Earth, The Circle

That means the sun's rays hitting Eratosthenes' home in Alexandria are parallel to the sun's rays hitting Syene, a town far to the south, which today we call Aswan. Generations of careful Egyptian land surveyors knew Syene was 5, stadia -- ancient measurement units equivalent to kilometers or miles -- south of Alexandria.

Eratosthenes knew that, too. In Syene was a deep, wide well. At local noon on every summer solstice earth's longest Earth and shortest nightthe sun's rays went straight down the well, which meant Syene was perfectly lined up with those parallel sun rays.

No shadow Earth in the well. Eratosthenes knew about the Syene well, and he also knew the sunshine in Alexandria, km or mi. Anything sticking up out of the earth in Earth -- like a stick -- cast a shadow at the same moment a stick in Syene cast no shadow.

If Eratosthenes could accurately measure the angle of the shadow of a stick driven perpendicular into Alexandrian ground, he could use only two pieces of information to calculate the circumference of the earth:.

Circumference is the distance around a circle or sphere. An arc is a portion or fraction of a circle's or sphere's circumference.

People in B. They knew about central angles and arcs. The distance from Alexandria to Syene is one such arc, a measurable and known fraction of earth's total circumference. That made the line from earth's inaccessible center, C, to Alexandria, A, a transversal of the sun's parallel rays. A transversal is a line that cuts across other lines, and in the case of parallel lines, a transversal creates corresponding angles.

Whatever angle it creates on one parallel line, it creates the same angle on the other. If he could accurately measure the stick's shadow angle in Alexandria at local noon on the summer solstice, Eratosthenes have both pieces of information needed to calculate earth's circumference.

Eratosthenes did the measurement and found the Earth was 7. Climb the tallest mountains. Discover cities around the world. Dive into the world's deepest canyons. Launch Earth. Create stories and maps With creation tools, you can draw on the map, add your photos and videos, customize your view, and share and collaborate with others. Create on Earth Draw on the map Add placemarks to highlight key locations in your project, or draw lines and shapes directly on the map. Adding placemarks and lines to Google Earth.

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Immerse yourself in new cultures and test your knowledge of the world. Catch Carmen Sandiego. Follow clues and track her down! Launch in Earth. Isaiah Isaiah Context 19 The workman melteth a graven image, and the goldsmith spreadeth it over with gold, and casteth silver chains. Other Translations for Isaiah It is he that sitteth vpon the circle of the earth, and the inhabitants thereof are as grashoppers; that stretcheth out the heauens as a curtaine, and spreadeth them out as a tent to dwel in: - King James Version - View Bible Scan It is He who sits above the circle of the earth, And its inhabitants are like grasshoppers, Who stretches out the heavens like a curtain Earth spreads them out like a tent to dwell in.

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