by Ann » Mon Apr 11, 2022 5:38 pm
A tidbit here:
The Sun used to be the roundest object in the Universe. 
(Not that we have a census of all the stars in the Universe, at least not yet.
)
The Guardian wrote in 2012:
The sun is the most perfectly round natural object known in the universe, say scientists who have conducted precise measurements of its dimensions.
As a spinning ball of gas, astronomers had always expected our nearest star to bulge slightly at its equator, making it very slightly flying-saucer shaped. The planet Jupiter demonstrates this effect well. Its high rate of spin - once every 10 hours - means that it is almost 7% wider across its equator than the distance from pole to pole.
Now a team led by the University of Hawaii's Dr Jeffrey Kuhn have made the first precise measurement of the sun's equatorial bulge, or its "oblateness". The results were a big surprise. "We were shocked," says Kuhn.
The sun doesn't bulge much at all. It is 1.4m kilometres across, but the difference between its diameter at the equator and between the poles is only 10 kilometres.
Scaled to the size of a beachball, that difference is less than the width of a human hair. Only an artificial sphere of silicon that was created as a standard for weights is known to be more perfectly spherical.
But a few years later another champion of perfect natural roundness was found:
Image credit: © Laurent Gizon et al. and the Max Planck Institute for
Solar System Research, Germany. Illustration by Mark A. Garlick.
Sci News wrote:
Kepler 11145123, a slowly rotating star roughly 5,000 light-years away, is the most spherical natural object ever measured, more spherical than the Sun, says an international team of astronomers.
The team, led by Dr. Laurent Gizon, an astronomer with the Max Planck Institute for Solar System Research and the University of Göttingen, was able to measure the oblateness of Kepler 11145123 using asteroseismology – the study of the oscillations of stars.
The technique revealed that the difference between the equatorial and polar radii of the star is only 3 km – a number that is surprisingly small compared to the star’s mean radius of 1.5 million km.
“This makes Kepler 11145123 the roundest natural object ever measured, even more round than the Sun,” Dr. Gizon said.
Asteroseismic measurement of surface-to-core rotation in a main-sequence A star, KIC 11145123
So the Sun is no longer the champion of cosmic sphericity. But even though dear old Sol looks kind of spotty and knotty in today's APOD, it is nevertheless pretty darn evenly spherical!
Ann
A tidbit here:
[b][color=#FF0000][i]The Sun used to be the roundest object in the Universe.[/i][/color][/b] :shock: (Not that we have a census of all the stars in the Universe, at least not yet. :wink: )
[quote][url=https://www.theguardian.com/science/2012/aug/16/sun-perfect-sphere-nature]The Guardian[/url] wrote in 2012:
The sun is the most perfectly round natural object known in the universe, say scientists who have conducted precise measurements of its dimensions.
As a spinning ball of gas, astronomers had always expected our nearest star to bulge slightly at its equator, making it very slightly flying-saucer shaped. The planet Jupiter demonstrates this effect well. Its high rate of spin - once every 10 hours - means that it is almost 7% wider across its equator than the distance from pole to pole.
Now a team led by the University of Hawaii's Dr Jeffrey Kuhn have made the first precise measurement of the sun's equatorial bulge, or its "oblateness". The results were a big surprise. "We were shocked," says Kuhn. [b][color=#FF0000]The sun doesn't bulge much at all. It is 1.4m kilometres across, but the difference between its diameter at the equator and between the poles is only 10 kilometres.[/color][/b]
[b][color=#0040FF]Scaled to the size of a beachball, that difference is less than the width of a human hair. Only an artificial sphere of silicon that was created as a standard for weights is known to be more perfectly spherical[/color][/b].[/quote]
But a few years later another champion of perfect natural roundness was found:
[float=right][attachment=0]Roundness of the Sun and Kepler 11145123 Mark A Garlick.png[/attachment]
[c][size=85][color=#0040FF]Image credit: © Laurent Gizon et al. and the Max Planck Institute for
Solar System Research, Germany. Illustration by Mark A. Garlick.[/color][/size][/c][/float][quote][url=http://www.sci-news.com/astronomy/kepler-11145123-most-spherical-natural-object-04378.html]Sci News[/url] wrote:
Kepler 11145123, a slowly rotating star roughly 5,000 light-years away, is the most spherical natural object ever measured, more spherical than the Sun, says an international team of astronomers.
The team, led by Dr. Laurent Gizon, an astronomer with the Max Planck Institute for Solar System Research and the University of Göttingen, was able to measure the oblateness of Kepler 11145123 using asteroseismology – the study of the oscillations of stars.
The technique revealed that the difference between the equatorial and polar radii of the star is only 3 km – a number that is surprisingly small compared to the star’s mean radius of 1.5 million km.
“This makes Kepler 11145123 the roundest natural object ever measured, even more round than the Sun,” Dr. Gizon said.[/quote]
[url=https://academic.oup.com/mnras/article/444/1/102/1009186?login=false]Asteroseismic measurement of surface-to-core rotation in a main-sequence A star, KIC 11145123[/url]
So the Sun is no longer the champion of cosmic sphericity. But even though dear old Sol looks kind of spotty and knotty in today's APOD, it is nevertheless pretty darn evenly spherical!
Ann