StarDate

It may be a cliche, but it’s true: If at first you don’t succeed, try, try again. That’s certainly the case for the scientists hunting for dark matter. They’ve conducted many big experiments over the past few decades. So far, though, they haven’t found a thing. So the hunt is going smaller — looking for extremely light particles known as axions.

Astronomers see the effects of dark matter all across the universe. The dark matter itself emits no energy, but its gravity pulls on the visible matter around it. Measuring the mass of that gravitational effect shows that there’s about five times more dark matter than normal matter.

For a long time, the leading theory of dark matter said it was made of WIMPs — weakly interacting massive particles. Such particles would be much heavier than the protons and neutrons that make up normal matter. Physicists have built detectors to look for WIMPs. The detectors are far underground, so other types of particles are filtered out. But the experiments have come up empty.

So in the past few years, the search has begun turning toward axions. If they exist, they’d be billions of times less massive than electrons, which are by far the puniest parts of atoms. As with WIMPs, axion detectors are far underground. The University of Washington has been operating one for years. And a group in Europe is just getting cranked up. So the search for most of the mass in the universe is going small.

Script by Damond Benningfield

Spring arrives in the northern hemisphere tonight, at the moment of the March equinox, as the Sun crosses the celestial equator. Day and night are about equal across the entire planet — hence the name “equinox,” which means “equal nights.”

The Sun is passing through Pisces, the fishes. In fact, it’s appeared in Pisces at the equinox for a couple of thousand years. Before that, it was in Aries, the ram. The shift is the result of an effect known as precession of the equinoxes.

Earth wobbles on its axis like a spinning gyroscope. As it wobbles, the Sun’s location against the background of stars moves, too. When the modern constellations were first drawn, the Sun appeared in Aries at the March equinox. So even today, the point of the equinox is sometimes called the First Point of Aries.

The Sun and equinox bring up a point about the constellations. There are actually two types of designations — one for astronomy, and the other for astrology. In astrology, the zodiac is divided into 12 roughly equal constellations. The Sun is “in” each constellation at set dates — they don’t change with precession.

In astronomy, each constellation has precisely defined borders. And the constellations are all different sizes. Pisces is fairly wide, so the Sun remains within its borders for a while. The Sun entered Pisces on March 11th, and won’t slide over into Aries — the next constellation over — for another month.

Script by Damond Benningfield

When he was just 14 years old, Franz von Paula Gruithuisen found himself in the middle of the Austro-Turkish War. He wasn’t a prisoner or a refugee. Instead, he was a field surgeon. But just a year later, he was using a small telescope to observe the Moon. Those episodes marked the beginning of a diverse career in science. It featured both important contributions and false starts.

Gruithuisen was born 250 years ago tomorrow, in a castle in Bavaria. His father was a servant, so his early education was limited. But the youngster was so bright that he quickly earned new opportunities. He taught medical students topics from A to Z — anthropology to zoology. And he devised new medical procedures and instruments. But in 1826, he became a professor of astronomy.

He was especially interested in the Moon, which he thought was inhabited. He even saw what appeared to be a city, which he named Wallwerk.

His main contribution to lunar science, though, was his idea about lunar craters. He was the first astronomer to suggest they were carved by collisions with space rocks. His idea didn’t gain a lot of early support. In fact, it was disputed until the 1960s. Today, though, there’s no doubt about it — the Moon’s craters are the result of giant impacts.

You can see some of the craters tonight. The Moon is high in the sky at sunset, and stays in view most of the night. It’s near the twin stars of Gemini.

Script by Damond Benningfield

The types of planets you have as neighbors may depend on your neighborhood. The planets discovered in our region of the Milky Way Galaxy come in just about every variety: hot Jupiters, super-Earths, mini-Neptunes, lava planets, ocean planets, and others.

But that may not be the case for other parts of the galaxy. As an example, there appear to be almost no super-Earths or mini-Neptunes outside the Milky Way’s disk.

