true for the star discovered by Edward Emerson Barnard in June of 1916. He was comparing photographic plates of the constellation Ophiuchus taken at different times when he noticed a faint star. It stood out because its position had changed from one plate to another — a sign that it was close by. It’s like driving down a highway — nearby road signs whiz by in a hurry, while the distant hills seem to hardly move.

It turns out that Barnard’s Star is just six light-years away. Only the three stars of Alpha Centauri are closer. But it’s extremely faint. In fact, the Sun emits more light in just one hour than Barnard’s Star will produce in the next three months — a testimony to Barnard’s skill in fishing this elusive neighbor out of the vast celestial sea.

Script by Ken Croswell, Copyright 2016

Two constellations that are entwined in both mythology and the sky climb into good view in the east and southeast this month. And they’re especially easy to find right now because a pair of bright planets is close by.

Ophiuchus, the serpent bearer, is one of the larger of the 88 constellations. Its brightest stars form a pattern that looks a bit like the outline of an old coffee pot. And it’s flanked by the two halves of Serpens, the serpent. Its head rises above the serpent bearer, with its tail below.

In mythology, Ophiuchus was associated with Asclepius, the son of the god Apollo. He became a great healer, in part because of an encounter with a snake. One day, he saw one snake resurrect another by laying some herbs atop it. Asclepius began using those herbs, and he not only healed the sick, but he managed to raise the dead as well.

That was bad for the business of Hades, the god of the underworld. He complained to Zeus, the king of the gods. Zeus killed Asclepius with a lightning bolt. But according to one version of the story, that set off a tiff between Zeus and Apollo. To end it, Zeus placed Asclepius in the stars — as the serpent bearer.

To find the serpent bearer and the serpent, look toward the southeast as night falls for two bright planets: Saturn, quite low in the sky, and orange Mars to its upper right. Ophiuchus and Serpens spread out to the left of these bright worlds.

We’ll have more about Ophiuchus tomorrow.

Script by Damond Benningfield

Starlight sprinkles down on Earth like raindrops in a spring shower. And like the raindrops, the sprinkles of starlight can appear to change direction.

This effect is known as aberration of starlight. It was discovered three centuries ago by an astronomer who was trying to measure the distance to Eltanin, the brightest star of Draco, the dragon.

James Bradley was looking for the star’s parallax. The idea is to observe a star when Earth is at opposite ends of its orbit. That causes stars that are close to us to shift position relative to stars that are farther away. Measuring the size of that shift reveals the star’s distance.

Bradley did see a shift in Eltanin’s position, but it wasn’t related to the star’s distance. Instead, it was caused by Earth’s orbital speed. It’s like watching raindrops fall from inside a car. If you’re sitting at a red light, the raindrops appear to fall straight down. But if you’re cruising down the highway, they appear to come toward you at an angle. The raindrops aren’t moving any differently, but you are.

The same thing happens with starlight. Thanks to Earth’s motion around the Sun, the “drops” of light appear to come in from different angles at different times of year. That causes a star to appear to shift position — the result of the aberration of starlight.

Look for Eltanin about halfway up the northeastern sky at nightfall. It’s a moderately bright orange star, to the upper left of brilliant Vega.

Script by Damond Benningfield

Saturn’s beautiful rings are constantly changing. Some of their bits of ice and rock spiral into Saturn’s atmosphere. Others change orbit as they’re kicked around by Saturn’s moons. And new particles join the rings when the moons get hit, blasting material out into space.

These changes make little difference to the overall appearance of the rings. But big changes may happen as well. Moons may be pulverized, creating new rings. Or ring material may coalesce to form new moons.

In fact, the entire ring system may have formed as recently as a hundred million years ago.

Just when the rings formed has been the topic of a lively debate. Most astronomers say the rings formed with Saturn itself. Others say they came along much more recently.

