StarDate

Most stars are members of giant families — hundreds or even thousands of stars that are born together. They form star clusters that can span hundreds of light-years. Because of that great size, though, the families are hard to keep together. The siblings all tend to head off on their own.

That appears to be happening with a star cluster that’s in good view on March nights. Messier 48 is halfway up the sky in the south-southeast as night falls. It’s well below the bright star Procyon. Under dark skies, it’s visible to the unaided eye as a small, hazy patch of light. And in any case, it’s an easy target for binoculars.

Recent studies have placed M48 at a distance of about 2400 light-years. It contains hundreds of stars. And it’s roughly 450 million years old, which is quite young.

The cluster is about 125 light-years across. At that size, the stars are well spread out. So as the cluster moves through space, the gravity of the rest of the galaxy tries to pull it apart. And it appears to be doing so. Astronomers have identified three “clumps” of stars within the cluster. Two of them are close together, and are still moving at about the same speed and in the same direction. The third is away from the other two, and is moving in a different direction.

Most clusters dissolve within about a billion years. So M48 may be well along in that process — a big stellar family whose brothers and sisters are heading off on their own.

Script by Damond Benningfield

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Most of the stars are so far away that they appear as no more than pinpoints of light to even the largest telescopes. But a few stars are close enough or big enough to see them as tiny disks. That allows astronomers to measure how big they are — measurements that help them understand how stars work.

One of the stars that’s been measured is Arcturus, in Boötes the herdsman. The star climbs into view in the east by about 9 or 10 o’clock. It’s one of the brightest stars in the night sky, so you shouldn’t have any trouble finding it.

Careful measurements reveal the star’s apparent diameter — how big it looks in the sky. That’s combined with measurements of its distance — 37 light-years. The numbers reveal that Arcturus is about 25 times the diameter of the Sun.

What’s particularly important is that the measurement matches nicely with predictions of how big the star should be.

Those predictions are based on models of how stars behave — how they produce energy or how they change as they get older, for example. If the models are correct, then astronomers can make a few basic measurements of any star — such as its temperature and brightness — and use those to determine the star’s size, its stage of life, and much more.

But it’s important to verify the models against stars with known distances. Most of those comparisons show that the models are spot on — allowing us to learn quite a bit about almost every star in the sky.
 

Script by Damond Benningfield

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One of the most ancient of all constellations soars high across the sky on March nights. Boötes the herdsman climbs into good view in the east-northeast by 9 or 10 p.m. Its brightest stars form an outline that resembles an ice cream cone. Its brightest star of all, Arcturus, is at the bottom of the cone. The rest of the herdsman stretches to the left of Arcturus as they rise, and above it later on. Arcturus is one of the brightest stars in the night sky, so you can’t miss it.

Boötes is thought to be one of the oldest of all the constellations. It was drawn so long ago that no one is sure just when it first came along. But the figure shows up in the skylore of China, Egypt, Greece, and many other cultures.

Perhaps not surprisingly for so ancient a star pattern, its mythology is a bit confused. There are several competing stories from Greek mythology, each giving a different origin and significance to the herdsman.

One story says that Boötes created agriculture by plowing the fields with the nearby Big Dipper, which represented a plow. Another saw him as a hunter in pursuit of two bears — the constellations Ursa Major and Ursa Minor. And yet another saw him as the overseer of a herd of oxen — hence the figure’s nickname, “the herdsman.”

Like many Greek myths, the details of Boötes involve deception, betrayal, and even murder — adding even more mystery to this ancient constellation.

We’ll have more about Arcturus tomorrow.

Script by Damond Benningfield

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A pair of glowing orange “eyes” stares down from the western sky this evening: the planet Mars and the star Aldebaran — the eye of Taurus, the bull. They’re high in the sky at nightfall, with Mars to the right of Aldebaran, which is the brighter of the two.

Like all stars, Aldebaran is so far away that no human emissary is likely to visit for a long time — if ever. Mars, on the other hand, has been receiving Earthly visitors for more than half a century. And one of the most successful arrived at Mars 15 years ago today.

