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Radiation astronomy
This image is a composite of several types of radiation astronomy: radio, infrared, visual, ultraviolet, soft and hard X-ray. Credit: NASA.

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

Seeing the Sun and feeling the warmth of its rays is probably a student's first encounter with an astronomical radiation source. This will happen from a very early age, but a first understanding of the concepts of radiation may occur at a secondary educational level.

Radiation is all around us on top of the Earth's crust, regolith, and soil, where we live. The study of radiation, including radiation astronomy, usually intensifies at the university undergraduate level.

And, generally, radiation becomes hazardous, when a student embarks on graduate study.

Cautionary speculation may be introduced unexpectedly to stimulate the imagination and open a small crack in a few doors that may appear closed at present. As such, this learning resource incorporates some state-of-the-art results from the scholarly literature.

The laboratories of radiation astronomy are limited to the radiation observatories themselves and the computers and other instruments (sometimes off site) used to analyze the results.

Selected resource


This is an image obtained from muon radiography of Japan's Asama volcano. Credit: H T M Tanaka.

"TeV muons from γ ray primaries ... are rare because they are only produced by higher energy γ rays whose flux is suppressed by the decreasing flux at the source and by absorption on interstellar light."[1]

Muon decay produces three particles, an electron plus two neutrinos of different types.


  1. Francis Halzen, Todor Stanev, Gaurang B. Yodh (April 1, 1997). "γ ray astronomy with muons". Physical Review D Particles, Fields, Gravitation, and Cosmology 55 (7): 4475-9. doi:10.1103/PhysRevD.55.4475. Retrieved 2013-01-18. 
Selected lecture

Radiation astronomy entities

This is an image of Johannes Vermeer's The astronomer. Credit: : Home : Info : Pic.

Radiation astronomy entities, radiation entities, are any astronomical persons or things that have separate and distinct existences in empirical, objective or conceptual reality.

Some of them, like the astronomers of today, or at any time in the past, are relatively known. But there are many entities that are far less known or understood, such as the observers of ancient times who suggested that deities occupied the sky or the heavens. Likewise, these alleged deities may be entities, or perhaps something a whole lot less.

Astronomical X-ray entities are often discriminated further into sources or objects when more information becomes available, including that from other radiation astronomies.

A researcher who turns on an X-ray generator to study the X-ray emissions in a laboratory so as to understand an apparent astronomical X-ray source is an astronomical X-ray entity. So is one who writes an article about such efforts or a computer simulation to possibly represent such a source.

"The X-ray luminosity of the dominant group [an entity] is an order of magnitude fainter than that of the X-ray jet."[1]


  1. A. Finoguenov, M.G. Watson, M. Tanaka, C.Simpson, M. Cirasuolo, J.S. Dunlop, J.A. Peacock, D. Farrah, M. Akiyama, Y. Ueda, V. Smolčič, G. Stewart, S. Rawlings, C.vanBreukelen, O. Almaini, L.Clewley, D.G. Bonfield, M.J. Jarvis, J.M. Barr, S. Foucaud, R.J. McLure, K. Sekiguchi, E. Egami (April 2010). "X-ray groups and clusters of galaxies in the Subaru-XMM Deep Field". Monthly Notices of the Royal Astronomical Society 403 (4): 2063-76. doi:10.1111/j.1365-2966.2010.16256.x. Retrieved 2011-12-09. 
Selected theory

Theoretical radiation astronomy

At the bottom of this visible emission model is a visual intensity curve. Credit: Stanlekub.

At its simplest theoretical radiation astronomy is the definition of terms to be applied to astronomical radiation phenomena.

Def. a theory of the science of the biological, chemical, physical, and logical laws (or principles) with respect to any natural radiation source in the sky especially at night is called theoretical radiation astronomy.

Exploratory theory is the playtime activity that leads to discoveries which better our world. In the radiation physics laboratories here on Earth, the emission, reflection, transmission, absorption, and fluorescence of radiation is studied and laws relative to sources are proven.

A principle is a law or rule that has to be, or usually is to be followed, or can be desirably followed, or is an inevitable consequence of something, such as the laws observed in nature or the way that a system is constructed. The principles of such a system are understood by its users as the essential characteristics of the system, or reflecting system's designed purpose, and the effective operation or use of which would be impossible if any one of the principles was to be ignored.[1]

Radiation astronomy consists of three fundamental parts:

  1. derivation of logical laws with respect to incoming radiation,
  2. natural radiation sources outside the Earth, and
  3. the sky and associated realms with respect to radiation.

Def. a spontaneous emission of an α ray, β ray, or γ ray by the disintegration of an atomic nucleus is called radioactivity.[2]


  1. Guido Alpa (1994). "General Principles of Law". Annual Survey of International & Comparative Law 1: 1. Retrieved 2012-04-29. 
  2. Philip B. Gove, ed (1963). Webster's Seventh New Collegiate Dictionary. Springfield, Massachusetts: G. & C. Merriam Company. pp. 1221. 
Selected topic


The Hubble Space Telescope [Advanced Camera for Surveys] ACS image has H-alpha emission of the Red Rectangle shown in blue. Credit: ESA/Hubble and NASA.

