Globular Cluster

A collection of stars that orbits a galaxy’s core. GCs are very tightly bound by gravity which gives them

their spherical shapes and high central density. The number of stars in a globular cluster varies, but

normally hundreds of thousands.“Globs” contain considerably more stars and are

much older (often > 13 billion years old) than open clusters. There are about 150 currently known

globular clusters in the Milky Way, with perhaps more still undiscovered.

Open Cluster

An open cluster is a group of up to a few thousand stars that were formed from the same gas cloud and

are roughly the same age. More than 1,100 open clusters have been discovered

within the Milky Way Galaxy.Open clusters only survive for a few hundred million years unlike the more massive globular clusters that

can survive for many billions of years.

Galaxy

A galaxy is a massive system of stars, gas, dust, and dark matter held together by gravity. The word

galaxy is derived from the Greek galaxias, literally "milky", a reference to the Milky Way. Galaxies range from dwarfs with as few as ten million stars to giants

with a hundred trillion, each orbiting their galaxy's own center of mass.

Supermassive black holes reside at the center of most galaxies.

Planetary Nebula

A planetary nebula consists of an expanding glowing shell of ionized gas ejected from old red giant stars late in their lives. The word 'nebula' is Latin for mist or cloud. They last only a few tens of thousands of

years.At the end of the star's life, during the red giant

phase, the outer layers of the star are expelled by strong stellar winds. Our sun’s evolution will probably result in the formation of a planetary nebula when it

has exhausted all its fuel in a few billion years.