StarDate

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

A busy galaxy is puffing out material like a factory smokestack. The “plume” is 20,000 light-years long, and it contains enough gas to make 50 million stars as massive as the Sun.

NGC 4383 is about 60 million light-years away. It’s a member of the Virgo Cluster – a collection of hundreds of galaxies.

Like our home galaxy, the Milky Way, NGC 4383 is a spiral. Bright “arms” of hot, young stars wrap around the galaxy’s heart.

The galaxy is a hotbed of star formation – it’s giving birth to thousands of stars. Many of them are especially hot and massive. They blow strong winds of hot gas. And when they die, they explode, creating an even heavier flow. That flow pushes the gas that’s around the stars, creating the powerful “chimney.” Gas in that outflow moves at an average of about 670,000 miles per hour. And every year, enough gas is added to make two more Suns.

All that activity reduces the amount of gas available to make more stars. So eventually, the outflow of gas will shut down the stellar nursery in this busy galaxy.

Although it’s a member of the Virgo Cluster, NGC 4383 is located within the borders of Coma Berenices. The constellation is low in the east in early evening. It consists of a faint spray of sparkly stars, although you need dark skies to see them. You need a telescope to see NGC 4383.

Script by Damond Benningfield

The sky is divided into 88 constellations. They’re named for animals, places, characters from mythology, and even scientific instruments. But only one is named for a real person. Coma Berenices represents the hair of Queen Berenice II of Egypt. She reigned more than 2200 years ago.

Her husband was King Ptolemy III. When he headed off to war, she pledged to sacrifice her beautiful hair to the gods if he returned safely. He did, so she placed her hair inside a temple. It vanished.

A court astronomer told the king that her locks had been placed in the stars, in a sparkly group near the tail of the lion. So the region became known as Berenice’s Hair, although it wasn’t depicted as a constellation until the 1500s. When astronomers drew up a formal list of constellations, in the 1900s, Coma made the cut.

Most of the visible stars there really are related. They belong to the Coma Star Cluster. It’s a group of dozens of stars, centered about 280 light-years away. The stars are all about 450 million years old – just one-tenth the age of the Sun.

Coma Berenices is low in the east in early evening. Its stars are faint, so you need a dark sky to see them – moonlight or city lights overpower the beautiful tresses of Queen Berenice.

Among astronomers, Coma is best known for its many galaxies, and we’ll talk about one of them tomorrow.

Script by Damond Benningfield

A long, wide bar of stars crosses the middle of our home galaxy, the Milky Way. And the center of the bar might be a good place for – well, a bar. A study published 50 years ago yesterday reported that a huge cloud near the galaxy’s heart contains vast amounts of ethyl alcohol – the form that people drink. Of course, it’s spread across tens of thousands of cubic light-years, so it might take a while to fill a frosty mug or a warm snifter.

Sagittarius B2 is about 27,000 light-years away. It contains enough gas and dust to make millions of stars the size of the Sun. The brew of material comprises many complex molecules, including several types of alcohol. Ethyl alcohol was the first to be discovered.

Alcohol consists of hydrogen, carbon, and oxygen, which are plentiful in the universe. In the cold of space, there’s not much energy to power the reactions that bind them together. But there’s a lot of space and a lot of time, so the level in the keg keeps rising.

The 1975 study concluded that the cloud contains two billion billion billion gallons of ethyl alcohol. As the study wryly noted: “This exceeds the total amount of all of man’s fermentation efforts since the beginning of recorded history.”

Sagittarius is low in the south-southeast before dawn. Its brighter stars form the outline of a teapot. Sagittarius B2 stands to the upper right of the spout – a good place to pour a cosmic brew.

Script by Damond Benningfield

You don’t need a thermometer to take a star’s temperature. All you need is your eyes. That’s because a star’s color is a direct result of its surface temperature. The hottest stars glow blue-white, while the coolest look reddish orange.

One example is the star Spica. It rises below the Moon this evening, and the Moon moves closer to it during the night.

Spica is a system of two stars locked in a tight orbit around each other. Both stars are bigger, heavier, brighter, and hotter than the Sun.

The main star, Spica A, is by far the more impressive member of the system. Its surface is a broiling 45 thousand degrees Fahrenheit, compared to just 10 thousand degrees for the Sun. That makes the star look blue-white. Under dark skies, with no moonlight, that color is pretty easy to see with the eye alone.

We can make out the color because Spica is both close and especially bright – more than 2,000 times the Sun’s brightness at visible wavelengths.

But if our eyes could see other forms of energy, Spica A would appear even brighter. Because its surface is so hot, the star emits most of its energy as ultraviolet light – wavelengths that are too short for the eye to see. So when you add up all wavelengths, Spica A glows more than 20 thousand times brighter than the Sun – a blue-white spotlight that tonight snuggles close to the Moon.

Tomorrow: bellying up to a cosmic bar.

Script by Damond Benningfield

Happy Friday! It’s the 73rd day of the year. And to astronomers and a few others, it’s day 2,460,749. That’s the tally under the Julian Date system. Its starting point was more than 6700 years ago.

The system was created by Joseph Scaliger, a French scholar and religious leader, in 1583. The system was named for his father, Julius.

Astronomers use the Julian Date system to record observations and events. And they don’t add minutes or seconds – they convert those to decimals. That makes it easier to compare the timing of their work to observations made long ago, or under different calendar systems or time zones. They don’t have to figure out the permutations of the calendars or other details – just subtract one date from another to find the difference.

A Julian day begins at noon Universal Time – 7 a.m. Central Daylight Time. So day 2,460,749 begins at 7 a.m. today, and ends 24 hours later – on the Ides of March.

Script by Damond Benningfield