StarDate

If you ever want to ponder the vastness of the universe, try this:

Look up into a dark, starry night sky, then hold out your hand at arm’s length in front of your face. Now look at the fingernail on your little finger. That tiny area is covering up millions of galaxies — and perhaps tens of millions. Yet every galaxy is enormous. It spans thousands to millions of light-years, and contains millions to trillions of stars.

The number of galaxies you’re covering up is uncertain because the number of galaxies in the universe is uncertain. There are just so many, and many of them are so faint, that we can’t count them all. Instead, astronomers estimate the total.

More than a decade ago, Hubble Space Telescope spent weeks looking at a tiny patch of sky. Based on the number of galaxies in that patch, astronomers estimated the total number at about 200 billion.

Later, though, another team said there should be 10 times more galaxies — about two trillion in all. But last year, one more study, based on observations by another spacecraft, put the number back in the hundreds of billions. Keep in mind that we’re seeing the most-distant galaxies as they looked when the universe was much younger. By today, they may have merged with other galaxies or disappeared in some other way.

Whatever the number, though, there are lots of galaxies in the universe — so many that you can block out millions of them with the tip of your little finger.
 

Script by Damond Benningfield

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Early risers have gotten all the best of the skywatching over the last few months. Several bright planets have been congregating before and during dawn, with the Moon periodically checking in on them. And it does so again for the next couple of days. The action gives us two pairs of bright solar-system worlds: the Moon and Venus, and Jupiter and Mars.

Jupiter and Mars rise first. They’re in view by a couple of hours before sunrise, low in the east. Jupiter is the brighter of the two planets. In fact, it’s the third-brightest object in the night sky — only the Moon and Venus outshine it.

Mars will stand to the right of Jupiter tomorrow. It’s only a fraction as bright as Jupiter, although still one of the brighter points of light in the night sky. And it shows a distinctively orange glow, compared to more of a cream color for Jupiter.

Tomorrow, Mars and Jupiter will be separated by a couple of degrees — the width of your finger held at arm’s length. But the planets will scoot closer together over the following few mornings. They’ll be at their closest on Sunday, when they’ll appear to almost touch each other. After that, they’ll slowly move apart.

The Moon and Venus rise a little later, and there’s a bigger gap between them. Even so, they’ll make a spectacular duo. And they’ll be a little closer together on Friday morning, with Venus to the upper right of the crescent Moon — a brilliant pairing in the dawn sky.
 

Script by Damond Benningfield

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Space flight is hard on the human body. Astronauts lose muscle mass and bone density. They’re exposed to radiation that increases the risk of cancer and other problems. And that’s just the beginning. Long flights aboard the International Space Station have led to changes in the eyes, blood, and brain.

Most astronauts who’ve spent at least six months in orbit have reported vision problems. The eye can change shape, and connections between the eye and the optic nerve can be frayed. Researchers aren’t sure what causes the problems. It could be simply the lack of gravity, but other factors could be at work as well.

Astronauts also suffer a loss of red blood cells. A recent study found that the body is actually destroying the cells. And it continues to do so as long as the person is in space. Cell production improves after landing, but levels remain low even a year later. Again, there’s no confirmed explanation.

Another study found that weightlessness also “rewires” parts of the brain. A dozen space travelers were scanned before and shortly after their trips, and again a few months later. The scans revealed changes to the connections between parts of the brain that control motor functions. And the changes persisted after the return to Earth. Researchers say the brain was adapting to weightlessness, where moving is quite different than it is on Earth.

So a long trip to space is no vacation for the human body.

Script by Damond Benningfield

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One of the oddest features on the Moon is a 40-mile-long tadpole. It’s much lighter than the surrounding landscape. And it has its own magnetic field, which is stronger than the Moon’s overall field.

Reiner Gamma is in the Ocean of Storms — a giant basin paved with volcanic rock. Reiner Gamma is one of the most famous features on the entire Moon — and one of the least understood. Scientists don’t know just what it is, how it formed, or how its magnetic field is generated. It could be the impact site of a comet, although that’s one of several possible explanations.

