StarDate

Saturn is putting in its best appearance of the year this week. The planet is at opposition — it lines up opposite the Sun in our sky. It rises around sunset, and it’s visible all night long. It’s in good view in the southeast by the time the sky gets fully dark. The planet’s also closest to us for the year, so it’s at its brightest — like a bright golden star.

Saturn looks so bright for a few reasons. For one, it’s the second-largest planet in the solar system — nine times the diameter of Earth. For another, its atmosphere is topped by clouds that reflect most of the sunlight that strikes them. Its rings are bright as well, although they’re not at a great angle now.

One thing that works against Saturn’s brightness is its distance from the Sun. It’s about nine and a half times farther from the Sun than Earth is. At that range, the Sun appears just one percent as bright as it does from Earth.

That’s one of a couple of distance-related challenges for spacecraft that study the planet. It takes long exposure times to get good pictures, which means the camera has to turn to track the planet and keep it in sharp view.

Another challenge is that it takes an average of 80 minutes for signals from a craft to reach Earth, and 80 more for a reply to reach Saturn. So a spacecraft has to be able to do a lot on its own, without direction from far-away Earth.

We’ll have more about Saturn’s beautiful rings tomorrow.
 

Script by Damond Benningfield

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The gibbous Moon and the heart of the scorpion — the star Antares — play a game of “hide and seek” this evening. The Moon will pass in front of Antares as seen from most of the United States, hiding the bright star from view.

The event is an occultation. The name comes from the Latin word “occult” which means “to hide.”

Occultations happen because Antares and the Moon follow similar paths across the sky.

Antares is almost atop the ecliptic — the Sun’s path. The Moon stays close to the ecliptic as well. So every month, it passes close to the scorpion’s bright heart. But the Moon’s orbit is tilted a bit, so the Moon doesn’t always cover Antares.

Occultations come in series, when the Moon’s orbital cycles bring it into the proper alignment. In fact, tonight’s occultation is the first in a series that will continue for five years. But the circumstances of each occultation are different, so each one is visible from a different part of Earth. From the United States, we’ll see only a few — with tonight’s as one of the best of the bunch.

The occultation gets under way at 8:20 p.m. Central Daylight Time, and continues for more than two hours. But the exact timing varies depending on location. From Kansas City, for example, Antares will disappear around 9:20 and return to view more than an hour later. Most of the U.S. will see the beginning, the end, or all of this game of celestial hide and seek.

Script by Damond Benningfield

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A planet in Aquila, the eagle, has fallen to its doom. The giant planet appears to have spiraled into its parent star. The star flared up for a few months, gave a little “burp,” then settled back to normal.

The exoplanet dinner was discovered in 2020 by telescopes on the ground and in space. Astronomers used bigger telescopes to examine the system in detail. A new analysis of those observations revealed the likely nature of the event.

The star is roughly the same mass as the Sun. But it’s past the prime of life, so it’s puffed up, pushing its surface out toward any planets that might orbit the star. One planet was about the size of Jupiter, the giant of our own solar system. The planet slowed down as it passed through gas and dust expelled by the dying star. Eventually, it slowed enough that it spiraled into the star.

That produced a bright outburst. It reached its peak in about 10 days, then faded over the following six months. The outburst also produced an eruption of hot gas, including enough hydrogen to make 33 planets as massive as Earth.

Astronomers have seen the aftermath of planetary ingestion in several stars — usually as a “pollution” of heavy elements in the star’s outer layers. But this is the first time they’ve seen it happen — a star gobbling up a planet.

The eagle is high in the southeast at nightfall, marked by its brightest star, Altair. You need a big telescope to see the planet-eating star.
 

Script by Damond Benningfield

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If you’re close to the right kind of supernova, it’s gonna getcha. Radiation from the initial blast can zap any planet within a few dozen light-years. Cosmic rays will hit hundreds to thousands of years later. And a recent study says the gap between those periods can be dangerous as well.

Astronomers looked at the type of supernova formed by a massive star. When the star can no longer produce energy in its core, the core collapses and the star’s outer layers are blasted into space. The blast produces radiation that can damage the atmosphere of any Earth-like planet within a few dozen light-years. Interactions with surrounding material creates cosmic rays that can do similar damage centuries later.

