APOD: The Sun Rotating (2020 Aug 19)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 4074
Joined: Fri Dec 04, 2009 3:27 am

APOD: The Sun Rotating (2020 Aug 19)

Post by APOD Robot » Wed Aug 19, 2020 4:07 am

Image The Sun Rotating

Explanation: Does the Sun change as it rotates? Yes, and the changes can vary from subtle to dramatic. In the featured time-lapse sequences, our Sun -- as imaged by NASA's Solar Dynamics Observatory -- is shown rotating though an entire month in 2014. In the large image on the left, the solar chromosphere is depicted in ultraviolet light, while the smaller and lighter image to its upper right simultaneously shows the more familiar solar photosphere in visible light. The rest of the inset six Sun images highlight X-ray emission by relatively rare iron atoms located at different heights of the corona, all false-colored to accentuate differences. The Sun takes just under a month to rotate completely -- rotating fastest at the equator. A large and active sunspot region rotates into view soon after the video starts. Subtle effects include changes in surface texture and the shapes of active regions. Dramatic effects include numerous flashes in active regions, and fluttering and erupting prominences visible all around the Sun's edge. Presently, our Sun is passing an unusually low Solar minimum in activity of its 11-year magnetic cycle. As the video ends, the same large and active sunspot region previously mentioned rotates back into view, this time looking different.

<< Previous APOD This Day in APOD Next APOD >>

BDanielMayfield
Don't bring me down
Posts: 2495
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by BDanielMayfield » 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. :shock:
Just as zero is not equal to infinity, everything coming from nothing is illogical.

User avatar
Ann
4725 Å
Posts: 10816
Joined: Sat May 29, 2010 5:33 am

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by Ann » Wed Aug 19, 2020 6:48 am

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. :shock:
I don't have to, fortunately, since I am a math idiot. (Actually, I could have a go at it if I felt so inclined... which I don't. :mrgreen: )

Anyway. The Sun rotating. I think we are fortunate that the Sun is rotating so slowly. If it was a fast rotator, I think it would be prone to having enormous outbursts, much, much larger and more frequent than now.

I remember reading about such stars, and the writer asked us to contemplate what it would be like to listen to the weather report in the morning and be told something like this:

"Today the Sun is likely to double in brightness, so stay in the shadow." :shock:

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?

Think again. It's doubtful that even Betelgeuse is that orange.

Ann
Color Commentator

LMMdT

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by LMMdT » Wed Aug 19, 2020 7:29 am

When I remember that our life depends on this mass of hot gas, I go down to soil level. We think we are powerful but in fact we are finished whether our sun gets angry any day.

Holger Nielsen
Ensign
Posts: 18
Joined: Fri Oct 14, 2016 7:45 am

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by Holger Nielsen » 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.

User avatar
orin stepanek
Plutopian
Posts: 5766
Joined: Wed Jul 27, 2005 3:41 pm
Location: Nebraska

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by orin stepanek » Wed Aug 19, 2020 12:10 pm

I guess there is a spin on everything; Earth; Sun; Solar System; Galaxy; Even the Universe! No wonder I'm dizzy! :mrgreen:
Orin

Smile today; tomorrow's another day!

E Fish
Ensign
Posts: 70
Joined: Thu Mar 09, 2017 2:29 pm

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by E Fish » 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. :shock:
All right. Let's start building that Dyson sphere! :mrgreen:

BDanielMayfield
Don't bring me down
Posts: 2495
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by BDanielMayfield » Wed Aug 19, 2020 1:24 pm

Holger Nielsen wrote:
Wed Aug 19, 2020 7:35 am
This does not require any math, a simple calculation will do:
What does the word math mean to you? Any calculation, no matter how simple or complex involves the manipulation of numbers in accord with the rules of mathematics , which you then proceed to do with skill. But your first statement is a non sequitur.
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.
So you either knew already or looked up the answer first and then
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.
You "did the math", working from the answer back to one of the givens, calculated to much higher precision. Well done sir, I appreciate your math skills, even if you don't. :ssmile:
Just as zero is not equal to infinity, everything coming from nothing is illogical.

BDanielMayfield
Don't bring me down
Posts: 2495
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by BDanielMayfield » Wed Aug 19, 2020 1:51 pm

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. :shock:
All right. Let's start building that Dyson sphere! :mrgreen:
Not to be confused with a vacuum cleaner, a Dyson sphere is a somewhat larger device designed to totally enclose a star so it can scarf up every last Joule of energy the star puts out. The ultimate in solar power!

Bruce
Just as zero is not equal to infinity, everything coming from nothing is illogical.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17513
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by neufer » Wed Aug 19, 2020 2:08 pm

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.>>
Art Neuendorffer

BDanielMayfield
Don't bring me down
Posts: 2495
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by BDanielMayfield » Wed Aug 19, 2020 2:24 pm

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.
It is challenging to comprehend a value that large. It might help to drop the exponential notation (or not), just to illustrate it's largeness. The Sun's output is, rounded to four significant digits, 382,600,000,000,000,000,000,000,000 Watts per second.
Just as zero is not equal to infinity, everything coming from nothing is illogical.

