StarDate

A triangle of three bright lights stands below the Moon at first light tomorrow. The closest point to the Moon is the planet Saturn, to the lower left of the Moon. The bright orange planet Mars is farther to the lower right of the Moon, with the orange star Antares at the bottom of the triangle.

Saturn is one of the solar system’s giants — it’s about nine times Earth’s diameter. It probably consists of a dense core surrounded by layers of hydrogen and helium. Motions within a layer of metallic hydrogen create a magnetic field that extends far into space.

[SFX: Saturn audio] Interactions between the magnetic field and the solar wind create radio waves, which were recorded by the Cassini spacecraft, then converted to sound.

The magnetic field forms a “bubble” that deflects much of the solar wind, causing it to stream around the planet. But some of the wind’s charged particles get through. They’re guided toward Saturn’s magnetic poles, where they form bright auroras — the shimmering curtains known on Earth as the northern and southern lights.

Saturn’s magnetic poles are almost exactly aligned with its geographic poles, which isn’t the case with any other planet. Earth’s magnetic field, for example, is tilted several degrees away from its axis. But so far, scientists aren’t sure why Saturn’s field is so different.

Again, look for Saturn — a giant planet inside a giant magnetic bubble — near the Moon at first light tomorrow.

Script by Damond Benningfield

It’s been clear for a while that Mars was much warmer and wetter in the distant past. Ancient riverbeds wind across its surface, and some of the minerals on the surface form only in a wet environment.

Some recent research suggests that the warm, wet days lasted longer than expected.

The Curiosity rover has been studying layers of rock at the base of a mountain inside a large crater. Their composition suggests they formed as pebbles and sand settled on the bottom of a lake that filled the crater.

The layers of sediment could be anywhere from a few hundred feet to half a mile thick. Thinner layers would have been deposited over millions of years. But it could have taken tens of millions of years to deposit thicker layers. Based on the age of the crater, that means it could have been filled with water as little as 3.3 billion years ago — much more recently than suggested by studies of the Martian climate.

Another study examined a salt flat near the Curiosity landing site with spacecraft in Mars orbit. The salt bed probably formed from sediments at the bottom of a lake or sea. The feature is no more than 3.6 billion years old — suggesting that this region of Mars was one of the last “wet spots” on the planet.

And look for Mars quite close to the Moon in the wee hours of tomorrow morning. It rises below the Moon, and looks like a bright orange star. The planet Saturn is below both of them, and we’ll have more about that tomorrow.

Script by Damond Benningfield

Sometimes, you can have too much of a good thing. That was the case with a constellation that was created thousands of years ago. It was so big that astronomers eventually split it apart.

Argo Navis represented the Argo — the ship that carried Jason and the Argonauts through many adventures. It proved so unwieldy, though, that in the 1750s Nicolaus Louis de la Caille divided it into three constellations: Carina, the keel; Vela, the sail; and Puppis, the deck at the stern of the ship.

Of the three, Puppis is the easiest to see from northern skies. As night falls this evening, it’s well to the left and lower left of Sirius, the brightest star in the night sky. The entire constellation is in view if you’re south of about Dallas, but most of it is visible from points farther north.

The constellation’s leading star, Zeta Puppis, looks fairly modest. But that’s only because it’s about a thousand light-years away. It’s actually quite impressive — hundreds of thousands of times brighter than the Sun.

The star is also somewhere between 20 and 40 times as massive as the Sun. Such heavy stars burn through the nuclear fuel in their cores at a furious rate. As a result, Zeta Pup will live only a few million years, versus billions of years for stars like the Sun. And when its time is up, it will go not quietly into that good night. Instead, it will explode as a supernova — briefly making the stern of the Argo one of the most prominent of all constellations.

Script by Damond Benningfield

A horse and rider gallop across the northeastern sky on spring evenings. They form the middle of the handle of the Big Dipper, which is low in the sky at nightfall and circles high overhead in the wee hours of the morning.

They’re the stars Mizar and Alcor. Mizar is the brighter of the two, with fainter Alcor just a whisker away. They’re so close together that the skywatchers of ancient Arabia thought of them as a horse and rider.