The new study used X-ray telescopes in space to examine 31 supernovas that were surrounded by lots of gas and dust. For decades after the explosion, the supernova blast wave heats that material, producing X-rays. The radiation could endanger Earth-like planets up to about 150 light-years away.

X-rays can destroy ozone in the planet’s upper atmosphere, allowing ultraviolet light from the planet’s own star to reach the surface. The X-rays might also create a nasty brown haze that can block the star’s light, killing plants.

Two or more nearby supernovas may have zapped Earth in the past few million years. But no likely future supernovas are close to us today — keeping our planet out of the danger zone.
 

Script by Damond Benningfield

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The Perseverance rover is building up a stockpile. It’s collecting samples of Martian rocks, dirt, and air, and storing them in small tubes. A complex retrieval mission will gather the tubes and bring them to Earth in about a decade.

By then, scientists may be analyzing another set of samples — of Mars’s larger moon, Phobos. A Japanese mission, MMX, is scheduled for launch in about a year. It’ll land on Phobos and gather a few grams of material. Return to Earth is scheduled for 2029.

The two sets of samples will provide different details about Mars. Perseverance is inside a large crater. It’s exploring the delta of an ancient river that once filled the crater with water. The sediments will tell us about conditions in the distant past, when Mars was warm and wet. And they could contain evidence of microscopic life.

MMX will tell us about the formation of both Martian moons, Phobos and Deimos. They could be captured asteroids. Or they could be debris from an ancient collision that blasted some of the Martian crust into orbit. Recent observations of Deimos by another mission, from the United Arab Emirates, appear to favor the impact scenario. The samples could help scientists confirm it.

Mars is quite low in the west at sunset, and sets by the time it gets dark. It’s just visible from the southern latitudes of the U.S. — Miami or San Antonio — but lost in the Sun’s glare for those farther north.
 

Script by Damond Benningfield

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One of the most famous of all skywatching directions is this: Arc to Arcturus, then spike to Spica. In other words, follow the arc formed by the handle of the Big Dipper until you come to the bright yellow-orange star Arcturus, which is high in the west at sunset now. From there, follow a straight line to Spica, the leading light of Virgo.

Tonight, there’s another way to find Spica: Look for the crescent Moon, low in the west-southwest at nightfall. Spica is close to the left of the Moon.

The best measurements put Spica at a distance of 250 light-years. That means the light we see from Spica tonight began its high-speed trip across the galaxy in 1773 — three years before the United States declared independence. That would make Spica a good “semi-quincentennial” star — marking America’s 250th birthday, in 2026.

Spica actually consists of two stars. They’re quite close together — so close that you need a special type of telescope to see them as individual stars. One of the stars is moving into its “giant” phase — puffing up to many times its previous size. Millions of years from now, it should blast itself to bits as a supernova.

The other star isn’t quite as massive as its companion, so it’s still in the prime of life. It should end its life in a more gentle process. But no one is sure how the evolution and explosion of the heavier star will affect the companion, so its future is a bit cloudy.
 

Script by Damond Benningfield

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The Big Dipper is in the northwest this evening, with its bowl below the handle. Starting with the handle, use one of skywatching’s most famous directions to find one of the sky’s brightest stars: Arc to Arcturus. In other words, follow the curve of the handle away from the dipper until you come to yellow-orange Arcturus, well up in the west.

The dipper’s stars belong to Ursa Major, the great bear. And “Arcturus” means “the bear watcher” or “guardian of the bear” — the star is always keeping an eye on the bear.

Arcturus has been a popular name right here on Earth. Some historians have suggested that the name “Arthur” came from Arcturus, which means the legendary King Arthur was named for the star. Several ships of the United States Navy have carried the name, along with several military and civilian aircraft.

And earlier this year, the name was bestowed on a variant of Covid-19 whose symptoms include pink eye.

Officially, the strain was XBB.1.16. But some scientists have applied nicknames to new variants to make them easier for the public to follow. At first, the names came from mythology. But after a kerfuffle over the name Kraken, the scientists switched to names from astronomy — many of which have their own mythological origins. That includes Arcturus — keeping an eye on the bear in the stars, and causing eye problems here on Earth.

