Answer:
Apparent magnitude: The brightness of a celestial object as it is measured from Earth
Hertzsprung: Russel diagram
Absolute brightness: The total amount of energy emitted from a celestial object
Nebula: An interstellar cloud of dust and gases
Explanation:
Astronomists define the brightness of stars from the earth as apparent magnitude. They measure how much celestial objects bright from the earth.
Ejnar Hertzsprung was a chemist and astronomer. He developed the Hertzsprung-Russell diagram that describes the luminosity of a set of stars as a function of temperature.
Absolute brightness is a measurement of total heat emitted from stars or celestial objects on a common scale. Apparent brightness can be changed when taken from another place
In astronomy, a nebula is a giant cloud of dust and gas in space.