The disk is about a hundred thousand light-years wide, but only a few thousand light-years thick. The Sun moves up and down within the disk, but never leaves it. But the orbits of many other stars are much more tilted than the Sun’s. These systems move above and below the disk like horses bobbing on a merry-go-round.

A recent study found that these stars have almost no super-Earths or mini-Neptunes, which are common in our region of the galaxy. Super-Earths are dense and rocky, like Earth, but a few times more massive. Mini-Neptunes are a bit heavier still — slightly less massive than Neptune, the smallest of the Sun’s giant planets.

Scientists aren’t sure why these types of planets are missing in the Milky Way’s outer precincts. Perhaps their star systems didn’t have enough raw materials for making such planets. Or maybe their systems have kicked out such planets. Or it could simply be that those kinds of worlds are harder to find — perhaps still awaiting discovery in their far-away neighborhoods.

Script by Damond Benningfield

The Moon hangs precariously above a star with a nasty-sounding name tonight: El Nath. The name comes from an Arabic phrase that means “butting” or “goring.” It indicates the star’s position in its constellation — at the tip of one of the horns of Taurus, the bull.

The star itself is impressive. It’s about five times the size and mass of the Sun. And it’s much brighter. If you consider just its visible light, El Nath is about 300 times brighter than the Sun. So it looks bright even though it’s more than 130 light-years away — the 25th-brightest star in all the night sky.

But the eye alone doesn’t reveal a star’s complete story. El Nath is many thousands of degrees hotter than the Sun. Hot stars shine blue-white. And they also produce a lot of ultraviolet light — wavelengths that are far too short for the eye to see. When you factor in the ultraviolet and all other forms of light, El Nath is about 700 times the Sun’s brightness.

El Nath appears to be about a hundred million years old — only a few percent the age of the Sun. Yet it’s already nearing the end of its life. It’s puffing up as a result of changes in the nuclear reactions taking place in its core. Before long — on the astronomical time scale — it’ll swell to hundreds of times the Sun’s diameter. So El Nath will shine much brighter than it is now — making the tip of the bull’s horn even more impressive.

Script by Damond Benningfield

If you’re ready for a taste of summer, look no farther than the dawn sky. The constellations in view at first light are just what you’ll see as night falls in July and August. Scorpius is low in the south, with Sagittarius in the southeast. The Big Dipper hangs from its handle in the northwest. And the Summer Triangle — the stars Vega, Deneb, and Altair — stands high in the east.

As Earth orbits the Sun, our viewing angle on the stars changes. As a result, each star rises about four minutes earlier each night. So a star that rises at dawn now, will rise eight hours earlier in July, 10 hours earlier in August, and 12 hours earlier in September.

Now you might think this all means that we’d see the current morning configuration 12 hours earlier in the night during September — half a year from now. And you’d be partially right. The same configuration of stars will be in the sky at that hour. But the Sun sets later then, so it’s still daylight when the stars stand in their current dawn positions. So by sunset then, Scorpius and the others will have rotated farther to the west. That means the best time to see this setup in the early evening sky is a month or two earlier — July and August.

That all sounds a bit confusing, but trust us: The stars have been following that pattern for a long time — moving the same stars we see in the dawn sky now into the evening sky during the short nights of summer.

Script by Damond Benningfield

Two beautiful objects team up this evening: the Moon and the Pleiades. The little star cluster is close above the Moon. Binoculars will help you pick out some of its brighter stars through the moonlight.

The Pleiades has more than a thousand stars. They were born from the same cloud of gas and dust. But that doesn’t mean the stars are all alike. They come in many varieties. The brightest of them are much more impressive than the Sun.

The brightest of all is Alcyone. It’s about six times the mass of the Sun, and about 2,000 times brighter. And it spins in a hurry — so fast that it bulges outward at its middle. That makes it much wider through the equator than through the poles.

Alcyone is an oddball. The overall cluster is more than 100 million years old. Yet Alcyone appears to be only about 70 million years old. That could mean that it’s been reborn in a way — from the merger of two stars. That would make it look brighter, hotter — and a good bit younger.

