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reblogged

The Bolt N’ Grind

The Bolt (c. 1778), Jean-Honore Fragonard / Bump N’ Grind, R. Kelly

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The Progress of Love: A Woman’s Worth

The progress of love, Jean Honore-Fragonard / A Woman’s Worth, Alicia Keys

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teded

The earth’s movement creates a few cycles. First of all, it rotates on its axis about once every 24 hours, producing sunrises and sunsets.  At the same time, it’s making a much slower cycle, orbiting around the sun approximately every 365 days. But there’s a twist. Relative to the plane of its orbit, the Earth doesn’t spin with the North pole pointing straight up. Instead, its axis has a constant tilt of 23.4º. This is known as the Earth’s axial tilt, or obliquity. This seemingly minuscule tilt is the reason…for the seasons.

Another feature of the Earth’s revolution is its orbital eccentricity. The earth’s orbit around the sun is an ellipse, with its distance to the Sun changing at various points. The corresponding change in gravitational force causes the Earth to move fastest in January when it reaches its closest point to the sun – the perihelion – and slowest in July when it reaches its farthest point – the aphelion. The Earth’s eccentricity means that solar noon – the time when the sun is highest in the sky – doesn’t always occur at the same point in the day. 

Learn about the Sun’s analemma by watching the TED-Ed Lesson The Sun’s surprising movement across the sky - Gordon Williamson

Animation by TED-Ed

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