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Stars don’t usually evolve fast enough for humans to notice them change within one lifetime. Even a hundred lifetimes won’t do – astronomical processes are just too slow. But not always. There are some phases of stellar evolution that happen quickly, and when they do, they can be tracked. A new paper posted to ArXiv last week uses astronomical observations found in ancient Roman texts, medieval astronomical logs, and manuscripts from China’s Han Dynasty to trace the recent evolution of several bright stars, including red supergiant Antares, and Betelgeuse: one of the most dynamic stars in our sky. With observations from across the historical record, the paper suggests that Betelgeuse may have just recently passed through the ‘Hertzsprung gap,’ the transitional phase between a main sequence star and its current classification as a red supergiant.

If you were to survey all the stars in the night sky for their color and luminosity, you would see that most stars fall within a distinct pattern known as the main sequence (the hydrogen-burning phase of a star’s life), with a smaller number of stars falling within a second category of giants (dying stars that have used up all the hydrogen in their cores). Surveying stars this way and plotting them on a graph is called a Hertzsprung–Russell diagram, and it is a useful tool for understanding stellar evolution. One of the key features of the diagram is a distinct gap between the main sequence and giant stars, known as the Hertzsprung gap. This gap doesn’t really mean that stars don’t exist within that gap – but rather that stars don’t stay there very long. It is a transitional phase, which can be crossed in a few thousand years, meaning that catching a star in the middle of the phase is rare – hence the gap in the diagram.

HRDiagram
A Hertzsprung-Russell diagram, with the Hertzsprung gap between main sequence stars and red giants. This gap indicates a life stage of stars that doesn’t last long, making observations of stars with that luminosity and color rare. Image Credit: Richard Powell (Wikimedia Commons).

With luck, this short-lived transitional phase could theoretically be observed within humanity’s written historical record, for any number of stars.

The key candidates for such a study are bright, nearby red supergiant stars visible to the naked eye – meaning they could have been observed and studied before modern telescopic lenses. Some ideal examples include Antares, a variable red supergiant in the constellation of Scorpius, and Betelgeuse (the right shoulder of Orion), a roughly 10 million-year-old star that is no longer burning hydrogen in its core. Nearing the end of its life, Betelgeuse is expected to explode in a dramatic supernova sometime in the next 100,000 years (astronomically speaking, that is not very long).

Most of our knowledge about these stars comes from modern observations. However, modern remote sensing techniques are not perfect, and it is valuable to have multiple redundant methodologies for calculating phases of stellar evolution. The historical record can therefore help corroborate, or constrain, the predictions of modern astrophysics.

The historical evidence: Betelgeuse in transition, and an unchanging Antares

A key marker of the transition across the Hertzsprung gap is a change in color toward the reddish end of the spectrum. As such, historical descriptions of Betelgeuse or Antares denoting anything other than red would hint at a recent transition.

You might be inclined to dismiss historical texts as potentially misleading or inaccurate – besides, a vague description of a star as ‘reddish’ isn’t very scientifically helpful by today’s standards. But the real value of historical documents occurs when ancient writers make comparisons between distinct astronomical objects: Betelgeuse to Saturn, or Antares to Mars, for example. Those kinds of statements give us a much more measurable, if still approximate, dataset to work with, because we can make the same comparisons in today’s sky with modern equipment.

This is exactly the kind of data the paper’s authors, led by Ralph Neuhäuser (AIU Jena), were able to find. Digging into a variety of historical records, they uncovered several early descriptions of bright supergiants like Betelgeuse and Antares. One of the key sources for Betelgeuse was De Astronomica, a Roman text attributed to Gaius Julius Hyginus (64 BC-AD 17), the keeper of the Palatine library during the reign of Augustus

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Should We Send Humans to Venus?

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NASA is preparing to send humans back to the Moon with the Artemis missions in the next few years as part of the agency’s Moon to Mars Architecture with the long-term goal of landing humans on the Red Planet sometime in the 2030s or 2040s. But what about sending humans to other worlds of the Solar System? And, why not Venus? It’s closer to Earth than Mars by several tens of millions of kilometers, and despite its extremely harsh surface conditions, previous studies have suggested that life could exist in its clouds. In contrast, we have yet to find any signs of life anywhere on the Red Planet or in its thin atmosphere. So, should we send humans to Venus?

