2 Basic Objects in the Universe
Stars
Stars are glowing balls of gas that undergo nuclear fusion; the Sun is a star.
![Image of stars in the night sky.](http://cel.fscj.edu/LUMENS/ast-1002-package/img/figure-1-stars.jpg)
Planets
Planets are moderately large objects orbiting a star. We see planets because they reflect the light of their central star, or in some cases, stars. Planets are generally rocky or gaseous in nature and spherical-shaped.
A new group of objects has been recently defined: the Dwarf Planets or Plutoids. These are objects that orbit the Sun, but have not cleared their orbits. Pluto is an example of a Dwarf Planet.
![Image of Planets in our Solar System, including Mercury, Venus, Earth, Mars, Saturn, Jupiter, Uranus, Neptune, and the moon.](http://cel.fscj.edu/LUMENS/ast-1002-package/img/figure-2-planets.jpg)
Public Domain | Image courtesy of NASA.
Satellite
A satellite orbits a planet; these objects are also called moons. For example, the Earth’s satellite is the Moon – a proper name.
![Image of the Moon, Earth’s Satellite, behind Earth in the distance.](http://cel.fscj.edu/LUMENS/ast-1002-package/img/figure-3-satellite.jpg)
Asteroid
An asteroid is a relatively small, rocky/metallic object usually orbiting a star.
![Image of the asteroid, Eros.](http://cel.fscj.edu/LUMENS/ast-1002-package/img/figure-4-asteroid.jpg)
Public Domain | Image courtesy of NASA.
Comet
A comet is a relatively small, icy object usually orbiting a star. Asteroids, comets, and miscellaneous small/irregular objects and “dust” are often categorized as Minor Bodies.
![Image of Comet Hyakutake by NASA photographer Bill Ingalls.](http://cel.fscj.edu/LUMENS/ast-1002-package/img/figure-5-comet.jpg)
Solar System
The Solar System is the Sun and all the objects that orbit the Sun, including the planets and their moons.
![Image of our Solar system, including Mercury, Venus, Earth, Mars, Saturn, Jupiter, Uranus, Neptune, Pluto, and the Sun.](http://cel.fscj.edu/LUMENS/ast-1002-package/img/figure-6-solarSytem.jpg)
Stellar System
A Stellar System is a star and other objects such as planets and/or other stars and other materials that orbit it.
Galaxy
A galaxy is a large island of stars, a few hundred million to over a trillion stars.
![Image shows spiral galaxy ESO 137-001, framed against a bright background as it moves through the heart of galaxy cluster Abell 3627.](http://cel.fscj.edu/LUMENS/ast-1002-package/img/figure-7-galaxy.jpg)
Galactic Cluster
A Galactic Cluster is a collection of galaxies gravitationally bound.
Supercluster
A Supercluster is a region where galaxies and galactic clusters are tightly packed.
Universe
The Universe is all matter and energy, and is also called the Cosmos.
![Image of a universe with vast amounts of stars and planets.](http://cel.fscj.edu/LUMENS/ast-1002-package/img/figure-8-universe.jpg)