Starship Asterisk*

neufer wrote: ↑Sun Oct 18, 2020 6:40 pm

https://en.wikipedia.org/wiki/Truthiness wrote:
<<Truthiness is the belief or assertion that a particular statement is true based on the intuition or perceptions of some individual or individuals, without regard to evidence, logic, intellectual examination, or facts.>>

https://en.wikipedia.org/wiki/Definition wrote:
<<A Definition is a statement of the meaning of a term (a word, phrase, or other set of symbols). Definitions can be classified into two large categories, intensional definitions (which try to give the sense of a term) and extensional definitions (which try to list the objects that a term describes). Another important category of definitions is the class of ostensive definitions, which convey the meaning of a term by pointing out examples. A term may have many different senses and multiple meanings, and thus require multiple definitions.>>

https://en.wikipedia.org/wiki/Color_temperature wrote:

SPDs for an incandescent lamp &a fluorescent lamp.

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SPD of Vega. The 15000 K black-body spectrum (dashed line) matches the visible part of the stellar SPD much better than the black body of 9500 K. All spectra are normalized to intersect at 555 nanometers.

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<<Light sources and illuminants may be characterized by their spectral power distribution (SPD). The relative SPD curves provided by many manufacturers may have been produced using 10 nm increments or more on their spectroradiometer. The result is what would seem to be a smoother ("fuller spectrum") power distribution than the lamp actually has. Owing to their spiky distribution, much finer increments are advisable for taking measurements of fluorescent lights, and this requires more expensive equipment.

In astronomy, the color temperature is defined by the local slope of the SPD at a given wavelength, or, in practice, a wavelength range. Given, for example, the color magnitudes B and V which are calibrated to be equal for an A0V star (e.g. Vega), the stellar color temperature T_C is given by the temperature for which the color index B-V of a black-body radiator fits the stellar one. Besides the B-V, other color indices can be used as well. The color temperature (as well as the correlated color temperature defined above) may differ largely from the effective temperature given by the radiative flux of the stellar surface. For example, the color temperature of an A0V star is about 15000 K compared to an effective temperature of about 9500 K.>>

Ann wrote: ↑Sun Oct 18, 2020 5:44 am

The 25 brightest stars in the sky. Note their colors.

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54 out of the 93 brightest-looking stars in the sky belong to spectral classes A, B and O. They shine with a blue-white light. But because the light-sensitive rods in the human retina are very good at picking up faint blue light (and "translate it" into white light), while simultaneously the color-sensitive cones are quite bad at discerning faint blue light, blue-white starlight usually looks white to us.

27 out of the 93 brightest-looking stars in the sky belong to spectral classes K and M. The cones in our eyes is a lot better at seeing faint yellow light than faint blue light, so we usually have no trouble seeing stars of spectral classes K and M as yellow. Also, since there are usually some bright stars of spectral classes A, B or O nearby in the sky, the sheer contrast brings out the yellowish hue of the K- and M-type stars.

But since astronomers fairly long ago decided to "define" the blue-white light of Vega as "pure white", the yellow-orange light of M-type stars gets defined as "red". The yellow light of a star like Pollux gets defined as "orange". And the Sun gets defined as "yellow". Tell me, if the Sun is yellow, how come daylight is white?

And F-type stars like Procyon gets defined as yellow-white. Give me a break. Do you realize how blue our day-light would be if the Sun suddenly took on the same color as Procyon?

https://en.wikipedia.org/wiki/Truthiness wrote:
<<Truthiness is the belief or assertion that a particular statement is true based on the intuition or perceptions of some individual or individuals, without regard to evidence, logic, intellectual examination, or facts.>>

https://en.wikipedia.org/wiki/Definition wrote:
<<A Definition is a statement of the meaning of a term (a word, phrase, or other set of symbols). Definitions can be classified into two large categories, intensional definitions (which try to give the sense of a term) and extensional definitions (which try to list the objects that a term describes). Another important category of definitions is the class of ostensive definitions, which convey the meaning of a term by pointing out examples. A term may have many different senses and multiple meanings, and thus require multiple definitions.>>

https://en.wikipedia.org/wiki/Color_temperature wrote:

SPDs for an incandescent lamp &a fluorescent lamp.

