The Sun’s closest planet is making a pretty good appearance in the early evening. As seen from Earth, it’s just about as far from the Sun as it ever gets. It looks like a bright star low in the west-northwest beginning shortly after sunset.

Mercury is getting ready to cross between Earth and the Sun – a point known as inferior conjunction. In the meantime, it’ll drop closer and closer to the Sun as viewed from Earth. It’ll vanish in the twilight in a couple of weeks.

Mercury’s orbit is carrying the planet closer to Earth. Tonight, it’s about 78 million miles away. At conjunction, it’ll close to just 53 million miles.

On average, Mercury returns to conjunction every 116 days. But the gap varies by more than 10 days in either direction. That’s because Mercury’s orbit is more lopsided than that of any other planet. When Mercury is closer to the Sun it moves faster; when it’s farther it moves more slowly. So the gap between conjunctions varies depending on where Mercury is in its orbit when it passes Earth.

For the next few nights, look for Mercury as evening twilight fades. Although the planet is bright, it’s so low that you need a clear horizon to spot it. It lines up to the lower right of the much brighter planets Venus and Jupiter. And the crescent Moon will join the lineup on Tuesday, helping point the way to the little planet.

Script by Damond Benningfield

A relic from the early universe is racing through Libra. It’s moving across the constellation at 800,000 miles per hour. That’s far faster than most of the stars around us. So it’ll move out of Libra in the blink of a cosmic eye.

The star is HD 140283. But it also has a nickname – the Methuselah Star. That’s because it’s probably about 13 billion to 14 billion years old. Since the universe itself is only 13.8 billion years old, that makes the star one of the oldest anywhere.

Astronomers have pieced together several bits of evidence to arrive at that age. The key bit is the star’s composition. It has very low levels of elements that are heavier than hydrogen and helium, the simplest elements. Heavier elements were created in the hearts of stars, then spewed into space when the stars died. Some of these elements then were incorporated into later generations of stars.

HD 140283 has less than half a percent as much iron as the Sun, with slightly higher levels of oxygen and a few other elements. Those abundances tell astronomers the star must have been born when the universe was brand new.

As night falls, the star is to the lower left of Zubeneschamali, Libra’s leading light. It’s too faint to see with the eye alone, but it is visible through binoculars.

Script by Damond Benningfield

Every star in the night sky is moving – orbiting the center of the galaxy. Some are moving toward us, while others are moving away. We can’t see that motion because the stars are so remote. But we can measure it with special instruments – one of the most important techniques in astronomy.

The instruments break the light of a star or other object into its individual wavelengths or colors. Each chemical element imprints its own “barcode” in that array of wavelengths. A star’s motion toward or away from us causes the barcodes to shift position.

If it’s moving away from us, the shift is toward longer, redder wavelengths: a redshift. And if it’s moving toward us, the shift is toward shorter, bluer wavelengths: a blueshift. The size of the shift reveals the speed.

The technique also can reveal how fast a star is spinning; the side that’s rotating toward us is blueshifted, while the opposite side is redshifted. And it can reveal orbiting companions; their gravity pushes and pulls the star, slightly changing its motion.

Two bright stars with well-measured shifts are in view as the sky darkens this evening. Regulus is in the west, well to the upper left of the brilliant planets Venus and Jupiter. Its light is redshifted; it’s moving away from us at about 9300 miles per hour. Antares, quite low in the southeast, is sliding toward us at about 8600 miles per hour – giving its light a definite blueshift.

Script by Damond Benningfield

For skywatchers in the United States, a grouping in the western evening sky right now is a case of the haves and the have-mores. The group is visible across the entire country. But the view gets better as you move farther south.

The group features the planets Venus, Jupiter, and Mercury, and the stars Pollux and Castor – the “twins” of Gemini. Venus is the brightest member, with the twins to its right, and Jupiter and Mercury to its lower right.

All five members of the group are near the ecliptic – the Sun’s path across the sky. And the angle of the ecliptic varies by latitude.

As seen from the equator, the ecliptic stands almost straight up from the horizon at sunset. The Sun drops straight down below the horizon, so the sky darkens quickly. At the same time, Venus and the others stand fairly high above the horizon. They’re still well up as twilight fades.

As you go farther north, the ecliptic tilts toward the south. The farther north you are, the greater that angle. So when the Sun sets, it doesn’t drop straight down – it also slides across the horizon. As a result, the sky remains bright for much longer than it does at the equator. Venus and the others are lower in the sky at sunset, so they’re more likely to be blocked by trees or mountains. And they’re immersed in the twilight longer. That leaves less time to enjoy this beautiful group of planets and stars in the evening sky.

Script by Damond Benningfield

A quadruple star system in Cygnus takes the concept of a close-knit family to extremes. It consists of three big, heavy stars packed into a region smaller than the orbit of Mercury, the Sun’s closest planet. A fourth star is looking on from a wider separation – about the distance between the Sun and Jupiter, the fifth planet.

The system was discovered by a planet-hunting space telescope. Over several years, it revealed two of the stars, then three, and now, four. Astronomers say the stars probably formed together, from the same cloud of gas and dust. That means the four stars are siblings.

All three of the central stars are bigger, brighter, and hotter than the Sun. Two of them form a binary – they orbit each other once every three days. The more massive of those stars is already nearing the end of its life. It’s beginning to puff up. It should get so big that it will engulf its close companion. That will begin a complicated process in which all three stars should merge. Within about 300 million years, all that will be left of them is a single, heavy “corpse” known as a white dwarf.

The fourth star will remain on its own. It’s about the same size and mass as the Sun. It’ll continue to shine for billions of years. Then it, too, will expire, forming another white dwarf. So this brilliant quartet will be reduced to a faint duo – two dead stars cooling and fading across the eons.

Script by Damond Benningfield

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