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Poster of types of optical telescope: Newtonian, Refracting, and Casserian.
Telescopes Poster

SEASONS: animation of the Earth moving around the sun showing how the seasons arise from the tilt of the Earth's axis.

THE SEASONS arise because the Earth (white, green & blue striped sphere) is tilted on its axis (yellow pole through Earth) and this tilt is maintained throughout the Earth's orbit (shown in purple) around the Sun (yellow sphere in the centre). Consequently, the northern and southern hemispheres receive different amounts of sunlight throughout the year. At the start of the animation (which is viewed from slightly north of the plane of the Earth's orbit around the Sun) the Earth is tilted so that the northern hemisphere receives most light (you can see the letter "N" above the North Pole inclined towards the sun). This position corresponds to the northern mid-summer or summer solstice and the southern mid-winter. At this point, the northern hemisphere experiences its longest day and the southern hemisphere its shortest day. As the animation progresses, the Earth moves in an anti-clockwise direction (as viewed from this vantage) to the equinox at middle front of the orbit. The Equinox is the point of equal day and night (from the Latin for equal night). At this point, the tilt of the Earth is directed at right angles to the sun. The Earth continues around to the right of the picture where the tilt is again maximal with respect to the sun. This time, however, the southern hemisphere is maximally pointed towards the sun (you can see the letter "S" below the South Pole is now inclined towards the sun). This corresponds to the southern mid-summer and northern mid-winter (solstice). At this point the southern hemisphere experiences its longest day and the northern hemisphere its shortest day. As the Earth progresses in its orbit around the sun, it passes through another equinox before completing the circuit at the northern mid-summer. This oscillating level of sunlight is heavily imprinted on nature as temperature and daylength vary.

In this movie, the Earth is divided into coloured bands:

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