Question

galaxy
nebula
star
milky way
hr diagram (hertzsprung - russell diagram)
elliptical galaxy
spectral class
irregular galaxy
a massive system of stars, gas, and dust held together by gravity.
cloud of dust and gas found in space, where stars are created
a giant ball of hot gas, primarily hydrogen and helium, that produces light and heat through nuclear fusion.
spiral galaxy where the sun and solar system are located.
a graph that shows the relationship between a stars brightness and temperature.
a system of stars that are oval or circular in shape
system of stars without a clearly defined shape
stars that are grouped according to characteristics like temperature.

Explanation:

Galaxy is a massive system of stars, gas, and dust held together by gravity. Nebula is a cloud of dust and gas found in space, where stars are created. Star is a giant ball of hot gas, primarily hydrogen and helium, that produces light and heat through nuclear fusion. Milky Way is the spiral galaxy where the sun and solar - system are located. HR Diagram (Hertzsprung - Russell Diagram) is a graph that shows the relationship between a star's brightness and temperature. Elliptical Galaxy is a system of stars that are oval or circular in shape. Spectral Class refers to stars that are grouped according to characteristics like temperature. Irregular Galaxy is a system of stars without a clearly defined shape.

Answer:

Galaxy: A massive system of stars, gas, and dust held together by gravity.
Nebula: Cloud of dust and gas found in space, where stars are created.
Star: A giant ball of hot gas, primarily hydrogen and helium, that produces light and heat through nuclear fusion.
Milky Way: Spiral galaxy where the sun and solar system are located.
HR Diagram (Hertzsprung - Russell Diagram): A graph that shows the relationship between a star's brightness and temperature.
Elliptical Galaxy: A system of stars that are oval or circular in shape.
Spectral Class: Stars that are grouped according to characteristics like temperature.
Irregular Galaxy: System of stars without a clearly defined shape.