StarDate

Depictions of the sky have been found on walls and ceilings that date back thousands of years. Other depictions are encoded in the layouts of monuments and burial sites. The oldest known portable view of the heavens is ancient as well — at least 3600 years old.

The Nebra Sky Disc was discovered 25 years ago, in Germany. It was buried with swords, axes, and other artifacts. The combination allowed archaeologists to date the burial of the cache to at least 1600 B.C., and possibly earlier.

The disc is a foot across and weighs more than four pounds. The front has a blue background inlaid with about three dozen features made of gold.

The features include a solid disc and a crescent. They’ve been interpreted as the Sun or full Moon, and a crescent Moon. There are also two gold arcs. One may depict a boat carrying the Sun across the sky. The other may show the Sun’s path across the sky from one solstice to the other. Finally, there are 32 smaller gold spots: the stars. Several of them form a tight grouping, which may represent the Pleiades star cluster.

There are many ideas about what it all means. The disc could have been a sort of calendar. On the other hand, it simply could have been decorative — an old and beautiful depiction of the heavens.

The Pleiades is high in the western sky at nightfall. Its brightest stars form a tiny dipper shape — a common landmark for skywatchers both ancient and modern.

Script by Damond Benningfield

When you’re headed toward the Moon or planets, there are no signposts to keep you on the right track. Fortunately, nature provides its own markers: the stars. Spacecraft orient themselves by sighting on the Sun and one or more other stars. In the early days of space exploration, the most popular of those stars was Canopus.

Canopus is a good navigational beacon because of a combination of brightness and location. It’s the second-brightest star in the night sky — only Sirius outshines it. And it’s far south in the sky, in a region with no other bright stars. That makes it an easy-to-find target.

Canopus is more than 300 light-years away. It looks so bright because it’s more than 400 times brighter than Sirius, and ten thousand times brighter than the Sun.

The star is eight times the mass of the Sun. So even though it’s billions of years younger than the Sun, Canopus is nearing the end of its life. It’s uncertain how its demise will play out. It straddles an important dividing line. On one side of the line, it would end as the Sun will — throwing off its outer layers, leaving a hot, small corpse known as a white dwarf. On the other side, it would blast itself to bits as a supernova — briefly providing an especially bright signpost for exploring the universe.

Canopus is so far south that you need to be south of about Dallas to see it. It’s due south about 9 or 10 p.m., well below Sirius — another bright beacon.

Script by Damond Benningfield

Sirius, the brightest star in the night sky, is in the south at nightfall. If you keep your eye on it for a few seconds, though, you’ll see that Sirius isn’t steady. It twinkles fiercely. It gets brighter and fainter, and it changes color rapidly — from red to blue to pure white.

The twinkling is beautiful — unless you’re an astronomer. Twinkling blurs and distorts the view of stars and other objects. That makes pictures of the universe look fuzzy — not good if you’re trying to see the smallest possible details. But astronomers have found a way to overcome the blur — a technique known as adaptive optics.

The stars twinkle as their light passes through different layers of the atmosphere. Air masses of different temperature and density “bend” and split the light. So starlight follows a bit of a zig-zaggy path through the air, making its source look blurry.

Adaptive optics uses a small, flexible mirror to compensate for the blurring. The system looks at a “guide star” — either a real star, or a fake one created by shining a laser beam high in the sky, causing certain atoms to glow. The mirror flexes to keep the guide star sharp. That keeps the images of the sky in sharp focus as well.

Adaptive optics has been around for more than two decades. Today, scientists and engineers are working on “next-generation” versions of the technology — overcoming the beautiful but annoying twinkling of the stars.

Script by Damond Benningfield

The brightest star of Orion stands due south at nightfall, marking one of the hunter’s feet. Rigel shines blue-white — a dramatic contrast to orange Betelgeuse, Orion’s second-brightest light.

Both stars are supergiants — stars that are among the biggest and heaviest in the galaxy. Rigel, for example, is up to a couple of dozen times the mass of the Sun, and perhaps 70 times the Sun’s diameter. But the different colors tell us that the surface temperatures of Rigel and Betelgeuse are quite different. Betelgeuse is much cooler than the Sun, while Rigel is thousands of degrees hotter.

