magnacycle

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Franklin D. Roosevelt, who formulated the Four Freedoms.

7 Alphabet Soup Agencies that Stuck Around

Close up of periodic table, focus on nickel, copper, zinc, palladium, silver, cadmium

When Was the Periodic Table Invented?

Solar eclipse of the sun.

The Sun Was Eaten: 6 Ways Cultures Have Explained Eclipses

Centimetres vs inches, metal rulers on a white background with clipping path.

15 Questions About Units of Measurement Answered

Space race (1957-1969) infographic between United States (U.S.) and Russia. America, Soviet Union, U.S.S.R., space exploration

Timeline of the Space Race, 1957–69

World map. Continents. Oceans. Mendel thumb ok

Just How Many Oceans Are There?

Leonardo da Vinci (1452-1519), Italian Renaissance painter from Florence. Engraving by Cosomo Colombini (d. 1812) after a Leonardo self portrait. Ca. 1500.

10 Famous Artworks by Leonardo da Vinci

magnacycle

geology

Learn about this topic in these articles:

cyclothems

In cyclothem
…have been referred to as magnacycles. These larger units are of doubtful validity and restricted utility.
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