Editing Electron (section)

== Observation ==
[[File:Aurore australe - Aurora australis.jpg|right|thumb|alt=A swirling green glow in the night sky above snow-covered ground|[[Aurora (astronomy)|Aurorae]] are mostly caused by energetic electrons precipitating into the [[atmosphere]]<ref>
{{cite press release
 |last=Wolpert |first=S.
 |date=July 24, 2008
 |title=Scientists solve 30&nbsp;year-old aurora borealis mystery
 |publisher=University of California
 |url=https://www.universityofcalifornia.edu/news/article/18277
 |url-status=dead |access-date=2008-10-11 |df=dmy-all
 |archive-url=https://web.archive.org/web/20080817094058/https://www.universityofcalifornia.edu/news/article/18277
 |archive-date=August 17, 2008
}}</ref>]]
Remote observation of electrons requires detection of their radiated energy. For example, in high-energy environments such as the [[stellar corona|corona]] of a star, free electrons form a [[Plasma (physics)|plasma]] that radiates energy due to [[Bremsstrahlung]] radiation. Electron gas can undergo [[plasma oscillation]], which is waves caused by synchronized variations in electron density, and these produce energy emissions that can be detected by using [[radio telescope]]s.<ref>
{{cite journal
 | last1 = Gurnett | first1 = D.A.
 | last2 = Anderson | first2 = R.
 | year = 1976
 | title = Electron Plasma Oscillations Associated with Type III Radio Bursts
 | journal = [[Science (journal)|Science]]
 | volume = 194 | issue = 4270 | pages = 1159–1162
 | doi =10.1126/science.194.4270.1159 | pmid =17790910
 | bibcode = 1976Sci...194.1159G | s2cid = 11401604
}}</ref>

The [[frequency]] of a [[photon]] is proportional to its energy. As a bound electron transitions between different energy levels of an atom, it absorbs or emits photons at characteristic frequencies. For instance, when atoms are irradiated by a source with a broad spectrum, distinct [[spectral line|dark lines]] appear in the spectrum of transmitted radiation in places where the corresponding frequency is absorbed by the atom's electrons. Each element or molecule displays a characteristic set of spectral lines, such as the [[hydrogen spectral series]]. When detected, [[Spectroscopy|spectroscopic]] measurements of the strength and width of these lines allow the composition and physical properties of a substance to be determined.<ref>
{{cite web
 | last1 = Martin
 | first1 = W.C.
 | last2 = Wiese
 | first2 = W.L.
 | year = 2007
 | title = Atomic Spectroscopy: A compendium of basic ideas, notation, data, and formulas
 | publisher = [[National Institute of Standards and Technology]]
 | access-date = 2007-01-08
 | df = dmy-all
 | url = https://physics.nist.gov/Pubs/AtSpec/
 | archive-date = 2007-02-08
 | archive-url = https://web.archive.org/web/20070208113156/http://physics.nist.gov/Pubs/AtSpec/
 | url-status = live
}}</ref><ref>
{{cite book
 | last = Fowles
 | first = G.R.
 | title = Introduction to Modern Optics
 | pages = 227–233
 | publisher = [[Courier Dover]]
 | year = 1989
 | isbn = 978-0-486-65957-2
 | url = https://books.google.com/books?id=SL1n9TuJ5YMC&pg=PA227
 | access-date = 2020-08-25
 | archive-date = 2021-01-07
 | archive-url = https://web.archive.org/web/20210107160307/https://books.google.com/books?id=SL1n9TuJ5YMC&pg=PA227
 | url-status = live
}}</ref>

