StarDate

An explorer that’s winding down its mission is scheduled to make a close pass by the rings of Saturn early Tuesday. It’ll fly less than 60,000 miles above Saturn’s cloudtops, putting it just beyond the edge of the planet’s magnificent rings.

Cassini has been exploring Saturn and its rings and moons for more than a decade. It’s running out of fuel, though, so it’s being targeted to slam into Saturn in September.

In preparation for that final maneuver, it’s been placed in an orbit that carries it above Saturn’s poles, and just outside the rings. That’s allowing it to study the rings in greater detail than ever before. The new observations may help scientists determine just how and when the rings formed.

In April, Cassini will move even closer to Saturn. Each orbit will carry it through the narrow gap between the planet and the inner edge of the rings, providing striking views of Saturn’s clouds.

These close passes also will allow the craft to make high-resolution maps of Saturn’s magnetic and gravitational fields. Those readings will reveal more about the planet’s core — a final accomplishment for a planetary explorer.

And Saturn is in good view at dawn the next couple of days. It looks like a bright golden star, and will stand close to the lower left of the Moon tomorrow, and about the same distance to the right or upper right of the Moon on Tuesday — about the time Cassini is sweeping past the giant planet’s rings.

Script by Damond Benningfield

The Orion Nebula stands halfway up the southern sky a couple of hours after sunset right now. To the eye alone, it looks like a fuzzy star. In reality, though, it’s the birthplace of thousands of stars.

Many of those stars are still in or around the nebula. But at least two that were born in that region are racing away from it at more than 200,000 miles per hour. They probably were kicked out by an encounter with two other stars, which appear just above the nebula.

One of the escapees stands high atop the sky, in Auriga, the charioteer. The other is in the opposite direction from Orion, down near the horizon in Columba, the dove. Under dark skies, that star, Mu Columbae, is visible to the unaided eye.

Simulations show that both stars were ejected from Orion about two-and-a-half million years ago.

The ejection happened after two binary systems passed close together. Each binary contained two big, hot, massive stars.

A study a few years ago found that the encounter split both binaries apart. One star from each system then came together to form a new binary. The remaining star from each binary was given a massive kick away from Orion. One star was hurled northward, while the other was kicked southward.

In the many years since then, both stars have traveled far across the galaxy — one all the way to Auriga, the other to Columba. And they continue to race across the galaxy today, putting even more distance between them and their birthplace.

Script by Damond Benningfield

In many ways, we know more about the surface of Mars than about the bottom of Earth’s oceans. Yet understanding the oceans not only reveals new wonders about our own planet, it may help us learn more about other worlds as well.

As an example, consider a discovery that was made 40 years ago today. Scientists were studying the Pacific Ocean near the Galapagos Islands, at a spot where new crust is being formed. They found a structure that was spewing super-heated water from deep below the ocean floor. The structure was surrounded by an astonishing variety of life.

Scientists have since discovered many more of these hydrothermal vents. They form when water seeps into the ocean floor, where it’s heated by molten rock. The water spews back into the ocean, carrying a variety of minerals.

Bacteria live off these minerals — something that had never been seen before. They form the first link in the food chain for their environment.

It’s possible that hydrothermal vents could be found on other worlds, including several moons right here in our own solar system. A vast ocean of liquid water probably lies below the icy crust of Europa, one of the moons of Jupiter, for example. Other oceans may be found on other bodies.

The vents on these worlds would have all the ingredients for life: water, minerals, and energy. So discovering life where it wasn’t expected here on Earth can tell us where to start looking for life on other worlds.

Script by Damond Benningfield

A faint but reliable comet is putting in an appearance in the evening sky right now, although you need binoculars or a telescope to see it. It should get a bit brighter over the next couple of weeks before it disappears in the Sun’s glare.

Encke’s Comet was first recorded in 1786. A few decades later, German astronomer Johann Franz Encke connected that first appearance with several others in the intervening years. He calculated the comet’s orbit, and predicted its next return. When it showed up as predicted, it was named in his honor.

