StarDate

The Coma galaxy cluster is like a cosmic iceberg. What you see is impressive. But what you don’t see is even more impressive.

The cluster is centered more than 300 million light-years away, and it spans 25 million light-years. It contains thousands of individual galaxies. Many of them are far bigger and heavier than our own galaxy, the Milky Way.

But in the 1930s, German astronomer Fritz Zwicky found something odd. He measured the motions of individual galaxies within the cluster. They were zipping along much too fast to be held in check by the gravity of the visible galaxies – they should all fly away from each other.

Zwicky concluded that something else was acting as a sort of gravitational “glue.” He called it dark matter – matter that couldn’t be seen, but that exerted a gravitational pull on the visible matter around it.

It took decades to confirm that finding. And even today, we don’t know what dark matter really is. The leading idea says it’s some type of subatomic particle. But despite many years of searching, no such particle has been found. All we know for sure is that dark matter accounts for about 85 percent of all the matter in the universe – the vast hidden depths of the cosmic iceberg.

The Coma Cluster is in Coma Berenices. The constellation is in the east at nightfall. It’s above brilliant Arcturus, the brightest star of Bootes, and to the lower left of Leo, the lion.

Script by Damond Benningfield

Astronomers love star clusters. All the stars in a cluster were born at the same time, from the same cloud of gas and dust. So any differences in the stars are the result of their evolution, which is a result of their mass. That makes it easier to learn what’s going on inside the stars.

One problem, though, is identifying which stars belong to a cluster. It takes detailed measurements of motion and brightness to separate members of the cluster from stars that just happen to line up in the same direction.

An example is the Coma star cluster, in Coma Berenices. The constellation is in the east at nightfall. Under dark skies, the cluster is a good target for binoculars.

The cluster is about 280 light-years away. But it spans dozens of light-years, so its stars are spread out. That makes it harder to pick out its members. And it takes big telescopes to pick out its fainter stars.

So despite decades of study, astronomers are still locking down the census of stars in the Coma cluster. A study about a decade ago confirmed eight small, faint members – the first of their kind known to belong to the cluster. And another study found that about a quarter of the stars in the cluster are binary or multi-star systems.

These discoveries bring the total number of stars in the Coma cluster to several dozen, with a few dozen more possibilities – members of a wide-spread stellar family.

More about Coma Berenices tomorrow.

Script by Damond Benningfield

The long-lost tail of the lion climbs high across the sky at this time of year – a spray of faint stars that trails behind Leo. Today, it’s known as Coma Berenices – the hair of Queen Berenice II of Egypt. It’s the only modern constellation that represents a real person. Originally, though, it was the tuft of hair at the end of the lion’s tail.

The stars came to represent Berenice about 2300 years ago. The story was invented by the court astronomer to the king of Egypt, Ptolemy III. The queen had left her beatiful locks in a temple – an offering to the gods to protect her husband, who was off at war. The hair disappeared, angering the king. So the astronomer told him that the gods had whisked the offering into the sky.

But to most of the western world, the stars remained part of Leo for centuries longer. They didn’t become a separate constellation until the 1500s, when they were named for Berenice.

Coma Berenices isn’t easy to find. All of its stars are faint, so you need especially dark skies to see them. Its brightest star is Beta Coma. It’s a near twin to the Sun – a little bit bigger, heavier, and brighter. Yet even it isn’t visible from light-polluted cities or suburbs.

The constellation is well up in the east at nightfall. It’s above brilliant Arcturus, the brightest star of Bootes, and to the lower left of Leo – the long-lost tip of the lion’s tail.

Script by Damond Benningfield

Most years, the Sun produces hundreds or thousands of sunspots – magnetic storms that look like dark splotches on its surface. From 1645 to 1715, though, sunspots all but disappeared. In many years, the number stayed in the single digits. And in some years, there were no sunspots at all.

Today, that period is known as the Maunder minimum. It’s named for British astronomer Edward Maunder, who was born 175 years ago today. He wrote about the period in the late 1800s.