Scientists may be able to explain Reiner Gamma before too long, though. NASA’s planning to send a mission there in the next two or three years. Known as Lunar Vertex, it’ll consist of a lander and a rover.

The lander will map the area with cameras, and measure details about the magnetic field. The rover will trundle at least a third of a mile away — well outside any contamination from the lander’s rocket engine. It, too, will study the magnetic field. It’ll also study the composition of the bright material that outlines the “tadpole” of Reiner Gamma.

Look for the Moon before dawn tomorrow. The bright planets Jupiter and Mars are to its left, with Jupiter by far the brighter of the two. The Ocean of Storms is a large dark area at the top of the lunar crescent — home to one of the strangest features on the Moon.
 

Script by Damond Benningfield

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Hercules is in his prime at this time of year. The strongman is well up in the eastern sky at nightfall, and stands high overhead in the wee hours of the morning. And as seems only proper, Hercules is a giant — only four constellations are bigger. It spans about 50 degrees both north to south and east to west — five times the width of your fist held at arm’s length.

Yet Hercules is also the faintest of the big constellations. Its brightest stars are only third magnitude. They’re easy to pick out under dark skies, but not so easy from a light-polluted city. And its fainter stars are completely blotted out by the glow from streetlamps, parking lots, billboards, and other artificial light sources.

The constellation’s official outline is invisible, too — its official borders. They form a polygon made of 28 individual segments.

Astronomers began developing those borders 100 years ago this month. There were many constellations, but their arrangement was a little sloppy. Some constellations overlapped others, while some parts of the sky had no constellation at all. So the International Astronomical Union brought some order to the chaos. It got rid of quite a few constellations, and drew official borders for the 88 that remained. That created a night sky that’s like the patches on a quilt, with each patch connected to others. And it gave every star a constellation of its own — through a process that began a century ago.
 

Script by Damond Benningfield

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To the eye alone, the colors of one of the moons of Saturn are subtle. One hemisphere of Tethys is almost pure white — the result of a steady “snow” of ice grains from one of Saturn’s rings. The other hemisphere is tinted light yellow by radiation trapped in Saturn’s magnetic field. And the zone between the two faces is pale blue.

If you crank up the intensity of the colors, though, some odd features pop out: long, thin arcs that are bright red. They’re no more than a few miles wide, but up to about 150 miles long.

Tethys is Saturn’s fifth-largest moon. It’s about 660 miles wide. It’s made almost entirely of frozen water, with just a dab of rock mixed in. Its most prominent feature is a giant crater. The impact that created it almost blasted the moon to bits.

The red arcs were discovered in images from the Cassini spacecraft, which revealed three sets of them. They’re in the northern half of the hemisphere that always faces away from Saturn. Some of them slice across the big crater, suggesting that it had nothing to do with their formation.

Scientists aren’t sure just why the arcs are red. One idea is that they’re cracks in the crust that allow minerals inside Tethys to bubble to the surface. But the mystery of the red arcs remains unsolved.

Saturn tags along with the Moon, which is almost at last quarter, early tomorrow. They rise about 3 a.m. Saturn looks like a bright star, directly above the Moon at first light.
 

Script by Damond Benningfield

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At least 150 globular clusters inhabit the Milky Way Galaxy. They’re giant balls of stars, and most of them are at least 10 billion years old — the Milky Way’s oldest members. Yet no two are alike. There’s a wide range in size, mass, and how tightly their stars are packed together.

One cluster is about 10,000 times the mass of the Sun, and spans more than 150 light-years, so its stars are widely spaced. Another cluster is about two million times the Sun’s mass, but is only a few light-years across. That makes it one of the most tightly packed of all the globulars.

That cluster is known as Terzan 5. It’s 19,000 light-years away, on the outskirts of the Milky Way’s core.

One of its distinctions is that it contains many pulsars — the ultra-dense cores of once-mighty stars that exploded. A pulsar spins rapidly. One of those in the cluster, in fact, is the fastest in the galaxy — more than 700 revolutions per second.

The large number of pulsars may be a result of the cluster’s density. Because stars are so close together, collisions may be common. That causes more supernova explosions, which create pulsars — among the most interesting residents of this giant “city” of stars.

