A partial solar eclipse will dim the skies over the northeastern United States early tomorrow – weather permitting, of course. Other parts of the world will have a slightly better view, including much of Europe and Asia.

A solar eclipse happens when the new Moon passes directly between Earth and the Sun. During a partial eclipse, the alignment isn’t perfect, so the Moon covers only part of the Sun’s disk.

This eclipse begins in the wee hours of the morning in the northeastern states. At the peak of the eclipse, the Moon will cover about 90 percent of the solar disk. That’s enough to make the sky appear a little dusky, and to lower the temperature a bit.

From the United States, the eclipse will be underway as the Sun rises. The best view will be from Maine.

As we all know from recent eclipses, it’s not safe to look directly at the Sun even when it’s partially covered up – it’s still so bright that it can damage your eyes. So use eye protection to stay safe – special eclipse glasses or dark welder’s glass. You can also stand beside a tree and watch as it casts tiny images of the partially eclipsed Sun on the ground. And you can always find an eclipse broadcast online.

For the rest of the United States, the eclipse will be over by the time the Sun rises. And the contiguous 48 states won’t see another good total eclipse – when the Moon completely covers the Sun – until August of 2045.

Script by Damond Benningfield

Those are the sounds of cosmic attacks – massive storms on the Sun firing energy and particles into Earth’s magnetic field. Such outbursts can damage orbiting satellites, cause radio blackouts, foul GPS signals, and even knock out power grids on the surface. And there are indications that we haven’t seen the worst the Sun can produce.

The outbursts are generated by magnetic storms on the Sun. Lines of magnetic force get tangled up, then snap, creating a solar flare. Such an outburst also can produce a massive eruption of charged particles. When those outbursts reach Earth, they cause problems.

The most powerful outburst yet seen was the first one ever seen, in 1859. It knocked out telegraph networks and created brilliant displays of the northern and southern lights. Tree rings and ice cores provide evidence of even stronger outbursts in centuries past.

And a recent study found that Sun-like stars produce outbursts that are a hundred to a thousand times more powerful than anything we’ve seen from the Sun. The researchers looked at observations made by Kepler space telescope more than a decade ago. They studied more than 50,000 stars that are similar to the Sun. And they found almost 3,000 superflares. That’s an average of one superflare per star every century – suggesting that we haven’t seen the worst from our sometimes-cranky star.

Script by Damond Benningfield

The star cluster Messier 3 is a beautiful sight – a sparkly ball of half a million stars. But the view from the cluster would be even more spectacular. M3 is high above the plane of the Milky Way, so the galaxy would spread out below it like a brilliant pinwheel.

M3 is a globular cluster – a dense ball a few hundred light-years in diameter. Its stars are among the oldest in the entire galaxy. They formed just a couple of billion years after the Big Bang. All of the cluster’s heavy stars have long since died, so almost all that’s left are stars that are less massive than the Sun.

Such stars are fairly faint. But there are so many of them that the cluster is an easy target for binoculars, even though it’s about 34,000 light-years away.

Most of the stars and clusters in the galaxy lie in a wide, thin disk. But globular clusters range far above and below that disk. Right now, M3 is about 30,000 light-years above the disk. So most of the galaxy would spread out below it. If there are inhabited planets in the cluster, its residents would have some spectacular views – hundreds of thousands of stars close by, and a giant galaxy of stars arrayed below them.

M3 is in Canes Venatici, the hunting dogs. The cluster is low in the east-northeast in early evening, and is a beautiful sight through binoculars or a telescope.

Tomorrow: super-flares.

Script by Damond Benningfield

The universe is put together like Swiss cheese – some regions are the cheese; others are the holes. The “cheese” consists of clusters and superclusters of galaxies. The “holes” are just that – cosmic voids. The largest voids span more than a billion light-years.

Cosmic voids were discovered half a century ago. Astronomers were looking deep enough into the universe to map its structure on the largest scale. They’d expected the universe to look the same in all directions – a smooth blend of galaxies. Instead, they found a web – overlapping filaments of galaxies, with big spaces between.

