StarDate

Mars and Venus are staging an amazing show in the western evening sky. Venus is big and bright — the “evening star.” Mars is just one-half of one percent as bright. But its closeness to Venus will help it stand out. Tonight, it’s only about a degree and a half away — the width of a finger held at arm’s length.

One reason Venus looks so much brighter is that it’s covered by clouds. They hide the surface, but they also help protect it.

The most common features on Venus are volcanoes and related structures. Impact craters — the scars of collisions with big space rocks — are much less common. Scientists have cataloged fewer than a thousand of them. The largest is only about 175 miles in diameter.

That’s largely because of Venus’s atmosphere. It’s extremely dense, and its clouds are made of sulfuric acid. So when a space rock slams into Venus, it’s likely to burn up or split apart before it hits the ground.

Mars, on the other hand, is a crater-lover’s paradise. Scientists have cataloged hundreds of thousands of them that are at least two-thirds of a mile in diameter. The largest is a shallow basin a thousand miles across.

Mars’s atmosphere is less than one percent as thick as Earth’s. So when a big space rock takes aim, there’s not much to keep it from hitting. And there’s not much to erase impact craters, either. So they just keep adding up — more big holes on the Red Planet.

More about Mars and Venus tomorrow.
 

Script by Damond Benningfield

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Star systems with more stars than you can count on one hand are rare. In fact, you could probably total them all up by yourself if you use your hands and feet.

One of those systems is called 65 Ursae Majoris. It consists of six known stars. The two stars at the center of the system orbit each other. All the other stars orbit them.

The stars at the center are almost identical — they’re almost twice as big and heavy as the Sun. They’re so close together that they orbit each other every couple of days.

The first two stars out from them are more than twice the Sun’s mass. One of them orbits the central pair every 21 months, and the other, once every 118 years.

The two most remote members of the system are less well known. One of them takes thousands of years to complete a single orbit. And the other — the one you need an extra hand to tally up — takes hundreds of thousands of years. Astronomers have been watching the stars for only a fraction of that time, though, so they haven’t plotted enough of their orbits to know the details. And it could take centuries to figure it all out.

65 Ursae Majoris is in Ursa Major, the great bear. The bear’s body and tail are outlined by the Big Dipper, which is in the northwest on July evenings. 65 Ursae Majoris is to the left of the dipper. At a distance of 700 light-years, though, even the combined light of its six stars isn’t enough to see without a telescope.
 

Script by Damond Benningfield

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If you want to hear the sounds of civilization, you’re likely to head downtown. If you want the sounds of nature, then you’re likely to head for the country.

That reflects the strategy in recent months of the world’s biggest search for extraterrestrial intelligence. It’s been aiming its radio telescopes toward the center of the Milky Way — the galaxy’s busy “downtown.”

Breakthrough Listen began in 2016. It uses radio telescopes in the United States and Australia to listen for signals from other civilizations. It also uses an optical telescope to look for high-powered lasers. It’s scanned hundreds of thousands of stars across a wide range of wavelengths. Most of its observations are still being analyzed.

In recent months, it’s taken aim at the center of the galaxy. There are a lot more scannable stars in that direction than in any other — stars in the center, and stars across the 27,000 light-years or so between Earth and the galaxy’s hub.

In addition, the center of the galaxy is considered the best location for a beacon to signal worlds throughout the Milky Way. It could even serve as the hub for a sort of galactic Internet.

Early results have found no evidence of powerful beacons. But researchers still have hundreds of hours of recordings to study in their quest to find other civilizations in our galactic home.

We’ll talk about efforts to find new stars in that region of the sky tomorrow.
 

Script by Damond Benningfield

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The black hole at the center of the Milky Way Galaxy is an underachiever. It’s much fainter than similar black holes in other galaxies. But that hasn’t always been the case. Long ago, it might have shined a hundred million times brighter.

The black hole is called Sagittarius A-star. It’s in the constellation Sagittarius, which is in the southeast as night falls. Some of its stars form the outline of a teapot. Sagittarius A-star is immersed in the “steam” above the spout.

