StarDate

Hydra, the water snake, is the longest of the 88 modern-day constellations. It’s so long that it takes hours for the entire thing to climb above the horizon. Yet Hydra is also one of the fainter constellations. In fact, from most cities, only one of its stars is easy to spot.

Alphard is about half way up the southern sky as night falls. There are no other bright stars anywhere close to it, so you shouldn’t have much trouble picking it out.

Alphard is about 175 light-years from Earth. At that great distance, the fact that we can see it so clearly tells us that the star is pretty remarkable. In fact, it’s a giant — it’s puffed up to about 50 times the diameter of the Sun.

The star is roughly 400 million years old — less than 10 percent the age of the Sun. Yet it’s also about three times as massive as the Sun. Heavier stars “burn” through their nuclear fuel faster than less-massive stars, so they age more quickly.

Alphard is already entering the final stages of life. As it uses up the fuel in its core, its outer layers are puffing up. They get cooler as they do so, giving Alphard a reddish orange color.

In a fairly short time — astronomically speaking — those outer layers will stream off into space. That will leave only the star’s hot but dead core — a tiny remnant known as a white dwarf. It’ll be far too faint to see with the eye alone — depriving the water snake of its one bright light.

Script by Damond Benningfield

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The constellation Vela represents the sail of the Argo, the ship that carried Jason and the Argonauts. It’s quite low in the south as darkness falls this evening. Only one of its stars is much to look at. But if our eyes were more sensitive, we’d see that Vela is home to one of the largest individual objects in the night sky — the remains of an exploded star.

The Vela Supernova Remnant was born as little as 11,000 years ago as seen from Earth when a giant star exploded. The blast sent the star’s outer layers racing into space at a few percent of the speed of light.

This cloud of material continues to expand. Today, it’s dozens of light-years across. At a distance of about 800 light-years, that makes it look about as big as your fist held at arm’s length.

As the debris rams into surrounding clouds of gas and dust, it heats them and causes them to glow. That creates a thin but beautiful nebula. It contains a diverse brew of chemical elements created in the heart of the star, or in the supernova blast.

Not all of the star was destroyed, though. Its core was crushed to form a neutron star. This bizarre object is more than twice as heavy as the Sun, but only as wide as a mid-sized American city. It spins 11 times per second.

With each turn, a beam of radio energy sweeps across Earth, so the star “pulses” on and off — a pulsating beacon for the ancient Argo.
 

Script by Damond Benningfield

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56 Ursae Majoris is dying. The star has completed the prime stage of life. Now, it’s going through some changes. It’s puffed up to giant proportions. Eventually, it will shed its outer layers, leaving only its hot, dense core — a white dwarf.

A companion star has already expired. And its death might have had a big impact on 56 Ursae Majoris — 56 UMa for short — in more ways than one.

A recent study says the companion might be a neutron star — a corpse that’s even smaller and denser than a white dwarf. It formed when the star exploded as a supernova, a hundred thousand years ago. The star’s outer layers were blasted into space at a few percent of the speed of light.

Today, the stars are separated by about 23 times the distance from Earth to the Sun. At the time of the blast, though, they probably were closer. So the supernova shockwave could have stripped away some of the surviving star’s outer layers. The explosion also created a rich brew of chemical elements. Some of those may have been embedded in the surviving star — perhaps explaining some odd chemistry seen today.

The supernova also could have blown away the material around the stars, creating an empty “bubble.”

A neutron star isn’t the only possible explanation for the companion to 56 UMa — but it might be the best one.

Under dark skies, 56 UMa is just visible to the unaided eye. It’s in the east at nightfall, to the right of the bowl of the Big Dipper.
 

Script by Damond Benningfield

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In astronomy, just because you can’t see something doesn’t mean you can’t study it. That’s the case for a lot of stars. Many systems consist of two or more stars. But in a lot of those systems, one or more stars are hidden from even the biggest telescopes.

A prime example is Spica, the brightest star in Virgo. That bright point is the combined light of two stars. But only one of them is visible.

H.C. Vogel discovered Spica’s dual nature in 1890. He used a spectroscope to break the star’s light into its individual wavelengths. That produced a “barcode” that revealed the star’s temperature, motion, and composition.

