The Universe harbors many magnetic bodies, ranging from planets and stars (fractions of a Tesla) to dwarf stars (intermediate fields), pulsars (10^8 T) and magnetars (10^11 T). Since the Universe is made mostly of spinning particles endowed with magnetic moments (electrons, protons, neutrons, muons and atomic nuclides, with non-magnetic particles being a minority), it is evident that magnetic resonance (MR) phenomena should be commonplace. Yet practical astronomy so far does not seam to take the possibility of detecting such phenomena into account, nor does it strive to exploit them actively on planetary and solar-system scales. This may be due simply to a lack of faith that such phenomena can be detected in a sufficiently specific manner.
This presentation lists possible MR phenomena occurring on astronomical scale and discusses their highly specific features which might make them experimentally accessible. The hope is that such a study might help establish magnetic resonance astronomy (MRA) as a new branch of MR.
The considered 'sample' sizes range from sub-planetary (sections of troposphere, seas and oceans, icecaps, etc) to planetary (atmospheres, ionospheres, radiation belts) and stellar (sunspots, atmospheres of dwarf stars, pulsars and magnetars). The particles to be observed include both electrons and nuclides (plus a few more) so that no conceptual distinction is made between ESR and NMR.
Depending upon the considered special case, Larmor frequencies range from a few kHz (like protons in the Earth field) to well beyond X-rays (electrons on magnetars). There are, however, unique characteristics of MR-related radiation (be it spontaneous or stimulated) which make it quite distinct. These are (i) exceptionally narrow spectral bands, (ii) precise direction vectors (Poynting vector aligned along the magnetic field) and, above all, (iii) strict chirality (implying circular polarization).
Experimentally, since induction coupling is ruled out by the size of MRA objects, one must resort to standard techniques of emission, absorption and stimulated-emission spectroscopy, both passive (remote observation) and active (using spacecraft-mounted transmitter-receiver systems). We will discuss the instrumentation and the techniques (some of which are similar to NMR 'pulse' sequences and data-averaging) which might make it possible to isolate MR signals from non-MR background.
Low-frequency MRA might help analyze the particle composition of sunspots and, in its active version, the composition of Jovian atmosphere. On a sub-planetary scale, even the low Earth field might be sufficient, for example, to actively monitor tropospheric storms (ESR), oceans, polar icecaps and other planetary surface features.
The author discusses also the MR phenomena which might be going on in the magnetic fields of the order of 10^8 Tesla present on pulsars. Though the possibility that the observed light flashes are really MR signals is just a far-shot hypothesis but, nevertheless, it should be taken into account. It appears, in fact, that there might be ways of how the interaction between spinning particles with the extremely high fields might explain the pulsed emissions in the optical and X-ray regions.