StarDate

Those hoping for a big encore after last year’s total solar eclipse will have to wait a while. The Sun and Moon will stage three solar eclipses this year, but they’re all pretty much duds. They’re all partial eclipses, so the Moon won’t fully cover the Sun. And all three will be visible mainly over open ocean or sparsely settled land, limiting the size of the audience.

The first of these eclipses takes place tomorrow. It begins around midday as measured here in the United States. But it won’t get anywhere close to the U.S. Instead, the eclipse path will sweep across Antarctica, the Southern Ocean, and into South America — mainly Argentina and Chile. At the eclipse’s peak, the Moon will cover about half of the Sun’s disk.

The next eclipse, in July, will be even meeker, and will appear above the ocean between Antarctica and Australia. And the one after that, in August, will be visible mainly from northeastern Russia and across the north pole.

Eclipses vary because the Moon’s orbit around Earth is tilted compared to Earth’s orbit around the Sun. So the configuration of Sun, Moon, and Earth is different each time the new Moon crosses between Sun and Earth. Most months the Moon skips above or below the Sun, so there’s no eclipse at all. For this year’s eclipses, the Moon will cover only part of the Sun. It’s only when the alignment is just right — when the Moon passes directly in front of the Sun — that we see the spectacle of a total solar eclipse.

Script by Damond Benningfield

 

Our home galaxy, the Milky Way, is on the move. It’s being pulled by the gravity of other galaxies, which are tugging in several directions.

The most immediate tug is toward M31, the Andromeda Galaxy. Like the Milky Way, it’s a cosmic pinwheel known as a spiral galaxy. It’s two-and-a-half million light-years away. But M31 and the Milky Way are quite heavy, so they exert a strong gravitational pull on each other. So in a few billion years they’ll merge, forming a galactic behemoth.

At the same time, the two galaxies are moving toward the Virgo Cluster of galaxies. It’s about 50 million light-years away, and contains more than a thousand galaxies. Many other galaxies will join the cluster. But a recent study says the Milky Way and M31 won’t — they’re about 12 million light-years too far away to be captured.

The same study shows that almost every galaxy in our region is flowing toward a flat sheet of galaxies known as the Local Sheet. And finally, everything including the Virgo Cluster is moving toward a region known as the Great Attractor, which is the core of a supercluster of galaxies. It contains tens of thousands of times the mass of the Milky Way. It’s the ultimate destination for a galaxy on the move.

And under a dark sky, you can see the outline of the Milky Way’s disk on February evenings. It arcs from the brilliant Dog Star, Sirius, in the southeast, directly overhead, and down to Deneb, the tail of the swan, in the northwest.

Script by Damond Benningfield

 

Not many people seek out dark skies on cold winter nights — they’re not prime skywatching time for much of anyone. But those who do find dark skies get a treat: a nice display of the Milky Way. It arcs high overhead in early to mid evening right now. It’s anchored in the southeast by Sirius, the night sky’s brightest star. It then climbs high overhead to the “horns” of Taurus, then drops toward M-shaped Cassiopeia in the north, and the tail of Cygnus, the swan, in the northwest.

The winter Milky Way is thinner than that of summer. That’s because we’re looking away from the crowded center of the galaxy and toward its thinly settled rim. In fact, the point directly opposite the galaxy’s center is at the tip of one of the horns of Taurus, near a star called El Nath.

The rim is about 25,000 light-years away — about a quarter of the diameter of the Milky Way’s bright disk of stars.

But the galaxy doesn’t end there — there’s more stuff outside the disk than inside. Up to 90 percent of the Milky Way’s mass consists of dark matter — material that produces no detectable energy, but that exerts a gravitational pull on the visible matter around it. Most of the dark matter forms a “halo” around the disk — a region that extends hundreds of thousands of light-years into space.

So while the stars may disappear as you look beyond the Milky Way’s disk, the galaxy itself most certainly does not.

More about the Milky Way tomorrow.

Script by Damond Benningfield

Many wonderful astronomical objects are visible to the eye alone — from the Moon to the Andromeda Galaxy. But binoculars add a whole new layer to our view of the universe. They’re especially good at revealing star clusters — families of stars that are packed close together.

