On Sept. 1, 1979, NASA’s robotic space probe Pioneer 11 became the first spacecraft to fly by Saturn.

Pioneer 11 launched in 1973 on a mission to explore the asteroid belt, Jupiter and Saturn. It launched directly toward Jupiter, then used Jupiter’s gravity to slingshot around the planet, make a sharp turn and start flying toward Saturn. Four years and nine months later, it finally made it to Saturn.

During its closest approach, it was about 13,000 miles (2,100 kilometers) above the planet’s cloud tops. Because NASA’s two Voyager probes were also on their way to Saturn at that point, they sent Pioneer 11 straight through Saturn’s rings so it could determine whether it was safe for the Voyagers to do the same thing years down the road. So Pioneer 11 pioneered the way through Saturn’s outer rings, going where no spacecraft had gone before — and nearly colliding with a small moon along the way.

Pioneer 11 actually discovered several moons, along with a new ring, and the first evidence of a magnetic field around Saturn.

Why it mattered

Pioneer 11 may have made history as the first spacecraft to visit Saturn, but its original mission was aimed at a very different planet.

The spacecraft was actually the twin of NASA’s Pioneer 10 probe, which launched toward Jupiter in March 1972 on a mission to prove spacecraft could survive passage through the asteroid belt and the harsh radiation environment at Jupiter. NASA wanted to be sure because of its next two missions, Voyager 1 and Voyager 2, which it hoped to launch on a tour of the outer planets (Jupiter, Saturn, Uranus and Neptune) due to a once-in-175-year alignment of the planets.

But before the Voyagers could launch in 1977, Pioneer 10 and Pioneer 11 had to make the voyage to at least one of those outer planets first. Their target: Jupiter.

• NASA’s Pioneer Spacecraft: A Solar System Legacy (Photos)

Pioneer 11 launched in April 1973, a year after Pioneer 10. By that time, Pioneer 10 had already made it safely through the asteroid belt and en route to Jupiter, which it flew by in May 1974.

Based on Pioneer 10’s success, NASA mission managers decided to slingshot Pioneer 11 around Jupiter in a gravity assist to send it even deeper into space for a Saturn flyby. The probe made it through the asteroid belt in April 1974, then zoomed by Jupiter on Dec. 2 of that year (taking the best photos yet of its Great Red Spot), before flying off toward Saturn.

Pioneer 11 set the stage for Voyager 2’s flyby of Saturn by testing the trajectory that later probe (which was already headed to the outer planets by 1979) would take when it flew by Saturn and headed off to Uranus and Neptune. The spacecraft also used its 12 instruments to observe the planet (as it did for Jupiter), and took 440 images of Saturn during its encounter.

It was Pioneer 11 that helped scientists discover two new moons of Saturn, as well as a previously unseen ring. The flyby also revealed that Saturn’s atmosphere is made of mostly liquid hydrogen and has a magnetic field, NASA has said. Pioneer 11 also photographed Titan, Saturn’s cloud-covered moon, showing it as an orange sphere with an average temperature of minus 315 degrees Fahrenheit (minus 192 degrees Celsius).

Pioneer 11 whipped by Saturn at a whoppping 71,000 mph, but kept studying the planet even as it departed, taking its final observations in October 1979.

While NASA originally hoped Pioneer 11 would last for 21 months, it survived in deep space for 22 years, ultimately passing the outermost planets on Feb. 23, 1990 to begin a trip toward interstellar space.

NASA received its final signal from Pioneer 11 on Nov. 24, 1995, ending its mission. The probe was 4 billion miles from Earth and still moving away. The probe also carried a plaque, designed by Carl Sagan, Frank Drake and Linda Salzman Sagan, designed to help a potential alien civilization learn about humanity and Earth’s location, a sort of precursor to the golden record on the Voyager probes.

Today, you can see a mock-up of Pioneer 11 and Pioneer 10 at the Smithsonian National Air and Space Museum in Washington, D.C.

