Starship Asterisk*

Cousin Ricky wrote: ↑Fri Aug 21, 2020 2:33 pm

BDanielMayfield wrote: ↑Wed Aug 19, 2020 2:46 pm Like the Ringworld it would be unstable, methinks. What was Dyson thinking! It would never work.

Dyson was thinking it would be unstable. His vision was of large orbiting solar panels. But there was no controlling what sci-fi authors did with the concept.

BDanielMayfield wrote: ↑Wed Aug 19, 2020 2:46 pm Like the Ringworld it would be unstable, methinks. What was Dyson thinking! It would never work.

Ann wrote: ↑Wed Aug 19, 2020 6:48 am And finally, an aside from the Color Commentator. All the images of the Sun in today's APOD are false color. You think the Sun is that yellow-orange color as it is portrayed as being in the visual-light image?

Ann wrote: ↑Thu Aug 20, 2020 3:34 am
So out of 78 stellar, substellar and "post-stellar" objects within 5 parsecs of the Sun, the Sun is both brighter, hotter and more massive than 71 of them. That doesn't make the Sun average. The Sun is a perfectly normal star, and there are undoubtedly dozens of millions or more of other G-type stars in the Milky Way. But that still doesn't make the Sun average.

Garrison Keillor wrote:

"Well, that's the news from Lake Wobegon, where all the women are strong,
all the men are good-looking, and all the children are above average."

De58te wrote: ↑Wed Aug 19, 2020 3:20 pm

BDanielMayfield wrote: ↑Wed Aug 19, 2020 5:20 am More fun facts about the Sun:

wikipedia" wrote:The Sun currently fuses about 600 million tons of hydrogen into helium every second, converting 4 million tons of matter into energy every second as a result.

Do the math (E=mc²) to see how much energy the Sun emits every second. Warning, it could blow your mind.

And to think, that the Sun is just an average star.

Wikipedia wrote:

Some 52 stellar systems beyond our own, the Solar System, currently lie within 5.0 parsecs (16.3 light-years) of the Sun. These systems contain a total of 63 stars, of which 50 are red dwarfs, by far the most common type of star in the Milky Way. Much more massive stars, such as our own, make up the remaining 13.

In addition to these "true" stars, scientists have identified 11 brown dwarfs (objects not quite massive enough to fuse hydrogen), and four white dwarfs (extremely dense collapsed cores that remain after stars such as our Sun have exhausted all fusable hydrogen in their core and have shed slowly their outer layers).

Ann wrote: ↑Wed Aug 19, 2020 6:48 am And finally, an aside from the Color Commentator. All the images of the Sun in today's APOD are false color. You think the Sun is that yellow-orange color as it is portrayed as being in the visual-light image?

Gyrochronology is a method for estimating the age of a low-mass star like the Sun from its rotation period. The term is derived from the Greek words gyros, chronos and logos, roughly translated as rotation, age, and study respectively. It was coined in 2003 by Sydney Barnes[1] to describe the associated procedure for deriving stellar ages, and developed extensively in empirical form in 2007.[2]

The technique builds on an insight of Andrew Skumanich,[3] who realized that another measure of stellar rotation (v sin i) declined steadily with stellar age. Gyrochronology uses the rotation period P of the star instead of the doubly ambiguous v sin i, which depends on the unknown inclination of the star's axis of rotation, i. In particular, the technique accounts for the substantial mass dependence of stellar rotation, as exemplified by early rotation-period work on the Hyades open cluster.[4] These two improvements are largely responsible for the precision in the ages provided by gyrochronology. The associated age estimate for a star is known as the gyrochronological age.