The voids might be there because there were tiny differences in the density of matter in the early universe – especially dark matter. The gravity in the denser regions pulled material together to make stars and galaxies. That left the less-dense regions almost empty. They contain a few galaxies, some gas and dust, and some dark matter, but not much else.

More than 6,000 voids have been cataloged. They clump together to make supervoids. One of the closest is the Boštes Void – “the Great Nothing.” It’s centered about 700 million light-years away, and it spans more than 300 million light-years – a giant “hole” in the universe.

Boštes climbs into view in early evening. Look for the bright yellow-orange star Arcturus, which is low in the east by 9 or 10 o’clock. The Great Nothing stretches to the upper left of Arcturus.

Script by Damond Benningfield

Our home galaxy, the Milky Way, belongs to a small cluster of galaxies – the Local Group. It has fewer than a hundred known members. But most galaxies reside in much more impressive clusters. And the closest of these is centered in the constellation Virgo, which steps up the eastern sky this evening.

The Virgo Cluster contains roughly 2,000 galaxies. They move through space together, bound by their mutual gravitational pull.

The cluster’s most impressive member is Messier 87. It marks the center of the cluster, more than 50 million light-years away.

M87 may span a million light-years and contain trillions of stars – many times the corresponding values for the Milky Way. And its total mass is more than twice the Milky Way’s.

M87 is a different type of galaxy. The Milky Way is a spiral – a flat disk highlighted by “arms” of bright stars that make it look like a pinwheel. M87, on the other hand, is elliptical – it resembles a fat, fuzzy football. It may have grown so large through the mergers of several big galaxies. That scrambled the stars, so they orbit the center of M87 in all directions.

The heart of the galaxy harbors a black hole more than a thousand times the mass of the central black hole in the Milky Way. It was the first black hole to have its picture taken – a dark shadow at the heart of a giant galaxy.

More darkness in Virgo tomorrow.

Script by Damond Benningfield

It might seem hard to lose a star cluster. But that’s what happened with Messier 48. It was cataloged by French astronomer Charles Messier in 1771. When other astronomers looked for it, though, they couldn’t find it. In the early 1780s, Johann Bode and Caroline Herschel did see a cluster five degrees from the position that Messier reported. So they sometimes get credit for the discovery.

What all of these folks actually discovered was the nature of the cluster. Under especially dark skies, it’s visible to the eye alone as a faint smudge of light, so people had always known it was there. But the telescope showed that the smudge consisted of many individual stars.

Today, we know that M48 contains hundreds of stars. They’re packed into a loose ball that spans about 125 light-years. Most of the stars congregate near the center of that ball, which is the part that’s visible to the eye alone. The stars near the edge of the cluster are being pulled away by the gravity of the rest of the galaxy. Someday, those stars will leave the cluster and head off on their own.

M48 is 2500 light-years away. That makes it one of the most distant clusters of its type that’s visible to the eye. As night falls, it’s high in the southern sky. It’s well to the upper left of Sirius, the brightest star in the night sky. Binoculars reveal some of the individual stars of M48 – a cluster that got lost.

Script by Damond Benningfield

If you have a compass – physical or virtual – let it point you to the southeast as night falls for the constellation Pyxis – the celestial compass. It’s a short line of faint stars, aiming toward the remnants of the Argo – the ship that carried Jason and the Argonauts. In fact, Pyxis represents the Argo’s compass.

You need a pretty dark sky to see even its brightest star. But that’s only because the star is about 900 light-years away. If you moved it to the distance of Sirius, the brightest star in the night sky, Alpha Pyxidis would outshine everything except the Sun and Moon.

In astronomical parlance, Alpha Pyxis is “class B.” Astronomers classify stars by their surface temperature and color – hot stars are blue, while cool stars look orange or red. The hottest stars are class O, followed by class B. Alpha Pyx is tens of thousands of degrees hotter than the Sun, so it shines blue-white.

The star is so hot because it’s more than 10 times as massive as the Sun. At that great mass, gravity squeezes the star tightly, making its interior intensely hot.