Mizar is a system of four stars, all of which are a little hotter and brighter than the Sun. Alcor consists of two stars — one of them more impressive than the Sun, the other less impressive. Both of these systems lie between 80 and 85 light-years from Earth.

One question that astronomers have asked for centuries is whether the two systems are bound to each other, or if they just happen to line up in the same direction in the sky.

They’re both members of a wide-spread cluster. That makes Mizar and Alcor stellar siblings — they formed at the same time, from the same cloud of gas and dust.

Just how close their relationship is has remained a mystery. Until recently, the best observations said the two systems were perhaps two or three light-years apart. At that distance, they probably would not be gravitationally bound to each other.

But recent observations put the separation at roughly one light-year. That may be close enough for them to be tied together to form a single unit — just like a horse and rider.

Script by Damond Benningfield

An impressive star system snuggles close to the Moon tonight. Spica, the brightest star of Virgo, is to the lower right of the Moon as they climb into good view in late evening.

Although it looks like a single pinpoint of light, Spica is really two stars. They’re separated by about 10 million miles — about a tenth of the distance from Earth to the Sun.

Each of Spica’s stars is much larger, heavier, and hotter than the Sun, and thousands of times brighter.

There’s no evidence of planets around the stars. If any exist, they probably orbit both stars, not an individual star.

To have conditions that are comfortable for life, planets would have to be billions of miles out. And even if such worlds did have life, it might not look familiar. That’s because Spica’s stars emit huge amounts of ultraviolet radiation — the form of energy that causes sunburn and skin cancers. Earth is protected from the Sun’s ultraviolet energy by ozone in the upper atmosphere. But it’s unlikely that a planet could have enough ozone to protect it from the intense ultraviolet emitted by the stars of Spica.

So life on worlds around such stars would be different from life on Earth. Plants, for example, might not look green — they might need different pigments to survive.

One other complication is that Spica’s stars are much younger than the Sun is. So even if they have planets, it’s unlikely that there’s been enough time for life to evolve around these bright, deadly stars.

Script by Damond Benningfield

If you place a pot of water on the stove, turn the burner on full blast, then leave it, the water will eventually boil away.

Something similar seems to be happening in the core of a distant galaxy. The heat is turned up so high that the surrounding gas is boiling off into space — blowing the galaxy to bits.

The galaxy — WISE 2246 for short — is more than 12 billion light-years away. That means we see it as it looked when the universe was about one-tenth its current age.

A supermassive black hole inhabits the galaxy’s core. Its powerful gravity pulls in vast amounts of gas, dust, and stars. This material forms a rotating disk around the black hole. Friction in the disk heats it to millions of degrees, so it produces enormous amounts of energy. This energy pushes back at surrounding material that’s falling toward the black hole.

And that’s what’s happening in WISE 2246. The energy from the disk around the black hole is pushing all of the galaxy’s gas and dust out into space — ripping the galaxy apart.

This activity warms vast clouds of dust, causing them to glow brightly at infrared wavelengths — which is how the galaxy was discovered. The combination of this energy, plus that from the disk around the black hole, help make WISE 2246 the most energetic galaxy yet seen. It emits about 350 trillion times as much energy as the Sun — and thousands of times more than all the stars in the Milky Way galaxy combined.

Script by Damond Benningfield

Last June, the astronomers who study exploding stars caught a whopper: the most brilliant supernova yet seen. At its peak, it shined almost 600 billion times brighter than the Sun. And it’s taking some gaudy physics to explain it.

The supernova was inside a galaxy that’s 3.8 billion light-years away. The galaxy itself isn’t giving birth to many stars, so any supernova would be a rare occurrence.

But supernova ASASSN-15lh was unlike any ever seen in any galaxy. It was more than twice as powerful as the previous record holder, and hundreds of times brighter than a typical exploding star.

Astronomers are still trying to understand the cause of the blast. One possible explanation involves a magnetar — one of the most powerful magnets in the universe.

The idea says the explosion was triggered by the collapse of the star’s core to form an ultra-dense neutron star. The outer layers fell inward, then rebounded, blasting into space. The core’s implosion caused it to spin about a thousand times a second. That generated an extremely powerful magnetic field — perhaps a hundred trillion times more powerful than Earth’s — turning the neutron star into a magnetar.

