StarDate

Mighty Hercules climbs high across the sky on June nights. Look for a lopsided square of moderately bright stars — the Keystone. It represents his body, with his legs below and his arms spread to either side.

Hercules was created by the Greeks, and represented a character from their mythology. Other cultures around the world have also seen those stars as a person — but not necessarily a mighty one. To the Potawatomi culture, for example, he’s exhausted.

Before the arrival of European settlers, the Potawatomi were members of a confederacy in the Great Lakes region. They drew pictures in the stars to pass along their culture and lore, and to describe objects and events that were part of their everyday lives.

An example is in the constellation Corona Borealis, the northern crown, which is to the upper right of the Keystone in early evening. To the Potawatomi, the semicircle of stars was Mdodoswen — the sweat lodge. The stars climb to prominence in late spring — the time traditionally reserved for sweat-lodge rituals.

After a few hours, a participant would come out of the lodge completely exhausted. Such a man was depicted in the stars as Wenondeshik — the exhausted one — the same stars as Hercules.

The Potawatomi and other native cultures are making new efforts to preserve their skylore — teaching new generations the stories passed down through many generations before them.

More about Hercules tomorrow.

Script by Damond Benningfield

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Io is the most active body in the solar system — hundreds of volcanoes make its surface look like a scarred apricot. It also has some of the tallest mountains in the solar system — but they’re not volcanoes. Yet the mountains and volcanoes are formed by related processes.

Io is one of the big moons of Jupiter. It’s at the middle of a tug-of-war between Jupiter and some of its other big moons. That battle squeezes and pulls Io’s interior, making it extremely hot. In fact, an “ocean” of molten rock may lie below its crust.

Some of the molten rock pushes its way to the surface, forming volcanoes. Some of them erupt almost non-stop. Others stage outbursts that can last for weeks. An outburst can coat many square miles with lava that sizzles at more than 2,000 degrees Fahrenheit. In all, the volcanoes produce enough lava to cover the entire moon with a layer a centimeter thick every year.

The volcanoes are all pretty low. But some of Io’s non-volcanic mountains are miles high. They form as parts of the crust are pushed upward. They may be shoved by hot rock that’s working its way upward; by slabs of old crust that are plunging below newer crust, or by a similar mechanism — giving Io some of the most active mountains in the solar system.

Look for Jupiter close above the Moon at dawn tomorrow. It looks like a brilliant star. Through binoculars, Io and Jupiter’s other big moons look like small stars quite near the planet.

Script by Damond Benningfield

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You might think that after centuries of carefully tracking the planets, astronomers could tell you precisely where they are, or where they will be in the future. And for the most part, you’d be right. They do know the positions of the planets well enough to send spacecraft to explore them. But they can still be off by a tiny bit.

They’re using one of those spacecraft to narrow the margin of error for Jupiter, the largest planet in the solar system.

An array of radio telescopes is tracking Juno, which has been orbiting Jupiter for five years. The array consists of 10 dishes that are scattered from Hawaii to the Virgin Islands. Combined, they provide observations that are as sharp as a single dish thousands of miles wide.

The same technique was used to track the Cassini spacecraft as it orbited Saturn, the second-largest planet. The observations improved the accuracy of Saturn’s orbit by a factor of about 10.

Scientists expect Juno to do the same for Jupiter. In fact, it’s already improved our knowledge of Jupiter’s orbit by a factor of four.

Juno’s mission had been scheduled to end in July. But NASA extended it to September 2025 — providing a lot more time to track the giant of the solar system.

Jupiter and Saturn line up near the Moon in the wee hours of tomorrow morning. Saturn is close to the upper right of the Moon, with brighter Jupiter farther to the left of the Moon.

More about the Moon and Jupiter tomorrow.

Script by Damond Benningfield

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The Moon climbs into view after midnight tonight. The bright planet Saturn lines up to its left as they rise, and to the upper left at first light.

The Moon is in its “gibbous” phase — sunlight illuminates more than half of the lunar hemisphere that faces our way.

Many people think the Moon’s phases are caused by Earth’s shadow. The phases are indeed caused by a shadow, but not Earth’s. When the Moon is new or a thin crescent, Earth’s shadow is aiming almost directly away from it. Instead, the shadow is cast by the Moon itself.