Mars Reconnaissance Orbiter — MRO — has mapped the mineral content of the Martian surface, found ice below the surface, and provided daily weather reports.

It carries the most powerful camera ever sent to the Red Planet. It can see details on the surface as small as a dinner table. It’s photographed avalanches, fresh impact craters, dust devils, and outbursts from the polar ice caps.

MRO has also supported other missions. It’s relayed signals between Earth and landers and rovers on the surface. Mission planners have used its pictures to help select landing sites, and to plan the routes for the rovers.

MRO completed its main mission in 2010. But it’s been given several extensions since then — allowing it to keep its powerful eyes focused on the Red Planet.

And you can keep an eye on Mars as it moves away from Aldebaran over the coming days — two bright orange lights in the evening sky.

Script by Damond Benningfield

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There’s a traffic jam in the early morning twilight tomorrow. Three planets will congregate near the Moon. There’s not much time to look at them, though. And you need a clear horizon — any buildings or trees will block the view.

The brightest of the planets is Jupiter, the giant of the solar system. It’s to the upper left of the Moon. Next-brightest is Mercury, the Sun’s tiniest major planet. It’s to the left of the Moon. And the faintest planet is Saturn, to the upper right of the Moon.

For the moment, Mercury shines at magnitude zero — the starting point for the brightness scale astronomers have used for millennia. In this system, the lower the number, the brighter the object. So magnitude zero is quite bright. In fact, when the system was created, that was the number given to the brightest of all stars.

Over the centuries, though, astronomers stopped assigning magnitudes based on observations with the eye alone. They used photographs, then sensitive light detectors, to precisely measure the brightness of a star. So four stars were assigned magnitudes that were negative numbers, led by Sirius at about minus 1.4.

The magnitudes of the planets vary as our distance from them changes. Right now, for example, Jupiter is at minus two. But at its peak, it reaches minus 2.8. And Mercury varies even more. Right now, it’s near its best — shining at magnitude zero, close to the Moon tomorrow morning.

Script by Damond Benningfield

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One of the best places in the solar system to look for life is a small moon of Saturn. It appears to have everything you’d need to brew up life: water, energy, and the right kind of chemistry.

Enceladus is only about 300 miles in diameter — the distance from Chicago to Cleveland. It’s coated with almost pure white ice, making it one of the most reflective objects in the solar system.

An ocean of liquid water lies below that icy crust. It could be miles deep and cover the entire moon.

Water from the ocean shoots out through cracks in the crust near the south pole. The Cassini spacecraft flew through this plume. It found that the water contained particles that form where rock and hot water interact. And the particles contained high levels of organic compounds — the chemical building blocks of life.

That suggests that hot water packed with minerals shoots into the ocean from cracks or vents on the ocean floor. The environment around the vents could be a lot like that around vents in Earth’s oceans. The Earthly vents are surrounded by microbes, which get their energy from the chemicals in the water.

We don’t know if anything lives in the ocean of Enceladus. But the odds of life appear to be better there than just about anywhere else in the solar system.

Saturn is close to our own Moon at dawn tomorrow. It looks like a star to the left of the Moon. Jupiter and Mercury stand to the lower left. More about that tomorrow.

Script by Damond Benningfield

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For the constellation Leo, its bright heart — the star Regulus — gets the lion’s share of attention. But the lion’s tail is no slouch, either. The star is bigger and brighter than the Sun. And it’s a lot younger — although there’s disagreement on just how young.

Denebola is low in the east as night falls now, far to the lower left of Regulus. It’s bright enough to see from all but the most light-polluted cities. Its name comes from a longer Arabic name — Dhanab Al-Asad — “the tail of the lion.”

The star is pretty impressive. It’s about three-quarters again the size and mass of the Sun. It’s about 15 times brighter than the Sun. And its surface is thousands of degrees hotter than the Sun’s, so the star shines pure white.

Denebola is encircled by bands of dust. The way the bands are distributed may indicate that planets orbit between them. So far, though, no planets have been seen.

