In 3–5 sentences, describe the matter that is considered baryonic matter, explain why it is in this category, and compare and contrast it with other materials in the universe. (4 points)

By definition, baryonic matter should only include matter composed of baryons. In other words, it should include protons, neutrons and all the objects composed of them (i.e. atomic nuclei), but exclude things such as electrons and neutrinos which are actually leptons. since on astronomical scales, protons and neutrons are always accompanied by electrons (in appropriate numbers for astronomical objects to possess all but zero net charge). Astronomers therefore use the term ‘baryonic’ to refer to all objects made of normal atomic matter, essentially ignoring the presence of electrons which, after all, represent only ~0.0005 of the mass. Neutrinos, on the other hand, are (correctly) considered non-baryonic by astronomers.