StarDate

When the skywatchers of ancient times named Jupiter after the king of the gods, they had no way of knowing how fitting that title really was. Jupiter is the largest and heaviest planet in the solar system, with the strongest gravitational influence. And it may have used that influence quite liberally when the solar system was young.

There’s evidence that Jupiter and the other giant planets moved around during their early days. Jupiter may have moved as close to the Sun as Mars is today. As it did so, its gravity would have pushed any small, rocky planets into the Sun. As Jupiter moved out to its current position, Earth and the other present-day rocky planets were then born from leftover debris. But Jupiter blocked the formation of another planet from debris beyond the orbit of Mars. Today, that material forms the asteroid belt.

Last year, researchers reported that Jupiter might have kicked another giant out of the solar system. They determined that the orbits of a couple of Jupiter’s moons were changed by an encounter with a planet as big as Neptune, the fourth-largest planet.

And early this year, other researchers reported that Jupiter or Saturn might have ejected a rocky world about 10 times as massive as Earth. That planet may reside far from the Sun, where its gravity pushes around many smaller worlds.

And the king of the planets is in great view tonight. It stands quite close to the upper left of the Moon this evening, and looks like a brilliant star.

Script by Damond Benningfield

Getting close to someone can sometimes lead to a broken heart. For a star, getting close can lead to a shrunken heart.

Consider Regulus, the brightest star of Leo, the lion, which stands just above the Moon as night falls. What we see as Regulus is a big, bright star that spins so rapidly that it looks like a flattened beachball. It has a tiny, invisible companion — the core of a dead star that’s only about half as massive as theory says it should be. The quirks of both stars can be explained by their closeness — they’re only about 30 million miles apart.

When the system was born, the companion was the heavier of the two stars. As a result, it burned through its nuclear fuel faster, so it “aged” more quickly. As it neared the end of its life, it puffed up to giant proportions. It then began to dump some of its gas onto the surface of the star we see as Regulus today. That caused Regulus to spin much faster — so fast that it bulges out at the equator.

Eventually, the dying star lost all of its outer envelope of gas. That should have left a hot, dead core more than half as massive as the Sun. Instead, though, Regulus just kept pulling material away from the core. That left the core with only about a third of the Sun’s mass.

So today, the Regulus system consists of one star that whirls like mad, and another that’s nothing more than a shrunken heart.

We’ll talk about the Moon and another bright light tomorrow.

Script by Damond Benningfield

One of the largest features on Mercury is also one of the planet’s hotspots. The Sun stands high above it every other time Mercury passes closest to the Sun. As a result, noontime temperatures can reach 800 degrees Fahrenheit. Because of that, it’s called the Caloris Basin — from the Latin word for “heat.”

In fact, it has an even hotter history. It probably formed billions of years ago, when a giant asteroid slammed into Mercury. The impact gouged a crater that’s a thousand miles wide. Molten rock bubbled up from below, coating the crater floor with smooth volcanic rock.

The effects of the impact were felt far and wide — all the way around the planet. There’s an area of chaotic terrain on the exact opposite side of Mercury from Caloris Basin. That region could have been sculpted by seismic waves from the impact. The waves might have raced around the planet and convered on the opposite hemisphere, rattling the crust and creating a jumble of hills, ridges, and valleys.

And Caloris Basin continues to show effects from its formation. Narrow cracks in the basin floor appear to be emitting volcanic gases — helping to create a thin atmosphere for the battered little planet.

And Mercury is in view in the western sky in early evening right now. It looks like a bright star, but it’s quite low in the sky as twilight begins to fade away, so you need a clear horizon to spot it. It’ll remain in view for a few more days.

Script by Damond Benningfield

Every now and then, a star can blow its top. Five years ago tonight, for example, a faint star in a faint constellation was seen to explode. For a while, it glowed thousands of times brighter than normal.

T Pyxidis is about 16,000 light-years away. It consists of two stars that orbit each other. One star dumps material onto the other. When the pressure in the infalling material gets too high, it triggers a nuclear explosion.