Some stars encounter supermassive black holes and live to tell the tale. New research shows why the flares these encounters cause dim over repeated episodes, and it may be down to the way these stars spin and an escaping binary partner that leaves them to be a stellar snack for a black hole.

Some stars are unfortunate enough to encounter the supermassive black holes that sit at the heart of every galaxy, being subjected to immense tidal forces that turn them into a strand of stellar spaghetti, a process called “spaghettification.” This plasma pasta wraps around the black hole and is gradually fed to it, with some former star stuff being ejected as near-light-speed jets. These occurrences are called tidal disruption events (TDEs).

However, other stars get a reprieve, passing close enough to a supermassive black hole for the cosmic titan to take a bite and strip off material, but not close enough to be fully destroyed. As the star orbits the supermassive black hole, it takes repeated “bites,” with this stellar snacking called a repeating partial tidal disruption event (rpTDE).

Each incident causes a flare of light from the vicinity of the black hole, as would be expected from the brightening seen during a standard TDE. But a strange pattern has emerged in rpTDES; each successive flare can become dimmer. Scientists have struggled to explain this dimming for some time, but finally a team of researchers from Syracuse University may have solved this puzzle.

To reach an answer to black hole flare dimming, the team considered a factor that hadn’t been thought of before: the spin of the star itself. This element explained the dimming of black hole flaring and also helped to explain why not all rpTDEs play out the same.

“We were puzzled by this for two years,” team leader Ananya Bandopadhyay of Syracuse University said in a statement.

A new spin on stellar snacking

Bandopadhyay and colleagues previously determined that how much material a star loses during repeated rpTDE episodes depends partially on its internal structure, which in turn depends on its mass.

Bandopadhyay compares a low-mass star to a fluffy meringue, which makes it more susceptible to the tidal forces generated by the black hole, allowing more material to be stripped from deeper within the star.

In contrast, a high-mass star has a structure more like an onion. That means that when such a stellar body buzzes a black hole in a rpTDE, its outer layers are stripped, but its core resists the influence of the black hole. Thus, as that outer layer is whittled away, there is less and less material to be stripped away in subsequent episodes.

However, that alone can’t fully account for the dimming of flares from four of the ten currently discovered rpTDEs, because of the influence the black hole has on the star as it passes.

The team’s prior work had identified that during rpTDEs, supermassive black holes exert a torque on the passing star that causes the star to spin faster during each passage.

That means even though less material falls to the black hole during each passage, the star returns over shorter and shorter periods of time. That helps keep flaring consistently bright. Thus, a recipe for dimming requires a new ingredient.

Bandopadhyay determined that this element could be a star that was already spinning rapidly before its first encounter with a supermassive black hole.

If a star is already rapidly spinning when it first encounters a black hole, the torque experienced doesn’t increase that spin much. And without that increase in spin, there is no shortening of periods between episodes, meaning less and less material being stripped would result in dimming.

Of course, that leaves another question: why would a star be spinning so rapidly in the first place?

Rogue stars could be the answer

The key to this mystery could lie in the fact that most stars don’t orbit the centers of their galaxies where supermassive black holes dwell alone, instead existing in binary partnerships.

“It is also extremely difficult to ‘bind’ a star to a supermassive black hole so tightly that it orbits the black hole in a matter of months, and yet they seem to do so in rpTDEs,” team member Eric Coughlin of Syracuse University said.

The loss of a partner star, could cause a stellar body to be tightly bound to a supermassive black hole, completing an orbit once every few months.

During a process called Hills capture, as a stellar binary orbits a supermassive black hole and the gravitational influence of the black hole rips the binary apart, ejecting one star while capturing the other.

If this stellar binary was particularly tight, with the stars closely orbiting each other, this ejection and capture process could leave the trapped star rapidly spinning on a tight orbit.

