Typical energy dispersive XRF spectrum for a number of elements is shown. Credit: LinguisticDemographer.
This is a typical spectrum of a rhodium target tube operated at 60 kV, showing continuous spectrum and K lines. Credit: LinguisticDemographer.

"Each element has electronic orbitals of characteristic energy. Following removal of an inner electron by an energetic photon provided by a primary radiation source, an electron from an outer shell drops into its place. There are a limited number of ways in which this can happen ... The main transitions are given names: an L→K transition is traditionally called Kα, an M→K transition is called Kβ, an M→L transition is called Lα, and so on. Each of these transitions yields a fluorescent photon with a characteristic energy equal to the difference in energy of the initial and final orbital. The wavelength of this fluorescent radiation can be calculated from Planck's Law:

${\displaystyle \lambda =h\cdot c/E.}$

The second image at right "shows the typical form of the sharp fluorescent spectral lines obtained in the energy-dispersive method.

"[E]lemental abundances which cannot be determined from meteorites include several of the most important for interstellar X-ray absorption: H, He, C, N, O, Ne, and Ar."[1]

## Backgrounds

This graph shows the power density spectrum of the extragalactic or cosmic gamma-ray background (CGB). Credit: pkisscs@konkoly.hu.

The diffuse cosmic X-ray background is indicated in the figure at right with the notation CXB.

In addition to discrete sources which stand out against the sky, there is good evidence for a diffuse X-ray background.[2] During more than a decade of observations of X-ray emission from the Sun, evidence of the existence of an isotropic X-ray background flux was obtained in 1956.[3] This background flux is rather consistently observed over a wide range of energies.[2] The early high-energy end of the spectrum for this diffuse X-ray background was obtained by instruments on board Ranger 3 and Ranger 5.[2] The X-ray flux corresponds to a total energy density of about 5 x 10−4 eV/cm3.[2] The ROSAT soft X-ray diffuse background (SXRB) image shows the general increase in intensity from the Galactic plane to the poles. At the lowest energies, 0.1 - 0.3 keV, nearly all of the observed soft X-ray background (SXRB) is thermal emission from ~106 K plasma.

## Electromagnetics

The electromagnetic spectrum. The red line indicates the room temperature thermal energy. Credit: Opensource Handbook of Nanoscience and Nanotechnology.

A spectral distribution is often a plot or intensity, brightness, flux density, or other characteristic of a spectrum versus the spectral property such as wavelength, frequency, energy, particle speed, refractive or reflective index, for example.

The first three dozen or so astronomical X-ray objects detected other than the Sun "represent a brightness range of about a thousandfold from the most intense source, Sco XR-1, ca. 5 x 10-10 J m-2 s-1, to the weakest sources at a few times 10-13 J m-2 s-1."[4]

## Oranges

In traditional colour theory, orange is a range of colours between red and yellow. Credit: Wilinckx.

The orange portion of the visible spectrum is from 590 to 620 nm in wavelength.

In optics, orange is the colour seen by the eye when looking at light with a wavelength between approximately 585–620 nm. It has a hue of 30° in HSV colour space.

## Hydrogens

This is the spectral series of hydrogen, on a logarithmic scale. Credit: OrangeDog.

The emission spectrum of atomic hydrogen is divided into a number of spectral series, with wavelengths given by the Rydberg formula. These observed spectral lines are due to electrons moving between energy levels in the atom. The spectral series are important in astronomy for detecting the presence of hydrogen and calculating red shifts.

## Atmospheres

The diagam is a plot of atmospheric transmittance in part of the infrared region. Credit: U.S. Navy.

The principal limitation on infrared sensitivity from ground-based telescopes is the Earth's atmosphere. Water vapor absorbs a significant amount of infrared radiation, and the atmosphere itself emits at infrared wavelengths. For this reason, most infrared telescopes are built in very dry places at high altitude, so that they are above most of the water vapor in the atmosphere. Suitable locations on Earth include Mauna Kea Observatory at 4205 meters above sea level, the ALMA site at 5000 m in Chile and regions of high altitude ice-desert such as Dome C in Antarctic. Even at high altitudes, the transparency of the Earth's atmosphere is limited except in infrared windows, or wavelengths where the Earth's atmosphere is transparent.[5] The main infrared windows are listed below:

Wavelength range
(micrometres)
Astronomical bands Telescopes
0.65 to 1.0 R and I bands All major optical telescopes
1.1 to 1.4 J band Most major optical telescopes and most dedicated infrared telescopes
1.5 to 1.8 H band Most major optical telescopes and most dedicated infrared telescopes
2.0 to 2.4 K band Most major optical telescopes and most dedicated infrared telescopes
3.0 to 4.0 L band Most dedicated infrared telescopes and some optical telescopes
4.6 to 5.0 M band Most dedicated infrared telescopes and some optical telescopes
7.5 to 14.5 N band Most dedicated infrared telescopes and some optical telescopes
17 to 25 Q band Some dedicated infrared telescopes and some optical telescopes
28 to 40 Z band Some dedicated infrared telescopes and some optical telescopes
330 to 370 Some dedicated infrared telescopes and some optical telescopes
450 submillimeter Submillimeter telescopes

## Red clumps

This Hertzsprung-Russell diagram shows the evolution of stars of different masses. The red clump is marked RC on the green line showing the evolution of a star of 2 solar masses. Credit: Jesusmaiz and Rursus.

The red clump is a feature in the Hertzsprung-Russell diagram of stars. The red clump is considered the metal-rich counterpart to the horizontal branch. Stars in this part of the Hertzsprung-Russell diagram are sometimes called clump giants. These stars are more luminous than main sequence stars of the same surface temperature (or colder than main sequence stars of comparable luminosity), or above and to the right of the main sequence on the Hertzsprung-Russell diagram.

## Hypotheses

1. The use of satellites should provide ten times the information as sounding rockets or balloons.

A control group for a radiation satellite would contain

2. a two-way communication system,
3. a positional locator,
4. an orientation propulsion system, and
5. power supplies and energy sources for all components.

A control group for radiation astronomy satellites may include an ideal or rigorously stable orbit so that the satellite observes the radiation at or to a much higher resolution than an Earth-based ground-level observatory is capable of.