StarDate

The eye of the bull — the star Aldebaran — stares into the Moon tonight. The brightest star of Taurus is to the lower left of the Moon at nightfall. The Moon will move closer to Aldebaran during the night — to less than the width of your finger held at arm’s length.

Aldebaran hosts at least one planet. The star is nearing the end of its life, though, so the planet’s future is bleak.

That shouldn’t be the case for a couple of other planetary systems in Taurus. Their planets are still taking shape.

Both systems consist of an infant star surrounded by a disk of gas and dust. An array of radio telescopes known as ALMA has revealed gaps in both disks. The gaps could be created by the gravitational influence of planets.

HL Tauri is less than a million years old. One model says the gaps in its disk are best explained by a system of three planets. The model says they range from roughly a fifth to a half the mass of Jupiter, the largest planet in the solar system.

CI Tauri is about two million years old. A study this year said it could have as many as four giant planets. Two are roughly the mass of Jupiter, with the other two the size of Saturn. One of the Jupiters is quite close to the star. That’s a bit of a surprise. Astronomers had thought that Jupiter-sized planets must be born far away from a star, then move inward later on. So the planets in Taurus are presenting some interesting puzzles for astronomers to solve.

Script by Damond Benningfield

The biggest and smallest of the solar system’s major planets are staging a get-together in the dawn sky. For the next few days, they’ll be separated by no more than a degree or two — less than the width of your finger held at arm’s length. They’re so low in the sky, though, that there’s not much time to look for them.

The brighter of the two worlds is also the bigger one: mighty Jupiter. Its companion is little Mercury, which is also the Sun’s closest planet.

Their appearance is deceiving — Jupiter far outranks Mercury in every category. It’s about 30 times Mercury’s diameter, and close to six thousand times its mass. In fact, Jupiter is more massive than all the other planets and moons combined.

Mercury looks so bright because it’s fairly close to Earth and to the Sun. So it receives a lot of sunlight, and it reflects a good amount of it in our direction.

Jupiter looks so bright because of its huge size, and because the clouds that top its atmosphere reflect more than half of the sunlight that strikes them. That makes the giant planet a giant presence in our night sky.

Look for Jupiter shining brightly quite low in the east-southeast as twilight begins to paint the dawn sky the next few days. Fainter Mercury will stand close above Jupiter tomorrow, then slide down to the left of the giant planet by Saturday. After that, Jupiter will pull away from Mercury, climbing higher into the sky as Mercury drops toward the Sun.

Script by Damond Benningfield

We know of thousands of planets in other star systems, including a few that are similar to Earth. But we’ve seen only a half-dozen or so. And even those appear as nothing more than tiny specks — they don’t tell us anything about the planets themselves.

But future space telescopes might show us hundreds of exoplanets. They wouldn’t reveal any features, but they should reveal the colors of the planets — a detail that would tell us a little about the nature of each world.

LUVOIR and HabEx are among several giant space telescopes that are under consideration. Right now, scientists and engineers are drafting detailed plans for both telescopes. They’re looking at main mirrors up to about 50 feet in diameter — about six times the size of the mirror in Hubble Space Telescope.

Both telescopes would look at a wide range of wavelengths, including some that are invisible to the human eye. These wavelengths can reveal important details about astronomical objects. In the case of an exoplanet, they can reveal surface temperature, the presence of an atmosphere, and what’s in the atmosphere — including molecules produced by living organisms.

The telescopes wouldn’t be limited to exoplanets. They’d also study the lives of stars, the structure of the universe, and much more.

The design studies will be completed next year. NASA will then decide whether to keep one of the projects going — perhaps leading to a launch in a couple of decades.

Script by Damond Benningfield

If a scientist on an alien world aims a telescope at Earth, it might pick up some interesting signals. The telescope might see the chemical signatures of oxygen, ozone, and methane, for example. And it might see a green color that’s missing on most planets. From those observations, the scientist might reach a startling conclusion: life inhabits this small, rocky world.

