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.

Representation of upper-atmospheric lightning and electrical-discharge phenomena are displayed. Credit: Abestrobi.

Lightning is more than ground-to-cloud electron transfer.

"Cloud flashes sometimes have visible channels that extend out into the air around the storm (cloud-to-air or CA), but do not strike the ground. The terms sheet lightning or intra-cloud lightning (IC) refers to lightning embedded within a cloud that lights up as a sheet of luminosity during the flash. A related term, heat lightning, is lightning or lightning-induced illumination that is too far away for thunder to be heard. Lightning can also travel from cloud-to-cloud (CC). Spider lightning refers to long, horizontally traveling flashes often seen on the underside of stratiform clouds."

"Large thunderstorms are capable of producing other kinds of electrical phenomena called transient luminous events (TLEs) that occur high in the atmosphere. They are rarely observed visually and not well understood. The most common TLEs include red sprites, blue jets, and elves."

The illustration on the left labels Elves, Sprites, and tendrils, a stratiform region producing positive cloud-to-ground flashes with spider lightning on the right to conventional cloud-to-air discharge, upward superbolt, blue jets and negative cloud-to-ground flash near convective core. Approximate altitudes in the Earth's atmosphere and ionosphere are indicated.

Selected lecture

## Radiation astronomy sources

Volcanic bombs are thrown into the sky and travel some distance before returning to the ground. This bomb is in the Craters of the Moon National Monument and Preserve, Idaho, USA. Credit: National Park Service.

In source astronomy, the question is "Where did it come from?"

Source astronomy has its origins in the actions of intelligent life on Earth when they noticed things or entities falling from above and became aware of the sky. Sometimes what they noticed is an acorn or walnut being dropped on them or thrown at them by a squirrel in a tree. Other events coupled with keen intellect allowed these life forms to deduce that some entities falling from the sky are coming down from locations higher than the tops of local trees.

Def. a source or apparent source detected or “created at or near the time of the [ event or] events”[1] is called a primary source.

Direct observation and tracking of the origination and trajectories of falling entities such as volcanic bombs presented early intelligent life with vital albeit sometimes dangerous opportunities to compose the science that led to source astronomy.

### References

1. primary source. San Francisco, California: Wikimedia Foundation, Inc. February 16, 2012. Retrieved 2012-07-14.
Selected theory

## Theoretical astronomy

This image is a theory for the interior of the Sun. Credit: Pbroks13.`{{free media}}`

Theoretical astronomy at its simplest is the definition of terms to be applied to astronomical entities, sources, and objects.

Def. an "expanse of space that seems to be [overhead] like a dome"[1] is called a sky.

Computer simulations are usually used to represent astronomical phenomena.

Part of the fun of theory is extending the known to what may be known to see if knowing is really occurring, or is it something else.

The laboratories of astronomy are limited to the observatories themselves. The phenomena observed are located in the heavens, far beyond the reach, let alone control, of the astronomical observer.[2] “So how can one be sure that what one sees out there is subject to the same rules and disciplines of science that govern the local laboratory experiments of physics and chemistry?”[2] “The most incomprehensible thing about the universe is that it is comprehensible.” - Albert Einstein.[2]

## References

1. Philip B. Gove, ed (1963). Webster's Seventh New Collegiate Dictionary. Springfield, Massachusetts: G. & C. Merriam Company. pp. 1221. Retrieved 2011-08-26.
2. Narlikar JV (1990). Pasachoff JM, Percy JR. ed. Curriculum for the Training of Astronomers ‘’In: The Teaching of astronomy. Cambridge, England: Cambridge University Press.
Selected topic

## Bands

This is Saturn imaged with the Stockholm Infrared Camera (SIRCA) in the H2O band. Credit: M. Gålfalk, G. Olofsson and H.-G. Florén, Nordic Optical Telescope.

At the right is Saturn imaged by the Stockholm Infrared Camera (SIRCA) in the H2O infrared band to show the presence of water vapor. The image is cut off near the top due to the presence of Saturn's rings.

The Sun's emission in the lowest UV bands, the UVA, UVB, and UVC bands, are of interest, as these are the UV bands commonly encountered from artificial sources on Earth. The shorter bands of UVC, as well as even more energetic radiation as produced by the Sun, generate the ozone in the ozone layer when single oxygen atoms produced by UV photolysis of dioxygen react with more dioxygen. The ozone layer is especially important in blocking UVB and part of UVC, since the shortest wavelengths of UVC (and those even shorter) are blocked by ordinary air.

Selected X-ray astronomy article
This X-ray image of Cygnus X-1 was taken by a balloon-borne telescope, the High Energy Replicated Optics (HERO) project. NASA image.

Cygnus X-1 (abbreviated Cyg X-1) is a well known galactic X-ray source in the constellation Cygnus. Cygnus X-1 was the first X-ray source widely accepted to be a black hole candidate and it remains among the most studied astronomical objects in its class. It is now estimated to have a mass about 8.7 times the mass of the Sun and has been shown to be too compact to be any known kind of normal star or other likely object besides a black hole.

