If there were no atmosphere, the sky would be all black, except for the area directly around the sun, which you would not be able to look anywhere near because it would be so bright, as there would be no atmosphere to block its rays.
Contagion and contagiousness refers to how easily the spread of Genetic Disease is possible from one person to another. Other words for contagion include infection, infectiousness, transmission or transmissability. Contagiousness has nothing to do with genetics or inheriting diseases from parents.
Communicable diseases are diseases that are caused by bacteria, virus, fungus, or parasites. They are spread from person to person, or animal to person, through direct or indirect contact. Pathogens. A pathogen is an infection causing agent (germ). Pathogens are the cause of communicable diseases. Bacteria, viruses, fungus, and parasites can all be pathogens. The most common pathogens are bacteria and viruses. Causative agent- This is the disease causing agent (bacteria, virus, fungus, parasite).