The second-brightest member of the cluster is Atlas. It’s actually a triple system — three stars bound by gravity. Two of the stars are quite close together, while the third is far away — it takes about 260 years to orbit the other two.

Again, look for the Pleiades, which marks the shoulder of the bull, above the Moon this evening. Aldebaran, the bull’s bright eye, is to the upper left of the Moon, with the brilliant planet Jupiter well below the Moon.

Script by Damond Benningfield

Scientists are finding so many moons of the solar system’s giant planets that they can hardly keep up with them. By the end of last year, Saturn was in the lead, with 146 confirmed moons. Jupiter — the biggest planet — came in second, with 95. But some of its moons are the most amazing of all — worlds with giant volcanoes, or hidden oceans that could host microscopic life.

Most of the moons of both planets are a lot less interesting. They’re basically big chunks of rock and ice. Some of them could be captured asteroids, but most probably are debris from shattered moons.

The population of known moons has exploded in the past decade or two. In part, that’s because modern technology makes it possible to find these tiny, faint objects. Also, scientists are putting a lot more effort into the search. That’s because, while the recent discoveries are all fairly boring on their own, they reveal a lot about the histories of both worlds. In particular, they tell us how the systems of moons and rings may have evolved — producing the busy planetary systems we see today.

Jupiter stands quite near our own moon tonight. It’s to the lower left of the crescent Moon at nightfall. Jupiter looks like a brilliant star — only the Moon and the planet Venus outshine it. It’s a world with plenty of known moons — and probably many more awaiting discovery.

We’ll talk about the Moon and some stellar companions tomorrow.

Script by Damond Benningfield

Stars come in a whole spectrum of colors, from icy blue to deep red. But our eyes can see the color in only a few stars — most of them are simply specks of white. That’s because most stars are too faint to show off their palette. The human eye can pick out the colors of only the brightest ones.

Our eyes contain two types of light receptors: rods and cones. They’re in the retina, at the back of the eye.

There are about a hundred million rods. They’re sensitive to low levels of light, so they allow us to see in the dark. But they don’t see the world as clearly as cones. And they don’t see colors.

The eye contains only about six million cones. They provide a sharper view. And they are sensitive to colors — some see red, others blue, and still others green. But they don’t activate when the light is faint. Ergo, they see the colors in bright stars, but not in faint ones.

Of course, the number of stars for which we see colors depends on the viewer. Some people have a greater sensitivity to color than others.

Most of us can see color in some of the brighter stars in view this evening. Betelgeuse, well up in the south-southwest at nightfall, is bright orange. So is Aldebaran, to its right. Rigel, below Betelgeuse, is blue-white, as is Regulus, in the east.

Some bright stars don’t show any color. The best example is Sirius, the brightest star in the night sky, which is in the south. It shines pure white — its true color.

Script by Damond Benningfield

Planetary scientists may see many descriptions this week that are similar to this one:

Return to Mimas

Blow up the Death Star (moon) and

Find hidden oceans.

That’s from a presentation about one of Saturn’s moons by Adeene Denton and colleagues at last year’s Lunar and Planetary Science Conference in Texas. It’s become a tradition for scientists to provide a simple description of their work as haiku. The conference has even held a contest for the best one. The winner in 2022 came from Benjamin Boatright, in a presentation about Mars:

Pitted crater floors:

Places permeated by

Perplexing pingos?

The first haiku was penned in 2001, by Allan Tremain, about a new instrument:

Bright leaves on dark sky:

Beyond the brilliant rainbow,

Vision fades away.

Others followed his lead the next year, and the approach caught on. This year’s conference starts today, and attendees can expect to see haiku in the descriptions of hundreds of presentations.

And some scientists have branched into other forms of poetry. Last year, for example, a team led by Jon Roberts described some work about another moon of Saturn with a limerick:

Induction and sounding and tides

Will get at Europa's insides

These techniques are superior

To probe the interior

And explore where life might reside.

Tomorrow: Looking for color in the stars.

Script by Damond Benningfield