The basic idea underlying gyrochronology is that the rotation period P, of a main-sequence cool star is a deterministic function of its age t and its mass M (or a suitable proxy such as color). The detailed dependencies of rotation are such that the periods converge rapidly to a certain function of age and mass, mathematically denoted by P = P (t, M), even though stars have a range of allowed initial periods. Consequently, cool stars do not occupy the entire 3-dimensional parameter space of (mass, age, period), but instead define a 2-dimensional surface in this space. Therefore, measuring two of these variables yields the third. Of these quantities, the mass (or a proxy such as color) and the rotation period are the easier variables to measure, providing access to the star's age, otherwise difficult to obtain.

Defining a star as "Sun-like" is very difficult, because to be Sun-like the star should have a mass, radius, age, temperature metallicity, and spectral type that is similar to the Sun's. Measuring most of these factors is difficult, and determining the age of a star is extremely difficult, so astronomers tend to ignore it when deciding if a star is Sun-like or not. However, this is not ideal, because the Sun, and all stars change over time. If a star's rotation period is less than 25 days, the star can be determined as being younger than the Sun, if the rotation rate is longer, the star can be determined as being older than the Sun.[original research?]

The relationship between rotation and age was initially discovered by Soren Meibom and colleagues by measuring the period of rotation of stars in a billion-year-old cluster. Because the ages of the stars were already known, the researchers could discover a relationship between a star's age and its rotation period.[5] A study of 30 cool stars in the 2.5-billion-year-old cluster NGC 6819 allowed to estimate the age–period relationship for older stars. Using these results, the ages of a large number of cool galactic field stars can be derived with 10% precision.[6]

MarkBour wrote: ↑Wed Aug 19, 2020 6:53 pm
It's interesting in the video that all of the UV and X-ray images show very brightly where the visible light image shows a dark spot. I had learned in the past that sunspots are cooler than the rest of the photosphere, and this lower temperature is what makes them appear darker than the rest, using a blackbody radiation approximation. But the very bright UV and X-ray intensities make me think that the situation is more complex than this approximation.

• When the "wound up" magnetic flux tubes of sunspot pairs with opposite magnetic polarity pinch off they act as particle accelerators.

https://en.wikipedia.org/wiki/Sunspot wrote:
<<It appears that sunspots are the visible counterparts of magnetic flux tubes in the Sun's convective zone that get "wound up" by differential rotation. If the stress on the tubes reaches a certain limit, a loop of the tube may project through the photosphere, the Sun's visible surface. Convection is inhibited at the puncture points; the energy flux from the Sun's interior decreases, and with it, surface temperature, causing the surface area through which the magnetic field passes to look dark against the bright background of the photosphere.

Although they are at temperatures of roughly 3,000–4,500 K, the contrast with the surrounding material at about 5,780 K leaves sunspots clearly visible as dark spots. This is because the luminance (which is essentially "brightness" in visible light) of a heated black body (closely approximated by the photosphere) at these temperatures varies greatly with temperature. Isolated from the surrounding photosphere, a single sunspot would shine brighter than the full moon, with a crimson-orange color.

Observations using the Zeeman effect show that prototypical sunspots come in pairs with opposite magnetic polarity. From cycle to cycle, the polarities of leading and trailing (with respect to the solar rotation) sunspots change from north/south to south/north and back. Sunspots usually appear in groups.>>

neufer wrote: ↑Wed Aug 19, 2020 5:42 pm

BDanielMayfield wrote: ↑Wed Aug 19, 2020 5:06 pm

De58te wrote: ↑Wed Aug 19, 2020 3:20 pm
And to think, that the Sun is just an average star. Stars like Antares and Betelgeuse are hundreds of time bigger. (Yet I think they are cooler. Does Betelgeuse use up more or less energy per second than the Sun? I haven't read any info on that.) Then you have stars like VY Canis Majoris that are thousands of times bigger! And there are several billion stars in the Milky Way Galaxy and billions of galaxies in the Universe. The amount of energy given off each second in the Universe is mind blowing. And this regular matter is only 6% of the energy in the Universe, compared to the 60% Dark Energy! And finally all this energy was created in a billionth of a second during the Big Bang! Talk about mind blowing.