Maunder was working at Britain’s Royal Observatory. He was assisted by his wife, Annie, who was a “computer” at the observatory – someone who did the tedious calculations.

Maunder discovered a pattern in the sunspots, which wax and wane during a cycle of about 11 years. When a new cycle begins, most of the sunspots are concentrated at the Sun’s middle latitudes. As the cycle peaks, they’re concentrated closer to the equator.

But he’s best known for the Maunder minimum. It occurred during the “Little Ice Age” – a period of unusual cold. That suggests a link between solar activity and Earth’s climate. But the link isn’t confirmed – it could be just a coincidence.

We still don’t know what caused the sunspots to vanish. It had happened at least once before. So the mystery of the Maunder minimum remains unsolved.

Script by Damond Benningfield

Gamma Cassiopeia is a busy star system. The main star is surrounding itself with a disk of gas and dust. The star is interacting with an invisible companion. And it’s building up to an impressive demise.

Gamma Cas is the middle point of the letter M or W formed by the stars of Cassiopeia, which is high in the north-northwest at nightfall. Gamma Cas is the most distant member of that pattern, at 550 light-years. Its main star – the one visible to the eye alone – is about 15 times the mass of the Sun. And it’s about 20,000 times brighter than the Sun.

The star spins at about a million miles an hour at its equator. That causes it to bulge outward, so it looks more like a lozenge than a ball. That high speed causes the star to fling gas from its surface, forming a disk around the star.

Its companion probably is the corpse of a once mighty star. Some of the gas from the main star may fall onto the companion.

Gamma Cas is only about eight million years old, yet it’s nearing its end. In a few million years more, it’s likely to explode – ending the life of this busy star.

Incidentally, Gamma Cas has another name: Navi. It was bestowed in the 1960s by the crew of Apollo 1. It’s the middle name of commander Virgil Ivan Grissom spelled backward. After the crew died in a launchpad fire, NASA placed Navi on the charts used by later crews to navigate to the Moon.

Script by Damond Benningfield

You might want to buckle up for this one. We’re going to take a wild ride through the universe. It’s a combination of several motions – involving our planet, our solar system, and our galaxy.

First up is Earth’s motion around the Sun. Our planet’s average orbital speed is about 66,600 miles per hour. At that speed, it takes exactly one year for Earth to make one full turn.

The Sun is moving as well, and it’s taking Earth and the rest of the solar system along for the ride. The Sun is about 27,000 light-years from the center of the Milky Way Galaxy. It circles around that center at almost 500,000 miles per hour. The galaxy is so huge, however, that it takes about 230 million years to complete one orbit.

And that’s not the fastest motion we’re experiencing. The Milky Way belongs to a small cluster of galaxies, the Local Group. The group is being pulled toward the Virgo Cluster, which contains thousands of galaxies. And the Local Group, Virgo Cluster, and much more are being pulled in by the gravity of the Great Attractor – the center of an enormous collection of galaxies and dark matter. The Milky Way is speeding toward it at more than 1.3 million miles per hour.

So while the ground beneath your feet feels steady, keep in mind that it’s on the move – tugged by the Sun, the galaxy, the Great Attractor – and perhaps even more.

Script by Damond Benningfield

Iodine is special. It’s the heaviest element that’s commonly needed by living organisms. In humans, it’s used by the thyroid to produce growth-regulating hormones. It’s found in seafood and other products.

The element itself is created in some of the most violent events in the universe. In fact, so were almost all of the heaviest elements – anything more substantial than iron.

The elements are forged in the rapid neutron-capture process. “Seed” elements are slammed by huge amounts of neutrons – the bits of an atomic nucleus with no electric charge. That builds heavier elements, including gold, silver, uranium – and iodine.

Lighter elements are forged in the hearts of stars. More-massive stars create heavier elements. But they can’t make anything heavier than iron. The element-making process shuts down, and the star explodes. The blast can produce huge numbers of neutrons, which are sent flying at high speed. They ram into the debris, creating heavier elements.