The black hole is four million times the mass of the Sun. It’s encircled by a faint disk of hot gas. Disks around similar black holes can shine a hundred million times brighter. Those black holes are pulling in a lot of gas and dust.

They’re heated to millions of degrees, so they shine brightly.

Sagittarius A-star is pulling in very little material, though, so it’s faint. It does occasionally flare up for a few hours — probably as it gobbles up an asteroid or other bit of debris. And a few hundred years ago, it shined up to a million times brighter than today.

Space telescopes have revealed what could have been even bigger outbursts in the past. There was one outburst from the galactic center about 15 million years ago. It could have been caused by the birth of many new stars. But it also could have been a flare-up of the black hole, perhaps as it devoured a star — a brilliant eruption for the Milky Way’s black hole.

More tomorrow.
 

Script by Damond Benningfield

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One of the biggest roller coaster rides in the Milky Way Galaxy is a star known as S2. It orbits the black hole at the galaxy’s heart. At its closest, it’s just 11 billion miles from the black hole. And pulled by the black hole’s powerful gravity, it reaches a top speed of almost three percent the speed of light.

Perhaps more important for astronomers, the star confirms the existence of the black hole. In this 2010 interview, Andrea Ghez, an astronomer at UCLA, explains.
GHEZ: The most definitive proof you can get of a supermassive black hole is to show that things are moving around under the gravitational influence, and from that motion you can show what the mass is directly. There’s no question there. It’s very much like the planets orbiting the Sun. From those planets’ orbits you can get the mass of the Sun and the orbit also tells you a size.

Ghez and her colleagues, along with a team led by Reinhard Genzel, have been watching S2 and other stars near the black hole for decades. Their work showed that the black hole is four million times the mass of the Sun. For their work, Ghez and Genzel shared last year’s Nobel Prize for Physics.

S2 is big, young, and hot. At the peak of its orbit, it’s about 170 billion miles from the black hole. After that peak, the star plunges back toward the black hole — continuing its roller-coaster ride through the heart of the galaxy.

More tomorrow.
 

Script by Damond Benningfield

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The downtown of a major city is bold, bright, busy — and crowded. And the same thing applies to galaxies. The downtown of our home galaxy, for example, is packed with millions of stars. Some of them are among the biggest and brightest in the entire Milky Way. And new stars are entering the picture at an impressive rate.

The center of the Milky Way is in the constellation Sagittarius. It’s in the southeast in early evening, and its stars form the outline of a teapot. The center of the galaxy is in the “steam” of faint stars above the spout of the teapot.

Astronomers aren’t sure just how far away “downtown” really is. Estimates range from about 23,000 to 30,000 light-years. A study last year came up with a bit less than 26,000.

The hub of the galaxy’s heart is a black hole about four million times the mass of the Sun. It’s encircled by a faint disk of hot gas. Many stars orbit the black hole, including some that come especially close; more about that tomorrow.

Several giant star clusters are within a couple of hundred light-years of the black hole. One of them is one of the busiest nurseries in the galaxy, giving birth to many new stars. Another is the densest cluster in the galaxy, with stars packed millions of times more tightly than out here in the suburbs. And yet another contains several stars that are at least a million times brighter than the Sun — brilliant lights for “downtown” Milky Way.
 

Script by Damond Benningfield

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While many Americans were celebrating Independence Day five years ago, a few were celebrating a milestone at another world: All stations on Junocord, we have the tone for burn cutoff on delta-v. Juno, welcome to Jupiter. (cheers)

The Juno spacecraft has been orbiting Jupiter ever since. It’s provided a peek into the interior of the solar system’s biggest planet. And it’s given us some impressive looks at Jupiter’s busy atmosphere.

Juno’s main mission was to measure Jupiter’s magnetic and gravitational fields. Those readings have shown that Jupiter’s interior is like a pat of butter that’s just been dropped into a skillet. It’s still a little firm in the middle, but the edges are gooey and indistinct. That could mean that another large body hit Jupiter long ago, stirring up its middle.

