StarDate

If you squished the planets of our solar system much closer to the Sun, you’d have something similar to the system known as Kepler 90. The smaller planets are closer to the star, while the giant planets are farther out.

The star is bigger, brighter, and heavier than the Sun, and about half the Sun’s age. Most important, it’s the only star system besides ours with eight known planets. The planets that are close to the star are a little bigger than Earth, the ones in the middle are bigger still, and the two at the outer edge of the system are giants.

There’s one big difference between Kepler 90 and the solar system. The Sun’s farthest major planet is Neptune — about 30 times farther from the Sun than Earth is. But at Kepler 90, the most-distant planet is only as far out as Earth. That means the planets are crowded together — smushed in close to their sun.

When our solar system was young, its giant planets moved much closer to the Sun. That could have scattered any planets that were even closer. But the planets of Kepler 90 appear to be stable. They align in such a way that the gravity of each planet helps keep the others in place — a tightly packed family of planets.

Kepler 90 is in Draco. Although the star is much too faint to see without a telescope, you can get an idea of its location. It’s low in the northwest at nightfall, to the upper right of the bright star Vega. And it’s in the northeast at dawn, to the left of Vega.
 

Script by Damond Benningfield

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A beautiful spiral galaxy spins into view in the northeast this evening, near the tip of the Big Dipper’s handle. It actually consists of two galaxies: a large one that’s interacting with a smaller one, with a “bridge” of stars and gas between them.

M51 is the first galaxy whose spiral nature was seen. It was revealed by the Leviathan of Parsonstown — the largest telescope in the world at the time. It entered service in 1847 — 175 years ago.

The Leviathan was the invention of William Parsons, the Earl of Rosse, in Ireland. He owned and operated a large estate, but was also interested in astronomy. And he designed a telescope that far outclassed anything else of the time.

Its main mirror spanned six feet — two feet wider than the second-largest. The metal mirror had to be taken out and polished every six months, so Parsons made two of them. The mirrors fit into a tube that was 58 feet long. It was suspended between two brick walls, and assistants used cables and pulleys to move it.

Parsons did some of the observing himself, but he also hired a professional. Together, they studied the odd, fuzzy objects known as nebulae. Astronomers hadn’t figured out what they were. The Leviathan revealed that some are clusters of stars. But more than a hundred were spirals. Decades later, astronomers showed that these objects are separate galaxies of stars — beautiful spirals first resolved with the Leviathan of Parsonstown.
 

Script by Damond Benningfield

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The Moon is bashful — it never shows us its backside. The same hemisphere always faces Earth. There’s a bit of a “wobble” that allows us to see around the edges a little. In all, though, two-fifths of the Moon is always hidden from view.

That part of the Moon is known as the back side, the far side, or the dark side.

People sometimes complain when it’s called the dark side. They argue that, over a cycle of phases, the near side and the far side receive equal amounts of sunlight. As a result, the far side is no darker than the side we always see. And they’re absolutely right.

The “dark-side” tag doesn’t refer to how much sunlight it gets, though. Instead, it refers to the fact that the far hemisphere is hidden from us. And until the Space Age, we had no idea what it looked like — it was completely unknown. It’s a lot like dark energy. It might not be dark, and it might not even be energy. For now, though, it remains unknown — a “dark” mystery for scientists to solve.

Today, of course, we know a lot about the dark side of the Moon. Orbiting spacecraft have mapped it in great detail. It has fewer dark volcanic plains than the near side, and lots more of the jumbled-up bright areas.

Most of the near side is in good view tonight — lit up by the Sun. And the bright star Aldebaran is close by. They wheel high across the sky during the night and set in the wee hours of the morning.

Tomorrow: Putting a leviathan to work.
 

Script by Damond Benningfield

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Life on Earth is sustained by photosynthesis. Plants and some bacteria combine water, carbon dioxide, and sunlight to make sugars and oxygen, which they release into the air and water. Without that process, modern life wouldn’t exist.

Scientists have been wondering whether the most common stars in the galaxy might sustain photosynthesis on their planets.

