- also called minor planets or planetoids, they are small sized celestial bodies (smaller than planets but larger than meteoroids) in orbit around the sun.
- the difference between asteroids and comets can been seen by visual appearance where comets show a clear coma (tail) though asteroids do not.
- also known as natural satelites, moons are calestial bodies that orbit a planet (the primary)
- up to september 2008,335 bodies have been classified as moons, including 167 moons orbiting six of the eight main planet in our solar system.
- about six moons, the four jupiter Galilean moons, Saturn's Titan, and Neptune's Triton, are also quite similar in size to Earth.
- a celestial body orbiting a star.
- planet is an ancient term that intertwines with science, myth, and religion.
- generally, planets are divided into two groups, either large, low-density gas giants or smaller, rocky terrestrial planets.
- of the eight planets in our solar system, four our rocky terrestrial (Mercury, Venus, Earth and Mars) and the other four our gas giants (Jupiter, Saturn, Uranus, and Neptune)
- furthermore, there are also five dwarf planets orbiting our sun, named Ceres, Pluto, Makemake, Haumea and Eris.
4. Stars (sun)
- a massive, bright ball of flames (plasma), held together by gravity.
- our sun is the nearest star to Earth and is also the source of most of our energy.
- other suns can be seen as stars at night light from thermonuclear fusion in the core releases an abundance of energy into space.
- the fusion process in stars also produces all other elements heavier than hydrogen and helium.
- a star system can also consist of twin stars (or more) that orbit each other
- a star can also age and burn up its 'fuel'.
- a dying star can collapse on its own gravity, thus forming a black hole in its place, or explode causing a supernova that triggers the formation of new stars.
- a massive, gravitationally bound system consisting of stars, astral bodies, gas and dust
- it also contains an important but poorly-understood component, dubbed as dark matter (accounting about 90 percent of the galaxy mass)
- can range from giants (with trillions of stars) to dwarfs containing only a few million
- the galaxy systems can contain several solar systems or just clusters of stars and various interstellar clouds
- there can also be multiple vshapes of galaxies, elliptical, spiral (disk-shaped), or irregularly shaped due to the disruption (gravitationalpull) of neighboring galaxies.
- it's estimated that there are over 100 billion galaxies in our universe
- it's also believed thay many (or all) galaxies (including ours) have one or more supermassive black holes in its centre.