BDanielMayfield
Don't bring me down
Posts: 2495
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by BDanielMayfield » 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. :lol2:
Just as zero is not equal to infinity, everything coming from nothing is illogical.

De58te
Science Officer
Posts: 320
Joined: Mon Sep 30, 2013 6:35 pm

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by De58te » 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. :shock:
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.

User avatar
johnnydeep
Science Officer
Posts: 244
Joined: Sun Feb 20, 2011 8:57 pm

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by johnnydeep » Wed Aug 19, 2020 4:40 pm

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. :lol2:
Hmm, very good observation. I haven't seen this "little" problem with Dyson spheres mentioned before, but I'm sure it must have been.

EDIT: apparently, it would not be a problem after all. See Neufer's post just below.
Last edited by johnnydeep on Wed Aug 19, 2020 7:57 pm, edited 1 time in total.
"To Boldly Go......Beyond The Fields We Know."

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17513
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by neufer » Wed Aug 19, 2020 4:53 pm

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. :lol2:
Solar photons have 2 to 3 times the effective (E/c2) mass of the solar wind (plus coronal mass ejections)
and (by moving at the speed of light) solar photons have ~2,000 times the momentum.

However, all forces drop off inversely with the square of the distance.

Thus a Dyson sphere is neutrally stable
and will only require a fraction of its energy to be used for stabilizing rockets
(or for adjustable louvers to release the photons on the side that starts to approach the sun).
Art Neuendorffer

BDanielMayfield
Don't bring me down
Posts: 2495
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by BDanielMayfield » Wed Aug 19, 2020 5:06 pm

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. :shock:
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.
This is exactly the line of thinking I hoped my initial comment would generate De58te.

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.

The Milky Way is now thought to contain 400 billion stars by some, but with each major advancement in telescopic resolution such estimates have increased ...


Bruce
Just as zero is not equal to infinity, everything coming from nothing is illogical.

Boomer12k
:---[===] *
Posts: 2691
Joined: Sun Apr 22, 2007 12:07 am

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by Boomer12k » Wed Aug 19, 2020 5:22 pm

I am sure the Sun is ALWAYS changing....

:---[===] *

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17513
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by neufer » 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
:!:
Art Neuendorffer

User avatar
MarkBour
Subtle Signal
Posts: 1100
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by MarkBour » 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.
Mark Goldfain

BDanielMayfield
Don't bring me down
Posts: 2495
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by BDanielMayfield » Wed Aug 19, 2020 7:48 pm

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
:!:
Very nice point Art, but (cue arm flailing robot, "Danger! Danger, Art Robinson!") solar sailing at only 1 AU from Eta Carinae is, not recommended.

At 1 AU from the Sun solar sailors will soak up 1361 W/m2.

4 to 5 million times that would be quite toasty.
Last edited by BDanielMayfield on Wed Aug 19, 2020 8:23 pm, edited 4 times in total.
Just as zero is not equal to infinity, everything coming from nothing is illogical.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17513
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by neufer » Wed Aug 19, 2020 7:58 pm

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.
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.>>
Art Neuendorffer

BDanielMayfield
Don't bring me down
Posts: 2495
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by BDanielMayfield » Wed Aug 19, 2020 8:57 pm

And, since the topic of today's APOD is the Sun's rotation;
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]
I had looked the above wikipedia article up because I was wondering, how fast was the Sun rotating "in the beginning", back when it first formed as a protostar. I'm still wondering, and would appreciate some help with this question. What is the rate of slowing in the Sun's rotation?
Just as zero is not equal to infinity, everything coming from nothing is illogical.

User avatar
Chris Peterson
Abominable Snowman
Posts: 15317
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by Chris Peterson » Wed Aug 19, 2020 9:51 pm

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?
That is probably an accurate description for the "visible light" image. The others are probably better described as pseudocolor, as I believe all represent single band data. That is, they are grayscale images where intensity is mapped to color.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
Ann
4725 Å
Posts: 10816
Joined: Sat May 29, 2010 5:33 am

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by Ann » Thu Aug 20, 2020 3:34 am

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. :shock:
And to think, that the Sun is just an average star.
I don't think the Sun is average. Check out this Wikipedia list of the nearest stars and brown dwarfs.
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).
So out of the 78 stellar, substellar and "post-stellar" objects within 5 parsecs of the Sun, only 3 are brighter than the Sun (Sirius A, Procyon and Alpha Centauri A), only 4 are more massive than the Sun (Sirius A, Procyon, Alpha Centauri A and Sirius B by a hair) and only 7 are hotter (Sirius A, Procyon, Alpha Centauri A by a hair, Sirius B and 3 more white dwarfs).

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.

Ann
Color Commentator

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17513
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: The Sun Rotating (2020 Aug 19)

Post by neufer » Thu Aug 20, 2020 4:21 am

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.
"
Art Neuendorffer