The phrase multi-messenger astronomy has been used to refer to astronomical research using multiple sources of information (i.e., multiple messengers), often counting all electromagnetic radiation as just one of the sources/messengers. Other non-EMR sources are cosmic rays, neutrinos, and gravitational waves. Possibly the phrase has also been used for disparate EMR observations, such as follow-up visible light observation to gamma-ray bursts. Often it involves alerts, i.e., when some transient phenomenon has been detected through one source, this fact is quickly broadcast to observers who can use independent types of observation.
Within the solar system, additional categories can be classified as independent, including direct magnetic field observation, gravity measurements and chemical analysis such as mass spectrometry.