Compton–Getting effect

The Compton–Getting effect is an apparent anisotropy in the intensity of radiation or particles due to the relative motion between the observer and the source. This effect was first identified in the intensity of cosmic rays by Arthur Compton and Ivan A. Getting in 1935.{{cite journal

| last = Compton

| first = A. H.

| authorlink =

|author2=Getting, I. A.

| journal = Physical Review

| volume = 47

| issue = 11

| pages = 817–821

| date = June 1, 1935

| doi = 10.1103/PhysRev.47.817

| bibcode = 1935PhRv...47..817C

| title = An Apparent Effect of Galactic Rotation on the Intensity of Cosmic Rays}} Gleeson and Axford provide a full derivation of the equations relevant to this effect.{{cite journal

| last = Gleeson

| first = L. J.

| authorlink =

|author2=Axford, W. I.

| title = The Compton-Getting Effect

| journal = Astrophysics and Space Science

| volume = 2

| issue = 4

| pages = 431–437

| date = December 1968

| doi = 10.1007/BF02175919

| bibcode = 1968Ap&SS...2..431G| s2cid = 121458708

}}

The original application of the Compton–Getting effect predicted that the intensity of cosmic rays should be higher coming from the direction in which Earth is moving.{{cite web| title =Pierre Auger Observatory Q&A| year =2005| url =http://www.auger.org/qa/qa.html| accessdate =2009-03-21| url-status =dead| archiveurl =https://web.archive.org/web/20090212100052/http://www.auger.org/qa/qa.html| archivedate =2009-02-12}} For the case of cosmic rays the Compton–Getting effect only applies to those that are unaffected by the Solar wind such as extremely high energy particles. It has been calculated that the speed of the Earth within the galaxy ({{convert|200|km/s|mi/s}}) would result in a difference between the strongest and weakest cosmic ray intensities of about 0.1%.{{cite book

| last = Clay

| first = Roger

| authorlink =

| author2=Dawson, Bruce

| title = Cosmic Bullets

| publisher = Allen & Unwin

| year = 1997

| location = NSW, Australia

| pages = 103

| url =

| doi =

| id =

| isbn = 978-1-86448-204-1}}

This small difference is within the capabilities of modern instruments to detect, and was observed in 1986.{{cite journal

| last = Cutler

| first = D. J.

| authorlink =

| author2= Groom, D. E.

| title = Observation of terrestrial orbital motion using the cosmic-ray Compton-Getting effect

| journal = Nature

| volume = 322

| issue = 6078

| pages = 434–436

| date = July 1986

| doi = 10.1038/322434a0

| bibcode = 1986Natur.322..434C| s2cid = 4314814

}}

Forman (1970) derives the Compton–Getting effect anisotropy from the Lorentz invariance of the phase space distribution function.{{cite journal

| last = Forman

| first = M.

| title = The Compton-Getting effect for cosmic-ray particles and photons and the Lorentz invariance of distribution functions

| journal = Planet. Space Sci.

| volume = 18

| issue = 1

| pages = 25–31

| year = 1970|bibcode = 1970P&SS...18...25F |doi = 10.1016/0032-0633(70)90064-4 }} Ipavich (1974) furthers this general derivation to derive count rates with respect to the flow vector.{{cite journal

| last = Ipavich

| first = F. M.

| title = The Compton-Getting effect for low energy particles

| journal = Geophys. Res. Lett.

| volume = 1

| pages = 149–152

| doi = 10.1029/GL001i004p00149

| year = 1974|bibcode = 1974GeoRL...1..149I

| issue = 4 | hdl = 2060/19750006513

| hdl-access = free

}}

This Compton–Getting effect is apparent in plasma data in Earth's magnetotail.{{cite journal

| last1 = Roelof | first1 = E. C. | authorlink =

| last2 = Keath | first2 = E. P.

| last3 = Bostrom | first3 = C. O.

| last4 = Williams | first4 = D. J.

| title = Fluxes of >50-keV Protons and >30-keV Electrons at ~ 35 Re 1. Velocity Anisotropies and Plasma Flow in the Magnetotail

| journal = J. Geophys. Res.

| volume = 81

| issue = 13

| pages = 2304–2314

| doi = 10.1029/JA081i013p02304

| date = May 1, 1976|bibcode = 1976JGR....81.2304R }} The Compton–Getting effect has also been utilized for analyzing energetic neutral atom (ENA) data returned by the Cassini-Huygens spacecraft at Saturn.{{cite journal

| last = Paranicas

| first = C.

| title = Periodic intensity variations in global ENA images of Saturn

| journal = Geophys. Res. Lett.

| volume = 32

| pages = L21101

| doi = 10.1029/2005GL023656

| date = 2 November 2005|bibcode = 2005GeoRL..3221101P

| issue = 21 | doi-access = free

}}

Notes

Category:Cosmic rays