But not all exploding stars produce the right conditions to make heavier elements – especially the heaviest of all. Those elements can be formed when two ultra-dense stellar corpses ram together. The merger splatters the region with neutrons. They can forge enough heavy elements to make many planets as massive as Earth.

Iodine probably is made by both types of events, which sprinkle this life-giving element throughout the cosmos.

Script by Damond Benningfield

A long-distance visitor might put in a good showing in the early morning sky this month. And astronomers will be paying close attention.

Comet C/2025 R3 PanStarrs was discovered in September. It probably is falling inward from the Oort Cloud. That’s a huge reservoir of balls of rock and ice that enwraps the solar system. This one might have been nudged inward by the gravity of a passing star.

Objects in the Oort Cloud were born when the planets were taking shape. Jupiter’s gravity hurled them far into space. In the cold and dark, those bodies have changed very little for billions of years.

As PanStarrs approaches the Sun, some of its ice vaporizes. That releases bits of rock and dirt. The debris forms a cloud around the comet, plus a long, glowing tail. Studying this material provides insights into the birth of Earth and the other planets.

The comet will pass closest to the Sun on April 20th. It’ll be closest to Earth a week later – 44 million miles away. If it survives the Sun’s heat, it then will rocket back into deep space, not to return for thousands of years, if ever.

PanStarrs is low in the east before and during dawn. Because we record in advance, we can’t tell you how bright it looks, or how bright it’ll get. We can tell you that it will zip across the Great Square of Pegasus next week, then move into Pisces. By then, it will appear so close to the Sun that it’ll be tough to spot, with or without optical aid.

Script by Damond Benningfield

In October of 1604, a brilliant “new” star blazed to life in the constellation Ophiuchus. It was bright enough to see in the daytime for weeks. German astronomer Johannes Kepler kept a close eye on it until it faded from the night sky, in 1606. So today, it’s known as Kepler’s Supernova. It’s the last known supernova in the Milky Way Galaxy.

A space telescope has been keeping a close eye on the aftermath of that event for the past 25 years. That’s revealed a lot about the supernova and the environment around it.

The supernova flared to life when a stellar corpse known as a white dwarf tipped above its weight limit. The star either stole gas from a companion star, or it merged with another white dwarf. Either way, the star was blasted to bits. The explosion expelled a huge cloud of debris – a nebula that today spans about a light-year. It’s extremely hot, so it produces a lot of X-rays.

Chandra X-Ray Observatory has taken many looks at the nebula. It’s found that one side of it is expanding at about two percent of the speed of light. The opposite side is moving only one-third that fast. The slower side is also hotter. That’s because it’s running into more gas and dust around the nebula.

Chandra will keep an eye on the nebula for as long as it can – telling us much more about the violent death of a star.

Script by Damond Benningfield

The Sun sprays Earth with a constant shower of charged particles – the solar wind. But the shower sometimes becomes a storm – a barrage that can damage satellites, overload power grids, and cause other mischief.

Predicting such storms can save a lot of grief. But better predictions require a better understanding of the Sun, Earth’s magnetic field, and how they interact. A mission scheduled for launch as early as this week should help.

SMILE is a joint project of Europe and China. The craft will orbit up to 75,000 miles from Earth. From that high perch, it’ll be able to see Earth’s magnetopause – the zone where the solar wind rams into Earth’s magnetic field. It will monitor that zone for up to 40 hours at a time – far longer than any glimpses we’ve had before.

Earth’s magnetic field deflects most of the particles in the solar wind. But some of them get through. They create the auroras – the colorful northern and southern lights.

Powerful storms on the Sun blast out huge amounts of particles. They can overwhelm the magnetic field, creating intense bouts of “space weather.” Among other effects, that causes especially intense auroras, which can appear in regions where they’re seldom seen. SMILE will watch the auroras to see how they change with the level of solar activity.

SMILE’s observations will tell us a lot more about how Earth and the Sun get along – improving our ability to protect ourselves from solar storms.

Script by Damond Benningfield