Betelgeuse is now nearly as faint as (the slightly variable) B2 star Bellatrix .... Betelgeuse is currently the coolest and least luminous yet observed. Since September 2019, the star's temperature has decreased by ~100 K while its luminosity ... has diminished by nearly 25%. At face value .... this implies an increase of the star's radius of ~9%. However, as pointed out by others, the current fainting episode could also arise from expelled, cooling gas/dust partially obscuring the star. The recent changes .... seem best explained from changes in the envelop-outer convection atmosphere of this pulsating, unstable supergiant. If these recent light changes are due to an extra-large amplitude light pulse on the ~420-day period, then the next mid-light minimum is expected during late January/early February, 2020. If Betelgeuse continues to dim after that time then other possibilities will have to be considered. The unusual behavior of Betelgeuse should be closely watched.
Keeping it cool:The US National Solar Observatory’s $344m (£265m) telescope features a four-metre mirror – the world’s largest for a solar telescope – and is located at the 3,000-metre (10,000ft) summit of the Haleakalā volcano on the island of Maui.
Valentin Pillet, the director of the National Solar Observatory, described the telescope, which had been under construction since 2013, as a “formidable technological achievement”. A major challenge was maintaining the telescope’s primary mirror at ambient temperature while it looked directly at the sun – any temperature deviation causes air turbulence that could ruin the image quality. The heat is intense enough to rapidly melt metal at the mirror’s focal point.
Photo/video at link.Each night, a swimming pool’s worth of ice is emptied into eight tanks. During the day, coolant is routed through the ice tanks and distributed through the observatory by 7.5 miles (12km) of piping. More than 100 air jets are also positioned behind the main mirror.
Incoming light from the sun is deflected from the primary mirror into a chamber of mirrors that sits below the observatory’s dome. Here, the light is bounced from mirror to mirror as it is apportioned between spectrometers, polarimeters and other various other instruments. The observatory’s full suite of instruments, which will allow scientists to measure the magnetic field from the sun’s surface up to its outer atmosphere, will come online later this year.
“The bright features [in the image] … are the foothills of magnetic fields that extend all the way up into the corona and beyond,” said Rimmele. “With the additional instruments that will come online in the next six months, we will be able to measure the magnetic fields from the surface all the way up to 1.5 solar radii.”
The observations could help resolve longstanding mysteries of the sun, including the counterintuitive feature that the corona – the sun’s atmosphere – is heated to millions of degrees when its surface is only 6,000C. Understanding the physics of solar flares and coronal mass ejections could also significantly improve the ability to predict space weather, which can render GPS systems unreliable, take down power grids and knock out communication channels.
The visual fading is not connected to a major change in total energy output from the star. Thus, while Betelgeuse may explode tomorrow or any time in the next few 1e5 yr, the unprecedented current visual faintness is unlikely to be a harbinger of its impending core collapse.
And they just keep on moving the goalposts.New Wrinkle Added to Cosmology’s Hubble Crisis
Date: 26 February, 2020
A problem confronts cosmology: Two independent measurements of the universe’s expansion give incompatible answers. Now a third method, advanced by an astronomy pioneer, appears to bridge the divide.
. Then in July, a new measurement of cosmic expansion using objects called quasars, when combined with the other measurement, pushed past “five sigma,” a statistical level that physicists usually treat as their standard of proof of an unaccounted-for physical effect. In this case, cosmologists say there might be some extra cosmic ingredient, beyond dark matter, dark energy and everything else they already include in their equations, that speeds the universe up.
But that’s if the measurements are correct. A new line of evidence, first announced last summer, suggests that the cosmic expansion rate may fall much closer to the rate predicted by early-universe measurements and the standard theory of cosmology.
What I find annoying..No, too strong, frustrating is that these cosmologists just keep on adding more 'well, maybe it's...' to the theory. Either the Standard Model of Cosmology is correct, or it isn't. There needs to be more emphasis on proving beyond all reasonable doubt the parts that the theory is comprised of.What specifically bothers you?
I only have a vague grasp of this!