Page 53 - Curriculum Visions Dynamic Book

Neptune is the eighth planet farthest from the Sun and half as far away again from the Sun as Uranus. Neptune is the only gas giant planet that is not visible with the naked eye.
Neptune moves around the Sun in a nearly circular orbit at a distance of 4.5 billion kilometres. It is about four times the size of the Earth and is roughly the same size as Uranus. Neptune has a density of about 1.6 g/cm3.
As on Uranus, the colour of the planet is affected by having an atmosphere that includes methane gas. The gas absorbs strongly in the red part of the spectrum, so that the reflected light occurs only in the complementary colour, in this case, blue.
Neptune moves once around the Sun every 164.8 Earth years. Each season on Neptune lasts 41 years, although day and night change quickly because each Neptunian day is just 16.1 Earth hours.
Neptune spins on an axis that is tilted similarly to that of the Earth. In Neptune’s case the tilt is 29.6° (Earth’s tilt is 23.5°).
At the equator Neptune is 49,528 kilometres across, but it is slightly flattened at the poles due to the centrifugal force exerted on it as it spins on its axis. Measured across the poles, the diametre is just 48,680 kilometres.
Neptune is so far from the Sun that solar radiation has little effect. However, Neptune has a small source of internal heat and as a result is somewhat warmer than Uranus. In general, Neptune sends out to space about twice as much heat as it receives from the Sun. This internal heat may help generate the great storms and fast winds seen in the atmosphere of the planet.
The atmosphere
The dominant gas in the atmosphere of Neptune is hydrogen, with helium second in importance. Most of the remaining 2% is methane.
atmosphere The envelope of gases that surrounds the Earth and other bodies in the universe.
axis (pl. axes) The line around which a body spins.
centrifugal force A force that acts on an orbiting or spinning body, tending to oppose gravity and move away from the centre of rotation.
complementary colour A colour that is diametrically opposite another in the range, or circle, of colours in the spectrum; for example, cyan (blue) is the complement of red.
density A measure of the amount of matter in a space.
equator The ring drawn around a body midway between the poles.
orbit The path followed by one object as it tracks around another.
pole The geographic pole is the place where a line drawn along the axis of rotation exits from a body’s surface.
reflect To bounce back any light that falls on a surface.
solar radiation The light and heat energy sent into space from the Sun.
 Neptune’s high-level clouds run in bands above the main cloud mass of the planet.
Although the edge of Neptune’s atmosphere is very cold
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