StarDate

Cetus, the whale or sea monster, stands low in the southwest as night falls. The constellation is faint. But its brightest star, Diphda, is fairly easy to pick out, to the lower right of Venus, the “evening star.”

Cetus is far from the glow of the Milky Way — the band of light that outlines the disk of our home galaxy. That provides a better view of the galaxies beyond the Milky Way. In fact, a giant cluster of galaxies is near Diphda. And one of those galaxies is home to the biggest black hole yet discovered.

Abell 85 consists of more than 500 galaxies. The one at the center is a monster — it’s much bigger and heavier than the Milky Way. It’s an old galaxy whose stars are spread fairly evenly, so it looks a bit like a fuzzy football.

But there are fewer stars in the galaxy’s heart than expected, so the core looks faint. By measuring the motions of the stars that are in the galaxy’s heart, astronomers in Germany discovered why: A black hole that’s 40 billion times the mass of the Sun sits right in the middle. It’s the heaviest black hole seen to date.

The black hole may have grown so monstrous during the merger of two galaxies. As the black holes in those galaxies came together, they whipped up the space around them like batter in a blender. Many of the stars around them were flung away from the core of the merging galaxies. That left the center of the combined galaxy with fairly few stars — but with a single giant black hole.

Script by Damond Benningfield

A star can be much more than meets the eye. An example is Regulus, the “heart” of Leo, the lion. Although it looks like a single star, it’s actually a system of at least four stars. But only one of them is bright enough to see without a telescope.

The bright star is quite impressive. Known as Regulus A, it’s bigger and heavier than the Sun, and much brighter. And it’s spinning like crazy — so fast that it’s barely holding itself together.

The star has a close companion — the likely corpse of a once-impressive star. Today, it’s so small and faint that it’s impossible to see through the glare of Regulus A, even with the biggest telescopes. So it wasn’t discovered until a little more than a decade ago.

The other members of the system are Regulus B and C. Regulus B is a little smaller and fainter than the Sun, while C is a cool, dim cosmic ember known as a red dwarf. They form a loosely bound pair that’s hundreds of billions of miles from the other two stars.

At that range, it takes the two pairs of stars more than a hundred thousand years to orbit each other. So it’s hard to be absolutely certain that B and C are really bound to the other two. But all four stars appear to move through space in sync — making the Regulus system more than meets the eye.

You should have no trouble eyeing Regulus tonight. It’s close to the right of the just-past-full Moon in early evening, and keeps tabs on the Moon throughout the night.

Script by Damond Benningfield

The Moon isn’t the only body in the night sky that shows phases. So do the planets of the solar system. As our viewing angle to a planet changes, so does the lighting on the fraction of the hemisphere that faces our way.

That’s especially true for Venus and Mercury, the only two planets that are closer to the Sun than Earth is. As seen from Earth, they can range from almost new to almost full. That’s because we can see them when they pass between Earth and the Sun, so they’re almost completely in shadow, and when they’re almost behind the Sun, in the full glare of the Sun’s rays.

Through a small telescope, you can see that effect for yourself right now. Venus and Mercury are both in the western sky as night falls. Venus is the “evening star,” so it’s easy to pick out. Smaller Mercury is much harder to see. It looks like a moderately bright star, but it’s quite low in the sky.

Sunlight illuminates more than two-thirds of the hemisphere of Venus that faces Earth now.

Only a bit less of the visible part of Mercury is in the sunlight this evening, so it looks similar to Venus. But Mercury will drop toward the Sun over the next few evenings. As it does, it’ll move a bit closer to the line between Earth and the Sun. So each evening, less and less of the hemisphere that faces our way will be in the light. In a bit more than a week, only about one-sixth of its surface will be in daylight — making the planet look like a tiny crescent Moon.

Script by Damond Benningfield

The surface of the Sun jiggles constantly. And by measuring those jiggles, astronomers learn about what’s happening inside the Sun — from the surface all the way down to its core.

The field is known as helioseismology. And it works along the same principles as seismology here on Earth. Geologists study Earth’s interior by measuring sound waves that ripple all through our planet. Astronomers do the same thing by measuring sound waves that ripple through the Sun.