The Sun is actually a little above average in mass, now that we know how abundant low mass stars are, but it's close enough to average for comparisons. And, since it is the only star we can study up close (for the foreseeable future, at least) we know it best, and it serves as the standard by which all other stars (and even galaxies) are measured.

Using the three Red Supergiant stars you mentioned, yes their surfaces are cooler, but their luminosities are enormous. Betelgeuse, Antares and VY Canis Majoris have total outputs of 90,000 to 150,000, 75,900 and 178,000 times the solar value of 3.826e26 watts per second.

https://en.wikipedia.org/wiki/Hypergiant#Luminous_blue_variables wrote:
<<A hypergiant (luminosity class 0 or Ia+) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of their extreme stellar winds. Astronomers are interested in these stars because they relate to understanding stellar evolution, especially with star formation, stability, and their expected demise as supernovae.

Eta Carinae, inside the Carina Nebula (NGC 3372) in the southern constellation of Carina. Eta Carinae is extremely massive, possibly as much as 120 to 150 times the mass of the Sun, and is four to five million times as luminous.>>

Eta Carinae's mass lose (from photons alone) is ~0.1 Earth masses per year.

A perfect reflectance solar sail at 1 AU from Eta Carinae
would experience a force of 40 Newtons per square meter
or about the same as the force on a Earth bound sailboat sail in an 11 knot wind

BDanielMayfield wrote: ↑Wed Aug 19, 2020 5:06 pm

De58te wrote: ↑Wed Aug 19, 2020 3:20 pm
And to think, that the Sun is just an average star. Stars like Antares and Betelgeuse are hundreds of time bigger. (Yet I think they are cooler. Does Betelgeuse use up more or less energy per second than the Sun? I haven't read any info on that.) Then you have stars like VY Canis Majoris that are thousands of times bigger! And there are several billion stars in the Milky Way Galaxy and billions of galaxies in the Universe. The amount of energy given off each second in the Universe is mind blowing. And this regular matter is only 6% of the energy in the Universe, compared to the 60% Dark Energy! And finally all this energy was created in a billionth of a second during the Big Bang! Talk about mind blowing.

The Sun is actually a little above average in mass, now that we know how abundant low mass stars are, but it's close enough to average for comparisons. And, since it is the only star we can study up close (for the foreseeable future, at least) we know it best, and it serves as the standard by which all other stars (and even galaxies) are measured.

Using the three Red Supergiant stars you mentioned, yes their surfaces are cooler, but their luminosities are enormous. Betelgeuse, Antares and VY Canis Majoris have total outputs of 90,000 to 150,000, 75,900 and 178,000 times the solar value of 3.826e26 watts per second.

https://en.wikipedia.org/wiki/Hypergiant#Luminous_blue_variables wrote:
<<A hypergiant (luminosity class 0 or Ia+) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of their extreme stellar winds. Astronomers are interested in these stars because they relate to understanding stellar evolution, especially with star formation, stability, and their expected demise as supernovae.

Eta Carinae, inside the Carina Nebula (NGC 3372) in the southern constellation of Carina. Eta Carinae is extremely massive, possibly as much as 120 to 150 times the mass of the Sun, and is four to five million times as luminous.>>

Eta Carinae's mass lose (from photons alone) is ~0.1 Earth masses per year.

A perfect reflectance solar sail at 1 AU from Eta Carinae
would experience a force of 40 Newtons per square meter
or about the same as the force on a Earth bound sailboat sail in an 11 knot wind

De58te wrote: ↑Wed Aug 19, 2020 3:20 pm

BDanielMayfield wrote: ↑Wed Aug 19, 2020 5:20 am More fun facts about the Sun:

wikipedia" wrote:The Sun currently fuses about 600 million tons of hydrogen into helium every second, converting 4 million tons of matter into energy every second as a result.