“This work demonstrates that each of these peculiarities can be explained by the same underlying phenomenon: the tidal destruction of a binary system and the capture of one of the stars,” Coughlin said. “From a theoretical standpoint, this is a major step forward in our understanding of the physics at play in these systems.”

The discovery may have implications closer to home too. Though the supermassive black hole of the Milky Way, Sagittarius A* (Sgr A*), isn’t currently involved in a rpTDE, it is orbited by many rapid stars. These findings may explain how they came to be there.

The team’s research was published on August 18 in The Astrophysical Journal.

Venus, which has been such a prominent object in the western evening twilight sky since the start of spring, is now entering its final full month of visibility. With each passing day, it drops a bit lower in the southwest sky and sets a bit earlier and closer to the vicinity of the sun. By month’s end, making a Venus sighting will be rather difficult as it will be following the sun to below the horizon by only about 30 minutes.

During the last week of September, Mercury pops up above the western horizon at dusk, primarily for those living in the southern half of the U.S., though you might need Venus to help direct you to this rocky little world.

Saturn is evident for much of the night, appearing low in the eastern sky as the sky darkens and reaching its highest point in the southern sky soon after midnight.

Mars is a planet that is visible during the predawn hours. While it was quite dim just a few months ago, it has been slowly approaching Earth and consequently has been slowly increasing in brightness. Now, as we move into the final quarter of this year, its brightening will become much more noticeable.

Finally, there is Jupiter, becoming increasingly obvious as a brilliant light, low in the eastern sky a few hours before sunrise.

In our schedule, remember that when measuring the angular separation between two celestial objects, your clenched fist held at arm’s length measures roughly 10 degrees. Here, we present a schedule below which provides some of the best planet viewing times as well as directing you as to where to look to see them

The sun

The sun crosses the celestial equator, heading south at 8:05 p.m. EDT on Sept. 22 (0005 GMT on Sept. 23). This equinox marks the beginning of autumn in the Northern Hemisphere and spring in the Southern.

Mercury

Mercury becomes visible during the final week of September from the southern US, low in the west-southwest in evening twilight. On the evening of Sept. 25, this planet, shining at magnitude -0.1 lies 21 degrees east of the sun and 1 degree above and to the right of the 1st magnitude star Spica. Try using Venus as a benchmark to locate them, as they will be positioned 14 degrees to Venus’ right. You’ll likely need binoculars to pick up Spica as it will shine only about ⅓ as bright as Mercury. On Oct. 9 this smallest of planets will attain greatest elongation, 25 degrees, but this is a decidedly poor apparition. For mid-northern latitudes, the planet will set only 45 minutes after sundown.

Venus

Venus will soon be relinquishing its dominance of the early evening sky.

Looking low near the southwest horizon an hour after sunset on Sept. 1, observers can enjoy spotting the 1st-magnitude star Spica only about 1.5 degrees above Venus. The gap between the two grows by 1 degree per day after that. The dazzling planet sets 1½ hours after the sun as September starts and only a little more than a half hour after as the month ends. Even worse, with respect to the sun, Venus’ path makes a very shallow angle to the horizon for those living near latitude 40 degrees north.

Sharp-eyed observers who can glimpse the planet’s pinpoint gleam around the time of sunset will find it in the west-southwest only about 14 degrees high on Sept. 1 and 5½ degrees on Sept. 30.

On the evening of Sept. 14, look low in the west-southwest sky 30 to 45 minutes after sunset this evening to make a sighting of a waxing crescent moon positioned about 5½ degrees to the left of Venus.

On Sept. 18, Venus reaches its greatest brilliancy (magnitude -4.8), about when telescopes show the planet presenting its “greatest illuminated extent” (321 square arc seconds of sunlit surface). Unfortunately for observers at mid-northern latitudes, this display occurs lower in the dusk sky than at any other time in Venus’s 8-year cycle of recurring appearances. Telescopes show Venus’s crescent lengthening and thinning throughout the month, but observers at mid-northern latitudes will find Venus’s image to be blurred by turbulence low in the sky. For the best telescopic views, try to catch Venus immediately after sunset — or even in late afternoon, if you can find a building or hill to block the sun from view.