That may be an indication that they’re in different phases. Both stars are destined to end their lives as supernovas — powerful explosions that leave only dense, crushed cores.

But it’s still not clear how that plays out. Astronomers aren’t sure if a supergiant first becomes red, then evolves to a blue phase, or does things in the opposite order, or oscillates between phases. It’s also possible that some supergiants explode while they’re red, while others go out while they’re blue. Either way, both stars are doomed.

Bright blue Rigel is more than 850 light-years away. That’s a long way for a star that’s visible to the eye alone — and especially for one that bright. It’s such a beacon because it’s hundreds of thousands of times brighter than the Sun — a big, hot, bright blue star with a brighter future.

Script by Damond Benningfield

Since the dawn of the Space Age, in 1957, the United States and other countries have sent tens of thousands of objects into space — some into orbit, and others far beyond. Yet the first object known to have reached space did so well before the Space Age — 75 years ago today. It didn’t go into orbit, but it did reach 244 miles — well above the altitude needed to reach “outer space.”

The flight was conducted by the U.S. Army, at White Sands Proving Grounds in New Mexico. At the end of World War II, the American military captured tons of parts from Germany’s V2 rockets. It also captured key German rocket experts, including the most prized of all, Wernher von Braun. He later led the development of the rockets that sent American astronauts to the Moon.

The military built its own versions of the V2, and started launching them in 1946. Early flights took the first pictures that showed Earth’s curvature, and carried fruit flies to study the effects of rocket flight.

On February 24th, 1949, the military launched a mission known as Bumper 5. It consisted of a V2 first stage, and a small second stage. It reached the highest altitude recorded up to that time, and the greatest speed — 5,150 miles per hour. And although its main goal was to study the rocket itself, it also studied the upper atmosphere and beyond — the first observations made from outer space.

Script by Damond Benningfield

The United States and China plan to build permanent bases on the Moon. For the people who inhabit those bases, daily life will be quite different from life on Earth.

For starters, the Moon’s gravity is only one-sixth as strong as Earth’s. So just walking will take some getting used to — a big step inside the base could result in a bump on the head.

There’s no air on the Moon. Without it, there’s an extreme range in temperature. At the equator, it can range from about 250 degrees Fahrenheit at noon, to more than 200 below zero at night.

A day on the Moon lasts about 28 Earth days. That means an average of two weeks of daylight, followed by two weeks of darkness — an arrangement guaranteed to mess with the body clock.

From the side of the Moon that always faces Earth, there’d be something else that might take some getting used to: Earth would always hang at the same point in the sky, day and night. So you could watch Earth go through the same cycle of phases as the Moon does as seen from Earth. Earth is bigger and more reflective than the Moon is, though, so it would be quite a sight.

Earth would be hard to see tonight. That’s because the Moon is full — it lines up opposite the Sun in our sky. Earth is between the Moon and Sun, so it’s new, so no portion of the Moon-facing side is in the sunlight.

The full Moon has a bright companion tonight — Regulus, the brightest star of Leo. It stays close to the Moon all night.

Script by Damond Benningfield

By far the most numerous objects in the solar system are asteroids — chunks of rock, metal, and ice. Scientists have discovered more than 1.3 million of them. They range from a few feet across to a few hundred miles. Most of them reside in the asteroid belt, between the orbits of Mars and Jupiter.

Until a few decades ago, the number of known asteroids was just a few thousand. But some asteroids can come close to Earth, possibly endangering our planet. So scientists launched big searches to find as many as possible. As the searches continue, the known asteroid population goes up by tens of thousands every year. Fortunately, almost all of the asteroids are no danger to Earth.

There are three major classes of asteroids. The most common are class C — they contain a lot of carbon. They account for roughly three-quarters of all asteroids. Next is class S. These objects are rich in silicon, so they’re like a lot of the rocks on Earth. And class M asteroids contain a lot of metal.