Do the math (E=mc²) to see how much energy the Sun emits every second. Warning, it could blow your mind.

And to think, that the Sun is just an average star. Stars like Antares and Betelgeuse are hundreds of time bigger. (Yet I think they are cooler. Does Betelgeuse use up more or less energy per second than the Sun? I haven't read any info on that.) Then you have stars like VY Canis Majoris that are thousands of times bigger! And there are several billion stars in the Milky Way Galaxy and billions of galaxies in the Universe. The amount of energy given off each second in the Universe is mind blowing. And this regular matter is only 6% of the energy in the Universe, compared to the 60% Dark Energy! And finally all this energy was created in a billionth of a second during the Big Bang! Talk about mind blowing.

BDanielMayfield wrote: ↑Wed Aug 19, 2020 2:46 pm

neufer wrote: ↑Wed Aug 19, 2020 2:08 pm

https://en.wikipedia.org/wiki/Solar_wind#Acceleration wrote:
<<The total number of particles carried away from the Sun by the solar wind is about 1.3×10³⁶ per second. Thus, the total mass loss each year is about (2–3)×10⁻¹⁴ solar masses, or about 1.3–1.9 Mt/s. This is equivalent to losing a mass equal to the Earth every 150 million years.>>

https://en.wikipedia.org/wiki/Coronal_mass_ejection wrote:
<<Coronal mass ejections reach velocities from 20 to 3,200 km/s with an average speed of 489 km/s, based on SOHO/LASCO measurements between 1996 and 2003. These speeds correspond to transit times from the Sun out to the mean radius of Earth's orbit of about 13 hours to 86 days (extremes), with about 3.5 days as the average. The average mass ejected is 1,900 Mt per ejection.>>

So a real Dyson sphere is going to have to handle or otherwise vacuum up Megatons of material every second, and Gigatons after CMEs. Dealing with the unbalanced forces from CME impacts would also be a huge structural problem.

Like the Ringworld it would be unstable, methinks. What was Dyson thinking! It would never work.

BDanielMayfield wrote: ↑Wed Aug 19, 2020 2:46 pm

neufer wrote: ↑Wed Aug 19, 2020 2:08 pm

https://en.wikipedia.org/wiki/Solar_wind#Acceleration wrote:
<<The total number of particles carried away from the Sun by the solar wind is about 1.3×10³⁶ per second. Thus, the total mass loss each year is about (2–3)×10⁻¹⁴ solar masses, or about 1.3–1.9 Mt/s. This is equivalent to losing a mass equal to the Earth every 150 million years.>>

https://en.wikipedia.org/wiki/Coronal_mass_ejection wrote:
<<Coronal mass ejections reach velocities from 20 to 3,200 km/s with an average speed of 489 km/s, based on SOHO/LASCO measurements between 1996 and 2003. These speeds correspond to transit times from the Sun out to the mean radius of Earth's orbit of about 13 hours to 86 days (extremes), with about 3.5 days as the average. The average mass ejected is 1,900 Mt per ejection.>>

So a real Dyson sphere is going to have to handle or otherwise vacuum up Megatons of material every second, and Gigatons after CMEs. Dealing with the unbalanced forces from CME impacts would also be a huge structural problem.

Like the Ringworld it would be unstable, methinks. What was Dyson thinking! It would never work.

BDanielMayfield wrote: ↑Wed Aug 19, 2020 5:20 am More fun facts about the Sun:

wikipedia" wrote:The Sun currently fuses about 600 million tons of hydrogen into helium every second, converting 4 million tons of matter into energy every second as a result.

