The Sun isn’t bothered by much. That’s because it travels through the Milky Way on its own. But most of the stars in the galaxy have at least one companion star. And the interactions between them can have a big impact.

Consider Spica, a bright star near the Moon tonight. Although it looks like a single star, it’s really at least two stars. One of them is more than 11 times the mass of the Sun, while the other is about seven times the Sun’s mass. That makes Spica one of the more impressive binary systems around.

The stars are extremely close together. They follow a stretched-out orbit that brings their surfaces to within about 10 million miles of each other.

So the stars have big effects on each other. For one thing, their mutual gravitational pull distorts both stars. They’re shaped like eggs, with the tapered end pointing toward the other star. Also, the pull of the smaller star appears to create ripples in the larger one. And the tapered end of each star is hotter than its opposite hemisphere.

In a few million years, the larger star will explode as a supernova. That’s likely to blast away some of the gas at the surface of the companion. And it’ll probably send the smaller star zipping across the galaxy – fired into space by a close companion.

Look for Spica to the right of the Moon early this evening. The fainter planet Mars is farther to the lower right of the Moon.

Script by Damond Benningfield

Mars is dry, cold, and quiet. But that hasn’t always been the case. Billions of years ago it was much busier – and perhaps a comfortable home for life.

Mars has had three major geological ages. The oldest was the Noachian. It’s named for a large highlands region in the southern hemisphere. It began about 4.1 billion years ago, and lasted for 400 million years.

The solar system was still packed with big “leftovers” from the birth of the planets then. Many of them slammed into Mars, forming wide basins that are still visible today.

At the same time, giant volcanoes belched gases into the atmosphere. That trapped heat, making Mars much warmer. Clouds might have produced rain or snow. The precipitation carved rivers and filled lakes and maybe even a large ocean. Conditions could have allowed the formation of microscopic life.

At the end of that period, there were fewer impacts and less volcanic activity. Mars cooled off, and the water dried up. So Mars became quieter as the Noachian Age ended, and the next age began.

Mars is close to the right or upper right of the Moon early this evening. It looks like a fairly bright star. But it’s quite low in the sky, especially as seen from the northern half of the country, so you need a clear horizon to spot it. The star Spica, which is about twice as bright as Mars, stands to the upper left of the Moon. We’ll have more about Spica tomorrow.

Script by Damond Benningfield

Every pilot knows to check the weather before takeoff – no one wants to fly into a storm. And in the future, they might want to check the space weather as well. Storms on the Sun can interfere with technology here on Earth – including aviation technology.

Solar storms are giant explosions of energy and charged particles. When these outbursts hit Earth, the effects can range from damaged satellites to power blackouts on the ground. Some radio frequencies can be blacked out as well.

Scientists recently looked at the impacts on aviation. They studied tracking information for three small aircraft recorded during a massive solar flare in February of 2024. The aircraft automatically reported their position and other details to air traffic control and to other aircraft. The position information came from GPS satellites.

But several times during the solar storm, the aircraft briefly lost touch, or they received bad position information. The problems were brief. But future storms could cause bigger problems. Bad information from GPS satellites, drops in radio links, and even radar blackouts could force flight controllers to rely on older methods to keep planes and passengers safe. That could cause delays and backups – or worse.

So the researchers suggested that space weather briefings be developed for pilots – helping them safely navigate through space weather.

Script by Damond Benningfield

As Earth was thawing out at the end of the last ice age, it was hit by a powerful blast from the Sun. The storm would have triggered spectacular displays of the northern and southern lights. And it left an imprint in tree rings. Using that imprint, scientists have found that the storm was the most powerful yet recorded. And they even have a time for the event: the first quarter of the year 12,350 BC.

Solar storms pelt Earth all the time. Most of the storms are small. But big ones can damage or destroy satellites, zap power systems on the ground, and cause other mischief.

The biggest one ever seen took place in 1859. It knocked out telegraph systems around the world. But scientists have found evidence of even bigger events in the more-distant past.