“Yes, we should send humans to Venus,” Dr. Paul Byrne, who is an Associate Professor of Earth, Environmental, and Planetary Sciences at Washington University in St. Louis, tells Universe Today. “But first, let’s talk about what ‘sending humans to Venus’ actually means. The surface of Venus is hellish, so nobody would last long there nor volunteer to go. Above the clouds, the temperature and pressure are almost like a nice spring day here on Earth, so aside from tiny sulphuric acid cloud droplets you’d be okay (with a breathing apparatus).”

These “hellish” conditions that Dr. Byrne alludes to are the extreme conditions across the surface of Venus, including surface pressures 92 times that of Earth’s surface and average surface temperatures of approximately 464 degrees Celsius (867 degrees Fahrenheit). In contrast, Earth’s average surface temperatures are a calm 15 degrees Celsius (59 degrees Fahrenheit). These extreme pressures and temperatures have made landing on the surface of Venus even more difficult, as the former Soviet Union continues to be the only nation to have successfully landed on Venus’ surface, having accomplished this feat with several of their Venera and Vega missions. However, the longest mission duration for the lander was only 127 minutes (Venera 13), which also conducted the first sound recording on another planet.

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Color images taken by the Soviet Union’s Venera 13 lander on the surface of Venus on March 1, 1982, with the lander surviving only 127 minutes due to Venus’s extreme surface conditions. (Credit: NASA)

“If we were to send humans to Venus, they’d be going in a spacecraft that would fly by the planet en route somewhere else,” Dr. Byrne tells Universe Today. “If we were to one day send humans actually to Venus itself for science and engineering purposes, then a cloud-based habitat is the way to go. Getting humans onto the Venus surface is going to require so much technology and expense that, for the foreseeable future, I don’t think anyone will think it worth doing.”

A 2015 study presented at the AIAA Space and Astronautics Forum and Exposition outlined a NASA study for the High Altitude Venus Operational Concept (HAVOC) mission that would involve a 30-day crewed mission using an airship equipped with solar panels within the upper atmosphere of Venus. This is because Venus’ upper atmosphere at approximately 50 kilometers (30 miles) above the surface exhibits much more hospitable conditions, including temperatures between 30 to 70 degrees Celsius (86 to 158 degrees Fahrenheit) and pressures very close to that of Earth. However, Dr. Byrne refers to HAVOC as an “unbelievably expensive concept”.

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Artist rendition of proposed habitable airships traversing Venus’ atmosphere, which has been proposed as the High Altitude Venus Operational Concept (HAVOC) mission. (Credit: NASA)

As for using Venus while en route to another location in the Solar System, Venus has been used on several occasions to slingshot spacecraft to the outer Solar System as well as for exploration of the inner Solar System, such as Mercury and the Sun. For example, NASA’s Galileo and Cassini spacecraft used gravity assists

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We Should Hit Peak Solar Activity Next Year

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You may be familiar with the solar cycle that follows a 22 year process shifting from solar minimum to maximum and back again. It’s a cycle that has been observed for centuries yet predicting its peak has been somewhat challenging. The Sun’s current cycle is approaching maximum activity which brings with it higher numbers of sunspots on its surface, more flares and more coronal mass ejections. A team from India now believe they have discovered a new element of the Sun’s magnetic field allowing them to predict the peak will occur early in 2024.

The Sun is a gigantic sphere of plasma or electrically charged gas. One of the features of plasma is that if a magnetic field passes through it, the plasma moves with it. Conversely if the plasma moves, the magnetic field moves too. This magnetic field is just like Earth and is known as a dipole magnetic field. You can visualise it if you can remember your school science days with a bar magnet and iron filings.

A dipole magnetic field has two opposite but equal charges and at the start of the Sun’s cycle the field lines effectively run from the north pole to the south. As the Sun rotates, with the equator rotating faster than the polar regions, then the plasma drags the magnetic field lines with it, winding them tighter and tighter.

The field lines become stretched causing the magnetic field to loop up and through the visible surface of the Sun. This localised event prevents the convection of super heated gas from underneath and appears as a cooler area of the surface which appears dark. As the solar cycle starts, these sunspots appear around the polar regions and slowly migrate toward the equator as it progresses with peak activity occurring when the sunspots fade away as we head toward the start of another cycle. 

