List and describe the three types of galaxies.

According to NASA and their Hubble Space Telescope, we have 4 different types of galaxies, the 3 main ones being elliptical, spiral, and irregular.

Explanation:

Elliptical galaxies are shaped almost like an oval. They do not have any "arms" like you imagine in most galaxies, like our own Milky Way. An example would be galaxy ESO 325-G004.

Spiral galaxies are shaped almost like a circle and has arms "spiraling" out from the center. An example of a spiral shaped galaxy would be our own galaxy, the Milky Way.

Irregular galaxies do not have a definite shape. They are usually shaped randomly and can consist of any shape. An example would be galaxy NGC 1569.

The 4th and obscene type of galaxy is called the Lenticular galaxy. This is simply almost like a cross section between an elliptical galaxy and a spiral galaxy combined together. It is shaped like a disk and has no arms. An example would be galaxy NGC 5010.

i will answer your question if you answer mine

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.