Some of the events are recorded in tree rings. Charged particles from the storms interact with Earth’s atmosphere to produce a radioactive form of carbon.

Trees take up some of the carbon, which decays to a more stable form at a known rate. So comparing the ratio of carbon isotopes in tree rings can tell us when big storms took place.

Researchers measured the carbon in rings from the end of the ice age. And they developed a new model of chemistry of the atmosphere during such cold periods. Their work showed that Earth was hit by the strongest solar storm yet discovered more than 14,000 years ago.

More about space weather tomorrow.

Script by Damond Benningfield

If you watch the stars on a dark night, it’s easy to think of the sky as a great dome. But as the night goes on, the dome rotates. New stars rise in the east, while others disappear in the west. So ancient skywatchers thought of the sky not as a dome, but a sphere that completely encircles us – the celestial sphere.

To the Greeks, the sphere was real – a perfect crystalline surface, with the stars hanging from it like lanterns. Earth stood still at the middle of the sphere, which turned around it.

Today, of course, we know that Earth is turning, and the stars are so far away that they appear to be fixed in place. Yet astronomers still use the celestial sphere. Their coordinate system is based on it. The system has lines of latitude and longitude, an equator, and north and south poles – all of which are projections of Earth’s coordinates.

The celestial poles, for example, are based on the projection of Earth’s poles – the directions in which our planet’s axis is pointing.

There’s also a celestial equator – an extension of Earth’s equator. As darkness falls tonight, it arcs from Aquarius, in the east; through Aquila, in the south; and down to Virgo, in the west.

Only those who live near the equator can see the entire celestial sphere. For everyone else, it’s clipped. And at the poles, only half of the sphere is ever visible – a great dome showing the same stars all year long.

Script by Damond Benningfield

Many “open” star clusters arch high overhead on summer nights. They’re lined up along the glowing band of the Milky Way – the outline of our home galaxy. Each cluster is a family of stars – from a few dozen to a thousand or more. But open clusters don’t stay together for long. Their stars eventually spread out, so the cluster disappears.

Some families begin to spread out early – before many of their stars are even fully formed. One recently discovered example is called Ophion. It consists of more than a thousand stars.

Astronomers found the group by analyzing data from Gaia, a space telescope. They looked through observations of more than 200 million stars. Then they narrowed their search to stars that are cooler than the Sun, and no more than 20 million years old. And Ophion just popped out.

The stars form a giant clump that’s centered about 650 light-years away. But all of its members are going their own way. So they don’t form an obvious “cluster” – a tight grouping that’s easy to pick out.

Ophion is on the edge of a region that’s given birth to many thousands of stars. Exploding stars in that region – or within Ophion itself – might have scattered the stars like bowling pins, keeping the family from sticking together.

Ophion is near the middle of Ophiuchus, which is well up in the south-southwest at nightfall. You can see many clusters there – but not a hint of the ill-fated Ophion.

Script by Damond Benningfield

Human eyes are perfectly tuned to see sunlight. But that’s a thin slice of the total range of light. As a result, we miss a lot of what’s out there – even objects that are big and close.

A recently discovered example is a cloud of gas and dust that’s been named Eos. It spans about 40 times the width of the Moon. But it’s thinly spread, and it produces most of its light in the far-ultraviolet – wavelengths we can’t see. And even if we could see them, Earth’s atmosphere blocks them. So Eos wasn’t discovered until astronomers combed through observations made two decades ago by a Korean space telescope.

The cloud’s inner edge is about 300 light-years away. It’s along the rim of the Local Bubble – a giant void around the solar system that’s been cleared out by exploding stars.

Eos is about 170 light-years across. It contains enough gas to make more than 5,000 stars as heavy as the Sun. But there’s no evidence that it’s ever given birth to any stars at all. And while it could spawn stars in the future, that’s not likely. The cloud is evaporating, and should vanish in about six million years.

