StarDate

An old friend is returning to view about now — the planet Venus, the brilliant “evening star.” It’s quite low in the west at sunset, so any trees or buildings along the horizon will block it from view. Because it’s so bright, though, if you have a clear horizon you should be able to pick it out.

Venus shuffles back and forth between morning and evening skies. And it repeats itself as it does so. It traces a series of five patterns that repeat every eight years. So in late February of 2026, Venus will stand almost exactly where it is tonight.

That’s because the orbital cycles of Earth and Venus are nearly synchronized. For every eight times that Earth orbits the Sun — a period of eight years — Venus orbits the Sun 13 times.

That could be an orbital resonance — a physical link caused by the gravitational pull that Earth and Venus exert on each other. But the cycle is off by a tiny bit, so the timing could be just a coincidence.

No matter the cause, though, it makes it easy to predict where Venus will appear at any time: the same place it was eight years earlier.

And Venus will put on a much better showing as we head into spring and then into summer. It will climb a little higher into the sky each evening, so it’ll be a little easier to spot. It will remain in view a little longer each night, too — providing more time to appreciate the beauty of this predictable planet.

Tomorrow: a vision in blue

Script by Damond Benningfield

A starship is headed toward the vicinity of the eye of the celestial bull. It’ll take a couple of million years to get there, and it’ll be dead quiet along the way. But just in case anyone finds it, it carries a helpful road map to help them figure out where it came from.

The bull’s eye is the bright orange star Aldebaran. It stands to the lower right of the Moon as night falls, and leads the Moon down the western sky later on.

Aldebaran is about 65 light-years away. In other words, the star’s light, traveling at 670 million miles per hour, takes about 65 years to reach us.

The Pioneer 10 spacecraft isn’t moving nearly that fast. When it was dispatched to explore the planet Jupiter, in 1972, it was the fastest probe ever launched, moving at more than 32 thousand miles per hour. And the Sun’s gravitational pull has slowed it down since then. So the craft is no Millennium Falcon — it’ll take about two million years to approach Aldebaran.

And it won’t be saying anything when it gets there. Its nuclear power source has faded, so it’ll be nothing more than a hunk of cold metal as it traverses the galaxy. Even so, it can convey a message. The craft carries a plaque designed to help anyone who finds Pioneer learn something about its makers and its home. The plaque includes drawings of a nude man and woman, as well as some directions for tracing its path — the path followed by one of the first starships from the solar system.

Script by Damond Benningfield

The Sun is a sedate, middle-aged star. It steadily “fuses” the hydrogen in its core to make helium, which releases the energy that makes the Sun shine. And the Sun changes very little — its size and brightness are always almost exactly the same.

A star in the big dog is much different — it pulses in and out like a beating heart.

Mirzam represents a paw of Canis Major, the big dog. As night falls, it’s close to the right of Sirius, the brightest star in the night sky, in the southeast.

Mirzam is much bigger and heavier than the Sun, and thousands of times brighter. And it’s only about 12 million years old, compared to billions of years for the Sun.

Even so, Mirzam is nearing the end of its life. It’s just about used up the hydrogen in its core, so it’s getting ready to fuse the helium to make other elements.

A layer around the core contains a lot of iron. The iron absorbs energy from the core. When enough energy builds up, that layer pushes outward. When the layer cools, it falls back. That process carries out to the star’s surface, causing it to pulse in and out.

There are actually many different pulsations, all working in different ways. The pulses last different amounts of time, for example, and they move at different speeds. Combined, they cause Mirzam’s diameter to vary by thousands of miles. That changes the star’s brightness, too, but not enough to see with the eye alone. So the dog’s paw looks steady, even though it pulses once every few hours.

Script by Damond Benningfield

When we look at the starry night sky, our eyes and brains play tricks on us. They make us think that if a star is bright, it’s also close by. That’s generally not the case, though. Instead, many of the fainter stars are actually more impressive than some of the brighter ones.

A couple of examples are in Canis Major, the big dog, which is in the south-southeast as night falls at this time of year.

The constellation’s brightest star is Sirius — the brightest star in the night sky. It is a good bit brighter than the Sun. But it looks so bright mainly because it’s quite close.