Mars

Mars rises around 1:40 a.m. local daylight time at the start of September; about a half hour earlier by month’s end. It’s quite high in the east before morning twilight starts. During much of September, Mars continues its interesting traverse of Gemini, before ultimately crossing over into Cancer.

The amber-hued planet passes less than one degree to the upper left of the 4th magnitude star Delta Geminorum, also known as Wasat, on the morning of Sept. 9. Yellow-orange Mars (magnitude +1.1) is 5.9 degrees to the lower right of the similarly bright yellow star Pollux on the morning of Sept. 17; compare their brightnesses and colors. More striking will be the view when Mars aligns in a straight line with Castor and Pollux on the morning of Sept. 25. That’s also the day when Mars crosses over from Gemini into Cancer.

Jupiter

Jupiter early in the month rises in the east-northeast at 3:50 a.m. local daylight time, but you’ll have to wait at least another week before it gets fairly high in the sky for steady telescopic viewing and that’s not until just before dawn’s first light.

If you make the effort to set up a telescope before dawn’s early light, you can be among the first to see what became of Jupiter’s tumultuous cloud belts and Great Red Spot while the planet was hidden in the glare of the sun from mid-June through mid-August. On the morning of Sept. 8, you’ll find it hovering about 4½ degrees below a waning crescent Moon. Later that afternoon, the moon will cross in front of Jupiter (called an occultation) for much of North America.

Saturn

Saturn is an engaging object all September. It rises due east earlier in the dusk each week. Later in the evening, it moves up into the southeastern sky, initially shining to us from a secluded section of Pisces, on Sept. 6, it crosses over into the non-zodiacal constellation of Cetus, the Whale. It is now shining at magnitude +0.4, its brightest in several years.

In telescopes, its famous rings are narrow but dramatic, now tilted 8 degrees to our line of sight. This is the last season we’ll see the rings so narrow for a dozen years. During the summer of 2027, their tilt will have increased to 14 degrees. On Sept. 26th, you’ll find Saturn appearing as a bright yellowish-white star, shining 6 degrees below the Harvest Full Moon.

Joe Rao serves as an instructor and guest lecturer at New York’s Hayden Planetarium. He writes about astronomy for Natural History magazine, Sky and Telescope, The Old Farmer’s Almanac and other publications.

Repairing an engineering marvel like the International Space Station is no easy feat by itself, but it’s even more impressive when it’s done 250 miles (400 kilometers) up.

What is it?

In this photograph, European Space Agency (ESA) astronaut Sophie Adenot works on the exterior of the International Space Station on Aug. 25, 2026.

The photo was taken while Adenot and NASA astronaut Anil Menon were conducting a 6.5-hour spacewalk, or extravehicular activity (EVA), to replace one of two Space-to-Ground antennas on the outside of the ISS.

This was the second EVA that Adenot and Menon performed to replace the antenna. During a previous spacewalk a week earlier, the pair ran out of time before the new antenna could be installed.

With that first spacewalk, Adenot became the first woman from France to ever conduct an EVA.

Why is it incredible?

It can be hard to conceptualize just how high up the ISS orbits until you see a photo like this one; few people on Earth have ever flown as high as 250 miles (400 km), so that altitude can feel a bit abstract. Seeing an astronaut like Adenot clinging to the space station with the clouds and blue oceans of Earth below puts things into perspective.

At that height, the ISS orbits at quite a high rate of speed. The orbital laboratory zips around Earth at 17,500 mph (28,000 kph), meaning it circles the planet 16 times a day. This photo was taken on day 194, or orbit 3010, of Adenot’s mission, which began in February when she launched to the ISS as part of NASA’s Crew-12 mission.