"[T]he extended red emission (ERE) [is] observed in many dusty astronomical environments, in particular, the diffuse interstellar medium of the Galaxy. ... silicon nanoparticles provide the best match to the spectrum and the efficiency requirement of the ERE."[1]


  1. Adolf N. Witt, Karl D. Gordon and Douglas G. Furton (July 1, 1998). "Silicon Nanoparticles: Source of Extended Red Emission?". The Astrophysical Journal Letters 501 (1): L111-5. doi:10.1086/311453. Retrieved 2013-07-30. 
Selected image
Hydra A gas cloud.jpg
Composite radio + x-ray.jpg

On the left is a Chandra X-ray Observatory X-ray image that reveals a large cloud of hot gas that extends throughout the Hydra A galaxy cluster. Image is 2.7 arcmin across. Right ascension (RA) 09h 18m 06s Declination (Dec) -12° 05' 45" in the constellation Hydra. Observation date: October 30, 1999. Instrument: ACIS. Credit:NASA/CXC/SAO. On the right is an image that has the radio image of Greg Taylor, NRAO, overlain on the X-ray image from Chandra. The radio source Hydra A originates in a galaxy near the center of the cluster. Optical observations show a few hundred galaxies in the cluster. Credit:NASA/CXC/SAO; Radio: NRAO.

Selected lesson

First X-ray source in Apus

The graph shows the spatial distribution of ROSAT all-sky survey X-ray sources in the Chamaeleon cloud complex. Credit: J.M. Alcalá, J. Krautter, J.H.M.M. Schmitt, E. Covino, R. Wichmann and R. Mundt.

The first X-ray source in Apus discovered by our X-ray observatory satellites or rockets is unknown.

Above is a sky plot of the X-ray sources detected by the ROSAT all-sky survey in the Chamaeleon star-forming cloud complex. X-ray sources (Xs in the diagram) along the 14:00 h longitude are in the constellation Apus.

This is a lesson in map reading, coordinate matching, and researching. It is also a research project in the history of X-ray astronomy looking for the first astronomical X-ray source discovered in the constellation of Apus.

Nearly all the background you need to participate and learn by doing you've probably already been introduced to at a secondary educational level.

Some of the material and information you'll be introduced to is at the college or university level, and as you progress in finding X-ray sources, you'll run into concepts and experimental tests that are actual research.

To succeed in finding an X-ray source in Apus is the first step. Next, you'll need to determine the time stamp of its discovery and compare it with any that have already been found. Over the history of X-ray astronomy a number of sources have been found, many as point sources in the night sky. These points are located on the celestial sphere using coordinate systems. Familiarity with these coordinate systems is not a prerequisite. Here the challenge is geometrical, astrophysical, and historical.

Selected quiz

Cyan astronomy quiz

The visual image shows the natural cyan color of planetary nebula NGC 7048. Credit: Aladin from CDS.

Cyan astronomy is a lecture as part of the astronomy department course on the principles of radiation astronomy.

You are free to take this quiz based on cyan astronomy at any time.

To improve your score, read and study the lecture, the links contained within, listed under See also, External links and in the {{principles of radiation astronomy}} template. This should give you adequate background to get 100 %.

As a "learning by doing" resource, this quiz helps you to assess your knowledge and understanding of the information, and it is a quiz you may take over and over as a learning resource to improve your knowledge, understanding, test-taking skills, and your score.

Suggestion: Have the lecture available in a separate window.

To master the information and use only your memory while taking the quiz, try rewriting the information from more familiar points of view, or be creative with association.

Enjoy learning by doing!

Selected laboratory

Astronomical analysis laboratory

Circinus X-1 is imaged with the Chandra X-ray Observatory. Credit: X-ray: NASA/CXC/Univ. of Wisconsin-Madison/S.Heintz et al.

This laboratory is an activity for you to analyze an astronomical situation. While it is part of the astronomy course principles of radiation astronomy, it is also independent.

Astronomical analysis is the detailed examination of the elements or structure of some astronomical thing (an entity, source, or object), typically as a basis for discussion or interpretation.

Once an astronomical situation has been selected, it must be separated into its constituent elements, for example, the identification and measurement of the chemical constituents of a substance or specimen.

You may choose an astronomical situation to dissect.

I will provide one example of this process. Please put any questions you may have, and your laboratory results, you'd like evaluated, on the laboratory's discussion page.

Enjoy learning by doing!

Selected problems

Cosmic circuits

Main source: Cosmic circuits
The arcing, graceful structure is actually a bow shock about half a light-year across, created from the wind from the star L.L. Orionis colliding with the Orion Nebula flow. Credit: NASA.
This diagram suggests a simple electrical circuit. Credit: GorillaWarfare.

Voyager 1 has found only electrons streaming into the heliosphere from elsewhere in the galaxy. This problem set poses several problems to calculate the possibility that a simple electrical circuit is involved.

The diagram at right suggests a simple electrical circuit.

Def. an enclosed path of an electric current is called a circuit.

In the diagram at right are three components:

  1. a voltage (V), or current (i), source,
  2. an enclosed path, and
  3. a resistance, or resistor, (R).

According to Ohm's law:

With respect to an enclosed path, consider a path from outside the heliosphere, inward toward the Sun, and out again. Let the incoming electrons have 500 MeV of energy and a flux of 8.5 x 104 e- cm-2 s-1.

Def. a time rate of flow of electric charge is called a current.

Def. that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 x 10–7 newton per metre of length is called an ampere.

Def. an amount of electrostatic potential between two points in space is called a voltage.

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