The waves are created by the motions of giant bubbles of hot gas that rise and fall through the Sun’s outer layers. The waves then travel great distances through the Sun. When they reach the surface, they cause the surface to rise and fall by a tiny bit — creating jiggles.

Since the waves travel through different parts of the Sun, each set carries information about the Sun’s interior — about differences in composition, temperature, and density, for example. So putting together many sets of waves helps astronomers map the Sun’s structure, and better understand what’s happening inside our star.

Astronomers use sensitive instruments to measure the tiny jiggles on the Sun’s surface. The measurements have revealed 10 million sets of waves traveling through the Sun. Those observations can be converted to sound. They allow us to hear the jiggles at the surface of the Sun — acting as probes into the heart of a star.

Script by Damond Benningfield

[SFX: solar sounds] That’s the sound of a gusty breeze. It’s not blowing across the Great Plains or some other icy domain, though. Instead, it’s blowing throughout the solar system — a million-mile-an-hour wind from the Sun.

The solar wind is a flow of electrons — the bits of atoms that have a negative electric charge. They’re shot out into space by the Sun’s magnetic field. The details of how that happens are still elusive, though.

The solar wind is always blowing. At times, though, it gets stronger — and gustier. That’s the result of magnetic storms on the Sun or in its outer atmosphere. As they’re kicked outward, the electrons produce radio waves. Receivers on Earth “hear” those waves.

As the solar wind reaches Earth, it collides with our planet’s own magnetic field. And when the solar wind is especially strong, the contact creates magnetic waves in the field’s outer regions. A group of European spacecraft recorded the waves from several of these encounters. Scientists recently converted the waves to sound.

The magnetic waves travel all the way to the surface. Scientists are trying to understand how that happens — and what it means for the interaction between Earth and the solar wind — a constantly changing breeze from the Sun.

We’ll hear more from the Sun tomorrow.

Script by Damond Benningfield

When the Sun gets unruly, it’s bad news for technology here on Earth. Outbursts of energy and particles can damage satellites, disrupt communications, and even knock out power grids.

But the outbursts we’ve seen so far may be puny compared to what the Sun might produce. Eruptions known as superflares could be hundreds or thousands of times more powerful — strong enough to damage or destroy much of our current technology.

The Sun’s outbursts are generated by its magnetic field. Lines of magnetic force get tangled like a bowl of spaghetti. When lines overlap, they can snap, triggering a solar flare — an outburst of radiation. Some flares are accompanied by eruptions of charged particles. Both radiation and particles can cause damage.

The biggest flare yet seen took place in 1859. There’s evidence in the geological record, though, of even bigger ones in the distant past. And studies in the last few years have seen flares that are bigger still on many Sun-like stars.

Most superflares come from stars that are younger than the Sun. They spin much faster than the Sun does, so their magnetic fields are much stronger.

But Kepler, a planet-hunting space telescope, detected superflares from several stars that are quite similar to the Sun — about the same age, temperature, and mass. That suggests that the Sun could produce superflares, too. They’d be quite rare. But it might take just one to zap our technology — leaving civilization in the dark.
 

Script by Damond Benningfield

When the Mariner 2 spacecraft was headed toward Venus, in 1962, it made the first measurements of a high-speed “wind” of charged particles from the Sun. And scientists have been trying to understand that wind ever since.

They should get some new clues from a spacecraft whose launch window opens tomorrow.

Solar Orbiter is a European mission. When it reaches its target orbit, in about three years, it’ll be able to view the Sun’s poles — something that’s impossible to do from Earth. Combined with other observations, that’ll provide the most complete view of the entire Sun to date.

The solar wind blows at a million miles per hour or faster. It clears out a magnetic “bubble” around the solar system called the heliosphere. It extends far beyond the orbit of Neptune, the most remote of the Sun’s major planets.

Astronomers are still unsure how the Sun drives the solar wind. They know it involves the Sun’s magnetic field, which goes through an 11-year cycle. The Sun gets more active at a cycle's peak. It produces more dark sunspots, as well as powerful outbursts. The outbursts can mess with technology here on Earth, so it’s especially important to understand how they work; more about that tomorrow.