Juno also has taken a look at Jupiter’s poles. It found a ring of giant storms encircling each pole. The swirling storms at the north pole resemble a pan of cinnamon rolls just out of the oven. Those at the south pole are more spread out.

The craft has also measured the composition of Jupiter’s atmosphere, found lightning in the highest clouds, and listened in to radio waves from its northern and southern lights.

Juno’s mission was supposed to end this summer. But its run has been extended for another four years. And it’ll branch out to study Jupiter’s rings and moons — perhaps prompting future celebrations of new discoveries.
 

Script by Damond Benningfield

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Earth’s orbit around the Sun is a bit wonky. It’s a little stretched out, so our distance from the Sun varies. Over the course of a year, it changes by about three million miles — roughly three percent of the average distance. We’re closest to the Sun in January, and farthest in July. In fact, we’ll be at our most distant on Monday.

One consequence of the changing distance is that Earth moves at different speeds in different parts of its orbit. In January, when the Sun is closest, Earth moves a little faster than average. And now, we’re moving a little slower than average.

The change in speed affects the length of the seasons. Winter is the shortest season in the northern hemisphere, while summer is the longest. Summer will last almost 94 days — about five days longer than winter.

There’s also a difference in the length of a day — the time from one local noon to the next. When we’re closest to the Sun, a day averages a few minutes less than 24 hours. But now, when we’re farther away, a day averages a few minutes more than 24 hours.

Unless you go out and plot the Sun’s position from day to day, though, it’s nothing you’re likely to notice. We keep time with mechanical or digital devices. And with Daylight Saving Time, the time on the clock can vary from local solar time by up to a couple of hours.

So the rhythm of the Sun doesn’t always match the rhythm of daily life — regardless of how far away the Sun is.
 

Script by Damond Benningfield

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The planet Venus is pushing a little higher into the sky each night. It’s the brilliant “evening star,” low in the west-northwest at sunset. It’s so bright that it’s easily visible even through the twilight, although you do need a clear horizon to spot it.

Skywatchers south of about Dallas or Little Rock should also be able to make out a couple of objects near Venus — especially with binoculars. The view will be more challenging north of that line because the array sets at a shallower angle, so it’s more obscured by the glow of twilight.

One of the companions is Messier 44, the Beehive star cluster. It will appear just to the left of Venus tonight, and just below it tomorrow night. Binoculars will reveal quite a few of the cluster’s individual stars.

The other companion is the planet Mars. It’s to the upper left of Venus. Tonight, it’s about six degrees away — roughly the width of three fingers held at arm’s length.

Mars looks like a humble star, with a slightly orange color. It’s dropping toward the Sun now, so it’ll disappear from view by early August for the entire country. Venus will pass by it at the end of next week, making its fainter sibling a little easier to pick out.

Venus is climbing away from the Sun. It will stand a little higher in the sky each evening over the next few months, and remain in view a little longer. It’ll hang around in the evening sky for the rest of the year.
 

Script by Damond Benningfield

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Fireflies are among the more pleasant features of a summer evening. Children chase them across the yard, and adults just enjoy their beautiful flashes.

But our own nightlights could be chasing them away. Recent work has found that artificial lights can interfere with the flashes, which are part of the mating ritual. That means fewer of these twinkling lights for future generations of children to chase.

In fact, research is showing that artificial light is a problem for all insects — not to mention professional astronomers and casual skywatchers. A study in Peru, for example, showed that insects were attracted to outdoor LEDs in droves. That made them easier for predators to catch, kept them from catching their own meals, and tired them out. The study did show that LEDs warmed with amber filters attracted fewer insects.

For fireflies in North America, though, amber had the opposite result. Scientists studied a species that’s common in the eastern U.S. and Canada. They exposed courting fireflies to different colors and intensities of light. And they found that amber light cut down on the “flashiness” of males and the response by females more than any other color.

And yet another study looked at fireflies in a forest in Brazil. It found that artificial lights were a bigger threat than habitat destruction or encroaching cities.

So for the insect kingdom, it seems, there’s no such thing as a good artificial nightlight.
 

Script by Damond Benningfield

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