Scientists here on Earth are starting to look for similar signs of life on some of the thousands of planets discovered in other star systems. In particular, they look for a planet to pass in front of its parent star. If the planet has an atmosphere, some of the star’s light filters through it. That adds the “fingerprints” of chemicals in the atmosphere to the light from the star itself.

Some of those chemicals could be produced by life. On Earth, for example, plants “exhale” oxygen. In the upper atmosphere, some of the oxygen is converted to ozone. And cattle and other animals produce methane.

Detecting those chemicals is no guarantee that a planet is inhabited, though. Scientists must take many factors into account — the size and mass of the planet, its distance from its star, the radiation it receives from the star, and many others.

The observations are tough to make with current technology. But future space telescopes, as well as giant telescopes on the ground, should make it easier to look for signs of life among the stars. More about that tomorrow.

Script by Damond Benningfield

A 500 million-year-old star cluster climbs high overhead during late fall and winter. It’s not quite visible to the unaided eye, but it’s a fairly easy target for binoculars.

Messier 37 probably is about 5,000 light-years away, and it contains about 500 known stars. And it could have even more stars, but they’ve been too faint, or too far from the cluster’s packed center, for astronomers to pick them out.

We know the cluster’s age because of its population of stars. When a cluster like M37 forms, it has a mixture of stars of all sizes and masses.

M37 is basically bereft of the two heaviest classes of stars, which burn out quickly. But it has quite a few of the next class, which last longer.

Since we know how long it takes all of those stars to expire, we have a pretty good idea of the cluster’s age: Longer than the lifespans of the heaviest stars, but shorter than the spans of medium-mass stars. When you plug in all the numbers, it works out to about half a billion years — barely more than one-tenth/the age of the Sun.

Auriga is in the east-northeast as darkness falls. It consists of a pentagon of stars, with brilliant Capella at its top left point. M37 is a little below the figure. In modest binoculars, it looks like a fuzzy star. Higher-power binoculars, though, reveal many of the cluster’s individual stars — a family of stars that’s still quite young.

Tomorrow: looking for signs of life.

Script by Damond Benningfield

The tales that describe many of the ancient constellations can be romantic, tragic, heroic, or majestic. But some are just weird.

A prime example is Auriga. The constellation is low in the east-northeast as night falls right now, and climbs high across the sky later on. It’s marked by a pentagon of stars. And it’s easy to pick out thanks to the brightest member of that figure, Capella — one of the brightest stars in the entire night sky.

Although Auriga is described as a charioteer, the character usually isn’t depicted with a chariot. But he is shown with a goat and her two kids on his shoulder.

There are several versions of his story. In one, he was Erichthonius, an early king of Athens. He was raised by the goddess Athena. Among other things, she taught him how to tame horses. He was so good at it that he became the first person to harness four horses to a chariot, like the chariot that carried the Sun across the sky. Zeus, the king of the gods, was so impressed that he placed the charioteer in the stars.

The goat, which is represented by Capella, isn’t actually a part of any of the legends of Auriga. It may represent the goat that suckled the infant Zeus, who placed her and her children in the sky in gratitude.

The goat and kids may once have formed their own small constellation. Today, though, they ride on the shoulder of the charioteer — who rides on nothing at all.

We’ll have more about the charioteer tomorrow.

Script by Damond Benningfield

A trip to Mars takes a while — with current rockets, about six months to get there and six months to get back. And thanks to the alignment of the planets, the layover between flights is a year or so.

All of that time in space and on Mars would expose astronauts to large doses of radiation. According to a European spacecraft, they’d be exposed to the equivalent of about 6,000 chest X-rays just during the round trip. Their time on Mars would add even more.

We don’t have to worry about space radiation here on Earth — we’re protected by the planet’s magnetic field and its atmosphere. The magnetic field also offers some protection to astronauts in Earth orbit.

Outside that field, though, crews would be exposed to solar storms, and to cosmic rays, which come from outside the solar system.

No one is sure how the radiation would affect astronauts — there aren’t enough studies. But they could suffer from radiation sickness, higher chances of cancer, or other problems.