Like all comets, Encke is a ball of rock and ice. It orbits the Sun once every 3.3 years. When it comes closest to the Sun, the extra solar energy warms the comet, vaporizing some of its ices. The gas flows out into space, along with tiny particles of dust. This material forms a glowing cloud around the comet. Sunlight and the solar wind push some of the gas and dust away from the comet, forming a tail.

Encke will pass closest to the Sun in less than a month, so it’s shining at about its brightest. Right now, it’s not far to the lower right of Venus, the brilliant “evening star,” which is in the west at sunset. The comet is dropping toward the horizon, though, so it moves a little farther from Venus, and a little lower in the sky, each evening. It’s getting brighter, too, which will make it an easier target for binoculars — until it disappears in the evening twilight in early March.

Script by Damond Benningfield

Centaurs are everywhere. Two constellations are named for these mythological creatures, which are half man and half horse: Centaurus, the centaur, and Sagittarius the archer, which is a centaur holding a bow and arrow.

But many more centaurs are hidden from view. These are big chunks of debris in the outer solar system. Many of them exhibit traits of both rocky asteroids and icy comets. This mixed identity led to the “centaur” name.

The first centaur was discovered 40 years ago, and astronomers have found hundreds more since then. They circle the Sun between the orbits of Jupiter and Neptune, the inner and outer giant planets. And they cross the orbits of one or more of the planets.

Centaurs may have come from the Kuiper Belt, a doughnut-shaped zone beyond Neptune. Interactions with other members of the Kuiper Belt may have pushed them toward the Sun. Now, they journey through the realm of the giants — but not for long. Within a few million years, the gravitational influence of the giant planets kicks a centaur either into the inner solar system, where it might hit the Sun or a planet, or out of the solar system entirely.

The largest known centaur is Chariklo. It was discovered 20 years ago today. It’s roughly 150 miles in diameter. A few years back, astronomers found that it has at least two rings. That makes Chariklo the smallest body in the solar system with known rings — perhaps adding a third identity to this solar-system hybrid.

Script by Damond Benningfield

A deceptive arc of three bright celestial objects climbs into good view late this evening: the Moon, the planet Jupiter, and the star Spica.

The deception is that although we see all three of them at the same time, we don’t see all three at the same moment in time. Instead, we’re seeing them as they looked at different moments in the past.

We see the Moon almost in real time. It’s only about a quarter of a million miles away — a bare hop by astronomical standards. At that range, it takes light — moving at 186,000 miles every second — less than a second and a half to reach Earth.

Brilliant Jupiter, which is below the Moon, is also quite close as astronomical objects go — about 450 million miles. At lightspeed, that’s just 40 minutes away. So as you look at Jupiter tonight, you’re seeing the giant planet as it appeared about 40 minutes earlier.

Fainter Spica, to the lower right of Jupiter, is much farther away — about 250 light-years. So we’re seeing it as it looked around the year 1767, give or take a decade or so — shortly before a young Alexander Hamilton first arrived in the American colonies.

All the other stars that are visible in the night sky range from a few light-years away to a few thousand. So the starry firmament isn’t like lights on a great dome, as our ancestors thought. Instead, it’s a 3-D extravaganza — a sparkling array of lights scattered in time as well as space.

Script by Damond Benningfield

The constellation Vela sails quite low across the southern horizon around midnight — but only from about the southern half of the United States. From the northern states, it stays below the horizon and out of sight.

Because of that, astronomers can’t really look at that region of space with telescopes in the U.S. But a recent study using telescopes in the southern hemisphere found something big. Really big: A supercluster of galaxies that may span hundreds of millions of light-years.

A supercluster is made up of many galaxy clusters, each of which may contain hundreds or thousands of individual galaxies. That makes a big, prominent wall of galaxies across the universe.

But the Vela supercluster is hidden behind dense clouds of stars, gas, and dust in the disk of our home galaxy, the Milky Way. That partially blocked the view of the supercluster.