The cycle begins at “new” Moon, when the Moon crosses the line between Earth and the Sun. The Moon is lost from view for a couple of days, but soon climbs into the evening sky as a thin crescent. The crescent is illuminated by sunlight, while the dark portion of the disk is immersed in the Moon’s own shadow. To put it another way, it’s nighttime on that portion of the Moon.

Over the following two weeks, the illuminated fraction increases until the Moon is full, when it lines up opposite the Sun. After that, the portion that’s in the sunlight gets smaller by the day. The Moon then once again disappears in the Sun’s glare, beginning a new cycle of phases.

Earth’s shadow does occasionally touch the Moon, but only two or three times a year, when the Moon’s orbit crosses the shadow at the time of full Moon. This shadow play is known as a lunar eclipse — an event that happened just four days ago.

Script by Damond Benningfield

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A giant planet may slide through the outer solar system. It may give other objects around it a gentle nudge, causing them to follow similar orbits around the Sun. Despite several years of searching, though, no one has seen it. So many astronomers consider it a phantom.

Several astronomers have proposed the existence of such a world, known as Planet Nine or Planet X.

The most recent proposal came about five years ago. Two astronomers looked at the orbits of many big chunks of ice and rock beyond Neptune, the Sun’s outermost major planet. And they found that several of the objects follow similar paths. The orbits are tilted at about the same angle, and the objects come closest to the Sun in the same region.

Such a grouping didn’t seem random. So the astronomers suggested that a heavier object was acting as a “shepherd,” pushing the smaller objects into similar orbits. They calculated that it was a planet perhaps five to ten times as massive as Earth. It would be hundreds of times farther from the Sun than Earth is — more remote than anything yet seen in the solar system.

Searches have covered a good bit of the area where Planet Nine might be found. So far, they’ve come up empty. But the planet would be quite faint, so it could take some time to find it.

On the other hand, some astronomers are saying that there are other ways to explain the odd orbits besides a planet — suggesting the search for Planet Nine may come up empty.

Script by Damond Benningfield

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If astronomy gave a “truth-in-naming” award, it would have to go to the object known as FarFarOut. It’s the most remote body in the solar system yet seen — more than 130 times the distance from Earth to the Sun.

FarFarOut is one of almost 3,000 objects discovered beyond the orbit of Neptune, the most remote of the Sun’s major planets. Most of them are pretty small, but a few are bigger chunks of ice and rock. The biggest is Pluto, which is about 1400 miles in diameter.

FarFarOut probably ranks in the top hundred or so. Estimates put its diameter at about 250 miles. It’s so far away, though, that it’s hard to tell. Astronomers don’t have the details they need to reveal its true size.

FarFarOut was discovered in January 2019, in observations made a year earlier. Astronomers have tracked it a few times since then. From those observations, they say that it takes about a thousand years to orbit the Sun.

Its orbit is quite lopsided. At its closest, FarFarOut dips inside the orbit of Neptune. Encounters with the giant planet probably sculpted FarFarOut’s orbit, as Neptune gave the little object a boost.

Although FarFarOut is a great name, it’s only temporary. Astronomers recently gave it a formal designation — 2018 AG37. Later on, they’ll give it a formal proper name — a new name for an object far, far out in space.

We’ll talk about a search for a bigger object in the outer solar system tomorrow.

Script by Damond Benningfield

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Objects that sound like exotic pizza ingredients sprinkle the realm beyond the planets: plutinos, twotinos, cubewanos, and many more — names that describe their orbits around the Sun.

Neptune is the most-distant major planet — almost three billion miles from the Sun. But astronomers have discovered almost 3,000 objects beyond Neptune. All of them are big balls or blocks of ice and rock.

The biggest and best known is Pluto. It’s about two-thirds the size of the Moon, and its lopsided orbit carries it well outside Neptune’s orbit. But the two orbits are related. The gravity of Neptune molds Pluto’s orbit, so Pluto completes two orbits around the Sun for every three that Neptune makes.

Quite a few other objects have similar relationships to Neptune. Since their orbits are like Pluto’s, they’re called “plutinos.”

Other objects have different relationships to Neptune. Some complete one orbit for every two that Neptune makes, for example, so they’re known as “twotinos.”

