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.

This is a Hubble Space Telescope Image of NGC 4414. Credit: Hubble Heritage Team (AURA/STScI/NASA).

"In 1995, the majestic spiral galaxy NGC 4414 was imaged by the Hubble Space Telescope as part of the HST Key Project on the Extragalactic Distance Scale. [The galaxy was] observed ... on 13 different occasions over the course of two months."

"Images were obtained with Hubble's Wide Field Planetary Camera 2 (WFPC2) through three different color filters."

"Based on [...] careful brightness measurements of variable stars in NGC 4414, [...] an accurate determination of the distance to the galaxy [was made]."

"The resulting distance to NGC 4414, 19.1 megaparsecs or about 60 million light-years, along with similarly determined distances to other nearby galaxies, contributes to astronomers' overall knowledge of the rate of expansion of the universe. The Hubble constant (H0) is the ratio of how fast galaxies are moving away from us to their distance from us. This astronomical value is used to determine distances, sizes, and the intrinsic luminosities for many objects in our universe, and the age of the universe itself."

"Due to the large size of the galaxy compared to the WFPC2 detectors, only half of the galaxy observed was visible in the datasets collected by the Key Project astronomers in 1995. In 1999, the Hubble Heritage Team revisited NGC 4414 and completed its portrait by observing the other half with the same filters as were used in 1995. The end result is a stunning full-color look at the entire dusty spiral galaxy. The new Hubble picture shows that the central regions of this galaxy, as is typical of most spirals, contain primarily older, yellow and red stars. The outer spiral arms are considerably bluer due to ongoing formation of young, blue stars, the brightest of which can be seen individually at the high resolution provided by the Hubble camera. The arms are also very rich in clouds of interstellar dust, seen as dark patches and streaks silhouetted against the starlight."

Standard-candles astronomy is the astronomical effort to find, study and develop standard-candle candidates for use as standard candles.

Standard candles are stars in visual astronomy that may be used to calculate distances because their characteristics are, or appear to be, distance independent.

Selected lecture

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

## Stellar fissions

W Ursae Majoris is an eclipsing binary, specifically a contact binary with a common envelope. The primary component has a radius of 1.08 solar. The secondary has a 0.78 solar radius. Credit: Aladin at SIMBAD.
This image shows the star Merope (23 Tauri) in the Pleiades. Credit: Henryk Kowalewski.

Star fission is the splitting of a star at a critical angular momentum, or period in its history, with the consequence of zero-age contact in the resultant binary star. This splitting may have its highest probability of occurring during early star formation.

Def. any small luminous dot appearing in the cloudless portion of the night sky, especially with a fixed location relative to other such dots or a luminous celestial body, made up of plasma (particularly hydrogen and helium) and having a spherical shape is called a star.

When any effort to acquire a system of laws or knowledge focusing on a stellar astr, aster, or astro, that is, any natural star in the sky especially at night, succeeds even in its smallest measurement, stellar astronomy is the name of the effort and the result.

Selected topic

## Continua

The 15" refractor at Comanche Springs Astronomy Campus had its finder scope (a Stellarvue 80/9D achromat) equipped with a Baader Herschel Solar Wedge and a Solar Continuum Filter for today's transit of Venus. Credit: Jeff Barton from Richardson, TX, USA.`{{free media}}`

Lyc photon or Ly continuum photon or Lyman continuum photon are a kind of photon emitted from stars. Hydrogen is ionized by absorption of Lyc photons. Lyc photons are in the ultraviolet portion of the electromagnetic spectrum of the hydrogen atom and immediately next to the limit of the Lyman series of the spectrum with wavelengths that are shorter than 91.1267 nanometres and with energy above 13.6 eV.

Selected X-ray astronomy article
RHESSI observes 2.2 MeV line emission from a solar flare. The solar flare at Active Region 10039 on July 23, 2002 exhibits many exceptional high-energy phenomena including the 2.223 MeV neutron capture line and the 511 keV electron-positron (antimatter) annihilation line. The RHESSI low-energy channels (12-25 keV) are represented in red and appear predominantly in coronal loops. The high-energy flux appears as blue at the footpoints of the coronal loops. Violet is used to indicate the location and relative intensity of the 2.2 MeV emission. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio.

Stellar surface fusion is one of the few direct views physicists have of thermonuclear fusion. Nuclear fusion usually occurs within a star as a part of stellar nucleosynthesis. However, an accreting star can undergo surface nuclear burning when the accretion rate exceeds a certain limit. The stellar luminosity then becomes dominated by hydrogen burning. The energy liberated by hydrogen burning exceeds that due to accretion by an order of magnitude or more, depending on the mass of the star. Steady hydrogen burning on the stellar surface processes hydrogen into helium at the rate of accretion. Surface fusion occurs above a star's photosphere to a limited extent as found in studies of near coronal and corona activity.

Based on the 3He-flare flux from the Sun's surface and Surveyor 3 samples (implanted 15N and 14C in lunar material) from the surface of the Moon, the level of nuclear fusion occurring in the solar atmosphere is approximately at least two to three orders of magnitude greater than that estimated from solar flares such as those of August 1972.

Objects
Selected image

The GOES 14 spacecraft carries a Solar X-ray Imager to monitor the Sun’s X-rays for the early detection of solar flares, coronal mass ejections (CMEs), and other phenomena that impact the geospace environment. Credit: NWS Internet Services Team.

Selected lesson

## First cyan source in Caelum

This is an image of NGC 1679 in Caelum. It is a spiral galaxy located two degrees south of Zeta Caeli. Credit: NASA/ESA (Wikisky).

The first cyan source in Caelum is unknown.

This is a lesson in map reading, coordinate matching, and searching. It is also a project in the history of cyan astronomy looking for the first astronomical cyan source discovered in the constellation of Caelum.

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

Some of the material and information is at the college or university level, and as you progress in finding cyan sources, you'll run into concepts and experimental tests that are an actual search.

To succeed in finding a cyan source in Caelum 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 cyan 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.

NGC 1679 in the image at left appears to contain some cyan, probably as a result of a mixture of light blue and yellow.

Selected quiz

This is an animation of a radiation scintillation counter. Credit: KieranMaher.

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

You are free to take this quiz based on radiation astronomy detectors 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.

This quiz may need up to an hour to take and is equivalent to an hourly.

Enjoy learning by doing!

 ...Archive Try the quiz...
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!

 ...Archive Experiment...
Selected problems

## 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:

${\displaystyle V=iR.}$

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.

 ...Archive Try the problems...
Selected X-ray astronomy pictures

On the right is the visual image of the constellation Orion. On the left is Orion as seen in X-rays only. Betelgeuse is easily seen above the three stars of Orion's belt on the right. The X-ray colors represent the temperature of the X-ray emission from each star: hot stars are blue-white and cooler stars are yellow-red. The brightest object in the optical image is the full moon, which is also in the X-ray image. Credit: Konrad Denner/Wolfgang Voges. The X-ray image was actually obtained by the ROSAT satellite during the All-Sky Survey phase in 1990-1991.

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