The largest object in the asteroid belt is Ceres — about 600 miles in diameter. It was the first asteroid ever discovered. Today, it’s classified as a “dwarf planet.” But when scientists study the overall story of asteroids, they still include Ceres.

Despite their numbers, asteroids don’t add up to much. Their total mass is only three percent of the mass of the Moon. So they’re basically little chips floating through the solar system.

Script by Damond Benningfield

Attitudes can change. That’s as true in science as in anything else. Today, asteroids are considered some of the most interesting objects in the solar system. But that wasn’t always the case. They went from eagerly sought, to absolutely despised. In fact, one astronomer called them the “vermin of the skies.”

Asteroids are chunks of rock, metal, and ice. Most of them reside in a wide belt between the orbits of Mars and Jupiter.

Astronomers first began looking for something in that region in the early 1800s. They noted that there was a mathematical progression in the distances between the Sun and the planets. But there was a gap in that sequence between Mars and Jupiter. So they launched a dedicated effort to find something.

The first asteroid was discovered on the first day of the 19th century. Several others soon followed. But there were so many that they eventually became a problem. They streaked across photographs of the sky, ruining some of the pictures. That made them “vermin.”

Today, though, asteroids are a lot more interesting. More than a million of them have been discovered. They’re leftovers from the early solar system, so they hold clues to the formation of Earth and the other planets. They might have brought water to the young Earth. And some of them can pass near Earth, endangering our planet. So it’s important to know as much as we can about them — big boulders that could be much more than just vermin.

Script by Damond Benningfield

Pollux, the brighter of the “twin” stars of Gemini, is a giant. It’s expanded to about nine times the diameter of the Sun — a beach ball to the Sun’s golf ball. That’s made Pollux much cooler than the Sun, so it looks orange. And it’s more than 30 times brighter than the Sun.

Careful measurements of its diameter, combined with measurements of subtle “ripples” across its surface, have yielded the mass of Pollux as well: 1.9 times the Sun’s mass. Astronomers have combined that with measurements of its weak magnetic field to learn about the history of Pollux.

In its prime, the star was class “A” — two classes brighter and heavier than the Sun. Its surface was much hotter then, so Pollux glowed pure white. And it rotated much faster than it does now, so it generated a stronger magnetic field. That means Pollux would have been much more “active” than it is today — producing more magnetic storms on its surface, and more explosions of particles and energy.

Because Pollux was so massive, though, it burned through the hydrogen fuel in its core in a big hurry. That triggered the changes that make the star what it is today. So even though Pollux is less than 20 percent the age of the Sun, it’s moved beyond the prime of life into “gianthood” — a stage the Sun won’t reach for billions of years.

Look for Pollux quite near the Moon this evening. Its “twin,” the star Castor, is a good bit farther from the Moon.

Script by Damond Benningfield

The planets that flank Earth huddle close together in the dawn sky over the next few days. Venus and Mars are quite low in the east-southeast during the waxing twilight, so you need a clear horizon to spot them. And binoculars wouldn’t hurt.

Venus is the second planet out from the Sun, Earth is third, and Mars is fourth. Their orbits are separated by tens of millions of miles. Yet all three worlds are inside the Sun’s “habitable zone.” That’s the distance from the Sun where the temperature is just right for liquid water on the surface of a planet — or could be.

Venus is far too hot for liquid water. And Mars is too cold. When the planets formed, however, conditions could have been different. There’s evidence that oceans could have covered much of the surfaces of both planets.

Over the eons, though, conditions changed. Venus’s thick atmosphere trapped heat from the Sun, making the planet hotter. It got hot enough to bake out gases from the rocks, making Venus even hotter. Mars, on the other hand, lost much of its atmosphere. Today, the air is much too thin for liquid water to last for more than a few minutes. That leaves only Earth as a comfortable home for life — in the middle of the habitable zone.

Venus is the “morning star.” Fainter Mars is below it tomorrow, and closer on Wednesday and Thursday. After that, they’ll separate, with Mars climbing a little higher each day, and Venus dropping into the Sun’s glare.

Script by Damond Benningfield