StarDate

The little planet Mercury is putting in a brief evening appearance right now. You need to look at just the right time to see it, though. And the view is best from southern latitudes; from the north, you might not be able to see it at all.

Mercury is the smallest planet in the solar system — only about half again the diameter of the Moon. And its surface looks a lot like the Moon’s — it’s covered with impact craters, mountains, and volcanic plains. And there’s evidence that the surface is still being sculpted by Mercury itself.

Mercury’s interior has been cooling since the planet was born. As it cools, it shrinks. That causes the crust to shrink as well.

Scientists have seen evidence of that shrinkage in the form of scarps — giant cliffs that can be miles high and hundreds of miles long.

A recently concluded mission to Mercury also found some smaller scarps. Such small features are quickly erased by meteorite impacts. The fact that they still exist means that they formed fairly recently. They probably formed as the crust continued to cool and shrink — although at a much slower rate than when Mercury was young. They show that Mercury is still geologically active — rattled by its ever-shrinking crust.

Look for Mercury quite low in the southwest about 30 to 45 minutes after sunset, far to the lower right of brilliant Venus. Mercury looks like a fairly bright star, but you may need binoculars to pluck it from the fading twilight.

Script by Damond Benningfield

For a star like the Sun, which travels through the galaxy alone, the future is pretty certain. But for stars with close companions, the future is tougher to see. Interactions between the two stars change their evolution, fuzzing the view through the astronomer’s crystal ball.

Consider Capella, one of the brightest stars in the night sky. The yellow star is in the northeast at nightfall, and soars high overhead later on.

What we see as Capella is really two stars. Each star is bigger, brighter, and heavier than the Sun.

The stars are only about 10 percent the age of the Sun. But because of their greater heft, they’ve aged much more quickly. Both stars have completed their “normal” lifetimes. Now, thanks to changes in their cores, their outer layers are puffing outward — especially the heavier star.

The stars are close together — only about two-thirds the distance from Earth to the Sun. So as the stars puff up, their surfaces will get closer and closer to each other. Eventually, the heavier star will begin to dump some of its gas on the companion. It’ll also generate strong “winds” that’ll surround both stars in a cloud of gas.

And that’s likely to alter the evolution of the smaller star. As it adds mass, its own nuclear reactions will crank up. The two stars also may spiral closer together — and could even merge. That could create a bigger star, or it could trigger an explosion. For now, though, just how it all plays out remains hard to foresee.

Script by Damond Benningfield

Before World War II, radio astronomy was more of a hobby than a science. After the war, though, the field blossomed, with radio telescopes popping up around the world. And that was no coincidence. The war provided a lot of experience at operating sophisticated radio gear, and a lot of leftover equipment for astronomers to nab.

The first observations of the radio sky were made in the early 1930s -- not as a scientific endeavor, but in an effort to discover the cause of static in trans-Atlantic phone calls. By 1940, there was only one real “radio astronomer” in the world.

World War II saw an outburst of new and improved technologies. One of those was radar, which uses radio waves to detect airplanes and other objects.

Much of the technology was developed by scientists who were contributing to the war effort, including astronomers. They became skilled at making the equipment, using it, and interpreting its findings. They even did a little science. A British scientist-turned-military officer, for example, discovered radio waves from the Sun.

When the war ended, many of the scientists put their new skills to work as radio astronomers. And the military was getting rid of surplus equipment, so the astronomers could snatch it up for little or no money.

So many post-war radio telescopes consisted of antennas and receivers that had seen service during World War II. They helped turn the field of radio astronomy from a hobby to a science.

Script by Damond Benningfield

As 1941 neared its end, McDonald Observatory was riding high. It had been dedicated just two and a half years earlier, and its astronomers were making amazing discoveries with the world’s second-largest telescope.

But 75 years ago this week, things changed.

FRANKLIN ROOSEVELT: December 7th, 1941 — a date which will live in infamy — the United States of America was suddenly and deliberately attacked by naval and air forces of the empire of Japan.