---

SPD of Vega. The 15000 K black-body spectrum (dashed line) matches the visible part of the stellar SPD much better than the black body of 9500 K. All spectra are normalized to intersect at 555 nanometers.

---

<<Light sources and illuminants may be characterized by their spectral power distribution (SPD). The relative SPD curves provided by many manufacturers may have been produced using 10 nm increments or more on their spectroradiometer. The result is what would seem to be a smoother ("fuller spectrum") power distribution than the lamp actually has. Owing to their spiky distribution, much finer increments are advisable for taking measurements of fluorescent lights, and this requires more expensive equipment.

In astronomy, the color temperature is defined by the local slope of the SPD at a given wavelength, or, in practice, a wavelength range. Given, for example, the color magnitudes B and V which are calibrated to be equal for an A0V star (e.g. Vega), the stellar color temperature T_C is given by the temperature for which the color index B-V of a black-body radiator fits the stellar one. Besides the B-V, other color indices can be used as well. The color temperature (as well as the correlated color temperature defined above) may differ largely from the effective temperature given by the radiative flux of the stellar surface. For example, the color temperature of an A0V star is about 15000 K compared to an effective temperature of about 9500 K.>>

VictorBorun wrote: ↑Sun Oct 18, 2020 5:53 am

Chris Peterson wrote: ↑Sat Oct 17, 2020 2:04 pm I'd say that the Hα is assigned to red, and the O[III] is assigned approximately equally to the green and blue (thus, cyan). That is consistent with the image histogram. So white will occur wherever the intensity from the two source channels is the same (subject to whatever aesthetic color balancing the imager used).

But look at thin shining layers around the Crescent! It's definitely RGB blue.
Some authors try to make OIII look the ghostly nebulium green-cyan that 501 nm + 496 nm really is. But not here.

neufer wrote: ↑Sat Oct 17, 2020 10:06 pm

Astronomy Picture of the Day : 2016 June 10

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ems57fcva wrote: ↑Sat Oct 17, 2020 8:22 pm
Where is the central star for the Soap Bubble nebula? The location if WR136 is fairly obvious (even if it is off-center). There is no star at the center of the Soap Bubble and nothing that I can see connects any of the stars in its range to the nebula. (My guess is that the star is obscured by dust, but that is just a guess.)

WR 136 is a 7.5 magnitude Wolf–Rayet star located in the middle of the 3 near-vertical stars in the June 10, 2016, APOD at left.

It is obscured by a heavy emphasis on narrow filter data in today's APOD.

Chris Peterson wrote: ↑Sat Oct 17, 2020 2:04 pm I'd say that the Hα is assigned to red, and the O[III] is assigned approximately equally to the green and blue (thus, cyan). That is consistent with the image histogram. So white will occur wherever the intensity from the two source channels is the same (subject to whatever aesthetic color balancing the imager used).

neufer wrote: ↑Sat Oct 17, 2020 10:46 pm

https://en.wikipedia.org/wiki/F-type_main-sequence_star wrote:

Procyon (top left), Betelgeuse, and Sirius form the Winter Triangle.

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<<An F-type main-sequence star is a main-sequence, hydrogen-fusing compact star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K. This temperature range gives the F-type stars a yellow-white hue. Because a main-sequence star is referred to as a dwarf star, this class of star may also be termed a yellow-white dwarf (so as not to be confused with actual white dwarfs).>>

A famous example is Procyon A which has a color index of 0.42, and its hue has been described as having a faint yellow tinge to it.

Ann wrote: ↑Sat Oct 17, 2020 8:05 pm

Canopus, spectral class F01b, second-brightest star in the sky, photographed from ISS. Note the star's typical F-type yellow-white color.

