There’s an extraordinary conjunction in tomorrow’s early morning sky – a tight grouping of the Moon, the planet Venus, and the star Regulus. They’re quite low at first light, so you may need a clear horizon to spot them. Venus is the brilliant “morning star,” just a fraction of a degree from the Moon. Regulus is a bit farther from the Moon. It’s much fainter than Venus, but its proximity to the brighter bodies will make it pretty easy to pick out.
This beautiful meeting is possible because all three bodies lie near the ecliptic – the Sun’s path across the sky.
Regulus, which marks the heart of the lion, is “fixed” in position just half degree a from the ecliptic. It does move through the galaxy, but it’s so far away that it takes centuries to notice any change.
Venus’s orbit around the Sun is tilted by about three degrees – about one and a half times the width of your finger held at arm’s length. The planet crosses the ecliptic during each orbit, so it’s always close. On rare occasions, it can even cross in front of Regulus, blocking it from view. That last happened in 1959, and it’ll happen again on October 1st, 2044.
The Moon’s orbit around Earth is tilted by about five degrees. So, like Venus, the Moon moves back and forth across the ecliptic. Tomorrow, it’ll be just about one degree from that path – setting up a beautiful conjunction in the dawn sky.
Script by Damond Benningfield
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New Dwarf?
A third of a century ago, we knew of only two solar-system bodies beyond the orbit of Neptune: Pluto and its largest moon. Today, the known population of such bodies is in the thousands. And quite a few of them are in the same class as Pluto itself: dwarf planets.
One of the newest members of that class is 2017 OF201. It was discovered in 2017. A recent study found that it may be about a third the size of Pluto. If so, then it most likely would qualify as a dwarf planet.
The object follows a highly elongated orbit around the Sun. It ranges from about 45 times to 1600 times the distance from Earth to the Sun. And it takes almost 25,000 years to complete a single orbit. Today, it’s about 90 times the Earth-Sun distance, and moving outward. Before long, it’ll be so remote that not even the biggest telescopes can see it.
Researchers say the object could be bad news for a possible Planet Nine. Studies of other objects in the outer solar system suggest that some of them may have been pushed around by the gravity of a much larger body. That body could be a planet roughly five to 10 times the mass of Earth, orbiting far from the Sun. But the orbit of 2017 OF201 shows no influence of such a planet.
There’s a lot to be done to understand the orbits of the bodies in the outer solar system – and use them to pinpoint a possible planet far from the Sun.
Script by Damond Benningfield
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Dwarf Planets
The roster of “dwarf planets” keeps growing. But it’s not official – there’s no league office to tell us who’s on the roster and who’s not. Various groups keep their own lists, but they don’t agree on which objects belong.
The dwarf-planet category was formalized a couple of decades ago. Astronomers had discovered some new Pluto-like objects beyond the orbit of Neptune. They had to decide whether to add those objects to the roster of planets, or to put them in a new category. So in 2006, the International Astronomical Union voted to create the “dwarf planet” designation.
A dwarf planet was defined as a body that’s large enough for its gravity to pull it into a rounded shape, but not large enough to clear its orbit of other bodies. The initial list included Pluto and three other distant objects, plus Ceres, the largest asteroid.
Since then, astronomers have discovered thousands more objects in the realm of Pluto and beyond. Most of them are fairly small. But some are larger. Because they’re so far away, though, it can be tough to figure out an exact size and mass. So that makes it harder to decide whether some of these bodies are dwarf planets, or just big comets or asteroids.
Today, most planetary scientists agree on a core list of about 10 dwarf planets. Another dozen or so are considered good candidates. And many more are possibilities – including a recently discovered one that we’ll talk about tomorrow.
Script by Damond Benningfield
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Moon and Companions
A bright star and planet team up with the Moon early tomorrow to form a tight, beautiful triangle. Pollux will stand close to the lower left of the Moon, with much brighter Jupiter about the same distance to the lower right of the Moon. Pollux is the brightest star of Gemini, while Jupiter is a planet.
Jupiter is by far the giant of the solar system. It’s more than twice as massive as all the other planets combined. And it’s about 11 times the diameter of Earth. That makes it big enough to hold 1300 Earths.
But a recent study says that Jupiter might have been much bigger during its infancy – about two or two-and-a-half times its current diameter. That would have made it big enough to hold thousands of Earths.
Scientists came to that conclusion by studying the orbits of two of Jupiter’s small, close-in moons. The orbits are slightly tilted. Simulations showed that the moons were pushed into those orbits by the larger moon Io as it moved away from Jupiter. Those calculations revealed Jupiter’s original size and other details.
Jupiter probably formed in just a few million years – much quicker than most of the other planets. By then, the supply of planet-making materials had dried up. So Jupiter’s gravity began squeezing it and making it spin faster. Eventually, the planet reached a point where it couldn’t shrink any farther – leaving the smaller but still-giant world we see today.
Script by Damond Benningfield
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Death Spiral
A star that may be in a death spiral wants the universe to know about it. Every four and a half days it creates a burst of X-rays. The cause of those outbursts may be leading to the star’s demise.
The possibly dying star is in a galaxy that’s about 300 million light-years away. During evening twilight now, that spot is quite low in the west, below the bright star Arcturus.
According to a recent study, the story probably involves the star; a black hole, nicknamed Ansky, that’s a million times the mass of the Sun; and a wide disk of hot gas around the black hole.
The star is following a tilted orbit around the black hole. Every few days, the star plunges through the disk. That heats the gas around the star, so gas blows away from the disk in bubbles that may be as massive as the planet Jupiter.
Each passage robs the star of a bit of its orbital energy, so it spirals closer to the black hole. If the star is the mass of the Sun, it could last another five or six years before it dives into the black hole or is ripped apart by the black hole’s gravity. If the star is heavier, it could survive a little longer.
Astronomers discovered the system in observations by two X-ray telescopes in space. They’ll use those same telescopes to watch the system in the years ahead. If the outbursts get more frequent, it’ll confirm they’re on the right track, and the star is on the wrong one – headed toward its destruction.
Script by Damond Benningfield
USA