Objects
Selected image

US Naval Research Laboratory (NRL) scientists J. D. Purcell, C. Y. Johnson, and Dr. F. S. Johnson among those recovering instruments from a V-2 used for upper atmospheric research above the New Mexico desert. This is V-2 number 54, launched January 18, 1951 (photo by Dr. Richard Tousey, NRL).

Selected lesson

## First X-ray source in Andromeda

This is an X-ray image of the Andromeda galaxy. Credit: ESA/XMM-Newton/EPIC/W. Pietsch.

The first X-ray source in Andromeda is not known. This lesson is also a research project that needs your help. And, in exchange you'll be free to learn about star maps, astronomy, and the speciality of X-ray astronomy. The first such source in the constellation Andromeda is an astronomical X-ray source detected at some point in human history between now and a distant time mark in the past. It is an astronomical X-ray source detected in the constellation Andromeda.

This learning resource is experimental in nature because each learner interested in seeking this first X-ray source may start with any source and attempt to determine if this source is in Andromeda and is an X-ray source. Each currently known source has a history that includes earlier and earlier detections. To succeed, the adventurer need only show that their source has an earlier detection date as an X-ray source than previous adventurers.

The celestial sphere has coordinate systems often used to place a point source in the heavens. Familiarity with these coordinate systems is not a prerequisite. An introductory geography or map reading course or some familiarity with following a map is all that's needed.

Over the history of X-ray astronomy a number of astronomical X-ray sources have been discovered and studied, usually because they have something special about them that intrigues the researcher. The challenge of this resource is geometrical, astrophysical, and historical. As the ultimate answer is unknown, this is actually a research project, yet you may succeed!

Enjoy learning by doing!

Selected quiz

## Radiation astrochemistry quiz

This is a natural color image of Titan. Credit: NASA/JPL/Space Science Institute.

Radiation chemistry, or astronomical radiation chemistry, is a lecture for the course principles of radiation astronomy about the abundance and reactions of chemical elements and molecules in the universe.

You are free to take this quiz at any time and as many times as you wish to improve your score.

Once you’ve read and studied the lecture, the links contained within, and listed under See also, External links and those in the `{{principles of radiation astronomy}}` template, you should have adequate background to get 100 %.

Enjoy learning by doing!

Selected laboratory

## Cratering astronomy laboratory

The crater in Santa Ana Volcano is photographed from a United States Air Force C-130 Hercules flying above El Salvador. Credit: José Fernández, U.S Air Force.

This laboratory is an activity for you to create or analyze a cratering. While it is part of the astronomy course principles of radiation astronomy, it is also independent.

Some suggested types of cratering to consider include a lightning strike, a bullet shot into some material, a water droplet hitting the surface of a beaker of water, a subterranean explosion, a sand vortex, or a meteorite impact.

More importantly, there is your cratering idea. And, yes, you can crater a peanut butter and jelly sandwich if you wish to.

Okay, this is an astronomy cratering laboratory, but you may create what a crater is. Another example is a volcanic crater.

I will provide an example of a cratering experiment. The rest is up to you.

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

## Furlongs per fortnight

It's about the chains. Credit: Stilfehler.`{{free media}}`

Furlongs per fortnight is a problem set with a contained quiz that focuses on the fundamentals of observational and deductive astronomy. In the activity Energy phantoms you learned about the value of distance, or displacement, and motion, speed, velocity, and acceleration. Here, you can practice and test yourself on converting from units that may or have occurred in the literature to units popular today.

Notation: let the symbol ${\displaystyle R_{\oplus }}$ indicate the Earth's radius.

Notation: let the symbol ${\displaystyle R_{J}}$ indicate the radius of Jupiter.

Notation: let the symbol ${\displaystyle R_{\odot }}$ indicate the solar radius.

Both physics and astronomy use units and dimensions to describe observations.

Units of Physics and Astronomy
Dimension Astronomy Symbol Physics Symbol Conversion
time 1 day d 1 second s 1 d = 86,400 s[1]
time 1 "Julian year"[2] J 1 second s 1 J = 31,557,600 s
distance 1 astronomical unit AU 1 meter m 1 AU = 149,597,870.691 km[1]
angular distance 1 parsec pc 1 meter m 1 pc ~ 30.857 x 1012 km[1]

### References

1. P. K. Seidelmann (1976). Measuring the Universe The IAU and astronomical units. International Astronomical Union. Retrieved 2011-11-27.
2. International Astronomical Union "SI units" accessed February 18, 2010. (See Table 5 and section 5.15.) Reprinted from George A. Wilkins & IAU Commission 5, "The IAU Style Manual (1989)" (PDF file) in IAU Transactions Vol. XXB
Selected X-ray astronomy pictures

Chandra X-ray Observatory image of Cygnus X-1. Credit: Chandra: NASA/CXC.

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