At its closest, Solar Orbiter will pass about 25 million miles from the Sun. Only one other spacecraft has gotten closer. That approach will take the craft close to the region where the solar wind takes shape — helping scientists understand its creation.
 

Script by Damond Benningfield

A star is the product of a delicate balance between gravity and radiation. They stay in balance for most of a star’s life. But as the star gets older the balance changes, causing big changes in the star itself.

An example of a star that’s going through that process is in good view tonight. Aldebaran, the bright orange eye of the bull, stands close to the Moon at nightfall.

Gravity squeezes a star tightly, smashing its gas into a compact ball. At the middle of the ball, the gas is heated to millions of degrees — hot enough to ignite nuclear fusion. The fusion produces radiation, which pushes outward, keeping the star in balance.

As the star ages, though, it uses up the hydrogen fuel in its core, producing helium. The helium doesn’t fuse at the same temperature as hydrogen, though. Without nuclear fusion, there’s no radiation to push outward, so gravity squeezes the core even tighter. And as the core shrinks, it gets hotter.

Eventually, it gets hot enough to ignite fusion in the helium. That achieves a new balance — one with a smaller, hotter core. The radiation from the core exerts a stronger outward pressure, causing the surrounding layers of gas to puff outward like a giant balloon.

And that’s what’s happening to Aldebaran. The star has used up its hydrogen, so it’s now ready to burn its helium. So Aldebaran has puffed up to many times the size of the Sun, causing its outer layers to cool — and giving the bull a bright orange eye.

Script by Damond Benningfield

Some people go their own way. And so do some stars. Instead of sticking with the stars around them, they follow their own path around the galaxy.

That’s the case with Dubhe, the star that marks the top right point of the bowl of the Big Dipper. Five of the seven stars that outline the dipper belong to a star cluster — a big stellar family. As a result, they move through the galaxy together. And they’re all about the same distance from Earth — roughly 80 light-years.

The dipper’s two other stars don’t belong to the cluster. Dubhe is the more distant of the two. In fact, it’s the most-distant of all the dipper’s stars — about 125 light-years away.

Dubhe forms its own little family. It consists of two pairs of stars. The leader of one pair is at the end of its “normal” lifetime, so it’s puffed up to giant proportions. It’s especially bright, so it contributes most of the light we see as Dubhe. Its companion is a couple of billion miles away from it, so the two stars orbit each other once every 45 years or so.

The other pair is pretty impressive as well, but a long way from its brighter siblings.

Because Dubhe isn’t related to the dipper’s other stars, it’ll move out of its position in the dipper much sooner than the others. That will stretch the dipper out, eventually pulling it apart.

For now, look for Dubhe in the northeast this evening. Dubhe leads the dipper up into the sky — and high across the north during the night.

Script by Damond Benningfield

There are many ways to mark the changing of the seasons. The modern calendar uses the solstices and equinoxes. Winter begins on the December solstice, for example, and ends on the March equinox.

In many cultures, though, those dates marked the mid-point of a season. The seasons changed roughly halfway between them — dates known as cross-quarter days.

One of those days was marked in early February. In ancient Scotland and Ireland, for example, it came around February 1st. It was known as Imbolc. It was a day to celebrate the arrival of the longer, warmer days of spring.

The early Christian church adopted its own celebration of the cross-quarter day. Known as Candlemas, it was the 40th day of Christmas — the official end of the celebration for some denominations. Candles were blessed on that day — providing light for the entire year.

One of the traditions of Imbolc was to watch the dens of snakes and badgers to see if they stuck their heads out to sample the weather. If it was cold and clear, the critters retreated to wait out a few more weeks of winter. If it was warm and cloudy, though, it was time to head out. A similar tradition was associated with Candlemas.

That tradition is preserved in a modern celebration of the cross-quarter day: Groundhog Day. There’s no correlation between the folklore and the actual weather. Still, it preserves a bit of astronomical tradition — the tradition of cross-quarter days.

Script by Damond Benningfield