M dwarfs are the smallest and coolest of all stars. But they probably account for more than half the stars in the galaxy, which makes them of special interest in the search for life. In addition, M dwarfs live a long time, so there’s plenty of time for life to develop. And because the stars are small and cool, any possible life-bearing planets would be close in, making them easier to find.

The light produced by M dwarfs is different from sunlight. It’s much redder, and there’s a lot more infra-red. Scientists have considered whether those wavelengths could support photosynthesis.

One study said that M dwarfs don’t produce enough ultraviolet light. But another said the spectrum of an M dwarf should be just fine for life. And yet another one, released last year, agreed. That study subjected bacteria that live by photosynthesis to lighting conditions like those around M dwarfs. And the organisms did well.

The issue is complicated by the fact that most M dwarfs produce big outbursts of X-rays. But it seems at least possible that microscopic life could get by on these little but common stars.
 

Script by Damond Benningfield

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Astronomers have discovered thousands of planets in other star systems. So far, though, only a few can possibly be described as “Earth-like.” And two of those are in the same star system.

Teegarden’s Star is a close neighbor — just 12 light-years away. But it’s so small and faint that it was discovered only a couple of decades ago. It’s a fraction the size and mass of the Sun, and less than a thousandth as bright.

Its two known planets are cataloged as objects “b” and “c” in the system. Both planets are just a few percent bigger and heavier than Earth. And both of them appear to lie in the “habitable zone” — the region where temperatures are just right for life. Since the star is so feeble, that zone is quite close — just a few million miles out.

A study a couple of years ago said that both planets could have comfortable atmospheres and liquid water. But a study last year said otherwise. It found that gravitational interactions between the planets and the star could have caused problems. They could have turned b into something like Venus, with a hot, thick atmosphere. And c could have been turned into a world of volcanoes — making both planets unfit for life as we know it.

Teegarden’s Star is in Aries, the ram, which is high in the southern sky on January evenings. The star is much too faint to see without a telescope. But its location is easy to spot tonight — just above the Moon.

More about extraterrestrial life tomorrow.
 

Script by Damond Benningfield

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If you’re a mighty Greek hunter who’s tired from being out with the dogs all day, then it probably feels pretty good to put your feet up. And fortunately for the celestial hunter, the people who drew the early constellations provided a convenient footstool.

Orion the hunter is well up in the east and southeast as night falls. Look for his three-star belt aiming almost straight up from the horizon. His foot is to the right of the belt — the blue-white star Rigel. A fainter star stands just above Rigel. It’s known as Cursa — from a longer name that means “the footstool of the Central One” — the Central One being Orion himself.

Yet the footstool doesn’t belong to the constellation Orion at all. Instead, it’s one of the brighter lights of Eridanus, the river. It’s a long, faint ribbon of stars that meanders far to the right and lower right of Orion.

Cursa is about 90 light-years away — much closer than Rigel. It’s roughly twice as big and heavy as the Sun. And it’s classified as a stellar giant. It’s used up the original hydrogen fuel in its core, causing its outer layers to begin puffing up like a balloon.

Over time, it’ll ignite a new series of nuclear reactions, which will make it get much bigger than it is now. It’ll also get much brighter, and it’ll get cooler, which will make its surface shine yellow, then orange. All of those changes will make the footstool even more impressive than the foot it’s there to support.
 

Script by Damond Benningfield

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Two bright planets are pinching closer together in the early evening sky. They won’t quite catch up to each other, but they’ll get pretty close.

Mercury and Saturn are quite low in the southwest at sunset. They quickly come into view as twilight begins to fade away. The best time to look for them is about 30 minutes to an hour after sunset. Mercury is the brighter of the two worlds — for now — with Saturn to its upper left. Both are easy to spot, but only if you have a clear horizon.

Mercury is actually making one of its better evening appearances of the entire year. It’s the closest planet to the Sun, so it never strays far from the Sun in our sky. At best, it’s visible for a little while after sunset or before sunrise.

Saturn, on the other hand, is the sixth planet from the Sun — far outside Earth’s own orbit. So the giant planet crosses the entire night sky. Right now, it’s just finishing up another crossing, so it’s dropping toward the Sun, and soon will pass behind it.

