StarDate

The stars that mark the ends of the Big Dipper are sometimes described as “renegades.” While the dipper’s five other stars move through the galaxy in unison, the stars at the ends go their own ways. In 50,000 years or so, their motion will have stretched the dipper so much that it will no longer look like a dipper.

The renegades are Dubhe and Alkaid. Dubhe marks the lip of the dipper’s bowl, while Alkaid is at the end of its handle.

The other five stars are all members of the Ursa Major moving group. These stars move through the galaxy at the same speed and in the same direction. Their chemistry is alike, too. That suggests that the stars were born together. In fact, they may once have formed a tight cluster. Over time, though, the cluster was pulled apart. But even though the stars are on their own, they maintain their similar motion through space.

The stars of the moving group are all roughly 80 light-years from Earth. Alkaid is right at 100 light-years, while Dubhe is about 25 light-years farther. And they’re moving more or less in the opposite direction across the sky from the others. So over time, that will distort the dipper’s shape, then eventually destroy it — leaving our descendants without one of the sky’s most recognizable star patterns.

For now, though, look for the Dipper high in the northwest at nightfall, with Alkaid at the top and Dubhe at the bottom.

Tomorrow: outlining the black hole at the heart of the Milky Way.

Script by Damond Benningfield

Although all the stars in the night look a lot alike, they actually glow in different colors. And tonight you can look for a pair of stars that makes a stunning color contrast. One star is blue, and the other is red.

This duo is known as Delta Lyrae, and all you need to see it is a pair of binoculars.

The different colors indicate that the stars have different surface temperatures. The blue star is hotter than the Sun, whereas the red star is cooler than the Sun.

The two stars aren’t a true binary — they’re not connected with each other in any way. They just happen to line up in the same direction from Earth.

The hot blue star is the more distant of the two — a bit more than a thousand light-years. It’s part of a small cluster of young stars.

The red star was once blue, too. But it used up the hydrogen in its core, causing its outer layers to expand. An expanding gas gets cooler, so the star’s surface went from being hot and blue to cool and red. The star is now a red giant, so it’s much bigger, brighter, and cooler than the Sun.

These colorful stars reside in the constellation Lyra, the harp. It’s easy to find because it’s home to Vega, one of the brightest stars in the night sky. It’s about half-way up the eastern sky at nightfall. Delta Lyrae is not far to the lower right of Vega, at the left point of a small diamond of stars. When you observe it through binoculars, you’ll see a lovely pair of stars: one blue, the other red.

Script by Ken Croswell, Copyright 2016

The religion of ancient Egypt said that when a pharaoh died, his soul ascended to the heavens to join with the god Osiris, in the modern-day constellation Orion. His tomb was filled with items he might need to help him on his way. And in the case of at least one pharaoh, some of those items probably came from the heavens.

The tomb of the boy king Tutankhamun contained thousands of artifacts. Many of them were made of gold, including a dagger buried inside his coffin. But Tut also had a second dagger, made of iron.

When Tut was buried, Egypt hadn’t started to work with iron ore, so the dagger probably was made from an iron meteorite — a space rock that fell to Earth. The iron hasn’t been tested to confirm a celestial origin. But a few years ago, scientists tested some iron beads buried 2,000 years before Tut, and confirmed that they were made from meteorites. So it seems likely that the dagger was as well.

Another artifact was an elaborate piece of jewelry known as a pectoral. Its centerpiece is a scarab beetle carved from yellow glass.

The glass formed about 26 million years ago when an asteroid or comet plunged toward Earth, either hitting the surface or exploding in the atmosphere. Heat from the explosion melted some of the desert sand, creating chunks of glass. One of those chunks eventually made its way to an Egyptian artist, and then to Tut’s tomb — a piece of glass from the heavens for a king ascending to the heavens.

Script by Damond Benningfield

The people of ancient Egypt didn’t begin mining iron ore until fairly late in the kingdom’s history. But that didn’t stop them from using iron. The iron came not from the ground, though, but from the sky.

A few years ago, British researchers studied an iron bead from London’s Petrie Museum. The bead had been found in 1911 in a tomb about 40 miles south of Cairo. The tomb was built more than 5,000 years ago — a few centuries before the first pharaohs ruled over a united Egypt. The tomb included necklaces and bracelets containing beads of gold, semi-precious stones — and iron.