Vogel found a second barcode, which was quite faint. It was produced by a companion star.

Detailed study since then has provided details on both stars. The main star is so massive that it will blast itself apart as a supernova. It’s more than 20,000 times brighter than the Sun. The companion is a little less massive, but it’s still more than two thousand times the Sun’s brightness.

The two stars are only about six million miles apart. The smaller, fainter star is so close to the main star that it’s overpowered by the flashier star’s light. So while astronomers have been studying the faint star for more than a century, they’ve never actually seen it.

We can see Spica tonight near the Moon. It climbs up below the Moon by about 9 or 9:30. It’ll be closer to the upper right of the Moon tomorrow night.
 

Script by Damond Benningfield

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When the United States and the Soviet Union sent the first robotic landers to the Moon, in the 1960s, they were lucky just to hit the Moon. But today’s missions are aiming for pinpoint landings — a requirement for reaching important scientific targets.

An example is called SLIM — Smart Lander for Investigating the Moon. It’s a Japanese mission that’s scheduled for launch within the next few weeks. It’ll share a ride to space with an X-ray telescope.

It’s Japan’s first lunar lander. And it’s designed mainly to evaluate the technology for precise touchdowns. The small craft will aim for a zone about the size of a football field. If it works, it’ll set the stage for more ambitious missions in the future.

SLIM’s target zone is near the Marius Hills Hole — a round pit that’s hundreds of feet wide, and perhaps 250 to 300 feet deep. It may be an entrance to a lava tube — a tunnel carved long ago by flowing lava. Such tubes hold clues to the Moon’s volcanic history. And they could serve as homes for future astronauts.

SLIM will carry a tiny passenger: a rover called Sora-Q. It was designed by the company that created the Transformers and other popular toys. It’ll fly to the Moon curled up to about the size of a baseball. On the Moon, its wheels will unfold and carry it across the surface.

It’ll take weeks for SLIM to reach the Moon. So it’ll be a while before we know if it achieved its main goal: a pinpoint landing on the Moon.
 

Script by Damond Benningfield

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The environment around a black hole is a maelstrom of superhot gas. Most of the gas funnels into the black hole, but some escapes in “jets” that fire out at almost the speed of light. The gas gets so hot that it shines mostly in X-rays. So to fully understand what’s going on around a black hole, we need to observe its X-rays. But Earth’s atmosphere absorbs X-rays, so we have to send telescopes into space to see them.

Japan is ready to do just that. It’s scheduled to launch an X-ray telescope called XRISM within the next few weeks.

Even from space, it’s not easy to catch X-rays — they zip into and even through normal mirrors. So X-ray telescopes consist of a set of concentric tubes that are coated in gold. X-rays skip off the surfaces of the tubes, like stones skipping off a pond, and into special detectors.

XRISM’s instruments will study many powerful objects and events. They’ll look at ribbons of hot gas inside galaxy clusters, for example. The temperature and speed of the gas helps astronomers understand the cluster’s birth and evolution.

XRISM also will study the chemical evolution of the universe — how different elements formed and were scattered through space. That will help us understand how and when the first stars were born, how the stars created new elements, and how those elements were incorporated into later generations of stars.

XRISM will share its ride to space with a mission to the Moon; more about that tomorrow.
 

Script by Damond Benningfield

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For a lot of skywatching, it’s all about the angles. That’s the case now for the planet Mercury. It’s in good view in the early evening, low in the west as twilight fades. It looks like a bright star, far below much brighter Venus, the “evening star.”

Mercury is the closest planet to the Sun, while Earth is the third planet out. That means Mercury’s orbit is entirely inside our own, so Mercury never moves very far from the Sun as viewed from Earth. At its best, it can be visible for a short time after sunset or before sunrise.

This is one of those “at its best” times. Over the next couple of weeks, the angle between Mercury and the Sun will offer a good view.

Mercury will actually climb a little farther from the Sun over that period, providing a few extra minutes to watch it. On the other hand, it’ll get fainter — the result of the change in its phase — like phases of the Moon.