We’ve seen several of these blasts. Light from the first one reached Earth in 1890. No one saw it then, but photographic plates captured it. Light from subsequent explosions reached Earth in 1902, 1920, 1944, and 1966. Then nearly half a century passed before the most recent eruption, which came in 2011.

Images from Hubble Space Telescope suggest that the star hasn’t always been so cantankerous. Instead, it started exploding only in the past 150 years. The Hubble images show debris hurled into space during each explosion. But there’s no material very far from the star, indicating that the first explosion probably occurred around the year 1866.

Although T Pyxidis has faded, you can still see its constellation tonight — if you have a good star chart and can get away from city lights. Pyxis is in low the southern sky as night falls, and wheels to the southwest later on. The obscure constellation represents a magnetic compass. But it’s best known for an explosive resident — T Pyxidis.

Script by Ken Croswell, Copyright 2015

High technology highlights the southern evening sky at this time of year — the technology of the 18th century. A couple of small, faint constellations are named for the high-tech devices of that time.

Pyxis, the compass, is due south as night falls, just above the southern horizon. Antlia, the air pump, is to its lower left.

Nicolas Louis de la Caille created these and other technology-themed constellations in the 1750s. He journeyed to Africa to map parts of the sky that were difficult or impossible to see from Europe. He drew new constellations that covered relatively barren regions of the sky.

His constellations honored the telescope and microscope, the pendulum clock, and an early instrument for navigating at sea.

In the case of Pyxis, several of its stars once belonged to the giant constellation Argo Navis, which represented the boat that carried Jason and the Argonauts. La Caille split the constellation into thirds, with each part representing a part of the boat.

He then took a few stars that were part of the ship’s mast and turned them into Pyxis — a magnetic compass. Its brightest stars form a line that aims almost due north and south. Those stars are faint, though, so you need a clear, dark sky to see them. More about Pyxis tomorrow.

The stars of Antlia are even tougher to spot. They represent an air pump that had been invented by a French engineer a few decades earlier — a bit of high technology from the 18th century.

Script by Damond Benningfield

The Moon nips at the heel of one of the celestial twins tonight. It passes quite close to Alhena, a moderately bright star at the foot of one of the twins of Gemini. The star is just below the Moon at nightfall, with the Moon moving a bit farther from it before they set, after midnight.

Alhena actually consists of two stars, but only one of them is visible to the eye. That star is bigger and heavier than the Sun, and much brighter. It’s also nearing the end of its life, so it’s beginning to puff up — a process that’ll make it even brighter.

The other star is similar to the Sun — about the same size, mass, and brightness. From Alhena’s distance of more than a hundred light-years, it’s too faint to see with the eye alone. And it’s so close to its brighter companion that, until recently, it wasn’t visible even through a telescope. Only in the last couple of years have astronomers been able to pick it out.

In fact, the companion was discovered only through its gravitational influence on the other star. When astronomers studied the spectrum of Alhena — its individual wavelengths of light — they saw the imprint of two stars. From that, they were able to calculate the details about both stars. And they found that the stars follow an elongated path around each other. At their closest, the stars are about as close as Earth is to the Sun. But at their greatest range, they’re almost 20 times farther — giving one of the twins a wider foot.

Script by Damond Benningfield

If explorers of the future ever get tired, aching feet from walking around on Ceres, they won’t have far to go for some relief. Deposits of Epsom salts seem to be sprinkled across much of the surface, forming bright white spots.

The spots were discovered by Dawn, a spacecraft that’s been orbiting Ceres for the last year. The craft saw the brightest of them when it was still tens of thousands of miles away from Ceres. There was much speculation about the nature of these spots — from deposits of pure ice to the lights of alien bases.

Ceres is the largest body in the asteroid belt between the orbits of Mars and Jupiter. Its surface is rugged and bumpy, with several large impact craters. One of those contains the bright spots that created all the excitement. Known as Occator, it’s about 60 miles wide and a mile deep. And it’s quite young — less than 80 million years old.

Most of the other white spots on Ceres are also associated with craters. That suggests that the material in the spots came from a layer below the surface. The impacts drilled down to that layer, exposing some of the deeper material.