That magnetic field created a powerful “wind” that slammed into the expanding cloud of debris from the explosion. That heated the debris and made it glow much brighter than a normal supernova — making ASSASSN-15lh the most luminous yet seen.

We’ll talk about something that’s even brighter tomorrow.

Script by Damond Benningfield

As the Moon orbits Earth, the same hemisphere always faces our way. But it’s like the face of a bobblehead doll — it bounces around a bit. Over the course of the Moon’s month-long cycle of phases, this “bounciness” allows us to see a total of 59 percent of the lunar surface. And until spacecraft began flying around the Moon, that provided the only way to see any of the Moon’s hidden farside.

Several factors contribute to these motions, which are known as librations. The main ones are the Moon’s tilt on its axis and its changing orbital speed.

The Moon’s axis is tilted a bit with respect to its orbit around Earth. That causes first its north pole and then its south pole to tip toward us. That allows us to see over the poles, revealing a smidgen of the Moon’s farside.

And the Moon’s distance from Earth changes by about 30,000 miles, which causes the Moon to speed up and slow down as it goes around our planet. But the Moon spins on its axis at a near-constant speed. The difference in those two motions allows us to see around the Moon’s eastern and western limbs — adding tiny slivers of lunar territory to the view from Earth.

And the view is especially impressive tonight, as the almost-full Moon keeps company with what looks like a brilliant star: Jupiter. The giant planet is quite close to the upper left of the Moon as darkness falls, and stays close to our satellite world as they arc across the southern sky during the night.

Script by Damond Benningfield, Copyright 2012

A couple of bright lights keep company with the Moon tonight. Regulus, the star that marks the heart of the lion, is close above the Moon as darkness falls. And a much brighter light — the planet Jupiter — stands farther to the lower left of the Moon.

As the night progresses, the Moon will move eastward against the background of more-distant lights. So by the time the Moon sets, shortly before dawn, the distance between the Moon and its two companions will be about equal.

It takes about 27-and-a-half days for the Moon to complete one full turn against the stars and return to the same point against the starry background. That means the Moon covers an angle equal to its own size in a little less than an hour.

From minute to minute, that motion is imperceptible. If you check in every couple of hours, though, you can tell a difference — particularly when the Moon is close to other bright objects, as it is tonight.

And from night to night, the difference can be astounding. When the sky darkens tomorrow night, for example, the Moon will be huddling right next to Jupiter.

The Moon’s motion against the stars isn’t synchronized with its phases, though. As the Moon circles through the stars, Earth and Moon are also circling the Sun. So it takes almost two days longer for the Moon to complete its cycle of phases — a cycle related to the brightest star in the entire sky: the Sun.

We’ll have more about the Moon and Jupiter tomorrow.

Script by Damond Benningfield

Spring arrives in the northern hemisphere at 11:30 p.m. Central Daylight Time tonight, when the Sun crosses the celestial equator from south to north — the vernal equinox. Over the next three months, the Sun will travel ever-farther northward, bringing longer, warmer days north of the equator.

“Vernal” comes from the Latin word for spring. And equinox means “equal nights.” Theoretically, all points on Earth should see equal amounts of daylight and darkness on the equinox. But for several reasons, the interval between sunrise and sunset — which should be exactly 12 hours — varies by a few minutes.

The vernal equinox marks the starting point for the system that astronomers use to plot the sky.

They measure the positions of astronomical objects using coordinates called right ascension and declination — the equivalent of longitude and latitude. Right ascension is measured in hours. The point where the Sun crosses the celestial equator — the projection of Earth’s equator on the sky — on the vernal equinox is designated as zero hours. It’s the equivalent of zero degrees longitude — the line that runs through Greenwich, England.

And just as Earth’s equator marks zero degrees latitude, the celestial equator is designated zero degrees declination. So at the moment of the vernal equinox, the Sun stands at celestial coordinates zero-zero — beginning a new cycle through the stars.

Tomorrow: the Moon and a couple of bright companions.

Script by Damond Benningfield