The dog’s third-brightest star doesn’t look nearly as impressive as Sirius. In reality, though, Wezen is a stellar heavyweight. It looks fainter than Sirius only because it’s almost 200 times farther.

Wezen is about 17 times as massive as the Sun, 200 times wider, and 50,000 times brighter. And it’s also much younger: just 10 million years old, compared to four-and-a-half billion years for the Sun.

You might think that the combination of size and youth would mean that Wezen will be around for a long time. But that’s another bit of stellar trickery. Heavier stars burn through their nuclear fuel at a prodigious rate, so they expire quickly. And in fact, Wezen is already starting to undergo some end-of-life changes. Within a few million years, it’ll explode as a supernova — a big sendoff for one of the leading lights of the big dog.

More about Canis Major tomorrow.

Script by Damond Benningfield

Winter brings out the big dogs — some of the most prominent constellations of all. And one of those really is a dog: Canis Major, the big dog. It’s best known for its leading light: Sirius, the Dog Star, the brightest star in the night sky. It’s a third of the way up the southeastern sky at nightfall.

But there’s more to Canis Major than just Sirius. It includes several bright stars, most of which are below or to the right of Sirius. When you link them up, they really do look like the outline of a dog.

Like all constellations, Canis Major consists of more than just a connect-the-dots pattern of stars, though. It covers a patch of sky that includes the area outside that pattern as well. And within those borders, you can find several deep-sky objects — objects like star clusters, which are far beyond most of the individual stars visible in Canis Major.

Perhaps the best known is M41. It’s not far below Sirius, and is an easy target for binoculars. It’s about 2300 light-years away, and consists of about a hundred stars.

The cluster probably is about 200 million years old. At that age, its biggest, heaviest stars have already expired, leaving small, dense corpses known as white dwarfs. The next-heaviest stars will soon follow that same path. Those stars have puffed up to become red giants. They’re easily visible through binoculars — sparkling red and orange jewels along the “collar” of the big dog.

More about Canis Major tomorrow.

Script by Damond Benningfield

Some moons lead dangerous lives. Two moons of the planet Uranus, for example, are likely to be destroyed in a million years or so when they smash into each other.

Uranus has 27 known moons, and nine of them form the most tightly packed system of satellites in the solar system. Their orbits all lie within just 11,000 miles of one another.

In that busy environment, accidents are inevitable. Although the moons are small, each moon’s gravity still tugs at all the others. Over long periods of time, that can make a moon swerve into the wrong lane, causing a collision.

Astronomers recently deduced the mass of the moon Cressida by studying its effects on one of the rings of Uranus. This work indicates that the moon is massive enough to perturb another moon, Desdemona. That will make them crash into each other in about a million years — not long compared with the solar system’s age of four-and-a-half billion years.

These moons aren’t the only ones whose days are numbered —the moons Cupid and Belinda are likely to collide as well.

Impacts like these may explain why Uranus has a couple of rings near the moons. The rings may contain the debris from earlier collisions — the remnants of moons that crashed into their neighbors.

Uranus is too faint to see with the eye alone. But it’s easy to see its position tonight. It’s above the Moon, by less than the width of a fist held at arm’s length. Binoculars will show the planet as a tiny orb amidst the stars.

Script by Ken Croswell

Here’s a phrase that you probably haven’t heard before: solar antapex. It’s the location in the sky that’s opposite the direction that Sun and Earth are moving through the galaxy. It’s marked by the constellation Columba, the dove, which scoots quite low across the south on February nights.

Like all the other stars in the Milky Way, the Sun is orbiting the center of the galaxy. And its path is taking it in the direction of Vega, a bright star in the summer constellation Lyra. That direction is known as the solar apex. So the opposite direction is the ant-apex.

That point may be the most interesting thing about Columba, which is to the lower right of Sirius, the brightest star in the night sky.

The constellation was created in 1592 by a Dutch astronomer. He used it to fill in a gap between some brighter star patterns.

Columba’s leading light is Alpha Columbae, which actually is quite impressive. It’s perhaps four-and-a-half times the diameter of the Sun, and a thousand time the Sun’s total brightness. But it’s also 260 light-years away — a distance that dulls its luster. So as seen in Earth’s night sky, it’s not much to look at.

