Earth and Moon Rotation ```Name: James Status: Educator Age: 30s Location: N/A Country: N/A Date: N/A ``` Question: I have read your answer to "How fast does the earth and moon rotate." What is the formula for determining the rotational speed for any given latitude? I would like to use my latitude or one close to it for my students. Replies: For ease of calculation, we will assume that the earth is a perfect sphere. This is a pretty good approximation; the surface IS extremely flat, and the oblateness at the equator is only a factor of about 0.3%. The formula is C=2 x Pi x R x Cos((Pi x L)/180) if you calculate the cosine of an angle in radians (many computer spreadsheets use radians), or C=2 x Pi x R x Cos(L) if you calculate the cosine from the angle's measurement in degrees. In this formula, Pi = 3.1415927..., L is the angle of latitude, and R is the radius of the earth, 6378 km. Richard E. Barrans Jr., Ph.D. Assistant Director PG Research Foundation, Darien, Illinois James, This question is related to the one on "Earth Circumference" at different latitudes that I answered a few days ago. The radius (r) of a circle (that is parallel to latitude) at any latitude (assuming the Earth to be a perfect sphere) is the Earth's radius (3963.5 miles) times the cosine of the latitude angle. The circumference at the latitude is then 2 x pi x r. The Earth rotates once per 23 hours, 56 minutes and 4 seconds (approximately 24 hours). By determining circumference at any latitude and dividing it by the time in a day, you get the rotational speed. Dr. Cook Click here to return to the Environmental and Earth Science Archives

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