Do the math (E=mc²) to see how much energy the Sun emits every second. Warning, it could blow your mind.

neufer wrote: ↑Wed Aug 19, 2020 2:08 pm

https://en.wikipedia.org/wiki/Solar_wind#Acceleration wrote:
<<The total number of particles carried away from the Sun by the solar wind is about 1.3×10³⁶ per second. Thus, the total mass loss each year is about (2–3)×10⁻¹⁴ solar masses, or about 1.3–1.9 Mt/s. This is equivalent to losing a mass equal to the Earth every 150 million years.>>

https://en.wikipedia.org/wiki/Coronal_mass_ejection wrote:
<<Coronal mass ejections reach velocities from 20 to 3,200 km/s with an average speed of 489 km/s, based on SOHO/LASCO measurements between 1996 and 2003. These speeds correspond to transit times from the Sun out to the mean radius of Earth's orbit of about 13 hours to 86 days (extremes), with about 3.5 days as the average. The average mass ejected is 1,900 Mt per ejection.>>

Holger Nielsen wrote: ↑Wed Aug 19, 2020 7:35 am The Sun's luminosity is measured to be 3.826·10²⁶ W, so the Sun emits an energy of E = 3.826·10²⁶ J each second.

Holger Nielsen wrote: ↑Wed Aug 19, 2020 7:35 am
The Sun's luminosity is measured to be 3.826·10²⁶ W, so the Sun emits an energy of E = 3.826·10²⁶ J each second.

Using E = m·c² (where c = 299792458 m/s is the speed of light) and a pocket calculator we get
m = E/c² = 4.257·10⁹ kg = 4.257 [Mt] each second.

https://en.wikipedia.org/wiki/Sun#Structure_and_fusion wrote:
<<The large power output of the Sun is mainly due to the huge size and density of its core (compared to Earth and objects on Earth), with only a fairly small amount of power being generated per cubic metre. Theoretical models of the Sun's interior indicate a maximum power density, or energy production, of approximately 276.5 watts per cubic metre at the center of the core, which is about the same power density as in body of a reptile or inside a compost pile.>>

https://en.wikipedia.org/wiki/Solar_wind#Acceleration wrote:
<<The total number of particles carried away from the Sun by the solar wind is about 1.3×10³⁶ per second. Thus, the total mass loss each year is about (2–3)×10⁻¹⁴ solar masses, or about 1.3–1.9 Mt/s. This is equivalent to losing a mass equal to the Earth every 150 million years.>>

https://en.wikipedia.org/wiki/Coronal_mass_ejection wrote:
<<Coronal mass ejections reach velocities from 20 to 3,200 km/s with an average speed of 489 km/s, based on SOHO/LASCO measurements between 1996 and 2003. These speeds correspond to transit times from the Sun out to the mean radius of Earth's orbit of about 13 hours to 86 days (extremes), with about 3.5 days as the average. The average mass ejected is 1,900 Mt per ejection.>>

E Fish wrote: ↑Wed Aug 19, 2020 1:18 pm

BDanielMayfield wrote: ↑Wed Aug 19, 2020 5:20 am More fun facts about the Sun:

wikipedia" wrote:The Sun currently fuses about 600 million tons of hydrogen into helium every second, converting 4 million tons of matter into energy every second as a result.

Do the math (E=mc²) to see how much energy the Sun emits every second. Warning, it could blow your mind.

All right. Let's start building that Dyson sphere!

Holger Nielsen wrote: ↑Wed Aug 19, 2020 7:35 am This does not require any math, a simple calculation will do:

The Sun's luminosity is measured to be 3.826·10²⁶ W, so the Sun emits an energy of E = 3.826·10²⁶ J each second.

Using E = m·c² (where c = 299792458 m/s is the speed of light) and a pocket calculator we get
m = E/c² = 4.257·10⁹ kg = 4.247 million tons
each second.

BDanielMayfield wrote: ↑Wed Aug 19, 2020 5:20 am More fun facts about the Sun:

wikipedia" wrote:The Sun currently fuses about 600 million tons of hydrogen into helium every second, converting 4 million tons of matter into energy every second as a result.

Do the math (E=mc²) to see how much energy the Sun emits every second. Warning, it could blow your mind.