StarDate

Until almost a century ago, the constellations were little more than stick figures. Various astronomers connected different dots to define their characters. And they used different borders to define each constellation’s chunk of celestial real estate.

Order was imposed upon the heavens in 1930. Belgian astronomer Eugene Delporte defined the borders of the 88 official constellations for the International Astronomical Union. Those borders have been maintained ever since.

The list of constellations includes Aries, the ram. It’s well up in the east as night falls right now, and stands due south a few hours later.

Despite its fame as a member of the zodiac, Aries includes only three bright stars. A fourth star is added to those to create a stick figure that looks like a lopsided boomerang.

But the formal constellation covers a much wider area — about one percent of the entire sky. It looks like a horizontal rectangle with chunks missing from the lower left and top right corners.

Its borders consist of 12 individual lines. When Delporte drew those borders, they followed strict lines of declination and right ascension — the equivalent of latitude and longitude on Earth’s surface.

Since then, thanks to a wobble in Earth’s axis, the borders have shifted position a bit. So some day, astronomers will have to redefine the borders — or watch as the stars of all the constellations shift across the borders of their neighbors.

More about Aries tomorrow.

Script by Damond Benningfield

We’re already several days into winter, but the signature star pattern of summer remains in good view in the evening sky. And one of its members does double seasonal duty — it anchors one of the signature star patterns of early winter.

The Summer Triangle is in the western sky as night falls. Its three points are Vega, the brightest member of the group, which forms the right point of the triangle; Altair, the left point; and Deneb, at the top of the triangle.

Although Vega looks brightest, Deneb is intrinsically brightest. In other words, if you lined up all three stars at the same distance from Earth, Deneb would outshine the other two, and by a wide margin: Altair is about a dozen times brighter than the Sun, Vega about 40 times — and Deneb as much as 200,000 times.

In fact, Deneb is one of the biggest, brightest stars in the entire galaxy — a monster that’s a couple of hundred times wider than the Sun. It’s also quite hot, so it shines blue-white. And someday, it’ll get even brighter — it’ll blast itself to bits as a supernova.

For now, though, Deneb marks the tail of Cygnus, the swan. At this time of year, the swan is diving toward the western horizon nose first. At that angle, its body and outstretched wings look like a crucifix, giving Cygnus a second name: the Northern Cross. Deneb serves as both the tail of the swan and the top of the cross — a bright star that’s beautiful no matter which way you look at it.

Script by Damond Benningfield

Winter offers some of the most beautiful night skies of the entire year: bright stars, prominent star patterns, and a few treats, which seems only right for the holiday season.

As the last blush of twilight drains from the sky this evening, for example, look toward the west for the Northern Cross. Those bright stars represent Cygnus, the swan. As the swan begins to set, though, it dives head-first toward the western horizon, so it looks like a cross. The swan’s brightest star, Deneb, stands atop the cross.

Not long after that, the signature constellation of winter climbs into view in the eastern sky: Orion the hunter. Look for his three-star “belt” extending straight up from the horizon. Orange Betelgeuse stands to the left of the belt, with blue-white Rigel to the right.

And an hour or so after Orion climbs into good view, follow the line made by the belt down toward the horizon for the brightest star in all the night sky: Sirius, the dog star. It twinkles fiercely as it ascends the sky, rapidly changing from red to blue to white.

One of the celestial treats is the Pleiades star cluster — a family of a thousand or more stars at the shoulder of Taurus, the bull. It looks like a tiny dipper. It’s more than 400 light-years away — one of the most-distant objects that’s easily visible to the unaided eye.

These and many other beautiful sights make a glimpse at the evening sky a pleasant and relaxing way to enjoy a holiday night.

Script by Damond Benningfield

One of the first things we notice about the stars is that they twinkle — their light doesn’t hold steady. That has nothing to do with the stars themselves. In fact, if you could watch the stars from out in space, you’d see they shine steadily. Instead, twinkling is a result of what happens to the starlight closer to home — in Earth’s atmosphere.

To the eye alone, a star is nothing more than a pinpoint of light. So as that light enters Earth’s atmosphere, it’s easily distorted.