The planet is moving closer to us. On April 11th, when it appears farthest from the Sun, it’ll be about 20 million miles closer to Earth than it is tonight. On the other hand, sunlight will illuminate a much smaller fraction of the hemisphere facing our way. Tonight, about three-quarters of that side is in sunlight. But by the 11th, only about a third will be lit up.

When you put the numbers together, Mercury will be less than half as bright then it is tonight — but still a nice target in the evening twilight.
 

Script by Damond Benningfield

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Regulus has always been one of the most respected stars in the sky. Some of its earliest names referred to it as a king. Others have called it “the heart,” because it represents the bright heart of the lion. And some have combined the names.

The name “Regulus” has been in use for about 500 years. It comes from the Latin word Rex, which means “the king.” Regulus means “the little king” or “the prince.”

The idea that it’s a king among stars goes back thousands of years earlier, to ancient Babylon. The name was passed down to the Greeks, then the Romans, then to the later cultures of Europe — who passed it on to us.

Regulus earned its “royal” reputation for several reasons. It’s one of the brighter stars in the night sky. It lies almost directly atop the Sun’s path across the sky, which means the Sun crosses near it every year. And it’s part of a constellation that represents a powerful animal — the lion, king of the beasts.

In fact, Regulus also has several names related to the lion. One is Cor Leonis — heart of the lion. In Arabic, it’s Kalb al Asad, which means the same thing. Both versions probably were handed down from Babylon. Indeed, the Babylonians combined the king and the lion in a single name: “the star that stands in the breast of the lion: the king.”

Whatever you call it, look for Regulus near the Moon the next couple of nights. It’s below the Moon tonight, and to the upper right of the Moon tomorrow night.
 

Script by Damond Benningfield

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James Webb Space Telescope is just getting started. Yet astronomers are already planning for future generations of space telescopes. It’s a process that can take decades.

Webb itself took a quarter of a century. Initial concepts were proposed in the 1990s. It took a while to get approval, then it took a lot longer than promised to get it built and launched.

The concept for the next big space telescope, called Nancy Grace Roman, was devised more than a decade ago. If things stay on schedule, it’ll launch in 2027. It saved some time by using a telescope that was built as a spy satellite, but was donated to NASA.

The process takes so long for several reasons. For one thing, it can take many tries just to get picked. For another, space telescopes are complicated, and each one is unique, so it takes more years to build one. It also takes a lot of testing — no one wants to repeat the mistake that blurred the view of Hubble Space Telescope. And it takes more time to launch and get checked out.

Astronomers outlined plans for several new missions at a recent conference. The list included CASTOR, to provide Hubble-quality views of wide slices of sky; Event Horizon Explorer, a combination of space- and ground-based telescopes to photograph black holes; and HEX-P, to study everything from black holes to dark matter. None is guaranteed to make it to space. And even if one does, it’ll be years or decades from now — a long lead time for a new view of the universe.
 

Script by Damond Benningfield

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If you’re a city, town, coastline, bit of tundra, or even a desert and you don’t have your own spaceport, you’re behind the times. New rocket launch sites have been sprouting like Texas bluebonnets after a spring rain. And several more are scheduled to open later this year.

They’ll be launching some brand-new rockets, by new companies, built with new technology. That’s because the market for space missions is really taking off. The space industry will launch thousands of craft this year. Most of them are communications satellites. Others are tiny payloads that will conduct science and technology experiments. And a few will head for the Moon or carry astronauts to orbit.

Among the spaceports that have opened in the past year, or that are expected to open this year, are sites in Texas, Nova Scotia, Scotland, Cornwall, Shetland Island, and the Canary Islands.

They’ll launch some brand-new rockets. Many of them are made possible by new materials, 3D printing, and A.I. The list of first-time rockets includes Vulcan, Terran, and Prime. Some will carry thousands of pounds of payloads, while others will carry single satellites that weigh only a few hundred pounds.

The payloads also include craft that have carried people to space — or will in the next few years — from spaceports around the world.

Some of those sites will launch future space telescopes, and we’ll talk about planning for some of those tomorrow.
 

Script by Damond Benningfield

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