Scientists had long suggested that the iron came from a meteorite — a space rock that landed on Earth. But they couldn’t confirm that until the recent study. The researchers scanned one of the beads with beams of neutrons and gamma rays. They found a structure that resembled that of iron found in meteorites. More important, they found high percentages of nickel, carbon, germanium, and phosphorous — elements that are found in iron meteorites but not in ore deposits on Earth.

Their scans revealed that the iron had been melted and hammered into thin sheets, then rolled to form skinny tubes. So the artisans of ancient Egypt were working with iron long before they began pulling it from the ground.

The iron beads aren’t the only trinkets from beyond Earth found in ancient Egyptian tombs. We’ll talk about some found in the tomb of King Tut tomorrow.

Script by Damond Benningfield

Countless numbers of space rocks have blasted Earth over its long history. These collisions gouge holes in the ground, known as impact craters. Wind and rain erase most of them, but a few survive. And scientists continue to search for more. One problem, though, is how to tell when a big, round hole in the ground is an impact crater and when it’s just a big, round hole in the ground.

In the last decade, for example, two possible impact craters were discovered in Egypt.

The first was discovered 10 years ago. Satellite photos revealed a round structure that’s almost 20 miles wide. Such a crater would have been formed by an asteroid almost a mile in diameter.

Because the crater is so remote, it took a while for scientists to get to it. When they did, they found no evidence of an impact. The rock hadn’t been subjected to a powerful shock, for example. So the feature’s origin remains unknown.

Another crater was spotted a couple of years later. It’s only about 150 feet across. But its rim is quite sharp, and “rays” of debris surround it — rocks and dirt blasted out by the possible impact.

This time, ground exploration confirmed the crater’s impact origin. Known as Kamil, the crater probably formed when an iron meteorite slammed into the desert about 5,000 years ago. Most of it was vaporized, but scientists gathered almost a ton of debris — bits of iron strewn across the Sahara.

We’ll talk about bits of meteorites buried in the desert tomorrow.

Script by Damond Benningfield

Herbert Friedman was hunting solar flares. At the time, in the 1950s, no one knew whether these explosions on the Sun produced X-rays or only less-powerful forms of energy. To find out, Friedman launched X-ray detectors on rockoons — balloons that carried rockets to high altitudes. If a solar flare was spotted, the rocket would fire and climb above the atmosphere, which blocks X-rays.

In June of 1956, one of the rockoons captured a flare’s X-ray flash, confirming the powerful nature of these outbursts.

It was one of many successful rocket experiments by Friedman, who was born in Brooklyn 100 years ago today. In 1940, he joined the Naval Research Laboratory, where he used X-rays to test various materials in the lab. He also developed a Geiger counter that sniffed out evidence of the Soviet Union’s first nuclear explosion.

In the 1950s, he turned his attention to the Sun, and became one of the first astronomers to use rockets to study the universe. He monitored our star with instruments carried aloft by small rockets that briefly climb above the atmosphere before falling back to Earth. He took the first X-ray picture of the Sun, and later developed the first Sun-watching satellite.

By then, he was also using rockets to explore the night sky. In 1964, for example, he watched as the Crab Nebula disappeared behind the Moon. The experiment showed that the entire nebula produced X-rays — the afterglow of an exploded star.

Script by Damond Benningfield

The Sun is at a standstill right now. Oh, it’s still orbiting the center of the galaxy at an impressive clip — about half a million miles per hour. And it’s still moving across the sky as Earth turns on its axis. But the points along the horizon at which the Sun rises and sets aren’t changing.

The reason is that today is the summer solstice. It’s a point in Earth’s orbit that marks the beginning of summer in the northern hemisphere and winter in the southern hemisphere.

We have seasons because Earth is tilted on its axis. At the June solstice, the north pole tilts toward the Sun, bringing more sunlight to the northern hemisphere. Six months later, at the December solstice, the south pole tilts sunward, giving the northern half of the globe shorter days and longer nights.

Between the solstices, the Sun moves north and south in the sky. As a result, its rising and setting points move north and south as well. At some times of year, if you have a good way to mark these points, you can see the difference from day to day.