In laboratory conditions, the interactions of individual electrons can be observed by means of [[particle detector]]s, which allow measurement of specific properties such as energy, spin and charge.<ref name="grupen">
{{cite journal
 | last = Grupen | first = C.
 | year = 2000
 | title = Physics of Particle Detection
 | journal = [[AIP Conference Proceedings]]
 | volume = 536 | pages = 3–34
 | doi =10.1063/1.1361756 |arxiv = physics/9906063
 | bibcode = 2000AIPC..536....3G
 | s2cid = 119476972
}}</ref> The development of the [[quadrupole ion trap|Paul trap]] and [[Penning trap]] allows charged particles to be contained within a small region for long durations. This enables precise measurements of the particle properties. For example, in one instance a Penning trap was used to contain a single electron for a period of 10 months.<ref name="nobel1989">
{{cite web
 | title = The Nobel Prize in Physics 1989
 | publisher = [[Nobel Foundation|The Nobel Foundation]]
 | year = 2008
 | url = https://nobelprize.org/nobel_prizes/physics/laureates/1989/illpres/
 | access-date = 2008-09-24
 | df = dmy-all
 | archive-date = 2008-09-28
 | archive-url = https://web.archive.org/web/20080928042325/http://nobelprize.org/nobel_prizes/physics/laureates/1989/illpres/
 | url-status = live
}}</ref> The magnetic moment of the electron was measured to a precision of eleven digits, which, in 1980, was a greater accuracy than for any other physical constant.<ref>
{{cite journal
 | last1 = Ekstrom
 | first1 = P.
 | last2 = Wineland
 | first2 = David
 | year = 1980
 | title = The isolated Electron
 | journal = [[Scientific American]]
 | volume = 243
 | issue = 2
 | pages = 91–101
 | url = https://tf.nist.gov/general/pdf/166.pdf
 | access-date = 2008-09-24
 | df = dmy-all
 | doi = 10.1038/scientificamerican0880-104
 | bibcode = 1980SciAm.243b.104E
 | archive-date = 2019-09-16
 | archive-url = https://web.archive.org/web/20190916211444/https://tf.nist.gov/general/pdf/166.pdf
 | url-status = live
}}</ref>

The first video images of an electron's energy distribution were captured by a team at [[Lund University]] in Sweden, February 2008. The scientists used extremely short flashes of light, called [[attosecond]] pulses, which allowed an electron's motion to be observed for the first time.<ref>
{{cite web
 | last = Mauritsson | first = J.
 | title = Electron filmed for the first time ever
 | url = https://www.atto.fysik.lth.se/video/pressrelen.pdf
 | publisher = [[Lund University]]
 | access-date = 2008-09-17 |df=dmy-all
 | archive-url = https://web.archive.org/web/20090325194101/https://www.atto.fysik.lth.se/video/pressrelen.pdf
 | archive-date = March 25, 2009
}}</ref><ref name=Mauritsson>
{{cite journal
 | last1 = Mauritsson | first1 = J. |display-authors=etal
 | year = 2008
 | title = Coherent Electron Scattering Captured by an Attosecond Quantum Stroboscope
 | journal = [[Physical Review Letters]]
 | volume = 100 | issue = 7 | page = 073003
 | doi =10.1103/PhysRevLett.100.073003 | bibcode=2008PhRvL.100g3003M
 | pmid=18352546 | arxiv = 0708.1060| s2cid = 1357534
}}</ref>

The distribution of the electrons in solid materials can be visualized by [[angle-resolved photoemission spectroscopy]] (ARPES). This technique employs the photoelectric effect to measure the [[Reciprocal lattice|reciprocal space]]—a mathematical representation of periodic structures that is used to infer the original structure. ARPES can be used to determine the direction, speed and scattering of electrons within the material.<ref>
{{cite journal
 | last = Damascelli | first = A.
 | year = 2004
 | title = Probing the Electronic Structure of Complex Systems by ARPES
 | journal = [[Physica Scripta]]
 | volume = T109 | pages = 61–74
 | doi =10.1238/Physica.Topical.109a00061
 | arxiv = cond-mat/0307085 |bibcode = 2004PhST..109...61D | s2cid = 21730523
}}</ref>