Over the ages, though, it’ll get brighter. The star is finishing up the original hydrogen fuel in its core. When the hydrogen is gone, the core will get smaller and hotter. That’ll cause the star’s outer layers to get bigger and brighter. So the dove will have something besides the solar antapex to set it apart.

Script by Damond Benningfield

The smallest of the solar system’s major planets is hiding in the Sun’s glare right now. That’s because Mercury is at superior conjunction — it lines up behind the Sun as seen from Earth. As it moves away from the Sun, it’ll climb into decent view in the early evening sky in a couple of weeks.

Mercury’s motion around the Sun played a big role in the development of Albert Einstein’s theory of gravity, known as General Relativity.

Mercury’s path around the Sun is lopsided, so the little planet’s distance from the Sun varies by quite a bit. Astronomers plotted that path, and used the laws of gravity devised by Isaac Newton to predict where Mercury should appear in the future. But they discovered that each time Mercury comes closest to the Sun, it’s a little farther along in its orbit than predicted.

Einstein saw gravity not as a force — something that pulls two objects together — but as a warp in space caused a massive object — in this case, the Sun. The closer to the Sun you get, the more pronounced that warp becomes. So each time Mercury comes closest to the Sun, it gets pulled forward a bit by the warp in space.

Mercury’s orbit was the first bit of tangible evidence in support of General Relativity. In fact, Einstein discussed it in his early papers on the subject. Since then, much more evidence has confirmed Einstein’s ideas — showing us that, for now, General Relativity is the best explanation of gravity.

Script by Damond Benningfield

Most of the spacecraft that have touched down on other worlds have been either stationary landers or wheeled rovers. But a possible mission to the biggest moon of Saturn would take a big jump in mobility — it would fly from point to point like a helicopter.

Dragonfly is one of two finalists for a mission that will launch in about a decade. The other is called Caesar. It would touch down on Comet Churyumov-Gerasimenko, which was studied in detail by an earlier spacecraft. Caesar would grab a sample from the comet’s surface and return it to Earth.

Dragonfly would study the moon Titan for about two years. The small drone would have a set of rotors, like a helicopter, to carry it from place to place. Each hop could cover dozens of miles, allowing the craft to visit dozens of locations across a wide area. It would spend several Earth days at each spot, studying Titan’s weather, surface chemistry, and more.

Titan is one of the most intriguing bodies in the solar system. Its frigid atmosphere is thicker than Earth’s, and it contains large amounts of organic compounds — the chemical building blocks for life. Liquid methane and ethane form lakes and seas on the surface. Titan also may have a massive ocean of liquid water deep below the surface. That combination means that Titan could be a good place to look for microscopic life.

NASA plans to pick the winning concept next year — setting the stage for a visit to a solar system neighbor.

Script by Damond Benningfield

Our planet Earth is like a target in a shooting gallery. It could be hit by a big space rock at any time. In fact, we were hit by one five years ago today, when a small asteroid exploded over Russia. A shockwave injured more than 1500 and damaged more than 7,000 buildings.

The Chelyabinsk asteroid was about 60 feet wide and weighed more than 10,000 tons when it hit Earth’s atmosphere. Its high-speed plunge heated the air around it, forming a fireball that was visible across thousands of square miles.

As the asteroid plowed deeper, it ran into thicker layers of air. At such high speed, that was almost like running into a concrete wall — the pressure caused the space rock to explode. Fragments fell across a wide area. The largest one plummeted into an ice-covered lake. It weighed about 1400 pounds.

Asteroids pass close to Earth all the time. Every month, in fact, several pass within a few million miles of us. And occasionally, one even passes within the Moon’s orbit around Earth. Many of those asteroids are much bigger that the one that hit Chelyabinsk, so their potential destructive power is much greater.

So far, astronomers have discovered and plotted the orbits of thousands of asteroids whose orbits bring them close to Earth’s orbit. None of those asteroids is on a collision course. But as Chelyabinsk demonstrates, smaller asteroids can slip through without detection — taking dead aim at planet Earth.

Script by Damond Benningfield