A study published last year said the material is probably a brine — a mixture of ice and magnesium sulfate — the same mineral found in Epsom salts. Ceres has no atmosphere, so once this mixture is exposed to space, the water vaporizes. In fact, some water vapor is still escaping from the crater today — leaving bright white deposits across its floor.

Script by Damond Benningfield

The Moon is a ball of solid rock. It’s more than 2,000 miles in diameter, and it’s about one percent as massive as Earth. Yet it may have formed in a hurry. Almost half of it may have clumped together in just a few months, with just about the entire thing assembling within a few centuries.

There’s pretty good agreement that the Moon was born after another planet slammed into Earth when the solar system was about a hundred million years old. Some studies say it was a glancing blow, while others say it was head-on.

In either case, the impact pulverized much of the young Earth and the other body. That created a large disk of gas and molten rock around Earth.

A good bit of the debris fell back to Earth. But material that was far enough away from the planet began clumping together. A recent study, led by Robin Canup of the Southwest Research Institute, says that within a few weeks, the debris had joined to form thousands of “moonlets” — bodies no more than a few miles across. And within a year or so, many of those had come together to form about 40 percent of the bulk of the present-day Moon.

After a brief lull, more material began clumping together. Within a few hundred years, this process had essentially created the full-grown Moon — the world that lights up the night.

And the Moon teams up with the star Aldebaran to light up the sky this evening. Aldebaran is the “eye” of Taurus the bull, and it stands just to the lower right of the Moon.

Script by Damond Benningfield

It’s often the case that an artist’s work isn’t fully appreciated until after the artist dies. And the same thing is true in the stars. We appreciate a star’s beauty as it twinkles through the night, but its greatest glory — a masterpiece of color and form — is also its final creation.

An example is the Cat’s Eye Nebula, in Draco, the dragon. The faint constellation is in the northeastern sky at nightfall, and slithers high across the north later on.

Photographs reveal swirls and loops of green and red — more like a flower than a cat’s eye. But the nebula’s real beauty is not as a photograph, but as a sculpture. It consists of an elongated bubble of hot gas attached to two bigger bubbles. Jets of gas shoot into space from the tops of the bubbles.

The process that sculpted the Cat’s Eye is the death of its star, which originally was several times as massive as the Sun.

Thousands of years ago, it began throwing off big rings of gas and dust. And about one thousand years ago, it began ejecting its outer layers into space — a process that eventually will leave nothing but its hot, dense core. Ultraviolet energy from the core lights up the expanding bubbles of gas, making them glow. And the nebula’s shape may be sculpted by the gravity of a small companion star.

The Cat’s Eye Nebula is expanding at tens of thousands of miles per hour. Eventually, it’ll spread so far that it will fade away — and a work of cosmic art will die with its artist.

Script by Damond Benningfield

Astronomers have not only discovered lots of planets in other star systems, they’ve also learned quite a few details about many of them. The list includes a planet’s size and mass, the length of its year, and in some cases, even the length of its day.

Given these amazing discoveries, it’s even more amazing to think that we didn’t know the length of the day on one of the planets in our own solar system until the 1960s.

Mercury is both the smallest planet and the closest to the Sun — and that was part of the problem. It stays quite close to the Sun as seen from Earth, so it’s almost always immersed in the twilight, making it difficult to study. It’s tough to see any features on the surface through a telescope, so it’s hard to measure how fast the planet is rotating.

Even so, careful observations seemed to indicate that Mercury’s day and year were the same length — 88 Earth days.

In the 1960s, though, radio telescopes began scanning the planet. They acted as a radar, sending out a beam of radio waves and then capturing their “echo” for study. That revealed that Mercury spins on its axis once every 59 days, so it makes three full turns for every two orbits around the Sun.

And Mercury is in view right now. It looks like a fairly bright star, quite low in the west not long after sunset. It can be difficult to spot through the twilight, but this evening it lines up to the lower right of the Moon — helping point the way to this tricky little planet.

Script by Damond Benningfield