That includes a team that released a study earlier this year. Researchers mapped the orbits of many of Saturn’s icy moons, and projected those orbits back in time. Their simulations showed that several of the moons probably formed about a hundred million years ago. That suggests that Saturn had a different collection of moons in the past. A couple of those moons may have slammed together — destroying the moons, but giving Saturn its beautiful rings.

And Saturn is at its beautiful best right now. The planet rises at sunset, remains in view all night, and shines at its brightest. Look for it low in the southeast at nightfall, shining like a bright golden star. It’s to the lower left of even brighter Mars.

Script by Damond Benningfield

As NASA prepared to send astronauts to the Moon, it wasn’t sure whether the lunar surface could actually support them. Most planetary scientists said there wouldn’t be a problem. But a few worried that the surface might be covered with powdery dust — a layer deep enough to swallow a lander.

That concern was laid to rest 50 years ago today, when Surveyor 1 landed in a volcanic plain known as the Ocean of Storms.

The Surveyor project was designed to pave the way for Apollo. Among other things, mission planners wanted to know how smooth the surface might be, how many boulders they could expect, and how well the surface reflected the radar waves that would help guide a lunar module to touchdown.

Surveyor 1’s radar system worked perfectly, guiding the craft to a gentle landing — the first soft landing on the Moon. An hour later, its TV camera snapped its first pictures. They showed that Surveyor’s footpads had barely dented the surface.

Over the next couple of weeks, Surveyor transmitted more than 10,000 pictures to Earth. They showed small rocks and boulders around the landing site, and the rims of some nearby craters — a surface that shouldn’t be a problem for a manned lander.

After the long lunar night, Surveyor transmitted even more pictures. It also measured temperatures and took other measurements. The mission helped provide a better understanding of conditions on the lunar surface — paving the way for Apollo.

Script by Damond Benningfield

When it comes to understanding a star, it’s all a matter of perspective. The angle at which you view the star makes a big difference in what you know about it.

Consider Vega, one of the brightest stars in the northern sky. It’s low in the northeast at nightfall, and climbs high overhead later on.

For a long time, astronomers thought the star was about three times as massive as the Sun, and perhaps no more than a hundred million years old. So when they discovered a cloud of dust grains around Vega, they thought it might be the raw material for planets.

But a decade ago, they found that they were seeing Vega from a completely different angle than thought. It turns out that we’re looking almost directly down on one of the star’s poles. That perspective makes it more difficult to measure Vega’s details.

Once they knew the correct angle, astronomers determined that the star rotates so fast that it’s almost ripping itself apart. They also found that it’s a bit smaller than thought, but a good bit older.

Yet even today, there’s uncertainty about its age. A study a few years ago placed the age at about 455 million years. But another study just a few years later gave the age as 700 million years. Either way, that means the dust around Vega can’t be the material for a newly forming planetary system. Instead, it’s probably debris from collisions between asteroids or other bodies that have already taken shape — perhaps including fully grown planets.

Script by Damond Benningfield

The planet Saturn is best known for its beautiful rings — wispy bands of rock and ice that are unlike anything else in the solar system. Yet the planet’s wispy clouds are just as beautiful as the rings, and in some ways a lot more interesting.

Through its equator, Saturn is more than nine times Earth’s diameter. Yet it takes less than 11 hours for Saturn to spin on its axis. That stretches the clouds that top its atmosphere into globe-circling bands. They’re colored in subtle shades of yellow, tan, and white by water vapor, ammonia, sulfur, and other compounds.

At the poles, the clouds form hurricane-like vortexes that are big enough to swallow Earth. The one at the north pole forms a hexagon.

Giant storms also form at lower latitudes. Many of them are as big as continents. Unlike the storms on Earth, which are powered by the Sun, those on Saturn get their energy from inside the planet itself. Heat radiates outward, stirring the upper atmosphere.

And sometimes, that heat stirs up storms that can wrap around the entire planet. These storms are brilliant white, so they stand out against the golden hues of much of the rest of this giant planet.

