StarDate

Sirius is the brightest star in the night sky. And it’s just starting to peek into view in the dawn twilight. It’s easier to pick out as you go farther south.

It’s especially easy to see from Cairo and southward along the Nile River. In ancient times, the star played a big role in Egypt’s religion and its daily life.

Egyptians called the star Sopdet – a name that means “skilled woman” – after a goddess of life and fertility. She was the sister and wife of the god Sah, who was represented by the stars of Orion. Eventually, she became identified with the goddess Isis.

The star Sopdet was an important calendar marker. Its first appearance in the dawn indicated that the annual flooding of the Nile was about to begin. The flood brought water and fresh soil to the fields, making them fertile for another year. So Sopdet’s return to view was so important that it marked the beginning of the year. The occasion was celebrated with a festival – “the Coming of Sopdet.”

At first, that all happened in June, around the beginning of summer. Today, though, Sirius doesn’t climb into view until August. That’s because Earth wobbles on its axis, causing the stars to move across the seasons – shifting Sopdet away from its honored position.

Look for Sirius quite low in the southeast as twilight brightens. If you can’t see it quite yet, be patient – it’ll be in view from the entire country by the end of the month.

Script by Damond Benningfield

Venus is just beginning a slow climb to prominence as the “evening star.” It’s quite low in the west at sunset and sets not long afterward, so it’s hard to spot. Tonight, it’s close to a slightly easier target – the crescent Moon. Even so, you need a clear horizon and good timing to see either one.

Venus and the Moon may have something in common: Both of them might have been involved in “big whacks” when the solar system was young.

There’s a pretty good chance that the young Earth was hit by a body as big as Mars. That blasted out a huge amount of material. Much of it coalesced to form one or more moons – including the one we see today.

It’s possible that Venus got a big whack as well. The impact made Venus spin in the opposite direction from most of the other planets in the solar system. As seen from above, Earth and most of the other planets rotate counterclockwise – the same direction in which they orbit the Sun. Venus also orbits counterclockwise, but it rotates clockwise.

When Venus was born, it probably spun in the same direction as the other planets. So something might have hit the young planet. The impact either flipped it upside down or caused it to reverse direction. The blast might also have created a moon. But unlike our moon, it didn’t survive.

Look for Venus and the Moon shortly after sunset, quite low in the west. The view is better as you go farther south.

Script by Damond Benningfield

A giant stellar nursery lies just 4500 light-years away. But the complex of brilliant stars and star-making materials is hidden – veiled by clouds of dust.

Cygnus X spans more than 600 light-years. It contains enough material to give birth to millions of stars as massive as the Sun. And it’s already spawned several thousand stars that are many times as massive as the Sun, and thousands of times brighter.

Astronomers study the region at wavelengths that shine through the dust. They reveal a complex web of ribbons, bubbles, rings, and pillars. They form several interlinked regions of starbirth.

A cluster of massive newborn stars is near the middle of the complex. They produce radiation and powerful “winds” that push and erode the surrounding gas and dust. That can stop the process of star formation. But it can also trigger the birth of new stars as it squeezes the gas and dust.

Especially heavy stars blow big bubbles in the gas. They also shape dense regions into pillars that can span dozens of light-years.

Cygnus X probably has been forming stars for the past 10 million years or so. But it’s just getting started – it’s likely to form tens of thousands more stars.

Cygnus X is in Cygnus, the swan, which is high in the east at nightfall. The complex is hidden behind dark clouds that run from the bright star Deneb, the swan’s tail, to Sadr, at the intersection of its long body and graceful wings.

Script by Damond Benningfield

Under a dark sky, the Milky Way is impressive – a milky band of light that outlines the disk of our home galaxy. But the band isn’t smooth. It’s lumpy, with some parts much wider and brighter than others. And a dark lane runs down its middle, bisecting the Milky Way into two bands. It, too, is lumpy.

That dark lane is known as the Great Rift, and it looks almost empty – as though a cosmic dragon has swallowed most of the stars. Instead, the darkness has simply swallowed the light of the stars behind it. That’s because the dark lane is made of giant clouds of dust. They block the visible light of the stars inside and behind them, just as a dark cloud here on Earth can block the Sun from view.