Eos is centered along the border between the northern crown and the head of the serpent. That point is high in the west-southwest at nightfall, to the upper left of the bright star Arcturus. But unless you have your own space telescope, there’s no way to see this giant neighbor.

Script by Damond Benningfield

Many centuries ago, people knew of only seven metals. That also was the number of known “planets” – the five true planets that are visible to the naked eye, plus the Sun and Moon. So each metal was associated with a planet – gold with the Sun, silver with the Moon, for example.

Another metal with a good match was quicksilver. It’s the only metal that’s liquid at everyday temperatures, so it was associated with the quickest planet: Mercury. And it was even given the planet’s name.

The planet moves back and forth between the morning and evening sky every few months. That quick motion is where the planet got its name. Mercury was the Roman messenger god, who flitted across the heavens on winged heels.

The only spacecraft to study the planet from orbit didn’t find any trace of the metal mercury on its surface. And if there’s any of it near the planet’s equator, it would go through all three everyday phases of matter. At night, the planet is so cold that the metal would be frozen solid. At noon, it’s so hot that it would vaporize, forming a gas. And for much of the rest of the daytime, it would be a liquid – quicksilver puddles on a quicksilver planet.

Mercury will stand close to the Moon during the dawn twilight tomorrow. It looks like a fairly bright star, to the lower right of the Moon. The brighter planets Venus and Jupiter align to their upper right – the planets of copper and tin.

Script by Damond Benningfield

Early risers are in for a treat tomorrow. Venus, Jupiter, and the twins of Gemini congregate around the Moon. The group climbs into good view a couple of hours before dawn. Venus is close to the lower right of the Moon, Jupiter is farther to the upper right, and Gemini’s twins are to the upper left of the Moon. The brighter twin, Pollux, is especially close to our satellite world.

Venus is the “morning star” – the brightest member of the group after the Moon. It shines so brightly because it’s close to Earth and the Sun, and because it’s topped by clouds of sulfuric acid. They reflect about three-quarters of the sunlight that strikes them.

Jupiter is the next brightest – mainly because it’s the largest planet in the solar system. It’s about 11 times the diameter of Earth, and it’s more than twice as massive as all the other planets and moons put together. And Earth is moving closer to Jupiter now, so the planet will grow even brighter over the next few months.

Pollux and Castor, the twins, are true stars. But they’re hundreds of thousands of times farther than the planets, which dulls their countenance. Even so, they’re easy to see through the moonlight – part of a beautiful panorama in the early morning sky.

Another bright light rises well below the group: Mercury, the Sun’s closest planet. The Moon will stand close to it on Thursday, and we’ll talk about that tomorrow.

Script by Damond Benningfield

The crescent Moon will slide past three bright planets over the next three mornings, growing thinner as it does so. First up is Jupiter, the largest planet in the solar system. It looks like a bright star below the Moon at dawn tomorrow.

The Moon is in the part of its orbit that carries it between Earth and the Sun. It’ll reach that point on Friday night. As it drops toward the Sun, the Earth-Moon-Sun angle changes. So the Sun lights up less and less of the lunar hemisphere that faces our way. As a result, the crescent gets thinner day by day.

Tomorrow, for example, about 15 percent of the lunar disk will be in the sunlight. By Wednesday, as it poses near Venus, it’ll be down to eight percent. And by Thursday, when it’s close to Mercury, it’ll be the barest of fingernails – it’ll be daylight across only about three percent of the visible disk.

On the other hand, as the crescent gets smaller, the dark portion of the Moon will get brighter. That’s because that part of the Moon is bathed in earthshine – sunlight reflected from our own planet.

As the Moon gets thinner and thinner in our sky, Earth will get fatter and fatter in the lunar sky, so earthshine will get brighter. It’ll reach its peak when Earth is full – at the same moment that the Moon is new. The Moon will be lost in the Sun’s glare then, but it will return to view a couple of days later – as a thin crescent in the evening sky.

Script by Damond Benningfield