Yellow astronomy

Completion status: Been started, but most of the work is still to be done.

This is a visual image of the Sun with some sunspots visible. The two small spots in the middle have about the same diameter as our planet Earth. Credit: NASA.

Yellow astronomy is astronomy applied to the various extraterrestrial yellow sources of radiation, especially at night. It is also conducted above the Earth's atmosphere and at locations away from the Earth as a part of explorational (or exploratory) yellow astronomy.

Educational level: this is a secondary education resource.

Seeing the yellow Sun and feeling the warmth of its rays is probably a student's first encounter with an astronomical yellow radiation source. This may occur at a secondary educational level.

Educational level: this is a tertiary (university) resource.

There are yellow objects and emission lines in the yellow portion of the visible spectrum from 570 to 590 nm in wavelength.

Educational level: this is a research resource.

Resource type: this resource is an article.

Resource type: this resource contains a lecture or lecture notes.

Subject classification: this is an astronomy resource.

Notation

Notation: let the symbol Def. indicate that a definition is following.

Universals

To help with definitions, their meanings and intents, there is the learning resource theory of definition.

Def. "[t]he colour of gold or butter; the colour obtained by mixing green and red light, or by subtracting blue from white light", per Wiktionary yellow, is called yellow.

Def. "[a] street lamp in which electricity is passed through sodium vapour to emit a yellow light", from Wiktionary sodium vapor lamp, is called a sodium vapor lamp.

Calcium

During the limb flares of December 18, 1956, a coronal line at 569.4 nm, a yellow line, occurred at 1822 UTC, 1900 UTC, undiminished up to 20,000 km above the solar limb, and at 2226 UTC, is identified as Ca XV. "The coronal temperature was 4000000°." "The December 18, 1956, flare appears to have been a violent condensation of material from a dense coronal cloud above an active region."

Emission lines

Broadening of emission lines is due to, per the Wikipedia article, Doppler broadening, "Doppler broadening is the broadening of spectral lines due to the Doppler effect caused by a distribution of velocities of atoms or molecules. Different velocities of the emitting particles result in different (Doppler) shifts, the cumulative effect of which is the line broadening."

Helium

"The helium emission lines behave in a qualitatively similar way to the calcium triplet. The 5876 Å line (Fig. 1e) is the dominant line in all the spectra, although two other transitions (6678 and 7065) are also in emission in most of the stars and have nearly identical profiles." He I is 587.6 nm, a yellow emission line. The He I photospheric emission line "narrow component is present in emission ... with [chromospheric] veilings larger than 0.4, being conspicuous even in those heavily veiled stars". The chromospheric veiling apparently results in the emission broadening of the He I emission from the chromosphere which is partially added to the He I narrow emission from the photosphere.

"The radiative loss for both broad and narrow emission--i.e., the excess of emission over the external continuum expressed in percentages of the photospheric fluxes--is F_ph(1 + ν)EW_obs, where F_ph is the nearby photospheric flux and EW_obs is the equivalent width of the observed emission component." "[B]y assumption, [the dynamo] controls the narrow component fluxes."

Io

This is a true-color image of Io taken by the Galileo probe. Credit: NASA.

Io "is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of 3,642 kilometres (2,263 mi), the fourth-largest moon in the Solar System. ... With over 400 active volcanoes, Io is the most geologically active object in the Solar System. ... Most of Io's surface is characterized by extensive plains coated with sulfur and sulfur dioxide frost. ... Io's volcanism is responsible for many of the satellite's unique features. Its volcanic plumes and lava flows produce large surface changes and paint the surface in various shades of yellow, red, white, black, and green, largely due to allotropes and compounds of sulfur." after the Wikipedia article on Io.

Nitrogen

Nitrogen has a yellow forbidden line, specifically N II at 575.5 nm, that may be used to indicate nitrogen abundances and contribute to nitrogen/oxygen (N/O) abundance gradients. Surveys of H II regions in spiral galaxies have suggested that N/O abundance ratios increase from outer-arm nebulae to inner-arm nebulae. "Electron temperatures are generally derived from the ratio of auroral to nebular lines in [O III] or [N II]." "[B]ecause of the proximity of strong night-sky lines at λ4358 and λλ5770, 5791, the auroral lines of [O III] λ4363 and [N II] λ5755 are often contaminated."