With the United States entering the war, there were brief concerns of an invasion through Mexico. So McDonald director Otto Struve considered removing the mirror from the big new telescope and burying it. But that plan was quickly dropped, so the telescope that now bears his name kept on working.

The working conditions weren’t easy, though. Many of the observatory’s astronomers and much of its support staff joined the war effort. Rationing made it hard to keep the facilities going, and even to travel to town to get supplies.

Yet Struve and a few others managed to keep on looking at the stars, although many of their observations weren’t analyzed until after the war. And some astronomers who were serving in the war made it back to West Texas when they could. During one of those breaks, Gerard Kuiper discovered the atmosphere of Titan, the largest moon of Saturn.

So McDonald stayed busy — and its telescope stayed intact — throughout the war.

More about astronomy and the war tomorrow.

Script by Damond Benningfield

AUDIO: The Japanese have attacked Pearl Harbor, Hawaii, by air, President Roosevelt has just announced.

75 years ago today, the United States was plunged into World War II. And within days of the attack on Pearl Harbor, many thousands of men had volunteered to join the war effort — including astronomers and other scientists. And for the next four years, American scientific knowledge and know-how were concentrated on winning the war.

Some astronomers and astronomy departments taught pilots and sailors how to navigate by the stars. Others worked on rockets, the optics for bomb sights, and the atom bomb. Just before the war started, in fact, the leader of the bomb project, J. Robert Oppenheimer, had helped develop the concept of black holes.

And still more astronomers worked on the developing technology of radar. Their work helped radio astronomy blossom when the war ended.

Most observatories scaled back their work during the war. The Palomar Observatory in California, for example, stopped preparing the mirror for what would become the world’s largest telescope.

But a few astronomers did keep looking at the stars. Most were too old or frail to serve in the military, or they were barred from war activities because they were German. With many American cities blacked out, these astronomers were treated to dark skies. They made important discoveries about the size of the universe, the nature of stars, and more — advancing scientific knowledge during World War II. More tomorrow.

Script by Damond Benningfield

Wallace Eckert was ahead of his time. Eckert was an astronomer at Columbia, who specialized in calculating the orbits of the Moon and planets. In 1940, though, he took over the job of producing the Nautical Almanac, a government publication that helped sailors navigate by the stars.

Eckert introduced two innovations. First, he used mechanical computers to do the calculations. And with war looming for the United States, he introduced a new publication — the Air Almanac — to help aircraft navigators.

Before Eckert came along, all of the calculations in the almanac were done by hand — millions in all. Eckert found a way to do them with machines — a combination of computers and some of his own innovations.

That was especially important for the Air Almanac. It was published three times a year, with 730 pages of tables and charts per issue. It provided positions of the Sun, Moon, planets, and other objects at 10-minute intervals for every day of the year. To determine location, a navigator measured the positions of these objects, then compared the readings to the listings in the almanac.

Since even a small error could lead an aircraft astray, accuracy was critical. Computers provided that accuracy — helping American aviators find their way throughout World War II.

Eckert continued to help pilots find their way long after the war. In fact, NASA used his calculations of the Moon’s orbit to guide Apollo astronauts to the Moon.

Script by Damond Benningfield

The Moon stands high in the south not long after sunset this evening, with three planets trailing to its lower right. Mars is the closest to the Moon, with Venus, the “evening star,” farther along the same line. Mercury is farther still, just above the horizon, and visible mainly from the southern half of the country.

For the past two and a half centuries, such an alignment has been more than a pretty picture for navigators at sea. It’s helped them determine their longitude — their position east or west on the globe.

Such a determination was made possible by two inventions. First was clocks that could keep accurate time at sea. And the second was the Nautical Almanac, a book first published by the British Astronomer Royal 250 years ago.

The almanac contained a lot of basic skywatching information. For navigators, though, its most important feature was a daily table of the Moon’s precise distance from bright stars and planets. The distance was listed at three-hour intervals for Greenwich, England. By measuring the angles between the Moon and the other objects, and calculating the difference from Greenwich, a navigator could determine his longitude — a critical detail for safe travels.

