StarDate

A long-distance visitor might put in a good showing in the early morning sky this month. And astronomers will be paying close attention.

Comet C/2025 R3 PanStarrs was discovered in September. It probably is falling inward from the Oort Cloud. That’s a huge reservoir of balls of rock and ice that enwraps the solar system. This one might have been nudged inward by the gravity of a passing star.

Objects in the Oort Cloud were born when the planets were taking shape. Jupiter’s gravity hurled them far into space. In the cold and dark, those bodies have changed very little for billions of years.

As PanStarrs approaches the Sun, some of its ice vaporizes. That releases bits of rock and dirt. The debris forms a cloud around the comet, plus a long, glowing tail. Studying this material provides insights into the birth of Earth and the other planets.

The comet will pass closest to the Sun on April 20th. It’ll be closest to Earth a week later – 44 million miles away. If it survives the Sun’s heat, it then will rocket back into deep space, not to return for thousands of years, if ever.

PanStarrs is low in the east before and during dawn. Because we record in advance, we can’t tell you how bright it looks, or how bright it’ll get. We can tell you that it will zip across the Great Square of Pegasus next week, then move into Pisces. By then, it will appear so close to the Sun that it’ll be tough to spot, with or without optical aid.

Script by Damond Benningfield

In October of 1604, a brilliant “new” star blazed to life in the constellation Ophiuchus. It was bright enough to see in the daytime for weeks. German astronomer Johannes Kepler kept a close eye on it until it faded from the night sky, in 1606. So today, it’s known as Kepler’s Supernova. It’s the last known supernova in the Milky Way Galaxy.

A space telescope has been keeping a close eye on the aftermath of that event for the past 25 years. That’s revealed a lot about the supernova and the environment around it.

The supernova flared to life when a stellar corpse known as a white dwarf tipped above its weight limit. The star either stole gas from a companion star, or it merged with another white dwarf. Either way, the star was blasted to bits. The explosion expelled a huge cloud of debris – a nebula that today spans about a light-year. It’s extremely hot, so it produces a lot of X-rays.

Chandra X-Ray Observatory has taken many looks at the nebula. It’s found that one side of it is expanding at about two percent of the speed of light. The opposite side is moving only one-third that fast. The slower side is also hotter. That’s because it’s running into more gas and dust around the nebula.

Chandra will keep an eye on the nebula for as long as it can – telling us much more about the violent death of a star.
The nebula is at the southern edge of Ophiuchus. At dawn tomorrow, it’s to the upper right of the Moon.

Script by Damond Benningfield

The Sun sprays Earth with a constant shower of charged particles – the solar wind. But the shower sometimes becomes a storm – a barrage that can damage satellites, overload power grids, and cause other mischief.

Predicting such storms can save a lot of grief. But better predictions require a better understanding of the Sun, Earth’s magnetic field, and how they interact. A mission scheduled for launch as early as this week should help.

SMILE is a joint project of Europe and China. The craft will orbit up to 75,000 miles from Earth. From that high perch, it’ll be able to see Earth’s magnetopause – the zone where the solar wind rams into Earth’s magnetic field. It will monitor that zone for up to 40 hours at a time – far longer than any glimpses we’ve had before.

Earth’s magnetic field deflects most of the particles in the solar wind. But some of them get through. They create the auroras – the colorful northern and southern lights.

Powerful storms on the Sun blast out huge amounts of particles. They can overwhelm the magnetic field, creating intense bouts of “space weather.” Among other effects, that causes especially intense auroras, which can appear in regions where they’re seldom seen. SMILE will watch the auroras to see how they change with the level of solar activity.

SMILE’s observations will tell us a lot more about how Earth and the Sun get along – improving our ability to protect ourselves from solar storms.

Script by Damond Benningfield

If we could send a spacecraft to the supergiant star Antares, it could take a really close look. In fact, it’s not hard to imagine that we could build a probe that could safely plunge into the star’s outer layers. Although those layers are hot, they’re also quite thin – a fairly decent vacuum. So a probe might be able to descend millions of miles below the surface and survive.

Antares is a monster. It’s roughly a dozen times the mass of the Sun, and 700 times the Sun’s diameter. So its average density is less than one-billionth of the Sun’s. And most of its mass is concentrated deep in the core, which is where the star generates its energy.

That means the outer layers are extremely thin – so thin that it’s tough to define the surface – it blends into the background.

The surface temperature of Antares is about 6100 degrees Fahrenheit, compared to 10 thousand degrees for the Sun. We’ve already built a probe that can approach to within a few million miles of the Sun. It has a shield that can withstand temperatures of about 2500 degrees. A plunge into Antares would be hotter, but building a shield to take the heat doesn’t seem impossible – providing a way to get an up-close look at this monster star.

Antares climbs into good view by 1 or 1:30 a.m. It’s close to the lower left of the Moon as they rise, with the Moon inching closer to the star before dawn.

Script by Damond Benningfield

Eighteenth-century astronomer William Herschel described the star system Beta Monocerotis as “one of the most beautiful sights in the heavens.” It’s one of the hidden beauties of Monoceros, the unicorn. The constellation is well up in the southwestern sky in early evening. It’s wedged between brilliant Orion and the “little dog” star Procyon.

There’s not much to see in Monoceros with the eye alone. But telescopes reveal a bounty of beautiful sights. And Beta Monocerotis straddles both domains. It’s faintly visible to the unaided eye as one of the unicorn’s two brightest stars. But to see the same beauty that Herschel did, you need a telescope. That view reveals three stars, not one, all with a fetching blue-white color.

The color comes from the temperatures of the stars – their surfaces are many thousands of degrees hotter than the Sun’s. And all three stars are much more massive than the Sun. That revs up the nuclear reactions in their cores, which is what makes them so hot. It also makes the stars extremely bright – as much as 3200 times as bright as the Sun. So the stars are visible across 700 light-years of space.

The two faintest members of the system probably form a wide binary, with the third star orbiting around them. Combined, they make Beta Monocerotis a beautiful skywatching sight – a vision in blue for an early-spring night.

Script by Damond Benningfield