"The nitrogen abundance appears to increase with decreasing galactocentric distance. ... A least-squares solution weighting the points equally gives a magnitude for the gradient d(log N/H)/dr = -0.10 ± 0.03 kpc^-1." "The ratio N/O clearly increases with decreasing R. A least-squares fit to the data ... gives d(log N/O)/dr = -0.06 ± 0.02 kpc^-1."

Optical astronomy

Optical astronomy includes those portions of ultraviolet, visual, and infrared astronomy that benefit from the use of quartz crystal or silica glass telescope components.

Per the Wikipedia article telescope: "An optical telescope gathers and focuses light mainly from the visible part of the electromagnetic spectrum (although some work in the infrared and ultraviolet)."

Sodium

Per the Wikipedia article astronomical spectroscopy: "Fraunhofer's original (1817) designations of absorption lines in the solar spectrum

Letter	Wavelength (nm)	Chemical origin	Colour range
A	759.37	atmospheric O2	dark red
B	686.72	atmospheric O2	red
C	656.28	hydrogen alpha	red
D1	589.59	neutral sodium	red orange
D2	589.00	neutral sodium	yellow
E	526.96	neutral iron	green
F	486.13	hydrogen beta	cyan
G	431.42	CH molecule	blue
H	396.85	ionised calcium	dark violet
K	393.37	ionised calcium	dark violet"

Sodium produces two spectral lines known as D1 and D2, or the "sodium doublet". Their average wavelength, 589.3 nm, is often just called "D".

Stellar classification

The Secchi Class II consists of yellow stars with evident metallic lines, per the Wikipedia article stellar classification.

From the Wikipedia article stellar classification, "The Harvard classification system is a one-dimensional classification scheme. Stars vary in surface temperature from about 2,000 to 40,000 kelvins. Physically, the classes indicate the temperature of the star's atmosphere and are normally listed from hottest to coldest, as is done in the following table:"

Class	Temperature K	Conventional color	Apparent color	Mass (solar masses, Mʘ)	Radius (solar radii, Rʘ)	Luminosity (bolometric, Lʘ)	Hydrogen lines	Fraction of all main sequence stars
O	≥ 33,000 K	blue	blue	≥ 16	≥ 6.6	≥ 30,000	Weak	~0.00003%
B	10,000–33,000 K	blue to blue white	blue white	2.1–16	1.8–6.6	25–30,000	Medium	0.13%
A	7,500–10,000 K	white	white to blue white	1.4–2.1	1.4–1.8	5–25	Strong	0.6%
F	6,000–7,500 K	yellowish white	white	1.04–1.4	1.15–1.4	1.5–5	Medium	3%
G	5,200–6,000 K	yellow	yellowish white	0.8–1.04	0.96–1.15	0.6–1.5	Weak	7.6%
K	3,700–5,200 K	orange	yellow orange	0.45–0.8	0.7–0.96	0.08–0.6	Very weak	12.1%
M	≤ 3,700 K	red	orange red	≤ 0.45	≤ 0.7	≤ 0.08	Very weak	76.45%

"Stars of spectral classes F and G, such as our sun Sol, have color temperatures that make them look "yellowish". The first astronomer to classify stars according to their color was F. G. W. Struve in 1827. One of his classifications was flavae, or yellow, and this roughly corresponded to stars in the modern spectral range F5 to K0. The Strömgren photometric system for stellar classification includes a 'y' or yellow filter that is centered at a wavelength of 550 nm and has a bandwidth of 20–30 nm." from the Wikipedia article about the color yellow.

Visual astronomy

Color	Frequency	Wavelength
violet	668–789 THz	380–450 nm
blue	631–668 THz	450–475 nm
cyan	606–630 THz	476–495 nm
green	526–606 THz	495–570 nm
yellow	508–526 THz	570–590 nm
orange	484–508 THz	590–620 nm
red	400–484 THz	620–750 nm

From the Wikipedia article visible spectrum: "The visible spectrum is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of frequency, this corresponds to a band in the vicinity of 400–790 THz. A light-adapted eye generally has its maximum sensitivity at around 555 nm (540 THz), in the green region of the optical spectrum (see: luminosity function)."