But the Sun appears to “stand still” along the horizon for a few days either side of the solstice. In fact, solstice means “Sun stands still.” At the June solstice, the Sun is farthest north for the year, so it rises and sets to the north of due west. Just how far north depends on your latitude.

Incidentally, the summer solstice is also the longest day of the year, so there’s plenty of sunlight as we head into summer.

Script by Damond Benningfield

The Moon makes itself scarce tonight. It’ll be “full” early tomorrow, so it rises shortly before sunset and remains in view for the rest of the night. But since the night is short, so is the time for moonwatching.

The length of time that the full Moon is in view varies by season and by latitude. At the equator, the full Moon is always in view for about 12 hours. As you move away from the equator, though, there’s a bigger difference based on the time of year.

That’s because Earth is tilted on its axis. At this time of year — summer starts tomorrow here in the northern hemisphere — the north pole dips sunward. So during the day, the Sun sails high overhead for northern latitudes, and it stays in view for a long time — up to about 16 hours as seen from the Lower 48 States, and up to 20 hours or more from parts of Alaska.

But since it lines up exactly opposite the Sun in the sky, the full Moon always does just the opposite of what the Sun does. So if the Sun is high in the sky and in view for a long time, then the Moon is low in the sky and in view for a much briefer time. Denver, for example, will see only about 10 hours of moonlight tonight, while Moon-deprived Anchorage will be graced with the Moon’s presence for only about seven hours. And tomorrow night will be about the same.

So wherever you are, enjoy the last evening of spring and the beautiful moonlight — but do it in a hurry.

More about the change in seasons tomorrow.

Script by Damond Benningfield

Johannes Hevelius was one of the first astronomers of the telescope age to map the Moon. He spent four years charting the lunar surface, and published an atlas of his illustrations.

Hevelius made one other contribution to lunar studies. Like many other scientists, he thought the Moon was inhabited by intelligent creatures. So he coined a name for them: Selenites, from the name of the Greek Moon goddess.

The existence of Selenites was a topic of debate for a couple of centuries. Because they couldn’t see any evidence of an atmosphere, some astronomers thought the Moon was barren. But others thought the Moon must be inhabited. That included William Herschel, who discovered the planet Uranus.

In 1824, Franz von Paula Gruithuisen reported seeing cities, roads, and a star-shaped temple. A few years later, Joseph Johann von Littrow may have suggested a way to contact the Selenites: excavate giant geometric patterns, fill them with kerosene, and set them ablaze.

Not long after that, the idea of a lunar civilization lost favor. But the idea of some form of life persisted — especially microscopic life. In fact, when the first Apollo astronauts returned from the Moon, they had to spend weeks in isolation to make sure they hadn’t brought any lunar “bugs” back to Earth.

The bug-free Moon has a couple of bright companions tonight. The planet Saturn looks like a bright star close to the Moon, with the orange star Antares to their lower right.

Script by Damond Benningfield

The Moon and some bright companions put on a beautiful show this evening. They’re in the south-southeast at nightfall, and set in the wee hours of the morning.

The brighest of the three companions is orange Mars, which is to the right or lower right of the Moon as darkness falls. The little planet was at its brightest just a few weeks ago, as Earth passed by it. But as we pull away, it’s beginning to fade. Even so, it’s still the third-brightest object in the night sky right now, after the Moon and the planet Jupiter.

Another planet is farther to the lower left of the Moon: Saturn, the second-largest planet in the solar system. It was at its best a couple of weeks ago. And like Mars, it’s beginning to lose a bit of its luster. But it won’t fade as quickly or as dramatically as Mars, so you won’t see much of a difference from week to week or even month to month.

The Moon’s final companion is Antares, the leading light of Scorpius. It’s farthest from the Moon, standing almost directly below it at nightfall.

Of the three companions, Antares is the only true star. And it’s one of the most impressive stars in the entire galaxy. It’s many times bigger and heavier than the Sun, and tens of thousands of times brighter. It looks fainter than the two planets only because it’s millions of times farther away — a blazing star that’s hundreds of light-years from Earth.

We’ll have more about the Moon and its bright companions tomorrow.

Script by Damond Benningfield