Estimates of Denebola’s age vary by hundreds of millions of years. Most estimates, however, say it’s especially young. A few studies put its age at a hundred million years. A couple of others say Denebola is even younger — just 45 million years. That would make it just one percent the age of the Sun — a bright youngster at the tail of the lion.

Again, look for Denebola low in the east as darkness falls and climbing high across the sky during the night. It’ll rise a little earlier each evening as we head into spring.

Script by Damond Benningfield

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When it comes to understanding an exploding star, one number trumps all: distance. If astronomers don’t know the distance to a dying star, they can’t be sure how the star is going out.

That may be the case with CK Vulpecula. Normally, it’s too faint to see with the eye alone. But centuries ago, it flared up. It first grew bright enough to see in 1670. Then it grew brighter still in March of 1671 — 350 years ago this month.

The leading idea has been that the flare-up was produced by the collision and merger of two stars. Different models have come up with different types of stars, but the basic idea has stayed the same.

A recent study, though, found that CK Vulpecula may be five times farther than shown by earlier measurements — about 10,000 light-years. If so, then the outburst was about twenty-five times brighter than thought.

A collision between two stars wouldn’t be powerful enough to make the star shine that brightly. Yet the outburst wouldn’t have been bright enough to be the result of a supernova — a titanic explosion that rips a star to bits. So CK Vulpecula may be an in-betweener — a type of explosion that can’t yet be explained.

CK Vulpecula is far too faint to see without a telescope. Yet its location is easy to pick out. It’s in Vulpecula, the fox. It stands near the middle of the bright Summer Triangle, which is high in the eastern sky at first light on March mornings.

Script by Damond Benningfield

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One of the big astronomical mysteries of the last decade or so has been the origin of fast radio bursts. In recent months, though, astronomers have found that at least some of them may be powered by magnetars — the super-magnetized remnants of exploded stars.

A fast radio burst lasts about a thousandth of a second. In that instant, though, it emits more energy than the Sun produces in several days. But most bursts are in other galaxies, so they’re hard to study.

Last April, though, a burst was recorded inside our home galaxy, the Milky Way. It came from a known magnetar.

A magnetar is the ultra-dense corpse of a star that exploded as a supernova. It’s heavier than the Sun, but only a few miles across. And it has a magnetic field that can be a trillion times as powerful as Earth’s.

Starting on April 27th, X-ray telescopes in space saw the magnetar produce a series of outbursts. After a few hours, it produced an especially powerful burst — a fast radio burst.

Astronomers aren’t sure just how a magnetar produces such an event. One study says it may begin with a “quake” — a crack in the magnetar’s crust. That shoots out a magnetic bubble that disrupts the surrounding magnetic field. The field reconnects behind the bubble, triggering a short but powerful burst of energy.

There could be more than one way to make fast radio bursts. But last April’s event suggests that at least some of them could come from super-magnetic stars.

Script by Damond Benningfield

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The merger of two neutron stars produces quite the fireworks. It creates most of the gold, silver, uranium, and certain other heavy elements in the universe. It causes space and time to “jiggle.” And it usually results in the birth of a black hole. But a merger seen last spring may have created something just as exotic: a magnetar.

A neutron star is the corpse of an exploded star. It’s more massive than the Sun, but only the size of a small city. A magnetar is a neutron star with an ultra-powerful magnetic field — a trillion or more times the strength of Earth’s magnetic field.

On May 22nd, space telescopes detected a brilliant outburst from a galaxy at the southwestern corner of Pisces, which is disappearing in the evening twilight now. The galaxy is more than five billion light-years away. The burst lasted just half a second. Yet it carried more energy than the Sun will produce in its entire 10-billion-year lifetime.

From the details of the outburst, astronomers concluded that it was produced by the merger of two neutron stars. Yet the afterglow was too bright to come from a black hole. That suggests the merger created a magnetar.

Astronomers aren’t certain that that’s what happened. But if it is, the magnetar should produce a lot of radio waves in anywhere from a few months to a few years. So they’ll aim their radio telescopes its way to try to confirm the birth of a magnetar.

More about magnetars tomorrow.

 
Script by Damond Benningfield

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