Yellow evolutionary void

"G is host to the "Yellow Evolutionary Void". Supergiant stars often swing between O or B (blue) and K or M (red). While they do this, they do not stay for long in the G classification as this is an extremely unstable place for a supergiant to be.", per Wikipedia stellar classification.

"[T]he yellow evolutionary void ... is an area in the Hertzspung-Russell diagram where atmospheres of blueward evolving super- and hypergiants are moderately unstable ... For [such stars] (in hydrostatic equilibrium)

1. a negative density gradient occurs,
2. the sum of all accelerations, including wind, turbulence and pulsations, is zero or negative,
3. the sonic point of the stellar wind is reached in or below photospheric levels, and
4. Γ₁ ≤ 4/3 indicating some level of dynamic instability in part of the atmosphere."

Yellow galaxies

This image shows a cluster of yellow galaxies near the middle of the photograph.

The image at right "shows several blue, loop-shaped objects that are multiple images of the same galaxy, duplicated by the gravitational lens effect of the cluster of yellow galaxies near the middle of the photograph. The lens is produced by the cluster's gravitational field that bends light to magnify and distort the image of a more distant object." after the Wikipedia article about astronomy.

Yellow hypergiants

"ρ Cas, HR 8752 and IRC+10420, three well-studied yellow hypergiants, are situated at or close to the red border of the [yellow evolutionary] void."

"Generally speaking, a yellow hypergiant is a massive star with an extended atmosphere, which can be classified as spectral class from late A to K, with a mass of as much as 20-50 solar masses. Yellow hypergiants, such as Rho Cassiopeiae in the constellation Cassiopeia, have been observed to experience periodic eruptions, resulting in periodic or continuous dimming of the star, respectively. Yellow hypergiants appear to be extremely rare in the universe. Due to their extremely rapid rate of consumption of nuclear fuel, yellow hypergiants generally only remain on the main sequence for a few million years before destroying themselves in a massive supernova or hypernova. Yellow hypergiants are post-red supergiants, rapidly evolving toward the blue supergiant phase." per the Wikipedia article about the yellow hypergiant.

"According to the current physical models of stars, a yellow hypergiant should possess a convective core surrounded by a radiative zone, as opposed to a sun-sized star, which consists of a radiative core surrounded by a convective zone (Seeds, 2005). Due to the extremely high pressures which exist at the core of a yellow hypergiant, portions of the core or perhaps the entire core may be composed of degenerate matter." from the Wikipedia article about the yellow hypergiant.

These stars have "powerful magnetic fields", also per Wikipedia yellow hypergiant.

Yellow supergiants

From the Wikipedia article on yellow supergiant, "A yellow supergiant (YSG) is a supergiant star of spectral type F or G. These stars usually have masses between 15 and 20 solar masses. These stars, like any other supergiant, are older and swing between blue and red phases depending on the chemical elements they consume in their cores. Until now it had been thought that few supergiants spend a long time in the transitional yellow phase. These systems may be the progenitors of rare supernovae linked to yellow supergiants. Only [a] few such supernovae have been detected - most supergiants go supernova when at the blue (or hot) phase or red (or cool) phase."

See also

• First yellow source in Aquila
• Green astronomy
• Orange astronomy
• Principles of Radiation Astronomy
• Radiation astronomy
• Radiative dynamo
• Theoretical radiation astronomy
• Visual astronomy

Further reading

• Eberhard Haug & Werner Nakel (2004). The elementary process of Bremsstrahlung. River Edge NJ: World Scientific. p. Scientific lecture notes in physics, vol. 73. ISBN 9812385789. http://books.google.com/books?hl=en&id=v4FMtIwTri8C&dq=bremsstrahlung+haug&printsec=frontcover&source=web&ots=THjay1eeFA&sig=aHe-xMFwT8jxhpAGJHDnxKC6Jjc#PPA29,M1. 

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