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Image of sunspots (Credit : NASA Goddard Space Flight Center // SDO)

On occasions the magnetic field of sunspots are disrupted and we can experience flares or coronal mass ejections hurling vast amounts of charged particles out into space. If they reach us here on Earth they give rise to the beautiful aurora displays but they do also have a rather negative impact to satellites, power grids and telecommunications systems.

Deep inside the Sun, a dynamo mechanism is driving all this. It is created by the energy from the movement of plasma and it is this that is responsible for the flipping of the Sun’s magnetic poles where the north pole becomes south and the south pole becomes north which happens every 11 years or so. It’s another aspect of the solar cycle.

It’s been known since the 1930’s that the rate of rise the sunspot cycle relates to its strength with stronger cycles taking less time to reach peak. In the paper published in the Monthly Notices of the Royal Astronomical Society Letters; Priyansh Jaswal, Chitradeep Saha and Dibyendu Nandy from the Indian Institutes of Science Education and Research announced their findings. They discovered that the rate of decrease in the Sun’s dipole magnetic field also seems to relate to the rise of the present cycle.

The team have looked back through archives and have shown how the observation of the dipole decrease rate along with observations of sunspots can predict the peak of activity with better accuracy than before. They conclude the current cycle is expected to peak somewhere between early 2024 and September next year. Being able to better predict the peak of activity will help understand the likely intensity of space weather events here on Earth providing us more warning to be able to prepare.

Source : Solar activity likely to peak next year, new study suggests

The post We Should Hit Peak Solar Activity Next Year appeared first on Universe Today.

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The Solar Radius Might Be Slightly Smaller Than We Thought

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Two astronomers use a pioneering method to suggest that the size of our Sun and the solar radius may be due revision.

Our host star is full of surprises. Studying our Sun is the most essential facet of modern astronomy: not only does Sol provide us with the only example of a star we can study up close, but the energy it provides fuels life on Earth, and the space weather it produces impacts our modern technological civilization.

Now, a new study, titled The Acoustic Size of the Sun suggests that a key parameter in modern astronomy and heliophysics—the diameter of the Sun—may need a slight tweak.

The study out of the University of Tokyo and the Institute of Astronomy at Cambridge was done looking at data from the joint NASA/ESA Solar Heliospheric Observatory (SOHO’s) Michelson Doppler Imager (MDI) imager. The method probes the solar interior via acoustics and a cutting edge field of solar physics known as helioseismology.

Interior of the Sun
A cutaway diagram of the Sun. NASA/ESA/SOHO

‘Hearing’ the Solar Interior

How can you ‘hear’ acoustic waves on the Sun? In 1962, astronomers discovered that patches on the surface of the Sun oscillate, or bubble up and down, like water boiling on a stove top. These create waves that ripple in periodic 5-minute oscillations across the roiling surface of the Sun.

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A view of the Sun, courtesy of SOHO’s MDI instrument. Credit: NASA

What’s more, astronomers can use what we see happening on the surface of the Sun to model the solar interior, much like terrestrial astronomers use seismic waves traveling through the Earth to model its core. Thanks to helioseismology, we can even ‘see’ what’s going on on the solar farside, and alert observers of massive sunspots before they rotate into view.

Solar Ffarside
Solar farside modeling using helioseismology. Credit: NSF/GONG

The study looked at p-mode waves as they traversed the solar interior. Previous studies relied on less accurate f-mode waves, which are surface waves considerably shorter than the solar radius.

The study defines the solar radius (half the diameter) as 695,780 kilometers… only slightly smaller than the generally accepted radius of 696,000 kilometers obtained by direct optical measurement. This is only smaller by a few hundredths of a percent, or 100-200 kilometers.

SOHO
An artist’s conception of SOHO in space. Credit: ESA/SOHO

The solar radius is a deceptively simple but crucial factor in astronomy. The Sun is a glowing ball of hydrogen and helium plasma without a distinct surface boundary. The photosphere—the glowing visible layer we see shining down on us on a sunny day—is what we generally refer to as the surface of the Sun.

The Solar Radius: A Brief
Did you miss our previous article…
https://mansbrand.com/if-warp-drives-are-impossible-maybe-faster-than-light-communication-is-still-on-the-table/

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