Perhaps the most famous cloud is the Coalsack, an especially big “hole” in the Milky Way. It’s in the Southern Cross, which is too far south to see from the continental United States. The Coalsack is about 600 light-years from Earth, and spans about 60 or 70 light-years.

There’s also the Northern Coalsack. It’s just about as big as the southern version, although it’s not quite as dark or well-defined. Still, there’s a definite gap in the stars there. It’s in Cygnus. As night falls now, it’s to the right of Deneb, the bright star that marks the swan’s tail.

The Northern Coalsack veils an especially bright region behind it – one of the biggest stellar nurseries in our part of the galaxy. More about that tomorrow.

Script by Damond Benningfield

For most Americans, the Milky Way is more of an idea than a reality. Light pollution blocks the view of the Milky Way and much more. So for most, the only way to see the Milky Way is to get out of town – to visit dark locations far from city lights.

Fortunately, there are still quite a few places where the skies are dark enough for the Milky Way to shine through. The International Dark Sky Association certifies many “dark-sky” locations – parks, towns, and even entire regions.

Such locations have taken steps to ensure that their skies remain dark. They use streetlamps that have a redder glow, which is less troublesome than blue light, for example. They ban certain types of outdoor lighting, and require that other types be shielded so their light goes down, not up.

There are about 140 certified sites in the United States. This year alone, the association has certified towns in Texas and Utah, a wildlife area in Michigan, and a large chunk of Oregon. The list includes many national parks, such as the Grand Canyon. And McDonald Observatory is inside one of the world’s largest dark-sky sanctuaries, in West Texas.

If you have nice, dark skies, tonight is a great time to look for the Milky Way. At nightfall, it arcs from the “teapot” of Sagittarius, in the south; through the swan, high in the east; and down to W-shaped Cassiopeia, low in the northeast – the magnificent glow of our home galaxy.

Script by Damond Benningfield

The hazy band of the Milky Way arches high across the sky on these mid-summer nights. At nightfall, it stretches from almost due north, high across the east, to almost due south. And it arcs high overhead by midnight. But you need to get away from city lights to see it.

The Milky Way is the combined light of millions of stars in the disk of our home galaxy. The galaxy’s busy core is in the teapot-shaped constellation Sagittarius, which is low in the southern sky at nightfall. We can’t actually see the core because it’s hidden behind clouds of dust, which form dark lanes within the Milky Way.

Astronomers use special instruments to peer through this dust. The instruments reveal some remarkable sights, including clusters of some of the hottest, brightest stars in the entire galaxy.

Two of the clusters are the Arches and the Quintuplet. Their stars probably formed just a few million years ago. Big clouds of gas and dust rammed together, triggering an intense bout of starbirth.

Many of the stars in these clusters are among the most massive in the galaxy. The heaviest is the Pistol Star. It’s probably more than a hundred times the mass of the Sun.

The cores of these massive stars are extremely hot, so the stars burn through their nuclear fuel in a hurry. Within a few million years, they’ll blast themselves to bits in titanic explosions. Even then, they’ll likely remain hidden from human eyes behind the cosmic haze.

Script by Damond Benningfield

Astronomers are about to need a really big photo album to store their new snapshots of the universe. That’s because their newest digital camera is ready to look skyward. Each image will consist of 3.2 gigapixels – almost a hundred times the size of the highest-resolution pictures on most smartphone cameras. It’s the largest camera ever for astronomy.

The camera was built for the Legacy Survey of Space and Time, which will use a giant telescope under construction in Chile. It will image the entire sky roughly once every two and a half nights.

Astronomers will use those observations to study dark energy and dark matter. They’ll find new asteroids and comets in the solar system – including some that might someday threaten Earth. They’ll look for stars that grow dimmer as their own planets pass in front of them. And they’ll look for exploding stars and other rapidly changing objects and events.