Terzan 5 is in Sagittarius. It climbs into good view, in the southeast, after midnight, and is low in the south-southwest at first light. Its stars form the outline of a teapot. Terzan 5 is above the spout — in the “steam” of the Milky Way.
 

Script by Damond Benningfield

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A star cluster on the outskirts of the galaxy is falling apart. Its stars are being pulled away, forming a ribbon tens of thousands of light-years long. And one of the causes may be a clump of black holes at the cluster’s heart.

Palomar 5 is a globular cluster — a giant ball of stars. It’s one of the Milky Way’s least impressive globulars. It’s about 10,000 times the mass of the Sun — much lighter than almost any other cluster. And its stars are much more thinly spread.

A study last year placed the blame on a clump of black holes.

Researchers simulated possible interactions within Palomar 5 until they got a match with what we see. They found that Palomar 5 might have started out like most globulars. Many of its big, massive stars quickly exploded, leaving only their dead cores: black holes. Today, there could be a hundred black holes that are roughly 20 times the mass of the Sun.

The black holes kicked other stars out of the cluster’s heart, pushing the black holes closer together. That allowed the gravity of the rest of the galaxy to strip away many stars from the cluster’s fringes. Today, they form a long trail through the galaxy’s outskirts.

A billion years from now, all the stars may have been stripped away, leaving only the black holes. After that, they, too, will go their own ways.

Palomar 5 is in Serpens, which is in the southeast at nightfall. It takes a telescope to spot Palomar 5 — a cluster that’s falling apart.

Script by Damond Benningfield

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The star cluster Messier 5 is big, old, and crowded. It contains hundreds of thousands of stars, all packed into a ball that’s about 165 light-years across. By comparison, a similar volume of space in our region of the galaxy would hold only a few thousand stars.

The cluster is ancient — it formed as early as 13 billion years ago — less than one billion years after the birth of the universe. That makes it one of the oldest components of the Milky Way.

But the stars of Messier 5 may not all be that old.

A recent study found the stars might have been born in waves. The first wave gave birth to massive stars — many times heavier than the Sun. They burned out in a hurry, though, and exploded. Shockwaves from the explosions might have helped trigger the second wave — huge numbers of smaller stars born in the central region of the cluster. And the third wave came later still, with many more stars born outside the center.

Whenever they were born, the stars form an impressive group. Messier 5 is about 25,000 light-years away, in Serpens Caput — the head of the snake. It’s in the southeast as the sky gets fully dark. It’s too faint to see with the eye alone. But binoculars reveal a smudge of light that looks like a fuzzy star. And long-exposure images show thousands of individual stars — some of the oldest residents of the Milky Way.

We’ll talk about another cluster in Serpens tomorrow.
 

Script by Damond Benningfield

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Some of the 88 constellations are a little disjointed. They meander in odd directions, making them hard to follow. But only one is really disjointed — it’s split into two parts.

They outline Serpens, the snake. One part represents its head, while the other contains its tail. They’re separated by the serpent bearer, Ophiuchus. The head is in the eastern sky at nightfall now, while the tail climbs into good view a couple of hours later. Ophiuchus is between them, with the snake curling behind his back.

The snake’s brightest star is in its head. It’s known as Alpha Serpentis or Unukalhai — from an Arabic name that means “the serpent’s neck.” It’s visible to the unaided eye under all but the most light-polluted skies.

Alpha Serpentis is a red giant. It’s used up the original hydrogen fuel in its core, and is now burning the helium “ash” to keep it going. That transition has made the core hotter, which has caused its outer layers to puff up like a giant balloon. In fact, the star is more than a dozen times the Sun’s diameter, and it’s likely to get even bigger.

Alpha Serpentis is also brighter than the Sun — roughly 40 times brighter at visible wavelengths. But as the star expanded it got cooler, turning it orange. Such cool stars produce a lot of infrared light. So when you add up all wavelengths, Alpha Serpentis is about 70 times brighter than the Sun — the brilliant head of the serpent.

More about Serpens tomorrow.
 

Script by Damond Benningfield

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