StarDate

A celestial grandfather strolls low across the south on winter evenings. He’s represented by two stars. In the western world, they’re part of the constellation Columba, the dove. But in ancient China they were known as the Grandfather.

The stars are Alpha and Epsilon Columbae. Coincidentally, they’re about the same distance from Earth – about 280 light-years. And both are much bigger and brighter than the Sun. But there’s a big difference in their ages, so the stars aren’t related.

Alpha – the First Star of Grandfather – is the brighter of the two – the brightest member of Columba. It’s less than a hundred million years old – about two percent the age of the Sun. But it won’t be around much longer. It’s about four and a half times the mass of the Sun. Heavier stars age more quickly. In the next 150 million years or so, Alpha will move out of the “prime” phase of life and into the next phase, as a giant.

Epsilon has already reached that phase. It’s not as massive as Alpha, but it’s about one and a half billion years older – a third the age of the Sun. It’s puffed up to many times the size of the Sun, so it shines much brighter. Before long, though, it will cast off its outer layers, leaving only its hot, dead core – and Grandfather will be down to a single star.

Columba is low in the south-southeast at nightfall. Alpha and Epsilon are close together, near the center of the constellation.

Script by Damond Benningfield

On summer nights, Earth faces the heart of the Milky Way Galaxy. That part of the Milky Way features dense clouds of stars. Under dark skies, it’s quite a sight. But during the long, cold nights of winter, we’re facing the opposite direction – toward the galaxy’s edge. So the Milky Way looks thin and faint – a bare ghost of its summer glory.

No matter which direction you face, the hazy band of light known as the Milky Way represents the combined glow of millions of stars that outline the galaxy’s disk. The disk is about a hundred thousand light-years wide, but only a few thousand light-years thick. It contains a few hundred billion stars.

The center of the galaxy is densely packed, like the downtown of a major city. But its outskirts are like the suburbs. There are fewer stars, and they’re more widely spread. And the closer to the galaxy’s edge, the more thinly spread the stars become.

The Milky Way doesn’t end at the edge of the disk. The disk is surrounded by a “halo” of stars and dark matter. It extends hundreds of thousands of light-years into space in every direction. But the halo is like the countryside – a few solitary residents spread far and wide. So nothing in the halo is visible without a good telescope – far outside the galaxy’s disk.

The Milky Way arcs high across the sky on February evenings. You need nice dark skies to see it – the thin but still beautiful glow of our home galaxy.

Script by Damond Benningfield

If you walk under a ladder after breaking a mirror, does that make your day doubly unlucky? Since we’re a science program, we’ll say no. But that double-trouble philosophy underpins the superstitions about Friday the 13th. Both Friday and the number 13 have been considered bad luck. Put them together, and you have what may be the most feared of any day-and-date combo.

The individual superstitions both have religious and mythological origins. In Christianity, for example, the Last Supper was shared by 13 men. And Jesus was crucified on a Friday.

Just when the two were put together isn’t clear. The idea of Friday the 13th being unlucky shows up in some publications in France in 1834. The first record of it in the United States dates to 1882.

How many people fear the date isn’t clear, either. But scientists have come up with a couple of names for it. The shorter one, believe it or not, is friggatriskaidekaphobia. Frigg was the Norse goddess for whom Friday is named, and triskaidekaphobia is fear of the number 13.

Other than some unlucky teens in the “Friday the 13th” movies, there’s no evidence that the day is any more dangerous than any other. A study in 2011 compared hospital records for 13 Fridays the 13th to other date combinations. There was no bump in the number of emergency-room visits – nothing unlucky about Friday the 13th.

Script by Damond Benningfield

The surface of Ariel looks like a sheet of paper that’s been loosely crumpled. It’s covered with ridges, wrinkles, and gashes. That may be telling us that Ariel once had a deep ocean of liquid water.

Ariel is one of the larger moons of the planet Uranus. It’s about 720 miles in diameter – a third the size of our moon. It orbits just a hundred thousand miles from the planet – much closer than the Moon is to Earth. It’s roughly a 50-50 mix of ice and rock.

Our only good look at Ariel came in 1986. Voyager 2 flew past it and photographed about a third of its surface. The pictures revealed a complex face. It has a mixture of old and young craters, deep ridges, and smooth plains that might have been paved by water gurgling up from inside the moon.

A recent study modeled the orbit of Ariel over the ages. It found that the orbit was once much more lopsided than it is today. As Ariel moved in and out, the gravity of Uranus stretched and squeezed the little moon. That could have melted some of the ice inside it, creating an ocean a hundred miles deep, topped by a thin crust of ice. The stress of all the stretching and squeezing could have cracked the ice, creating the wrinkly surface we see today.

Uranus is high overhead at nightfall. It’s below the Pleiades star cluster, and farther to the right of the bright orange star Aldebaran. Through good binoculars, the planet looks like a faint star.

Script by Damond Benningfield

Ursa Major III is doomed. It’s falling apart, and may vanish completely in a couple of billion years.

There’s not much to it even now. It’s so faint that it wasn’t discovered until 2023. It contains about 60 stars – all of them ancient, and all much smaller and fainter than the Sun. They add up to only about 16 times the Sun’s mass. They’re packed into a loose ball about 20 light-years wide.

But the total mass is about 2,000 times greater than the mass of the visible stars. That’s led to some confusion about its nature.

One idea is that it’s a small galaxy that’s orbiting the Milky Way. Most of its mass would consist of dark matter – matter that produces no energy, but that reveals its presence through its gravitational pull on the visible matter around it.

A study last year suggested a different nature – a star cluster held together by a clump of black holes. The cluster might have been born with a hundred thousand stars or more. When some of the stars died, they formed black holes, which congregated near the cluster’s middle.

The gravity of the Milky Way pulled away many of the cluster’s stars. Encounters with the black holes kicked out many more. And the study says the cluster will fall apart completely in about two billion years.

The cluster – or galaxy – is about 30,000 light-years away, in the great bear. But Ursa Major III is far too faint to see, even with a telescope.

Script by Damond Benningfield