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Some things to know about chapter 18……..did you know this? rotation- spinning motion of a planet on its axis creating day and night revolution- the motion around an object such as the planet going around the sun or the moon revolving around the earth orbit- the path a planet makes as it revolves around the sun The period of rotation or the period of revolution is the time that it takes to complete that motion. Such as the period of revolution for earth is one year. The period of rotation for earth is 24 hours. equinox-on the first day of spring (vernal equinox) the amount of daylight and darkness are equal. On the first day of fall (autumnal equinox) the amount of daylight and darkness are equal. year- is the time required for the Earth to orbit the sun once leap year- a year with and extra day added on the calendar (February 29th). This happens every 4 years due to the length of the year being 3651/4 days. 1/4day +1/4day+1/4day+1/4day= 1 extra day constellations- are sections of the sky that contain recognizable star patterns

light year- is a unit of length equal to the distance that light travels through space in one year. Wow at 300,000 km/sec or approximately 186,000 mi/sec …..I bet that is a long distance in a year! 186,000mi/sec X 60sec/min. X 60min/hr X 24hours/day X 365days/year= 5,865,696,000,000 miles equals 1 light year! You try the equation but instead of miles substitute the kilometers per second and see what you get for kilometers per year.