StarDate

Saturn has more moons than any other planet in the solar system – 274 as of this spring. All of the bigger ones are interesting worlds in their own right. Some of them are balls of ice mixed with rock. And they offer some especially eye-catching features.

Mimas has a huge impact crater that makes it look like a Star Wars death star. It’s a third as wide as Mimas itself, with walls three miles high and a floor 10 miles deep. It was created by an impact that almost ripped the moon apart. Shockwaves raced all the way around Mimas, creating a jumbled landscape on the opposite side.

Iapetus has a couple of giant craters. But it stands out for two other reasons. One is its coloring. One hemisphere is covered with ice, so it’s as white as snow. The other is covered with dust that’s as dark as charcoal. The other thing that makes it stand out is its shape – it resembles a walnut. A mountain range circles its equator. It’s a dozen miles wide, and averages about nine miles high.

A region of Dione is marked by cliffs that form bright slashes. The cliffs are up to a thousand feet high, and they stretch across hundreds of miles. They probably formed as Dione shrank, wrinkling its crust – sculpting an intriguing feature on one of Saturn’s moons.

Saturn is near our moon at dawn tomorrow. It looks like a bright star to the lower right of the Moon. But you need a telescope to see any of the giant planet’s ice-ball moons.

Script by Damond Benningfield

If you look toward the west the next couple of evenings and feel like you’re having double vision – well, you are. But it’s nothing to worry about. It’s a conjunction between the two brightest points of light in the night sky – the planets Venus and Jupiter. They’re separated by less than two degrees – the width of your finger held at arm’s length.

Venus is the brighter point – the brilliant “evening star.” Jupiter is only about one-seventh as bright, but it still outshines all the other planets and stars.

Jupiter is the largest and heaviest planet in the solar system. It’s a ball of gas with a dense, oozy center. Its atmosphere is topped by bands of clouds painted tan, yellow, red, and ivory. The clouds reflect most of the sunlight that strikes them, making the planet bright.

Venus is only the sixth-largest and -heaviest planet – right behind Earth. It’s also covered by clouds. But they don’t form colorful stripes. To the eye alone, in fact, they look featureless – a smooth blanket of white. But they’re more reflective than Jupiter’s clouds. Venus is also much closer to both Earth and the Sun than Jupiter is. That combination makes it the brightest pinpoint in the night sky.

Venus and Jupiter will be closest together tonight and tomorrow night. Then Venus will pull away, increasing the gap by about one degree per night – slowly ending the “double vision” in the evening sky.

Script by Damond Benningfield

Any residents of a galaxy in the constellation Serpens have a big problem: They’re being blasted by a death ray from a black hole.

The galaxy is a companion to a bigger galaxy, known as 3C321. They’re more than a billion light-years away.

A supermassive black hole inhabits the heart of the larger galaxy. It’s surrounded by a giant disk of gas that’s heated to millions of degrees. Powerful magnetic fields funnel charged particles from the disk into jets. They squirt away from the poles of the black hole at almost the speed of light.

One of those jets is firing toward the companion galaxy, which is just 20,000 light-years away. Observations by telescopes on the ground and in space show that the jet is hitting the edge of the companion, creating a hotspot. The encounter deflects the beam off its original course, but the beam continues for hundreds of thousands of light-years.

The particles and radiation in the beam could destroy the ozone layer of any planet the beam hits. That would leave the planet exposed to radiation from the beam itself, and from other cosmic sources. So anything living on the planet would be in danger.

And the situation is getting even worse. The smaller galaxy appears to be just entering the black-hole jet. Over time, more of the galaxy will pass through the jet – possibly exposing even more planets to this “death ray” from another galaxy.

Script by Damond Benningfield

The sky is divided into 88 official constellations. In fact, though, it’s more like 88 and a half. That’s because the constellation Serpens consists of two disconnected parts – a head and a tail. They wrap “behind” the body of Ophiuchus the serpent bearer.

Serpens is in full view in the east and southeast by a couple of hours after sunset. The half that represents the head is highest, above Ophiuchus, with the tail below the serpent bearer.

The front of the snake, Serpens Caput, is the more prominent half. It has several stars that are fairly easy to see. The brightest is Alpha Serpentis, also known as Unukalhai – “the serpent’s neck.” It’s a red giant – an old, bloated star that’s much bigger and brighter than the Sun. Its surface is much cooler than the Sun’s, so the star looks yellow-orange.

The back half of the snake, Serpens Cauda, is tougher to spot. Its brightest star, Eta Serpentis, is the second-brightest star in the whole constellation. It’s about half as bright as Alpha. But the two stars are quite similar. Eta is also a giant – a puffed-up star that’s nearing the end of its life. It’s a little farther along than Alpha, so it’s a little bigger and brighter. It looks fainter because it’s farther away.

The two stars will end their lives in the same way. Each will cast its outer layers into space, leaving behind a hot but tiny corpse known as a white dwarf.

More about Serpens tomorrow.

Script by Damond Benningfield

Venus and Jupiter are staging one of the top skywatching events of the year – an especially close encounter of the two brightest points of light in the night sky. It plays out in the west over the next few evenings.

Venus is the beautiful “evening star” – the brightest object in the night sky after the Moon. Jupiter is the next-brightest. Even so, right now it’s only about one-seventh as bright as Venus, so it’s easy to tell them apart.

The two planets can pass especially close because both of them stay near the ecliptic – the Sun’s path across the sky. They pass by each other every year or so. But both worlds wander a little bit to either side of the ecliptic, so they usually just miss each other. And even when they are close, they’re sometimes so near the Sun that we can’t see them.

At times, though, Venus can pass in front of Jupiter, blocking it from view That last happened in 1818. It’ll happen again in 2065. But that’s one of those times when they’ll be too close to the Sun to see.

Tonight, Jupiter is close to the upper left of Venus. But over the coming evenings, Venus will overtake it. They’ll stand side by side on Sunday, and be especially close on Monday and Tuesday – separated by about the width of your finger held at arm’s length. They don’t drop from view until about 10:30 or 11, so there’s plenty of time to watch this impressive planetary encounter.

Script by Damond Benningfield