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The characteristic
yellow-white hue
of an F-type star?


Give me a break.

https://en.wikipedia.org/wiki/F-type_main-sequence_star wrote:

Procyon (top left), Betelgeuse, and Sirius form the Winter Triangle.

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<<An F-type main-sequence star is a main-sequence, hydrogen-fusing compact star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K. This temperature range gives the F-type stars a yellow-white hue. Because a main-sequence star is referred to as a dwarf star, this class of star may also be termed a yellow-white dwarf (so as not to be confused with actual white dwarfs).>>

A famous example is Procyon A which has a color index of 0.42, and its hue has been described as having a faint yellow tinge to it.

ems57fcva wrote: ↑Sat Oct 17, 2020 8:22 pm
Where is the central star for the Soap Bubble nebula? The location if WR136 is fairly obvious (even if it is off-center). There is no star at the center of the Soap Bubble and nothing that I can see connects any of the stars in its range to the nebula. (My guess is that the star is obscured by dust, but that is just a guess.)

neufer wrote: ↑Sat Oct 17, 2020 2:34 pm

https://en.wikipedia.org/wiki/Gamma_Cygni wrote:

Gamma Cyg nebula , NGC 6914 , IC 1311 & Crescent nebula

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Compared to the Sun this is an enormous star, with 12 times the Sun's mass and about 150 times the Sun's radius. It is emitting over 33,000 times as much energy as the Sun, at an effective temperature of 6,100 K in its outer envelope. This temperature is what gives the star the characteristic yellow-white hue of an F-type star. Massive stars such as this consume their nuclear fuel much more rapidly than the Sun, so the estimated age of this star is only about 12 million years old.>>

JohnD wrote: ↑Sat Oct 17, 2020 10:21 am There's a black dot in the centre of the Crescent Nebula. Small dust cloud outside it, or what?
JOhn

https://en.wikipedia.org/wiki/Gamma_Cygni wrote:

Gamma Cyg nebula , NGC 6914 , IC 1311 & Crescent nebula

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<<Gamma Cygni (γ Cygni, abbreviated Gamma Cyg, γ Cyg), officially named Sadr is a star in the northern constellation of Cygnus, forming the intersection of an asterism of five stars called the Northern Cross. Based upon the Hipparcos mission, it is approximately 1,800 light-years (560 parsecs) from the Sun. With an apparent visual magnitude of 2.23, Gamma Cygni is among the brighter stars visible in the night sky. The stellar classification of this star is F8 Iab, indicating that it has reached the supergiant stage of its stellar evolution. The spectrum of this star shows some unusual dynamic features, including variations in radial velocity of up to 2 km/s, occurring on a time scale of 100 days or more. Indeed, on the Hertzsprung–Russell diagram, Gamma Cygni lies close to the instability strip and its spectrum is markedly like that of a Cepheid variable. This star is surrounded by a diffuse nebula called IC 1318, or the Gamma Cygni region.

Compared to the Sun this is an enormous star, with 12 times the Sun's mass and about 150 times the Sun's radius. It is emitting over 33,000 times as much energy as the Sun, at an effective temperature of 6,100 K in its outer envelope. This temperature is what gives the star the characteristic yellow-white hue of an F-type star. Massive stars such as this consume their nuclear fuel much more rapidly than the Sun, so the estimated age of this star is only about 12 million years old.>>

VictorBorun wrote: ↑Sat Oct 17, 2020 9:25 am What does make RGB white here?
Frames:
• red channel is Hα filtered with Chroma 3nm, integrated across 10.0 hours
• blue channel is OIII filtered with Chroma 3nm, integrated across 10.0 hours

So what is white?

sillyworm 2 wrote: ↑Sat Oct 17, 2020 12:40 pm Someone must have been having a less than imaginative day.The Screaming Praying Mantis Head Nebula.