Further Physics - Observing the Universe - Looking Into Space

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Further Physics - Observing the Universe - Looking into Space

The Earth Fully Rotates west-east on its axis in just under 24 hours. We cannot feel the Earth spinning, but it is due to this rotation, that the stars appear to move east-west across the sky once in just under 24 hours.

The Sun, planets, and Moon also appear to travel east-west across the sky. Their motion and the time they take to cross the sky, is affected by their relevant orbits. In the case of the sun, it appears to travel across the sky once every 24 hours.

The Earth and the Sun

A sidereal day is the time it takes for the earth to rotate 360° on it's axis. A solar day it the time from noon on one day to noon on the next day, ie. 24 hours. As the Earth rotates once on its axis, it is also orbiting the sun. It is this orbiting movement that results in a sidereal day being shorter than a solar day, by 4 minutes.

The Position of the Stars

Due to the orbiting movement around the Sun, an observer looking at the night sky from the Earth can see different skies at different times of the year, depending on the Earth' position, in relation to the Sun's position.

Plotting Astronomical Objects

When astronomers look into space, they describe the position of objects in terms of the angles of declination and ascension. These angles describe the positions of the stars relative to a fixed point on the equator.

A star with a positive declination will be visible from the northern hemisphere. A star with a negative declination will be visible from…


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