For now, look for these worlds in the southwest in early evening. They’ll be closest together on Thursday, separated by less than four degrees — the width of two fingers held at arm’s length. Mercury is fading with each passing day, though. As it drops away from Saturn, later in the week, it’ll also drop below Saturn’s brightness. It’ll be lost in the twilight by about next weekend, with Saturn disappearing a few days later.
 

Script by Damond Benningfield

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The planet Venus is changing things up this week. Tonight, it crosses the line between Earth and the Sun — a moment called inferior conjunction. As it does, it moves from the evening sky to the morning sky. Within a few days, it’ll climb into view low in the east-southeast during the dawn twilight — as the brilliant “morning star.”

Venus is at its closest now — just 25 million miles away. Yet the planet doesn’t shine at its brightest, as you might expect it to. That’s because it’s a very thin crescent. The Sun is lighting up the hemisphere that’s facing away from Earth right now — just like a new Moon. That means it’s nighttime on the hemisphere of Venus that’s facing us, with only a thin sliver in the sunlight.

Over the next few months, Venus will move farther from the Earth-Sun line, so the Sun will shine on more of the planet’s Earth-facing side. In other words, Venus will be getting fuller. That’ll make it brighter. At the same time, though, Venus will be moving farther from us. That will make it fainter. When you combine those factors, Venus will shine at its brightest in mid-February.

Regardless of how bright it looks on any given date, though, Venus always ranks as the second-brightest object in the night sky — only the Moon outshines it.

Look for Venus beginning later this week, quite low in the late dawn twilight. It’ll stay in the morning sky all the way through summer — the beautiful “morning star.”
 

Script by Damond Benningfield

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A star system in the unicorn stays busy. An old, puffy star pours gas onto a small, dead companion. That forms a bright disk, high-speed jets, and powerful outbursts — with perhaps a much bigger outburst in the system’s future.

MWC 560 is in Monoceros, the unicorn, which follows bright Orion across the sky.

The “dead” star is a white dwarf — the hot, dense core of a once normal star. The other star is a red giant — a star at the end of its life. It’s puffed up to giant proportions, so its grip on the gas at its surface isn’t very strong. That allows the gravity of the white dwarf to pull some of its gas away.

The gas forms a wide, thin disk around the white dwarf. Some of the gas falls onto the white dwarf, making the star heavier. But some of it shoots back out into space in skinny jets. They reach speeds of millions of miles per hour. Earth lines up directly in the path of one of the jets.

MWC 560 has grown much brighter several times in the last few decades. The most recent outburst started in 2016, and it took a while to fade. The companion probably was dumping more gas onto the white dwarf. As a result, the jet that faces Earth got thicker and faster, carrying a lot more material away from the white dwarf.

It’s possible that the white dwarf could become a nova later in this century. That would blow its outer layers into space, making it shine thousands of times brighter — a powerful eruption from a busy star system.
 

Script by Damond Benningfield

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When two stars come together, the result can be spectacular. Twenty years ago today, for example, astronomers observed a brilliant eruption in Monoceros, the unicorn. It probably was triggered by the merger of two stars. At its peak, the outburst was a million times brighter than the Sun.

The system is known as V838 Monocerotis. It’s about 20,000 light-years from Earth. It’s on the rim of the Milky Way Galaxy, in its outermost spiral arm. And it appears to belong to a small cluster of bright, heavy stars.

The system became famous a couple of years after the outburst thanks to Hubble Space Telescope. Its pictures showed a brilliant red star surrounded by rings that looked like puffs of cotton candy. The rings weren’t related to the stars, though. Instead, they were clouds of dust around the stars that were being lit up by the eruption.

V838 Mon originally consisted of at least three stars. Two of them were especially big — roughly eight times the mass of the Sun. The third star was only about a third the Sun’s mass. And on January 6th of 2002, as viewed from Earth, the small star appears to have plowed into one of the bigger ones. That triggered the eruption — a spectacular lightshow from a pair of merging stars.

Monoceros climbs into view in the east and southeast by about 8 p.m., to the lower left of Orion. The unicorn is quite faint, though, so you need dark skies to see it.

More about the unicorn tomorrow.
 

Script by Damond Benningfield

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