The United States began publishing its own almanac in the 1850s. The two almanacs linked up in 1960, and in 1981 became the Astronomical Almanac. By then, they’d been joined by one more publication — a key tool for pilots in World War II. More about that tomorrow.

Script by Damond Benningfield

The Moon slides past the planet Mars tonight. Mars looks like a bright orange star close to the left of the Moon. Venus, the “evening star,” stands well to their lower right.

In many ways, Mars is the most Earth-like world in the solar system. And one of those ways is the weather. Mars has clouds, cold fronts, dust storms, frost, and even snow.

The biggest and most menacing weather events are the dust storms. They can cover many thousands of square miles — and on rare occasions, they can blanket the entire planet.

These giant storms usually begin around the start of spring in the northern or southern hemisphere. Frozen water and carbon dioxide in the polar ice caps vaporize and enter the atmosphere. This stirs up the powdery orange dust around the poles, then whips it around the planet. A planet-wide dust storm may have doomed two Soviet landers that arrived at Mars in 1971. Storms could prove troublesome to future human explorers as well.

The Martian clouds typically form thin streamers, not the billowy piles we see on Earth. But when a low-pressure system spins across Mars, the clouds form the same spiral pattern as storm systems here. And the clouds occasionally drop a blanket of fresh snow — made not of water, but of carbon dioxide.

And as dawn breaks across Mars, a layer of frost usually coats the landscape. As the Sun climbs into view, though, the frost quickly vaporizes — leaving the Martian surface bone dry.

Script by Damond Benningfield

Learning the constellations can be hard work. Most of their connect-the-dots patterns are faint and difficult to find, especially from light-polluted cities.

Sometimes, though, Mothern Nature offers a sort of cheat sheet — one or more bright objects that point the way. And that’s the case right now for Capricornus the sea-goat.

The constellation is low in the south and southwest as night falls. Its brightest stars outline the bottom of a bikini bathing suit. Once you identify it, you shouldn’t have much trouble finding it again on later nights.

That’s especially true right now, because the solar system offers three bright lights to help you find the sea-goat: Mars, the Moon, and Venus.

Tonight, the Moon is at the constellation’s western edge, so the bathing suit is arrayed to the left of the Moon. Venus, the “evening star,” is below the Moon, just outside the constellation. It’s moving toward Capricornus, though, and will cross its borders in a few nights. It’ll spend the rest of the month transiting the constellation. So if you follow Venus through the end of the year, you’ll see all of Capricornus.

Orange Mars is also moving across the constellation. Tonight, it stands next to Iota Capricorni, a star that’s visible only from areas with dark skies. Early next week, though, Mars will pass by a couple of brighter stars, at the left end of the bikini — helping you learn this famous constellation.

More about the Moon and Mars tomorrow.

Script by Damond Benningfield

The Moon and the planet Venus form a beautiful pairing early tonight. Venus is the brilliant “evening star,” not far to the left of the Moon. They set by about eight o’clock.

Venus looks so bright in part because its atmosphere is topped by an unbroken layer of clouds. The clouds reflect most of the sunlight that strikes them back into space.

Those clouds do something that doesn’t happen on Earth or any other planet in the solar system. They race around Venus much faster than the planet spins on its axis.

Venus takes about 243 Earth days to complete one turn. But the clouds at the top of its atmosphere whip around the planet once every four days — an effect called super-rotation. That means the clouds can complete 60 trips around the planet for every Venusian day. On Earth and the other planets, the clouds rarely move any faster than the planet’s rotation rate.

The cause of the super-rotation is a mystery. Even though planetary scientists have been studying it for decades, they don’t have a good explanation. They do have some ideas, though.

One says that the atmosphere above the clouds interacts with the solar wind — a stream of charged particles from the Sun. That creates waves in the atmosphere, which carry momentum down to the cloudtops, about 40 miles above the surface. That gives the clouds a big push.

But another idea says the super-rotation is driven by pressure from the Sun’s light — revving up Venus’s high-speed clouds.

Script by Damond Benningfield