- ancient = here: a long time ago
- ancient = old
- arrange= to put into a special position or order
- asteroid belt= many small rocky objects that move around the sun between Mars and Jupiter
- century = a hundred years
- certain = special
- comet = an object in space that looks like a bright ball with a long tail; it moves around the sun
- convince= to prove to someone that what you say or think is true
- crop= plant, like wheat, corn or rice, which is grown by farmers and used as food
- data = information
- diameter= straight line from one side of a circle to the other
- discovery= when you find something new, that was not known before
- distant = far away
- elliptical path= route that moves around an object in an ellipse
- examine= look at very carefully
- explain = make clear
- finding= discovery, result
- galaxy= one of the large groups of stars that make up our universe
- gravity = the power that causes an object to fall to the ground; it also pulls things to other planets
- however = but
- image = picture
- in fact = the truth is; in reality
- in great detail= here: to put in a lot of information
- in operation = here: working
- later = future
- map = draw
- measure= to find out how far away something is
- movement= when an object moves
- naked eye=to see something without anything to help you
- navigate = to find out which way you need to go
- observe = watch closely
- occur = happen
- on a daily basis = every day
- orbit = to move around
- pattern = design, shape
- predict= say that something will happen in the future
- prove= to show that something is true
- relating to = about something
- rely = depend on; need
- revolve = move around
- sample= here: rock ; piece of something from another planet
- scientist= person who has studied science and works in a laboratory
- simulate=to make something feel real
- solar system = the sun and the planets that move around it
- support = back up ; help
- surface= the top part of something
- telescope = object that is shaped like a tube and used to make faraway things look closer and bigger
- trillion = 1,000,000,000,000
- unmanned spacecraft= object that can travel into space without anybody guiding it