As a result of those high temperatures, Alpha Pyxidis is “burning” through its hydrogen fuel in a hurry. So even though the star is less than one percent the age of the Sun, it’s already nearing the end of its life. Within a few million years, the star may go out with a bang: a titanic explosion known as a supernova.

We’ll have more about Pyxis tomorrow.

Script by Damond Benningfield

Almost two decades ago, astronomers detected a little “squeak” of radio energy from the stars – a blip that lasted a fraction of second. Since then, hundreds more have been detected. But they’re more than just little squeaks. They’re massive outbursts of energy that can be heard across the universe.

Fast radio bursts last from less than a thousandth of a second to about three seconds. They come from galaxies that are millions or billions of light-years away. At that distance, an outburst of just a thousandth of a second must produce as much energy as the Sun will emit in several years.

Scientists are still trying to figure out the cause of fast radio bursts. Because the bursts are so short, they must come from small, compact sources. Most explanations involve neutron stars – the ultra-dense corpses of once mighty stars.

A neutron star is more massive than the Sun, but no bigger than a small city. That makes it extremely dense, so its gravity is millions of times the strength of Earth’s gravity. So if anything hits a neutron star, it creates a titanic explosion. An asteroid a few miles wide, for example, would explode with the power of billions of hydrogen bombs.

That’s not the only possible explanation, though. Bursts could be caused by disruptions to a neutron star’s powerful magnetic field, by exploding stars, or by something else – outbursts that can be heard across the universe.

Script by Damond Benningfield

On a map of Earth, coordinates zero-zero are in the eastern Atlantic Ocean, near the coast of Africa. All the other latitudes and longitudes are marked from that point.

On a map of the sky, those coordinates are in the constellation Pisces. And that’s just where the Sun appears early today – at the moment of the spring equinox. Confusingly, though, that spot is known as the First Point of Aries.

More than 2,000 years ago, the Sun appeared against the stars of Aries at the equinox. That spot was marked as the zero-point of the celestial coordinate system – the equivalent of latitude and longitude.

But Earth wobbles on its axis. As it wobbles, the Sun changes position relative to the background of stars. That causes the First Point of Aries to shift as well. And as the point moves, the rest of the celestial coordinate system moves with it. The constellations don’t change, but their coordinates do.

The First Point of Aries moves westward by one degree every 72 years. So today, it’s in Pisces, where it’s been for the past two millennia. Around the year 2600, it’ll shift into Aquarius, the next constellation over. So spring will arrive in the northern hemisphere when the Sun is in Aquarius.

The Sun will return to its current equinox location when Earth completes one full wobble on its axis – in 26,000 years.

Tomorrow: collisions heard across the universe.

Script by Damond Benningfield

The Maya of Central America were careful skywatchers. They built observatories for tracking the Sun, Moon, and stars. They developed accurate calendars, and could predict the motions of astronomical bodies. There’s even evidence that they could predict eclipses with a fair degree of accuracy.

One example of their astronomical prowess may be found in the ancient city of Chichen Itza, in the Yucatan Peninsula. A shadowy snake appears to descend one side of a massive pyramid there on the equinoxes. It may represent Kukulkan, the god of the underworld – a serpent with plumes of feathers.

The pyramid was built as early as a thousand years ago. It’s about 80 feet tall. It consists of multiple tiers, like a limestone layer cake. Each side has a staircase with 91 steps, which lead to a temple at the top. That creates 365 total steps – the number of days in a year.

For a couple of weeks around the equinox, the northwestern corner of the pyramid casts a shadow on the raised sides of the northern staircase. As the shadow descends, it looks like a snake slithering down the pyramid. It culminates when the shadow reaches the base of the staircase, which features a carved head that looks like a snake.

It’s not certain that the alignment was intentional. Even so, it’s one of the world’s most famous equinox markers, drawing thousands of visitors each year to mark the start of spring – which arrives tonight.

More about the equinox tomorrow.

Script by Damond Benningfield