Over the last few years, though, astronomers observed galaxies in that region with telescopes in South Africa and Australia. They found several clusters packed tightly together, centered at roughly 800 million light-years away — a new supercluster. The astronomers hope to use some new telescopes in the coming years to better define this giant wall of galaxies.

And if you’re south of about Kansas City, look for Vela due south around midnight, just above the horizon. It contains only a couple of bright stars — residents of our own galactic home.

Script by Damond Benningfield

When we look into the sky from here on Earth, we see one big, bright star — the Sun. All the other stars we see are mere pinpoints of light; the brightest star in the night sky looks less than a hundred-billionth as bright as the Sun.

But the residents of many other star systems would have two or more bright stars to look at it. That’s because most of the stars in the galaxy are members of systems with two stars, three stars, or even more.

An example is Dubhe, the star that marks the lip of the Big Dipper’s bowl. It’s low in the northeast as night falls right now, but wheels high across the north later on.

Dubhe actually consists of two pairs of stars.

The brighter pair is quite impressive. It includes a stellar giant — a star that’s nearing the end of its life. Changes in its core have caused its outer layers to puff up. That’s made the star about 30 times wider than the Sun, and hundreds of times brighter. Its bloated surface is relatively cool, though, so it glows bright orange.

The star’s companion is no slouch, either. It’s still in the prime of life, just as the Sun is. But it’s more massive than the Sun, so it shines brighter. And its surface is much hotter than its companion’s, so it shines pure white.

The two stars are a couple of billion miles apart — more than 20 times the distance from Earth to the Sun. Even so, if a planet orbits either star, both stars would shine brightly in its sky — giving it two “suns” for the price of one.

Script by Damond Benningfield

The almost-full Moon washes out much of the sky tonight. The fainter stars are overpowered by its light, leaving only the brighter ones to shine through. One example is Regulus, the brightest star of Leo, which is to the upper right of the Moon during the evening hours.

The stars of the Big Dipper are in pretty good view as well. They circle a good distance around the sky during the night as they loop around the North Star, Polaris.

From most of the United States, most of the stars of the Big Dipper are so close to the North Star that they never set — they’re in view every night of the year. At the latitude of Kansas City, for example, only the star at the tip of the dipper’s handle ever dips below the horizon.

As Earth orbits the Sun, though, the dipper appears in different parts of the sky at different times of year. Right now, it’s low in the northeast as night falls, climbs high across the north during the night, and is in the northwest at first light.

As the months roll by, though, so will the dipper. By the start of summer, it’ll stand in the northwest at nightfall — just where it stands at dawn right now. After that, it’ll dip back toward the horizon — skimming just above it for those in the north, and partially dipping below the horizon for those at more southerly latitudes.

It’s all part of the clockwork order of the stars — no matter how much moonlight fills the sky.

We’ll talk about one of the dipper’s stars tomorrow.

Script by Damond Benningfield

The Moon slowly closes in on one of the brightest stars in the sky tonight: Regulus, the heart of Leo, the lion. The star stands to the lower left of the Moon as night falls, but closer above the Moon at first light tomorrow.

The Moon passes Regulus once every 27 and a third days. That’s known as the Moon’s “sidereal” period — the time it takes to make one full turn against the background of stars.

But Earth and the Moon are orbiting the Sun, which shifts position against the stars from day to day. Because of that, it takes the Moon about two days longer to catch up to the Sun from one month to the next. Since the Moon’s cycle of phases is determined by its position relative to the Sun, that means the Moon is at a different phase every time it passes Regulus or any other star.

Tonight, for example, the Moon is full. When it sneaks up on Regulus again, in early March, it’ll be a couple of days before full. And in each succeeding month, it’ll be a few days farther from full on each passage. By the time the Moon goes by Regulus in August, it’ll be new, so both the Moon and Regulus will be lost in the Sun’s glare.

And as you watch the Moon early this evening, see if you can notice a faint bit of shading on its face, caused by Earth’s outer shadow, the penumbra. This barely-there eclipse is tough to see. But the Moon itself isn’t — it blazes brightly all night, near the heart of the lion.

Script by Damond Benningfield