An example is M48. It’s in the southeast this evening, well to the left of sparkling Sirius, the brightest star in the night sky.

French astronomer Charles Messier cataloged the cluster in 1771. It was the 48th object in his list of deep-sky objects that might be mistaken for comets, so it’s known as Messier 48.

When Messier was calculating its position, though, he made a mistake. That caused him to place it in the wrong spot. So when other astronomers looked for it, they couldn’t find it. In the 1780s, though, two astronomers found what they thought was a different cluster, which became known as NGC 2548. And in the twentieth century, yet another astronomer discovered the error in Messier’s calculations. When the error was corrected, it turned out that M48 and NGC 2548 were the same object — a beautiful star cluster.

The cluster is about 1500 light-years away, and contains more than a hundred stars. They’re all about 300 million years old — just a few percent the age of the Sun. So some of its higher-mass stars are still around — stars that shine far brighter than the Sun. They help make M48 a pretty target for a good pair of binoculars.

Script by Damond Benningfield

 

The strongest winds on Earth top out at more than 200 miles per hour — the winds at the hearts of powerful hurricanes. Yet the winds on the solar system’s giant outer planets make that sound like a gentle breeze. Winds on Saturn, for example, can reach more than a thousand miles per hour — the fastest winds measured on any planet. What’s more, those winds blow all the time, not just during big storms.

Saturn is in the southeast at first light right now, and looks like a bright golden star. Tomorrow, it stands just below the crescent Moon, making it an especially easy target.

The strongest winds on Saturn are at the equator. They blow from west to east, at speeds that are always in the hundreds of miles per hour, and sometimes faster. They’re powered by the planet’s fast rotation and by its internal heat; Saturn radiates more than twice as much energy into space as it receives from the Sun.

The heat may come from a “rain” of liquid helium tens of thousands of miles below Saturn’s cloud tops.

Saturn has a lower percentage of helium in its atmosphere than any of the other giant planets. That suggests that the helium has fallen deep into Saturn. Models show that the helium forms droplets. As they descend, the energy of their fall is converted to heat. That warms Saturn’s interior. Some of the heat then rises back toward the surface, where it drives Saturn’s weather — including the most powerful winds in the solar system.

Script by Damond Benningfield

 

The pre-dawn sky offers a beautiful start to the weekend tomorrow: a lineup that features the crescent Moon plus three bright planets and one bright star. It stretches across the southeastern quadrant of the sky at first light.

The lowest member of the lineup is Saturn, the second-largest planet in the solar system. It stands to the lower left of the Moon, and looks like a bright golden star. The Moon will slide toward Saturn over the following 24 hours, so the two worlds will stand quite close together on Sunday morning; we’ll have more about that tomorrow.

Two other bright dots stand about the same distance to the right and upper right of the Moon. The one on top is Mars, while the other is Antares, the leading star of the scorpion.

Mars and Antares are just about the same brightness right now. That’ll change rapidly in the months ahead, though. We’re moving closer to Mars, so it’s getting brighter in a hurry. At its peak, in July, it’ll be 40 times brighter than it is now.

By then, it’ll outshine the final member of tomorrow’s lineup: Jupiter, the solar system’s largest planet — a monster that’s big enough to hold more than 1300 Earths. It’s to the upper right of Mars and Antares, and outshines everything else except the Moon, so you can’t miss it. And it, too, is getting brighter. It’ll reach its peak in early May — shining almost twice as bright as it will tomorrow, when it forms the top end of a beautiful morning lineup.

Script by Damond Benningfield

Two legendary “rivals” are huddling close together in the dawn sky this month. Both shine bright orange, making them easy to find. And the Moon passes by them tomorrow, so they’re even easier to pick out.

The ancient rivalry between Mars and Antares comes from their resemblance. Mars reminded ancient skywatchers of the color of blood, so they named the planet for the god of war: Ares in Greece, and Mars in Rome. Since the heart of the scorpion looked so much like Mars, it was called Ant-Ares, which means rival of Ares or, in the Roman version, rival of Mars.

Mars is colored by iron-rich dust that covers much of its surface. The dust is generally orange or yellow-orange. Combined with darker areas of exposed rock, that gives the planet an overall orange appearance.