After arcing to Arcturus, it’s time to spike to Spica, which we’ll do tomorrow.
 

Script by Damond Benningfield

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Nicolaus Copernicus changed the universe. He brushed aside the dogma of the 16th century, which held that Earth was the center of the universe. Instead, he calculated that the Sun was the center, with Earth going around it. It was an idea that eventually brought him recognition as one of the great scientists in history. Scientists have named a space telescope, a chemical element, and a star in his honor.

He’s also the subject of many monuments, one of which was dedicated 50 years ago today, in Philadelphia.

Kopernik is a 12-foot stainless-steel sculpture. It uses his original Polish name, Mikolaj Kopernik. It was commissioned by a group of Polish-Americans to honor his 500th birthday.

The monument was created by Dudley Talcott. Born in 1899, he studied art in New York and Paris, then spent years in Norway — an experience that inspired him to write and illustrate several books. In 1932, art was an Olympic event, so he entered two works in the Los Angeles Games. He didn’t win any medals, but he was one of America’s leading sculptors for decades.

Kopernik features a 16-foot ring, which represents Earth’s orbit around the Sun; a disk inside the ring, which is the Sun beaming its light into the cosmos; and a connecting triangle, representing the astronomical instruments of the day.

The sculpture is still on display, at 18th Street and Benjamin Franklin Parkway — a monument to a man who changed the universe.
 

Script by Damond Benningfield

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Our home galaxy, the Milky Way, is a galactic shepherd. It controls the movements of maybe 60 or more smaller galaxies. They’re satellites of the Milky Way, so they circle around it in the same way that Earth orbits the Sun.

Two of the satellite galaxies are bright enough to see with the eye alone — the Large and Small Magellanic Clouds. The large cloud is the biggest of the satellites.

All of the others are so far, small, and faint that they’re visible only through telescopes. Most of them are no more than puffballs. As a result, most of them weren’t discovered until this century.

The closest may be the Canis Major Dwarf — about 25,000 light-years from Earth. But there’s disagreement about whether it’s a galaxy or just a star cluster.

The closest confirmed satellite is the Sagittarius Dwarf — about 65,000 light-years away. It’s plunged through the Milky Way’s core several times, disrupting the orbits of some of the stars in the bigger galaxy.

The Milky Way’s gravity is pulling the Sagittarius Dwarf apart. Some day, all of its stars will be incorporated into the Milky Way — and a member of the Milky Way’s flock will disappear.

The Sagittarius Dwarf is in the constellation Sagittarius, which is low in the south at nightfall. Its stars form the outline of a teapot. The Sagittarius Dwarf is to the left of the teapot. But it’s veiled by clouds of dust — a hidden satellite of the Milky Way.
 

Script by Damond Benningfield

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If you look at a map of just about any state, you’ll see a few major cities, a few more mid-sized ones, and a whole bunch of small towns. And the same thing happens if you look at a map of our galactic neighborhood. There are a couple of giant galaxies, a few mid-sized ones, and a whole bunch of little ones. They’re all bound to each other by their mutual gravitational pull.

This collection of galaxies is known as the Local Group. It spans about 10 million light-years, and contains a hundred or so known members, with more added every year.

The “big cities” of the Local Group are our home galaxy, the Milky Way, and the Andromeda Galaxy, M31. Each is a disk that’s at least a hundred thousand light-years wide, and contains hundreds of billions of stars.

After these two behemoths, the list includes a few mid-size members. The largest is the Triangulum Galaxy. It’s about half the diameter of M31 and the Milky Way, but only a few percent as massive.

A couple of mid-size galaxies are satellites of M31. One is a spiral, while the other is a small elliptical galaxy, which looks like a fuzzy rugby ball. And two more members of the mid-size brigade orbit the Milky Way — the Large and Small Magellanic Clouds.

Most of the other members of the Local Group are tiny — far smaller, and with far fewer stars, than the larger galaxies. Many are satellites of the Milky Way, and we’ll have more about them tomorrow.
 

Script by Damond Benningfield

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