In particular, layers of air of different density act as lenses. They bend the rays of starlight as they pass through the atmosphere, causing them to wiggle back and forth as they descend. To the eye, that makes a star look like it’s shifting position.

Another effect is that the light is sometimes bent away from you, so the star suddenly looks fainter.

And different wavelengths of light — different colors — are bent at different angles. Sometimes only one color makes it to your eye, so a star can appear to change color rapidly, flashing from red to blue to white.

To see all of these effects at work, look southeast this evening for Sirius, the brightest star in the night sky. It climbs into good view by about 8 or 9 o’clock. As it climbs away from the horizon, its light passes through an especially thick layer of air, so it twinkles fiercely. It flashes on and off, and goes through a rapid cycle of color changes — all in the twinkling of an eye.

Script by Damond Benningfield

The oddest of the Sun’s dwarf planets is shaped a bit like a rugby ball and has two small moons. And as astronomers reported a couple of months ago, it also has a thin ring. That makes it the most-distant object in the solar system with a known ring.

Haumea orbits at an average distance of about four billion miles from the Sun — about the same distance as Pluto. And in some ways, it’s similar to Pluto. It’s made mainly of ices, so it has a bright surface. Unlike Pluto, though, it has an odd shape — it looks like a 1400-mile-long rugby ball, or a long, skinny potato.

Back in January, Haumea passed in front of a star. Such an event is known as an occultation. By observing it from several locations, astronomers can measure an object’s size and shape, and look for evidence of moons and rings. That’s especially helpful for objects like Haumea, which are so small and far away that they appear as little more than pinpoints in even the biggest telescopes.

The passage was visible from much of Europe, so 10 observatories there turned their gaze toward the occultation. And they noticed that the star’s light flickered a bit before and after the star passed behind Haumea itself. That revealed that Haumea has a ring. It might consist of debris from an impact by a small asteroid, or material spun out into space by the dwarf planet’s fast rotation. Either way, it makes Haumea the farthest body in the solar system with a known ring.

Script by Damond Benningfield

Winter begins in the northern hemisphere today. And tonight, as if to celebrate the new season, the Ursid meteors will be at their peak.

In most years, the Ursids produce no more than a few meteors an hour. On rare occasions, though, they can produce a hundred per hour, making the Ursids one of the best meteor displays of the year. Such outbursts took place in 1945, ’86, ’93, and 2000. And no one knows what will happen tonight.

The meteors form when debris from Comet Tuttle burns up in the upper atmosphere. The comet is named for American astronomer Horace Tuttle, who discovered it in 1858. But the meteor shower it spawns was discovered only in the last century.

The meteors appear to radiate from the constellation Ursa Minor, the little bear. Some of its stars form the Little Dipper, with the tip of its handle marked by the North Star. Because the meteor radiant is so far north, the farther north you are, the more meteors you’re likely to see. In fact, the very best place for meteor watching in the U.S. may be Alaska.

The best time to observe the shower is before sunrise tomorrow — something that’s easy to do when the nights are so long.

Although the Ursids probably will be weak, they could stage a surprise outburst. So if you’re up early tomorrow, why not get away from city lights and watch for yourself? There won’t be any moonlight to interfere, and you just might catch sight of some falling stars.

Script by Ken Croswell

The cycles of day and night, of years, and even of the seasons are all astronomical phenomena — they’re the results of the motions of Earth, one of the Sun’s eight major planets.

Day and night are obvious — they’re caused by Earth’s rotation on its axis. And so is the year — it’s the amount of time it takes Earth to make one full circle around the Sun.

The seasons may not be quite as obvious, but they, too, are caused by Earth’s year-long journey around the Sun. In fact, that journey will take us to the start of winter tomorrow. It arrives at 10:28 a.m. Central Time — the moment of the winter solstice. The Sun stands farthest south for the year, and it’s the shortest day of the year north of the equator.

The seasons change because Earth’s tilt toward the Sun changes.

Earth is always tilted at the same angle — about 23 degrees. And the axis always aims at the same point in the sky — Polaris, the North Star.

