The angle that a planet's rotational axis makes with its orbital plane. In Earth's case, it is called the obliquity of the ecliptic. Obliquity gives a good indication of how extreme the seasons would be on a given world. Earth's obliquity of 23.5° means that at the summer solstice, the north pole tilts toward the Sun by 23.5°, and at the winter solstice, it tilts away by the same amount. This leads to fairly extreme temperature changes. Uranus, on the other hand, has an obliquity of about 97.86° – almost a right angle. This means that at its summer solstice, the north pole points almost directly at the Sun, and there is continuous daylight in most of the planet's northern hemisphere.
Related category• CELESTIAL MECHANICS
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