The new camera was built by a national laboratory in the United States. It’s as big as a small SUV and weighs about three tons. Its field of view will cover 40 times the area of the full Moon. The project will capture about 15 terabytes of data every night – the equivalent of more than a year of high-definition video or a couple of decades of music.

The project is set to begin sometime next year – compiling a huge album of pictures of the universe.

Tomorrow: the glory of the summer Milky Way.

Script by Damond Benningfield

On modern maps of the universe, every star belongs to a single constellation. But in ages past, some stars were known as connecting stars – they belonged to two constellations. And one of those stars is close to the Moon early tomorrow.

The star is Elnath. Its name means “the butting one” – a reference to its position at the tip of one of the horns of Taurus, the bull. In fact, a second name for the star is Beta Tauri – an indication that it’s the second-brightest star in the constellation.

But until almost a century ago, Elnath was also known as Gamma Aurigae. That name indicated that it was one of the brighter stars of Auriga the charioteer. And in many older star atlases, it’s depicted as part of the charioteer’s outline.

Until the early 20th century, there were no rules about where a star might belong – it could be a member of more than one constellation with no problem. In the 1920s, though, the International Astronomical Union tidied up the geography of the heavens. It designated 88 official constellations. And it defined precise boundaries for each one. So every star was given its own home in the cosmos – including Elnath, the horn of the bull.

Elnath stands close to the Moon at dawn. Three other bright lights form a triangle to the upper right of the Moon: Mars, at the top of the triangle; brilliant Jupiter, at the lower left; and Aldebaran, the bull’s eye, at the lower right.

Script by Damond Benningfield

The Moon and three bright companions form a figure that resembles the outline of a sail early tomorrow. Mars is close to the lower right of the Moon, and looks like a bright orange star. Much brighter Jupiter is farther below the Moon. And the star Aldebaran is to the right of Jupiter. It looks like a near-twin of Mars – almost exactly the same brightness and color.

Robotic ambassadors from Earth are studying three of the four bodies from close range – all but Aldebaran, which is 65 light-years away.

Several spacecraft are studying the Moon, with quite a few more scheduled for arrival over the coming year or two. The longest-lived current mission is Lunar Reconnaissance Orbiter. It’s been mapping the Moon for 15 years.

Only one mission is active at Jupiter. Juno entered orbit around the giant planet eight years ago. It’s studied Jupiter itself, plus several of the planet’s large moons.

And a whole bunch of missions are operating at Mars – orbiters and rovers launched and controlled by the United States, China, Europe, India, and the United Arab Emirates. Two of the orbiters have been operating for more than two decades. And the Curiosity rover has been trundling along the surface for 12 years.

The pace of Mars missions has slowed down. But several missions are in the planning stages – including some that would bring Martian samples back to Earth.

More about the Moon and its companions tomorrow.

Script by Damond Benningfield

The Moon dashes through a region packed with bright stars and planets the next few mornings. It’ll pass especially close to Mars, Jupiter, and Elnath, the tip of one of the bull’s horns. Aldebaran, the bull’s eye, will remain a little farther from the Moon.

The meetings occur near the ecliptic – the Sun’s path across the sky. The planets all stay close to the ecliptic as they move through the starry background. The stars are in fixed positions relative to the ecliptic, with Elnath and Aldebaran especially close to it. Finally, the Moon’s orbit around Earth is tilted a bit relative to the ecliptic, so the Moon stays close to that path as well.

The Moon sometimes occults Elnath or Aldebaran, passing in front of the star and blocking it from view. Aldebaran is about five degrees south of the ecliptic, while Elnath is about five degrees north. That puts the stars at the limits of the Moon’s path.

The Moon moves north and south of the ecliptic in cycles, so occultations come in groups. The next set of Aldebaran occultations won’t start until 2033. But for Elnath, the next cycle starts in September and continues into 2027. The Moon won’t occult either star this month, although it’ll come close to Elnath on Wednesday.

Tomorrow, look for these four bright objects aligning to the lower left of the Moon at first light. Jupiter is the brightest member of the quartet, with Mars ranking second. More tomorrow.

Script by Damond Benningfield