Science Study Guide Space and Gravity VOCABULARY gravity – the force of attraction that exists between all objects in the universe accretion – the process of becoming larger by adding more material coalesce – to unite; to grow centrifugal force – the force that tends to push an object outward when it rotates around the center inertia – a property of matter that keeps an object moving in a straight line and at a constant speed free fall – the unchecked fall of an object trajectory – the path of an object moving through space comet – an icy chunk of rock from a region of space beyond the orbit of Neptune eclipse – the passing of one object through the shadow of another satellite – a natural body, like the moon, or an artificial object that orbits another object space probe – a robot vehicle used to explore deep space photosphere – the surface of the sun corona – the sun’s atmosphere universe – everything that exists – planets, stars, dust, gases, and energy light-year – the distance light travels in one Earth year ►Gravity pulls us toward Earth’s center. Mass and distance between objects determine the force of gravity. ►High and low tides are cause by the gravitational pull of the sun and moon. ►There are 8 planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. ►All planets have 3 things in common: 1. Orbit the sun 2. Spherical (round) 3. Their gravity controls objects around them ►The Earth revolves around the sun. ►The Earth rotates on its axis. ►The moon has 8 phases. A waxing moon appears to grow larger. A waning moon appears to get smaller. ►Galileo invented the telescope, and used it to observe the moon. ►The sun is a huge ball of very hot gases. It is the center of our solar system. ►Energy from the sun travels in waves: light waves, heat waves, radio waves ►How bright a star looks depends on two things: brightness and distance from Earth ►Blue stars are the hottest stars; red stars are the coolest stars. ►There are 4 types of galaxies: spiral, barred, elliptical, irregular ►Our galaxy is the Milky Way Galaxy; it is a spiral galaxy. You will be asked to answer one of the following questions (one, detailed paragraph): Why do we weigh more on Earth than on the moon? What causes ocean tides? Why are planets round? Why don’t planets crash into each other?