Antares looks orange because of its temperature. Like all stars, it’s a glowing ball of gas. The color of that gas depends on its temperature. Cool stars shine red or orange, while hot stars are blue or white. Antares is at the cool end of that range, so it shines bright orange.

As Mars travels against the starry background, it passes by Antares once every couple of years. In a few days it’ll pass within about five degrees of Antares — about half the width of a fist held at arm’s length. They’ll be in the south at first light, with Antares to the lower right of Mars. As a bonus, the brilliant planet Jupiter will stand to the upper right of these colorful celestial rivals.

Script by Damond Benningfield

 

An impressive array of lights joins the Moon at first light tomorrow: the planets Jupiter and Mars, and the star Antares.

Jupiter is the brightest of those pinpoints, to the right of the Moon. It outshines everything else in the night sky other than the Moon and the planet Venus, so it’s an easy target. And it’ll grow even brighter over the next few months as Earth catches up to it in our smaller, faster orbit around the Sun.

Mars and Antares stack up to the lower left of the Moon, with Mars closer to the Moon.

Mars, too, will grow brighter over the coming months, and for the same reason — we’re getting closer to it. The distance will shrink from about 150 million miles tonight to just 36 million miles in late July, so Mars will shine about 40 times brighter then. In fact, for a few nights it will even outshine Jupiter.

Antares, on the other hand, shines at the same brightness all year long. It’s hundreds of light-years away, so the change in distance as Earth moves around the Sun is negligible — it doesn’t make any difference in how bright the supergiant star appears.

If you look carefully, you may see that Mars and Antares both look orange. The color is harder to see with the bright Moon so close, but if you block the Moon with your hand it becomes more obvious. Because of the similarity in color and, sometimes, brightness, long-ago skywatchers thought of Mars and Antares as rivals, and we’ll have more about that tomorrow.

Script by Damond Benningfield

 

The surface of Earth is constantly changing. On small scales, the changes are caused by wind, rain, and flowing water. On a large scale, though, they’re caused by the motions of Earth’s crust. New crust is created on the ocean floor, where molten rock pushes up from the mantle, the layer below the crust. And old crust disappears as one plate plunges below another, pushing its rock back into the mantle.

A similar process may be at work on Europa, one of the big moons of Jupiter. In that case, though, the plates are made of ice.

Europa’s crust consists of frozen water, with smatterings of minerals mixed in. That crust probably sits atop a global ocean of liquid water that could be miles deep. Geothermal vents at the bottom of that ocean could pump hot, mineral-rich water into the ocean. That would provide the energy and chemistry needed for possible life.

A recent study says that additional support for life could come from the motions of the plates of ice that make up the crust. Water bubbling through cracks in the ice could deposit minerals on the surface, making a plate denser and heavier. That could make the plate plunge beneath another. Some of its ice would melt, adding important nutrients to the ocean — a possible home for life in the outer solar system.

And Jupiter is in great view at first light tomorrow. It’s to the lower left of the Moon, and looks like a brilliant star.

We’ll talk about the Moon and another planet tomorrow.

Script by Damond Benningfield

Comets are the most unpredictable of astronomical objects. They can delight, they can disappoint, they can vanish with a puff of dust. On rare occasions, though, they can be great — brilliant spectacles that are visible even in daylight.

One such over-performer was first reported 175 years ago today. The Great Comet of 1843 was a member of a group of comets with orbits that carry them quite close to the Sun. They’re fragments of a much bigger comet that shattered about 900 years ago.

The great comet passed closest to the Sun on February 27th, at a distance of just half a million miles. At that range, solar energy vaporized much of the comet’s ices, which in turn released vast amounts of dust. Solar radiation and the solar wind blew the gas and dust away from the comet, forming a long, glowing tail.

The comet became easily visible by late February. It was quite close to the Sun, but so brilliant that it was visible in daylight. As it moved away from the Sun it became even more impressive. Its tail grew longer, stretching across 200 million miles — the longest known comet tail until the 1990s. Seen from Earth it spanned three or four times the width of a fist held at arm’s length.

By the end of March, though, the Great Comet of 1843 was gone, headed into the chill of the outer solar system. Astronomers couldn’t track it long enough to plot its orbit. They know only that it won’t return to the inner solar system for several centuries.

Script by Damond Benningfield