Saturn is putting on its best showing of the year right now. It rises at sunset and remains in view all night. It’s at its brightest for the year, too. Look for it low in the southeast as darkness falls, shining like a bright golden star. It’s well to the lower left of the even brighter planet Mars.

Script by Damond Benningfield

Just a couple of weeks after Mars was at its dazzling best, another planet is ready to stage its brightest showing of the year.

Saturn, the second-largest planet in the solar system, will reach opposition on Friday night, standing opposite the Sun in the sky. That means it’ll rise at sunset and remain in the sky all night. It’ll also be closest to Earth shortly after opposition, so it’ll shine brightest for the year.

You don’t have to wait for Friday to see the planet, though. Look for it low in the southeast after darkness falls the next few nights, shining like a bright golden star. It’s well to the lower left of much brighter Mars, which is still putting on quite a show. The two arc low across the south during the night.

In all the night sky right now, only the Moon, Mars, Jupiter, and a couple of stars clearly outshine Saturn.

On the brightness scale that’s been in use for centuries, it’s peaking at magnitude zero. On this scale, the brighter the object, the lower its magnitude. Mars is shining at about minus two, which is about six times brighter than magnitude zero. On the other hand, the faintest objects visible to the unaided eye are at roughly magnitude six — about 250 times fainter than Saturn is right now.

The giant planet soon will begin a gradual fade. When it disappears in the Sun’s glare around Thanksgiving, it’ll be only about half as bright as it appears this week.

We’ll have more about Saturn tomorrow.

Script by Damond Benningfield

Hydrogen is the most abundant element in the universe — it accounts for more than 90 percent of all the normal matter. It also accounts for more than 90 percent of the matter that makes up the Sun and most other stars.

Here on Earth, though, it’s seldom found in its pure form. Instead, it’s combined with other elements to make water and other compounds. As a result, it wasn’t “discovered” until 250 years ago.

All that hydrogen was forged in the Big Bang. As the universe expanded and cooled, energy was converted to matter — the first subatomic particles. These then merged to form protons — the nuclei of hydrogen atoms. Some of those nuclei linked up to form helium, so the early universe consisted almost entirely of hydrogen and helium.

Over time, clouds of these gases collapsed to form stars. Nuclear reactions in the hearts of the stars forged more elements. And stellar explosions forged even more. So stars that formed later, such as the Sun, incorporated a smidgen of these newly formed elements.

Even so, their main ingredients are still hydrogen and helium. The Sun “burns” almost 700 million tons of hydrogen every second. These nuclear reactions produce helium, plus the energy that makes the Sun shine.

That process has been going on for four and a half billion years. Yet despite its prodigious rate of consumption, the Sun contains so much hydrogen that it won’t run out anytime soon. It’ll continue to shine for billions of years more.

Script by Damond Benningfield

Henry Cavendish was one of the wealthiest men in England, which gave him plenty of time to purse his passion: science. But he also was antisocial; he often waited until after meetings of the Royal Society were under way to enter the room so he could slip in unnoticed.

Despite that shyness, though, his first published paper was read to the Society 250 years ago tomorrow. It reported the details of “inflammable air” — a gas that’s lightweight but highly combustible. It marked the discovery of a new chemical element: hydrogen.

It’s the most abundant element in the universe, and the third-most abundant at Earth’s surface. Yet it hadn’t been “discovered” as a separate chemical element because it almost never appears in its pure form on Earth. Instead, it’s bound to other elements to make water, hydrocarbons, and other substances.

Other scientists had seen hydrogen before Cavendish did. But they didn’t conduct the experiments needed to understand its nature.

Cavendish dropped bits of iron, tin, and zinc into vats of acid. Chemical reactions produced a gas, which Cavendish collected. He then weighed the gas, tested its flammability, and conducted other measurements. Those experiments showed that the gas was a separate chemical element.

Later experiments showed that “burning” the element produced water. So another scientist named the new element “hydrogen” — a word that means “water forming.”

We’ll have more about hydrogen tomorrow.

Script by Damond Benningfield