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Physics:

MAIN IDEA Discover how the and its shadow is used to tell by creating a sundial – an instrument that tracks the to indicate time of .

SCIENCE BACKGROUND For , have utilized the power of the sun as a light source, to grow food, and to tell time. Ancient civilizations used the sun to understand basic . By tracking the height of the sun in the , these civilizations developed for the and were able to identify harvesting and planting (fall and ) all by tracking the of the sun. This also helped certain civilizations find the , an imaginary around the that divides it into two halves, the northern and . By tracking the sun’s apparent position through the creation of , these ancient civilizations were able to divide the day into and . A sundial is a device used to track time by marking a shadow on its surface as the sun moves. Light travels as a wave, similar to waves in the . Shadows occur when this light wave is blocked by an object, creating a dark silhouette of that object on nearby surfaces as light continues to travel all around the object. Based on where the light source is, and the object that is blocking it, the shadow will look different. This is why for a sundial, the shadow will change throughout the day and even more noticeably throughout the year for the same time of day. A sundial’s also plays an important role in how the shadow will look. The latitude is the angular distance a location is or of the Equator, from 0° (Equator) to 90° (north or ). Think of shadows on a wall. If you change the position of the light source, such as a flashlight, you can observe how the shadows change. This can mimic the movement of the sun in the sky based on time of day and throughout the year! The Earth takes 23 , 56 , and 4.09 to rotate from to , with hours varying based on time of year and latitude. A classic sundial will have 12 markings similar to a , and thus the shadow of the sun will pass over each marking up to two a day. Some shadows will only occur once a day as the sun is not visible during nighttime, meaning that there is no light to block and there would not be a shadow. MATERIALS or Compass App Marker Paper plate Pencil or Stick Ruler Tape