Some of the big iceballs aren’t controlled by Neptune’s gravity. The first to fit this category was 1992 QB1. The ones that followed are sometimes called “cubewanos” in its honor.

The farthest object yet seen is about 130 times farther than Earth is from the Sun. It’s informally known as FarFarOut; more about that tomorrow. The orbits of some other known objects, though, will carry them much farther — far into the deep freeze of the outer solar system.

Script by Damond Benningfield

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The Moon slips through Earth’s long shadow early tomorrow, creating a total lunar eclipse — but just barely. The Moon will pass through the edge of the shadow, so the total portion of the eclipse won’t last long. Almost all of the United States will see at least part of the eclipse.

Lunar eclipses occur only at full Moon, when the Moon lines up opposite the Sun. The Moon’s orbit is tilted, though. So most months, the Moon passes above or below Earth’s shadow, so there’s no eclipse.

But the dark inner portion of the shadow, which creates both total and partial eclipses, is about three times the Moon’s diameter, so it’s a big target. The Moon can stray from a precise alignment with the Sun and still dip into the shadow.

That’s what happens tonight. The Moon will slip into the edge of the shadow as seen from Earth, so it’ll be fully darkened. But the edge of the shadow will be just off the edge of the lunar disk. As a result, the total eclipse will last only slightly longer than the shortest possible duration.

The partial eclipse — when only part of the lunar disk is in the shadow — begins at 4:45 a.m. Central Time. The Moon will be fully eclipsed by 6:11. Totality will end about 15 minutes later. From roughly the eastern half of the U.S., the Moon will set before the total eclipse begins. The western U.S., including Hawaii and Alaska, will see all of the total eclipse, and all or most of the partial eclipse.

Script by Damond Benningfield

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Mercury and Venus, the Sun’s closest planets, huddle together in the twilight the next few evenings. They’re quite low in the west-northwest at sunset. Venus is by far the brighter of the two. Mercury stands to its the upper left for the next few nights, then just a whisker away from it on Saturday.

The two planets have that region of the solar system mostly to themselves. Over the last couple of years, though, astronomers have discovered some asteroids that share the space. One of them is the first asteroid whose orbit stays completely inside Venus’s orbit.

In January 2019, a telescope in California spied an asteroid now called 2019 AQ3. Its orbit carries it from just outside Venus’s orbit to just inside Mercury’s. It comes to within a few million miles of each planet.

A year later, the same telescope recorded another asteroid, 2020 AV2. And it stays completely inside Venus’s orbit.

That won’t always be the case, though. The asteroid came from the asteroid belt, which is beyond the orbit of Mars. The gravity of the planets and other asteroids pushed AV2 toward the Sun. Over the next few million years, similar nudges will continue to alter its orbit — at times pushing it beyond Venus and toward Earth’s orbit.

One simulation suggests the asteroid will end its life in a few million years. It will slam into one of the inner planets — most likely Venus — leaving the inner solar system a bit emptier.

Script by Damond Benningfield

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The Moon has a bright companion tonight. Spica, the leading light of Virgo, is to the right of the Moon at nightfall.

The Moon is waxing toward full early Wednesday, just a few hours after it’s closest to Earth for the month. The combination will produce especially high and low tides.

The tides have many profound effects on Earth and its life. One of them may be influencing how much of a greenhouse gas finds its way into the air.

Methane — the main compound we burn as natural gas — is found in copious amounts on or below the ocean floor. Some of it consists of pockets of gas, and some is frozen. Some of it bubbles to the surface, where it can enter the atmosphere. But methane is a powerful greenhouse gas — it traps far more of the Sun’s heat than carbon dioxide does.

A couple of studies in recent years have found that the amount of methane released from the ocean floor varies with the tides. One study looked at deposits off the coast of Canada’s Vancouver Island. It found that more methane bubbled into the water at low tide than at high tide. And another study, late last year, found similar conditions in the Arctic Ocean, north of Norway.

At high tide, there’s a taller column of water above the methane, so there’s more pressure. One study said that may seal cracks in the ocean floor that allow methane to escape. But at low tide, the pressure is lower, so the cracks open up and the methane bubbles away — released by the Moon.

Script by Damond Benningfield

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