# Physics observing the universe

further physics

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## Looking into space

the earth fully rotates west  - east on its axis once in just under 24 hours

the stars appear to move east - west across the sky once in again just under 24 hours

the sun, planets and moon also appear to travel east to west.

the sun appears to travel across the sky once every 24 hourse

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## the earth and the sun

A sidereal day is the time is takes for the earth to rotate 360 degrees on its axis,

A solar day is the time from noon to noon the following day so 24 hours

whilst the earth rotates once on its axis, it also orbits the sun. it is this orbiting movement that makes a sidereal day shorter than a solar day.

a sidereal day is 4 minuets shorter than a solar day.

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## Solar eclipses and Lunar Eclipses

A solar eclipse occurs when the moon passes between the earth and the sun. this can happen during the new moon and it results in the moon casting a shadow on the earth

a total solar eclipse occurs when the moon is directly in front of the sun and completely obscures the earths view of the sun

A lunar eclipse is when the earth is between the moon and the sun. this results in the earth casting a shadow on the moon

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## Convex lenses

A convex lens bends rays of light inwards as they pass through the lens. if the rays of light entering the lens are parallel, the rays will be brought to a focus at the focal point.

the greater the curvature of a lens, the more powerful it will be. so if two lenses are made of the same material, a highly curved lens will be more powerful that a flatter lens

you can calculate the power of the lens by the following

power of lens = 1 / focal length (metres)

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