All comets, like Comet Ison, emit spectra of light that scientists can observe here on earth. By measuring these patterns (a process known as spectroscopy) scientists are able to discover which elements and compounds a comet is made of, even when the object is still almost a year away from the sun. This spectrum of light is radiated from a comet's coma: a small atmosphere of gas and dust that forms around the comet's surface.