As viewed from the Sun, though, Earth appears to nod up and down over the course of a year. At the start of northern summer, the north pole dips toward the Sun during the day. That gives us longer days here in the U.S. At the start of northern winter, though, Earth is on the opposite side of the Sun, so the south pole nods toward the Sun. That brings long days to the southern hemisphere, but short days and long nights to the north.

So the seasons are a result of astronomy — an interaction between a planet and a star.

Script by Damond Benningfield

Giant galaxies like the Milky Way didn’t start out as behemoths. Instead, they began small and grew larger as they swallowed other galaxies. An example of a galaxy that’s still under construction is in the faint constellation Fornax, the furnace.

Fornax skirts across the southern sky during the evening hours tonight. Beyond its dim stars lies one of the nearest galaxy clusters — 60 million light-years away. Its brightest member is NGC 1316.

The brilliant galaxy is a cross between a spiral and an elliptical. Most elliptical galaxies look like glowing footballs or spheres, with little gas and dust — the raw materials for making more stars. But NGC 1316 looks so odd that an astronomer once called a photograph of it “defective” because it showed such strange features. We now know that those features are lanes of dark dust — one of the main features of a spiral galaxy.

NGC 1316 may be the remnant of two spirals that smashed together. It emits copious amounts of radio waves — a sign of disturbance. And loops outside its disk trace the paths of smaller galaxies that are falling into it.

Although NGC 1316 is the brightest galaxy in the Fornax cluster, it’s not at the cluster’s center. Instead, it’s off to the side, in a clump of galaxies that’s probably falling into the main cluster. So just as the galaxy is still assembling itself, so is the entire cluster of galaxies.

So the universe, it seems, is still a work in progress.

Script by Ken Croswell

A constellation with connections to both scientific advancement and the horrors of war and revolution scoots low across the southern sky tonight.

Fornax rises in the southeast shortly after nightfall. It’s not much to look at; its three brightest stars form a wedge that aims toward the south. In fact, it’s so feeble and so far south that it wasn’t drawn until the mid-1700s.

Fornax was one of 14 constellations created by French astronomer Nicolas Louis de la Caille, after a trip to South Africa. All of them are so far south that they were barely visible or not visible from Europe.

La Caille named this constellation for a chemical furnace, in honor of fellow scientist Antoine Lavoisier. Lavoisier had developed accurate descriptions of how things burn and how chemical reactions take place.

Among other things, Lavoisier used his knowledge to develop gunpowder for the French government. One of his employees later emigrated to the newly formed United States, where he founded the DuPont company. One of his first jobs was developing gunpowder for the American government.

Lavoisier also worked with an agency that collected taxes. After the French Revolution, that wasn’t a popular group of folks. Many of them were guillotined — including Lavoisier.

So the patchwork quilt that forms the constellations tells some interesting stories about our legends and our history — but some of them have unhappy endings.

More about Fornax tomorrow.

Script by Damond Benningfield

Jolly old Saint Nick will be heading our way soon. But he can’t hold a candle to jolly old Saturn, a Roman god of agriculture. A year-end festival honored the god, and it was the biggest party of the year — a week-long holiday that ended with rounds of gifts — including wax candles.

Saturnalia began as a single-day celebration, on December 17th. Over the centuries, it was extended to three days, then a full week. It came after the autumn planting season had ended, and coincided with the coming winter solstice — the shortest day of the year.

It began with a day of public festivities, including a sacrifice at the Temple of Saturn and a big banquet. It then segued to private celebrations, although the official holidays continued. People decorated their houses with greenery and other festive touches.

One of the main features of Saturnalia was unrestrained merry-making — lots of eating, drinking, gambling, and otherwise making merry. Another was a temporary upheaval of Roman social status. Masters served meals to their slaves, and the slaves were free to move about.

Saturnalia ended with a day of gift giving — fruits, small terracotta figurines, and wax candles. The candles may have been given to symbolize the solstice and the longer days that would follow.

Some of the customs of Saturnalia were folded into the new celebration of Christmas — banquets, candles, gifts, and more — keeping some of the “jolliness” going long after Saturnalia disappeared.

Script by Damond Benningfield