NASA and others are looking at ways to protect Mars travelers. They’re trying to develop lightweight shielding, for example, or Star Trek-like force fields. And they’re studying ways to enhance a person’s resistance to radiation — everything from gene therapies to suspended animation. So far, though, there are no good solutions to the problem of space radiation.

Mars is in great view tonight. The planet looks like a bright star just above the Moon as night falls.

Script by Damond Benningfield

It’s prime time for the celestial bull. Taurus is well up in the east at nightfall, and climbs high across the sky later on. Look for his bright orange “eye” — the star Aldebaran — with his shoulder — the Pleiades star cluster — standing above it. And over the next few nights, a visitor will streak across the constellation.

Comet Wirtanen just made its closest approach to the Sun for its current orbit, a bit outside Earth’s orbit. As the comet heads away from the Sun, it’ll fly past Earth. It’ll make its closest approach on Sunday night, at a distance of about seven million miles. That’s the 20th-closest approach by a comet ever recorded.

Astronomers are taking advantage of that approach. They’re measuring the size and rotation of the comet’s nucleus, which is less than a mile across. And they’re measuring the composition of the comet and its long tail.

Because we record our show in advance, we can’t tell you how bright the comet will become. But some predictions say that, under dark skies, it could be bright enough to see with the unaided eye. From brighter areas, you’ll probably need binoculars or a telescope.

Tonight, Wirtanen will stand far to the right of Aldebaran and the Pleiades. But it will pass between them on Sunday night — closer to the Pleiades than Aldebaran. After that, it’ll sweep off to their left, quickly leaving the bull behind — but perhaps staying bright enough to watch for a few more weeks.

Script by Damond Benningfield

The asteroid 3200 Phaethon is the type of object that doesn’t usually get a lot of attention. It’s a boulder about three miles across that orbits the Sun once every year and a half. It passes so close to the Sun that any ice it might have been born with should have vaporized long ago, leaving only bare rock.

Yet Phaethon is of special interest because it’s the parent of the Geminid meteor shower. The shower is expected to be at its best over the next couple of nights. And the Moon sets early enough that it will allow the meteors to shine through.

Over the last few years, as Phaethon passed closest to the Sun, it behaved more like a comet than an asteroid — it grew much brighter, and sprouted a tail.

Comets have lots of frozen water and gases. When they get close to the Sun, some of the ice vaporizes, releasing gas and dust into space. This material surrounds the comet, making it much brighter. Sunlight and the solar wind blow some of it away from the comet, forming the tail.

Phaethon has long since lost its ice, though. Instead, the intense heat probably cracks its rocky surface, releasing grains of dust into space. This material briefly surrounds Phaethon, making it brighter. The Sun pushes the dust away, forming a tail. Most of the dust is quickly blown into space. But some of the larger bits join the cloud of debris that causes the Geminid meteor shower — providing fresh material for a celestial lightshow.

Script by Damond Benningfield

A galaxy from the early universe appears to be churning out massive stars the way GM churns out cars — by the bunch.

The galaxy is more than 13 billion light-years away. That means we see it as it looked when the universe was just a few hundred million years old.

Astronomers from Texas A&M, the University of Texas, and other institutions studied the galaxy with one of the giant Keck telescopes in Hawaii.

The scientists are looking at an era when the universe went from transparent to opaque then back again. It became opaque when conditions after the Big Bang cooled enough for protons and electrons to join to make atoms of hydrogen. That was like water molecules binding together to make droplets — it created a sort of cosmic fog. But energy from early stars and galaxies split the atoms apart again, banishing the fog.

Studying this era shows when the fog dissipated. It also reveals details about the birth of those early stars and galaxies.

The galaxy studied with the Keck telescope, for example, could be giving birth to stars up to 300 times the mass of the Sun. Almost no stars are born that heavy in the modern universe. But the mixture of elements in the early universe produced stars that were massive, hot, and brilliant.

A possible supermassive black hole in the center of the galaxy could be responsible for some of its energy. But much of it could be coming from massive stars — brilliant beacons from the early universe.

Script by Damond Benningfield